Active Stabilized Rocket Wyatt

8/13/2019 Active Stabilized Rocket Wyatt

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Hofstadter's Law: It always takes longer than you expect, even when you take intoaccount Hofstadter's Law.

!ouglas Hofstadter, Gdel, Escher, Bach: An Eternal Golden Braid

I here"y declare that, except where specifically indicated, the work su"#itted hereinis #y own original work.

An Actively StabilisedModel Rocket

by

David Wyatt (TH)

Fourth-year undergraduate project in

Group C, 200!200"


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Table of Contents

$ Introduction........................................................................................................................... $% &oplevel design....................................................................................................................

%.$ (oncept selection........................................................................................................................................................ %.% (ontrol syste# architecture.................................................................................................................... ................... )%. *afety........................................................................................................................... ................................................. +

echanical design.................................................................................................................-.$ otor selection and flight si#ulation...................................................................................................................... -.% &hruster force............................................................................................................................... ............................... . /irfra#e design...................................................................................................................... ....................................

0 1neu#atics syste#..............................................................................................................$$0.$ 2verall pneu#atics syste# design......................................................................................................................... $$0.% 3as supply........................................................................................................................ ......................................... $$0. &hruster no44le design.............................................................................................................................. ............... $%0.0 5alve selection............................................................................................................................................ ............... $0

0.) 16 fre7uency selection........................................................................................................................................ $)) 8lectronic design................................................................................................................. $+

).$ 1rocessor selection............................................................................................................................................ ........ $+).% /ttitude sensor selection................................................................................................................................. ......... $-). 1ower supply.................................................................................................................. ........................................... $).0 (ircuit design............................................................................................................................................ ................ $

+ *oftware and control...........................................................................................................$9+.$ *yste# #odel............................................................................................................................................................ $9+.% ate gyro sensor inputs................................................................................................................. ........................... %;+. (ontrol law.................................................................................................. .............................................................. %;+.0 *i#ulation................................................................................................................................................. ................. %%+.) *oftware structure.......................................................................................................... ........................................... %0+.+ !evelop#ent environ#ent and toolchain............................................................................................................. %)

- (onstruction and testing....................................................................................................%)-.$ &i#e and expenditure....................................................................................................................................... ....... %)-.% 1hase $: &urnta"le test"ed............................................................................................................................. .......... %+-. 1hase % < airfra#e construction.......................................................................................................................... %-.0 ass reduction................................................................................................................................ .......................... %9-.) =ench tests........................................................................................................... ....................................................... ;-.+ aiden flight................................................................................................................................. ............................ %

(onclusions..........................................................................................................................).$ 1ro>ect achieve#ents and validity of concept........................................................................................................ ).% 1ro>ect significance........................................................................................................................ ............................ +. 8valuation of approach.................................................................................................................. .......................... +.0 ?uture work................................................................................................................................... ............................ -

9 /cknowledge#ents............................................................................................................ 9$; eferences...........................................................................................................................0;/ppendix /: *tructural design of pri#ary truss and landing legs................................ 0/ppendix =: &hruster no44le final design..........................................................................0)/ppendix (: e7uire#ents for rocketry avionics.............................................................0+/ppendix !: /vionics circuit diagra#s and circuit "oard layouts................................0-

ain avionics "oard.................................................................................................................................... ................... 0-5alve driver "oard........................................................................................................................... ............................... 03yro "oard...................................................................................................................................... ................................. 01hotographs of asse#"led circuit "oards.................................................................................................................... 09

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1 Introduction

ockets @ like #any aerospace syste#s, or indeed any structure travelling in

free fall @ are inherently unsta"le in flight, in that any external distur"ance or internal#isalign#ent of the thrust vector with the centre of #ass will cause the vehicle to

deviate fro# its intended path, and any restoring force #ust "e provided "y the

vehicle itself. &he principal source of distur"ance forces in the a"sence of

aerodyna#ic loads is #isalign#ent of the thrust vector with the centre of #ass, as

shown in ?igure $A reaction forces Be.g. fro# explosive lowerstage separationC #ay

also "e i#portant.

&o co#"at this pro"le#, conventional rockets and #issiles fro# the *econd

6orld 6ar onwards have used active sta"ilisation: electro#echanical control

syste#s to detect such deviations fro# the predeter#ined path and correct for the#.

/ wide range of these syste#s has "een developed Bsee section %.$C.

&his contrasts with s#aller rockets Bscientific sounding rockets and ho""yists'

constructionsC which use passive sta"ility through aerodyna#ic effects as shown in

?igure %. &he distri"uted aerodyna#ic drag #ay "e considered as a point force

acting at the centre of pressure B(o1CA if the (o1 is "ehind the centre of #ass

B(oC, achieved "y placing "allast in the nose of the rocket and fixed fins at the rear,

the drag force produces a restoring tor7ue to "ring the two into line and

aerodyna#ic forces provide da#ping. If a distur"ance tor7ue is applied Be.g. through

thrust vector #isalign#entC the drag force, and thus the air speed of the vehicle,

#ust "e sufficient to overco#e it @ thus passive sta"ilisation works only at high

speeds. &he techni7ue is also only feasi"le on s#aller rockets Bdue to the fin si4es thatwould "e necessary on larger vehiclesC, "ut it is i##easura"ly si#pler to i#ple#ent

than active sta"ilisationA indeed, the co#plexity and expense of the latter, coupled

with the s#all si4e of ho""y rockets, #eans that a#ateur activelysta"ilised rockets

have rarely "een "uilt in the past BD$E, D%EC.

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Figure 1: Rocket flight dynamics in the absence of aerodynamic

forces. n general it is im!ossible to ensure !erfect alignment ofthe thrust "ector #ith the centre of mass $ thus a disturbancetor%ue of magnitude &' is created, #hich if uncorrected #ill

lead to accelerating rotation of the "ehicle.

Figure (: )assi"e aerodynamic stability. &he centre of

!ressure is denoted . A tor%ue *+sin seeks to dri"e to -. n general, the larger the distance + the more stable

the rocket.

However, passive sta"ilisation has certain disadvantages:

$. / co##on ai# in ho""y rocketry is "reaking apogee altitude records. Here

passive sta"ility can "e a hindrance on a windy day as it causes rockets to turn

into the wind BweathercockingC, reducing their apogee height and

increasing the drift distance fro# the launch point. /n active sta"ilisation

syste# fitted to a highpower ho""y rocket would allow vertical flight even in

windy conditions and could reduce lateral drift.

%. Fonaerodyna#ic attitude control syste#s are o"ligatory for vehicles that

operate outside the at#osphere @ for exa#ple, landing on the lunar surface.

F/*/'s recent 5ision for *pace 8xploration BDEC involves the develop#ent of

hovering rocketpowered lunar landers, to which end the agency #ade

develop#ent of a such a vehicle one of its (entennial (hallenges with a G%

#illion pri4e BD0EC. 2n a s#aller scale, (a#"ridge niversity *paceflight's

artlet pro>ect BD)EC ai#s to launch a s#all rocket fro# a weather "alloon at an

altitude of ;k#A since the density of air at this altitude is $.) of that at sea

level BD+EC, and thus the sta"ilising aerodyna#ic forces are significantly

reduced, nonaerodyna#ic sta"ilisation is one of the options under

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mg

D

Directionofmotion

Aerody

namic

dragfo

rces

mg

T


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consideration.

&he goal of this pro>ect, therefore, is the design and construction of a s#all

Bho""yscaleC activelysta"ilised rocket that uses nonaerodyna#ic #eans to effect

sta"ilisation a"out the pitch and yaw axes Bfor the definition of pitch, yaw and roll,see?igure CA control of the roll axis of the rocket was not re7uired as that axis does

not affect its sta"ility in flight. (o##erciallyavaila"le co#ponents and #aterials

were used wherever possi"le, "oth for reasons of cost and to allow this pro>ect's

achieve#ents to "e replicated elsewhere. axi#ising apogee height was not "e

consideredA instead, the ai# is to #aintain a long sta"le flight at a low altitude.

Figure : &he !itch, ya# and roll a/es of arocket

2 Top-level design

2.1 Concept selection

Fu#erous #ethods of nonaerodyna#ic attitude sta"ilisation and control have

"een i#ple#ented over the history of spaceflightA &a"le $descri"es so#e of the #ain

#ethods Bpartially taken fro# D-EC. 2ther #ethods that have "een used in largescalevehicles in the past include: >et ta"s, the >etavator, fluidic steering and control

#o#ent gyrosA however, it was >udged that they were not practical for this pro>ect.

&he concepts are scored in &a"le %for their applica"ility in this context. &he two

#ost pro#ising concepts gi#"alled engine and attitude thrusters were

investigated in #ore detail leading to (/! #ockups, renderings of which are

shown in ?igure 0and ?igure )respectively, and refine#ents of the scores for these

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x

y

z

roll

pitch

yaw


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concepts. sing the scores and weightings indicated, attitude thrusters were chosen

as the #ost appropriate concept to pursueA in contrast, previous ho""y rockets using

nonaerodyna#ic active sta"ilisation BD$E, D%EC have e#ployed the gi#"alled engine

#ethod.

3i#"alled engine Jet vanes/ttitudethrusters

eaction wheels

D

iagram

D

escription

ain engineBsC isKareoffset fro# the centreof #ass with actuatedrotary degrees offreedo#, producingcontrol #o#ents "y

tilting the thrustvector.

/erodyna#ic vanesof a refractory#aterial are placedin the exhaust plu#eof the rocket toredirect it and B"y

reactionC exerttor7ues on thevehicle.

*#allthrottla"lethrusters areoffset fro# thecentre of #assand activated

selectively toprovide control#o#ents.

Heavy flywheelsare accelerated ordecelerated toprovide B"yreactionC control#o#ents a"out

their axes.

Examples

=lack /rrow,*aturn I=K5, *pace*huttle B#ainenginesC, /polloLunar oduleBdescent stageC, ho""yrockets: 3yroc BD$EC,(asi#iro BD%EC

8arly 3oddardrockets, 5% #issile

*atellites,/pollo Lunarodule BascentstageC, *pace*huttle Breactioncontrol syste#C,Harrier aircraft

*atellites, urata=oy "alancingro"ot BDEC

&able 1: 0once!ts for nonaerodynamic attitude control

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Criterion

Weight Concept

Gimballedmain engine

Jetvanes

Attitudethrusters

Reactionwheels

(ost %

/pplica"ility to ho""y rockets %*i#plicity of design

*i#plicity of construction

o"ustness < relia"ility

ass %

Independence fro# rocket #otor

!/&

; ; $

$ $ %% $ $

$ $ ;

$ $ ;

; $ %

; $ $

&otal score ; $; $;

&able (: Attitude control system conce!t e"aluation

Figure 2: 3ocku! of a rocket #ith agimballed engine. &he motor is the

black cylinder in the centre of thegimbals in the lo#er !art of the

"ehicle4 a light#eight truss se!aratesit from the u!!er section, #hich

houses the a"ionics 5 gyros and acircuit board are indicated6, t#ohobby ser"omotors to actuate the

gimbals and a battery !ack.

Figure 7: 3ocku! of a rocket #ith attitude thrusters. &he motor is theblack cylinder in the centre of the base!late4 it is surrounded by four

solenoid "al"es and four thruster no88les 5to#ards the edge of the!late6. 9ther com!onents sho#n include the gas cylinder and regulator,

a battery !ack and the a"ionics circuit board.

2.2 Control system architecture

&he functional architecture of the attitudethruster"ased control syste# is

shown in ?igure +. &he #icrocontroller reads the angular velocity values fro# the

pitch and yaw rate gyros over the *1I serial "us BD9EC to esti#ate the current state

Borientation and angular velocitiesC of the vehicle. &he control law is then applied to

the esti#ated state to derive thruster co##ands in the for# of tor7ues a"out the

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pitch and yaw axes. &he flow of co#pressed gas to the thruster no44les is governed

"y solenoid valves, driven "y the thruster co##ands fro# the #icrocontroller. / log

is kept of all key varia"les in nonvolatile #e#ory on a *ecure !igital card to allow

de"ugging and future develop#ent of the control syste#A this co##unication alsotakes place over the *1I "us.

Figure : 0ontrol system architecture. n the com!lete system there are multi!le solenoid "al"es and thrusters4 for clarity,only one of each is sho#n.

2.3 Safety

*afety considerations have "een para#ount throughout the pro>ect. /s well as

su"#itting a co#prehensive risk assess#ent to (a#"ridge niversity 8ngineering

!epart#ent, the ocketry /ssociation B/C's pu"lished *afety (ode BD$;EC, in

particular the section relating to experi#ental rockets, has "een adopted and

per#ission was sought fro# the / *afety and &echnical (o##ittee "efore

flying. &he first test flight was held at an 8ast /nglia ocketry *ociety B8/*, D$$EC

launch day under the supervision of a designated ange *afety 2fficer, and all

spectators were #ade aware of the potential risks "efore launch. (alculations were

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Microcontroller

Pitch

rate gyro

Digital signals

on SPI bus

Estimated

orientation

Thruster

commands

Control law

Signal processing

and integration

SD card

Solenoid valveGas supply Thruster

Control

signals

Flow

of gas

Yaw

rate gyro

Digital signals

on SPI bus

Flow

of gas

Raw sensor

values

Valuestoberecorded


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also undertaken to esta"lish the "allistic range achieva"le, for the purposes of

esta"lishing a safe distance for spectators. *ince the flight profile Bsee section .$C

involves an initial i#pulsive acceleration to $.0#Ks followed "y a prolonged coast

under a net acceleration of approxi#ately ;.$g, standard for#ulae for "allistic#otion of pro>ectiles can "e used to esti#ate the #axi#u# range Bachieved for a

launch angle of 0)MC:

vy initial0!aytlanding= 0

rma!= v! initialtlandingv! initial= vy initial= vinitial/"

6ith vinitialN $.0#Ks and ayN ;.9$#Ks%, this gives tlandingN %.;s and r#axN

%.;#In the event of a side wind, the rocket #ay drift and travel further than this

distance. sing conservative assu#ptions of a drag coefficient B(!C of $, a cross

sectional area of ;.;#%and a wind speed of )#s$, it was esti#ated that the rocket

#ight travel $.# during the course of a s flight.

3 Mecanical design

3.1 Motor selection and flight simulation

&he rocket #otor taken as the "aseline for this pro>ect is the 8stes 891, with a

total i#pulse of %.)Fs, a "urn ti#e of .;9s and an average thrust of 9F BD$%EC. *ince

the thrust curve of the rocket #otor is fixed Bto within #anufacturing tolerances, a

standard deviation of around + for this #otor according to D$EC, and since

aerodyna#ic forces are relatively uni#portant at the low flight speeds at which the

vehicle will operate, the #ain varia"le affecting the flight profile is the rocket's #ass.

?light profiles were si#ulated in atla" for a range of #asses Bdisregarding dragC

using a sa#ple 891 thrust curve fro# D$EA the results are shown in ?igure -. ?or a

liftoff #ass of over $.;;kg the flight ends "efore #otor "urnout, which is

potentially dangerous. However, it is desira"le to #ini#ise the landing velocity to

avoid da#age to the vehicle's co#ponents. / no#inal #ass of $.;$kg was thus

chosen, giving an apogee height of $.)# and landing velocity of 0.#Ks. &he flight

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profile for this #ass is shown in ?igure .

Figure ;: 3odelled "ariation of flight !arameters #ithmass. &he shar! : 3odelled flight !rofile for a 1.-1kg rocket. ?ince the

thrust is a!!ro/imately constant during the !lateau and slightlyless than the rocket@s #eight, after the initial thrust !eak the"ehicle@s motion resembles a !arabola in 1( gra"ity. At motorburnout the rocket is -.m off the ground and freefalls toim!act.

It was recognised that a longer flight could "e achieved "y using longer

"urning #otors with approxi#ately the sa#e thrust level as the 8stes 891. 2ne

option is the /erotech 3$%(& D$0E, with a thrust of a"out 9F #aintained over

seconds. /n alternative nonexplosive for# of propulsion would "e an electric

ducted fan #ounted in place of the rocket engine.

3.2 Thruster force

&o set specifications for the thruster tor7ue, the radius of gyration was

esti#ated to "e )c#. In order to translate hori4ontally "y )# in %s Bduring the steady

thrust section of the 891's "urn ti#eC, the vehicle would have to tilt "y 0OA allowing

a tilt #anoeuvre ti#e of ;.%s i#plies that the #axi#u# thruster tor7ue should "e

;.$)F#, corresponding to a ;.-)F thruster on a ;.%# #o#ent ar#. &hus the no#inal

thruster force for design purposes was chosen to "e $F to leave a #argin for

#anufacturing i#perfections.

3.3 Airframe design

*ince a strea#lined shape for the rocket was not re7uired, there was great

freedo# in the #echanical design of the airfra#e. &he overall design o">ective was to



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keep the #o#ent of inertia s#all for a thruster #o#ent ar# of ;.%#, while

acco##odating all the co#ponents of the rocket and achieving sufficient ro"ustness

to survive the shock of landing.

&wo alternative layouts for the pitch and yaw thrusters relative to the centre of#ass were considered. &hese are depicted and descri"ed in &a"le .&o si#plify the

control syste#, the altese design was chosen as #anufacturing tolerances were

less likely to lead to crosscoupling "etween the pitch and yaw axes and the vertical

force exerted "y the thrusters could "e used to decelerate the rocket on landing.

Design issile altese

Diagram

Bside view Bshowing centre of #assC and "aseviewA rocket #otor no44le shown in "lack,thruster no44les shown in dark greyC

Proposed structural materials ?i"reglasstu"e

*heet alu#iniu#Kpoly#er, kite spar truss

Linear motion direction aected b!thrusters

Hori4ontal 5ertical

Axis most aected b! pitch thrustermisalignment"

Paw oll

Eect o side wind High Low

Roll moment o inertia Low High

Robustness on impact High Low

&able : 0om!arison of alternati"e mechanical layouts for the "ehicle. C3isalignment of a !itch thruster #ill cause its thrustto ha"e com!onents #ith moments about the ya# and roll a/es4 assuming misalignment errors are e%ual in these t#odirections, the a/is about #hich the thruster has the greatest moment arm #ill be most affected4 in the


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#otor, solenoid valves, "atteries, gas supply and avionicsCA and four identical

fi"reglassKcar"onfi"re kite spar truss structures supporting the thrusters and

landing legs at their tips. &he rocket #otor #ount was designed to accept either the

%## dia#eter /erotech 3$%(& #otor BD$0EC or, via an adapter, the %0##dia#eter 8stes 891 #otor BD$%EC.

&o acco##odate a worstcase landing condition, the trusses were designed

using static e7uili"riu#, pin>ointed truss analysis and 8uler "uckling so that each

could support an upwards load of $;;F at the tip Bcorresponding to a single landing

leg decelerating a $kg #ass fro# )#Ks to rest in ;.$s with a peak force twice the

averageC. ?ull details of the calculations are provided in /ppendix /. /s well as the

inelastic collision "etween the landing leg and the ground, additional energy

a"sorption would "e effected if necessary "y elastic "uckling of the truss seg#ents

and shear failure of the Breplacea"leC nylon screws.

/ (/! rendering of the #echanical design is shown in ?igure 9.

Figure : A 0A* rendering of the mechanical design of the rocket. &he central bo/ 5translucent dark grey6 is made fromsheet aluminium and houses the rocket motor, batteries and gas cylinder 5red64 the four solenoid "al"es 5black and grey6 are

mounted on its e/terior faces. &he thrusters 5yello#6 are su!!orted at the ends of the !rimary fibreglass kite s!ar truss5#hite6, to #hich the 0FR) kite s!ar landing legs are also attached. )neumatic tubing and a"ionics are not sho#n $ the

latter are secured to the to! surface of the central bo/.

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! "neu#atics syste#

4.1 Overall pneumatics system design

&he function of the pneu#atics syste# is to distri"ute a throttlea"le flow of

highpressure gas fro# a supply to a nu#"er of attitude thrusters. In this case four

attitude thrusters were used, a pair each for pitch and yaw.

&hrottle control is given "y onoff solenoid valves, driven with a pulsewidth

#odulation B16C wavefor# fro# the #icrocontrollerA this allows the effective

thrust to "e varied continuously fro# 4ero to the thrust fro# a constantly open valve

"y changing the duty cycle. &he alternative would have "een the use of

proportional solenoid valves which give a flow rate that varies with the solenoid

currentA however, since the dyna#ics of the rocket approxi#ate a lowpass filter the

16 #ethod can "e used, and 16 has the advantages of #ore efficient use of gas

Bthe input flow to the thruster no44le is at a constant high pressure while the valve is

open, giving a higher average specific i#pulseC and lower co#ponent cost.

4.2 as supply

&he gas supply for the attitude thruster syste# consists of a s#all cylinder

containing $+g of li7uid car"on dioxide, co##ercially availa"le for the inflation of

"icycle tyres D$)E. *uch cylinders are designed to "e disposa"le, using a special fitting

to pierce the seal on the cylinder as it is screwed in.

Figure 1-: A 1g dis!osable cylinder of li%uid carbon dio/ide, of the ty!e used for this !roDect, and a fittingto attach it to a bicycle tyre. &he fitting !ierces a seal on the stem of the cartridge #hen scre#ed on.

&he vapour pressure of (2%at %0 is 0).at# D$+EA in order to use readily

availa"le pneu#atics fittings and valves Bwhich are designed to run at pressures of

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up to $;"ar for industrial pneu#atics applicationsC a #iniature pressure regulator is

used as the first co#ponent in the circuit, i##ediately after the gas "ottle and fitting.

&his also eli#inates the reduction in pressure as the cylinder e#pties, which would

cause the effective gain of the control syste# to reduce over ti#e.

4.3 Thruster no!!le design

&he analysis in this section follows the #ethod fro# D-E, which assu#es steady

unifor# isentropic onedi#ensional flow of an ideal gas. &his was >ustifia"le in this

pro>ect since the no44les are s#all B#eaning that startup transients are shortC,

pressures and te#peratures are near a#"ient and the accelerating no44le flow would

reduce the thickness of the "oundary layer such that it would not have an effect.

&he thrust fro# a no44le consists of two ter#s, the i#pulse thrust Bthe reaction

to the expulsion of exhaust gases, e7ual to the #ass flow rate #ultiplied "y the

exhaust velocityC and the pressure thrust, as shown in the following e7uation Bter#s

at the exit of the no44le are denoted "y the su"script eC:

F= m ve "e #e#atm

It #ay "e shown that the #axi#u# thrust for a given supply pressure is

achieved when the exhaust gas supply is expanded to a#"ient pressure, #eaningthat the pressure thrust is 4ero. &his #ay "e achieved using a convergingdiverging

de Laval no44le: the inlet flow is co#pressed while at su"sonic velocities in the

converging section of the no44le, reaches sonic velocity at the throat and expands

supersonically in the diverging section.

&he efficiency of a rocket #otor can "e #easured "y its specific i#pulse @ the

i#pulse delivered "y a given #ass of propellant divided "y its weight:

Is#=m ve

m g =

ve

g

&he theoretical specific i#pulse of (2% at )"ar a"ove at#ospheric pressure

exhausting to at#ospheric pressure is 0$s Bfor co#parison, the specific i#pulse of

solid fuel rocket #otors ranges fro# $9+s to ;0s and li7uid propellants can achieve

specific i#pulses of 0%s in the case of hydrogenoxygen co#"ustion BD$-ECC. 6ithout

the pressure reduction Boperating in "lowdown #ode, as #any satellite attitude

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control syste#s functionC the specific i#pulse would "e )s @ however, such

operation would "e i#practical in this application for the reasons outlined a"ove.

?or this design it was assu#ed that the inlet gas pressure was )"ar a"ove

at#ospheric at a te#perature of %9 and that a thrust of $F was re7uired. &heexhaust velocity for this ratio of pressures is given "y:

ve = " # R Tsu##ly##atm

#su##ly#

= $0#ms#&his then deter#ines the #ass flow rate of gas re7uired for a given thrust:

m =F

ve= "$%#0

&$gs

#

&he re7uired throat area Bthe area over which the sonic velocity is reachedC can

then "e calculated fro#:

"throat= mR Tsu##ly

#su##ly= #$'#0' m"

where Q is the 5andenkerckhove function:

= "# #" #

&he exit area of the no44le can then "e calculated fro# continuity and !e *aint

5enant's e7uation:

"e =

" ##atm

#su##ly" ##atm#su##ly

#

"throat= ""'

m"

&he corresponding throat and exit dia#eters are $.0## and $.-##

respectivelyA a $+g cylinder would last +.0s with a car"on dioxide consu#ption of

%.)gKs.

?our valves were fa"ricated to these specifications "y echanics La"

techniciansA an engineering drawing and photograph of the valve are shown in

/ppendix=. nder tests, the no44le produced ;.F using car"on dioxide at )"arA a

supply pressure of -"ar was needed to give the full $F of thrust.



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4.4 "alve selection

&he solenoid valves control the flow of car"on dioxide fro# the gas supply to

the thruster no44les. *election criteria for the valves included low #ass, high input

pressure rating and high flow coefficient kvBi#plying a low pressure loss across thevalveC as well as low costA in particular, the valve is re7uired to supply %.)gKs of

car"on dioxide at )"ar Bgauge pressureC to the thruster. &hese values are shown for

s#all solenoid valves fro# a range of different #anufacturers in &a"le 0Bdata

o"tained fro# #anufacturers' data sheetsCA ?igure $%shows a scatter plot of the flow

coefficient and pressure rating of these valves, together with a portion of the

"oundary of the selection criterion. /s can "e seen, a nu#"er of valves are eligi"le for

selection "ased on these two propertiesA of these, the valve chosen was the H8%

produced "y ?esto D$E, on the grounds of #ass and cost.

#anuacturer and name#aximum

pressure $bar%&v

value#ass$&g%

(lippard 8& - ;.;- ;.;-

!yna#co dash$ !$, $.+## orifice $; ;.)- ;.;)

!yna#co dash$ !$, %.## orifice ) $.$0 ;.;)

?locontrol F series $.+## orifice /l "ody -.) $.$ ;.$

?locontrol F series %.;## orifice /l "ody 0.) $.) ;.$

?locontrol F series %.0## orifice /l "ody 0 % ;.$

etalwork 1I5.I inline valve %.0## orifice +.) % ;.$0

?esto H8% $.9 ;.;+

?esto H8 %.- ;.$%

&able 2: )ro!erties of small solenoid "al"es from a range of manufacturers

II= 1ro>ect ?inal &echnical eport $0 !avid 6yatt


17/52

Figure 11: A scatter !lot of the flo# coefficient and !ressure rating of small solenoid "al"es from a range of differentmanufacturers. &he solid s%uares, and the lines Doining them, re!resent the boundary of the selection criterion for

ma/imum inlet !ressure and flo# coefficient4 "al"es abo"e and to the left of the line are acce!table.

4.# $%M fre&uency selection

&ests were conducted to deter#ine the relationship "etween average thrust and

16 wavefor# properties. &he ?esto H8% valves responded to 16 at

fre7uencies up to ;;H4A a high 16 fre7uency is desira"le as it ena"les a faster

response of the control syste# and reduces the likelihood of exciting structural

vi"ration in the vehicle. However, with increasing 16 fre7uencies the relationship

"etween duty cycle and average thrust was found to "eco#e increasingly nonlinear,

as shown in ?igure $%A this is assu#ed to "e due to the inertia of the valve spool,

which will act as a lowpass filter to attenuate the har#onic co#ponents of the 16

wavefor# that define the duty cycle. /s a co#pro#ise "etween nonlinearity and

perfor#ance, a 16 fre7uency of );H4 was chosen.

II= 1ro>ect ?inal &echnical eport $) !avid 6yatt

& &! $ $! ! !! ' '! ( (! ) )! % %! #0 #0!

0"!

0!

0(!

#

#"!

#!

#(!

"

""!

"!

"(!

&

Dynamco dash*# D#+, #'mm

Dynamco dash*# D#-, "&mm orifice .lo*control / series #'mm orifice Al ody

.lo*control / series "0mm orifice Al ody

.lo*control / series "$mm orifice Al ody -etalwor1 2343 in*line 5al5e "$mm orifice

.esto -67"

.esto -67&

-axim8m inlet press8re 9ar:

.low

coefficient,

15


18/52

0% 20% 40% 60% 80% 100%

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

10Hz

50Hz

100Hz

Interpolation from 0to full thrust

Duty yle

!ore

"#$

Figure 1(: &he a"erage force e/erted by a thruster no88le as a function of the duty cycle, for anumber of different fre%uencies. &he solenoid "al"e used #as the Festo 3E(4 the #orksho!com!ressed air su!!ly #as used #ith a no88le entry !ressure of 2bar. A linear inter!olation

bet#een 8ero and the ma/imum thrust achie"ed is also !lotted.

$ %lectronic design

#.1 $rocessor selection

&he on"oard processor for the vehicle is a vital part of the digital control

syste#A if during develop#ent it was discovered to lack a necessary capa"ility,

replacing it with one that did would likely involve significant changes to the

hardware and software associated with the pro>ect. In order to avoid this, and also to

develop expertise that would "e useful for future pro>ects re7uiring si#ilar

hardware, the union of the esti#ated future capa"ilities re7uired for this pro>ect and

other proposed rocketryrelated pro>ects were taken as a #ini#u# specification

when selecting the processorA in particular, the nu#"er of analogue input channels

and the speed re7uire#ent restricted the choice significantly. &he full specification is

listed in /ppendix (.

&he processor selected was the L1(%$ BD$9EC Ban /-&!I core with a

variety of on"oard peripheralsC, produced "y FR1 *e#iconductor BD%;EC. &his device

was chosen since it not only #et the criteria set "ut was also readily availa"le fro#

8#"edded /rtists BD%$EC as a #odule with support circuitry, an *%% connector and

II= 1ro>ect ?inal &echnical eport $+ !avid 6yatt


19/52

on"oard nonvolatile storage, reducing the electronic design and asse#"ly

co#plexity.

#.2 Attitude sensor selection

/ttitude sta"ilisation first re7uires attitude deter#ination a"out the two

sta"ilised axes of the vehicle Bpitch and rollC. In general, the rotation of a platfor# can

"e #easured "y a nu#"er of #eans BD$-EC: either "y tracking external pheno#ena

Bcelestial "odies or the a#"ient #agnetic field directionC or "y #easuring the inertial

effect of rotation. In the latter case, several different technologies exist, all collectively

known as gyroscopes a co#prehensive overview is given in D%%E.

&he s#allest and lightest gyros availa"le are of the vi"rating structure typeA

in these, the sensor #easure#ent is derived fro# the (oriolis acceleration's effect on

a #icro#achined structure that is driven to oscillation Bsee D%E for a description of

the different ways in which such sensors #ay "e constructedC.

*everal #anufacturers produce such devices, including urata, *ilicon *ensing,

F8(&okin, 3yration and /nalog !evices. &he selected co#ponent was the

/!I*$+%); produced "y /nalog !evices BD%0E, D%)EC, whose "uiltin analogueto

digital conversion B/!(C and cali"ration features si#plified the develop#ent of thecontrol syste#. / picture of the sensing ele#ent fro# this gyro is shown in ?igure $.

Figure 1 5taken from (6: A closeu! of the sensing element from the Analog *e"ices A*HR?IA*?series of micromachined rate gyros. &he resonating mass oscillates hori8ontally #ithin the inner frame4the 0oriolis force induced by this causes the inner frame to oscillate "ertically, #hich is detected by the0oriolis sense fingers. &he t#o identical sensing elements oscillate in anti!hase, allo#ing the control

electronics to remo"e commonmode noise 5e.g. due to e/ternal shock6.

II= 1ro>ect ?inal &echnical eport $- !avid 6yatt


20/52

#.3 $o'er supply

&he electrical power supply for the vehicle is re7uired to provide )5 at under

0;;#/ for the processor and sensors and %05 at up to $/ for the solenoid valves,

while si#ultaneously "eing light in weight and s#all in volu#e. /fter exa#ining anu#"er of options, including a stepup converter fro# lowvoltage rechargea"le cells

and a series interconnection of pri#ary Bnonrechargea"leC cells, a decision was #ade

to use lithiu# poly#er "attery packs specifically designed for electric #odel

aviation, due to their high voltage output and high energy density. &he "attery packs

used were #anufactured "y &hunder 1ower BD%-EC and are rated to produce $$.$5 at

up to 9/A two connected in series supply the solenoid valves, while a voltage

regulator produces )5 for the logic. &he co#paratively low capacity of the "attery

packs B-;#/hC is not an issue thanks to the short duration of the flight.

#.4 Circuit design

Initial prototyping of the interface "etween the processor and the other

co#ponents was carried out using a develop#ent "oard supplied "y the

#anufacturer of the processor #odule D%$E.

&hanks to the integration of the processor and other supporting co#ponents onthe processor #odule, the #a>ority of the avionics circuit design constituted

interconnection. &he avionics functions are divided "etween three groups of circuit

#odules:

$. &he #ain avionics "oard, holding the processor #odule, voltage regulator,

!I1 switches for input, L8!s and a pie4oelectric "u44er for output, a slot for

an *! card for datalogging, as well as connectors for the other "oards.

%. &he valve driver "oard, holding four power 2*?8&* to interface the

processor to the solenoid valves. B&he circuit for this "oard was designed "y

3ary =ailey.C

. &he two gyro "oards, each carrying a single rate gyro and a connector, to "e

#ounted in appropriate orientations to the airfra#e. B&he circuit and layout

for these "oards were designed "y 3ary =ailey, who also asse#"led the#.C

*tandard %.)0## pitch olex cri#p connectors were used throughout, to allow



21/52

for easy asse#"ly and #odification of the wiring harness.

&he rate gyros and the *! card are connected to the processor's *1I "us D9E and

the four valves were connected to four channels of the processor's "uiltin 16

generator. &he re#aining input and output devices on the circuit "oard areconnected to generalpurpose inputKoutput B31I2C pins. 1rogra##ing and

de"ugging of the #icrocontroller was carried out through the processor #odule's

"uiltin *%% connectorA when the avionics "oard was under test outside of the

vehicle, the circuit was also powered fro# the )5 supply provided "y a *=

connection.

?or safety reasons, the avionics did not control the ignition of the rocket #otor

to avoid accidental triggering of the launch circuit. Instead, a pair of #icroswitches

are wired in series and attached to two opposite landing legs such that the switches

are closed when the legs are in contact with the groundA when either of the

#icroswitches loses contact with the ground, one of the processor's 31I2 pins was

pulled high to trigger the sta"ilisation control loop.

(ircuit diagra#s and printed circuit "oard layouts for the avionics are shown in

/ppendix!.

& Soft'are and control

(.1 System model

It was deter#ined fro# a (/! #odel of the #echanical co#ponents of the

vehicle that the #o#ents of inertia around the pitch and yaw axes were

approxi#ately identicalA #oreover, the offdiagonal ter#s in the #o#ent of inertia

tensor were at least a factor of %;; less than the diagonal ter#s.

&hus, for the purposes of control syste# design the vehicle was #odelled as

two uncoupled linear singleinput, singleoutput B*I*2C syste#s with identical

dou"leintegrator dyna#ics fro# thruster duty cycle rBfro# $ to S$, corresponding

to full activation of the negative or positive thrusters respectivelyC to angle Bin

radiansC:

II= 1ro>ect ?inal &echnical eport $9 !avid 6yatt


22/52

=Tfull r

%

TFr =Tfull

% s"

&he no#inal #o#ent of inertia a"out each axis is +.0 x $; kg #% Bfro# the (/!

#odelC, with an assu#ed thruster tor7ue of ;.%F# at $;; duty cycle. 8sti#ated

variations in these values and thus in the overall gain are indicated in &a"le ).

Parameter 'ominal #aximum estimate #inimum estimate

o#ent of inertia, J Bkg #%C +.0 x $; -.- x $; ).$ x $;

?ullyactivated thrustertor7ue, &fullBF#C

;.% ;. ;.$)

2verall gain, &fullKJ 0;. -+.9 %).0

&able 7: Jominal "alues and ranges for the dynamic !ro!erties of the "ehicle. &he range in the moment of inertia #asdetermined as the nominal "alue K(-4 for the thruster tor%ue, the thrust from the no88le had been measured to be bet#een-.;7J and 1.7J de!ending on test conditions, #hile the moment arm remained -.(m.

(.2 )ate gyro sensor inputs

&he /!I*$+%); rate gyros used D%)E have "uiltin analoguetodigital converters

B/!(C and are factorycali"rated to give an output in degrees per second. However,

due to variations in te#perature Band other factorsC the analogue voltage outputfro# the sensing portion of the device when at rest varied over ti#eA thus the

#anufacturer's reco##ended procedure for resetting the null point was followed

every ti#e the avionics syste# was powered up.

&o o"tain esti#ated orientation #easure#ents around each axis, the angular

velocity reading fro# each rate gyro is sa#pled at the fre7uency of the control loop

Bsee section+.C and integrated nu#erically. &he rate gyros have a default analogue

"andwidth of );H4, as well as a digital =artlett window ?I filter with an ad>usta"le

cutoff fre7uencyA the latter was set to % taps, giving a cutoff at approxi#ately

$;H4, to prevent aliasing.

(.3 Control la'

&he approach and ter#inology in this section is taken fro# D%E.

/ dou"leintegrator syste#, such as the transfer function fro# tor7ue to angle

II= 1ro>ect ?inal &echnical eport %; !avid 6yatt


23/52

in a rocket in free flight, has a constant phase of $;O at all fre7uencies. &o sta"ilise

such a syste#, one approach involves the use of a lead co#pensator @ a low

fre7uency 4ero and a highfre7uency pole straddling the crossover fre7uency @ to

give a good phase #argin at crossover without re7uiring high gain at any fre7uency.&he settling ti#e for the controlled syste# &sBwith a % criterionC was set at $s

with a da#ping coefficient T of ;.0). &his gives a continuousti#e control law as

follows:

&cs =0$$"s0"!")

00"%%%s#

&he fre7uency of the 4ero is ;.9$H4 and that of the pole is ).;H4.

&he continuousti#e control law thus deter#ined was then transfor#ed todiscrete ti#e using &ustin's "ilinear transfor#ation. / sa#ple fre7uency of %;H4

was chosen in order to lie inter#ediate "etween the ;d= fre7uency of the closedloop

syste# and the );H4 16 fre7uency of the valves. &he discreteti#e control law

was i#ple#ented in statespace for# with a onedi#ensional state /as follows:

!n# = 00%0)!n "nrn =&0"'%!n %#)'!n

=ode fre7uency response plots of the plant transfer function, continuousti#econtrol law, discreteti#e control law and the closedloop transfer function are

shown in ?igure $0.

II= 1ro>ect ?inal &echnical eport %$ !avid 6yatt


24/52

Figure 12: Bode !lots of the !lant, continuous and discretetime control la#s and the o!en and closedloo! transferfunctions. &hanks to the addition of the !hase lead com!ensator described abo"e, the !lant is stabilised #ith a !hase margin of

27L at a crosso"er fre%uency of 1.>rads15(.186.

(.4 Simulation

&o deter#ine whether the sta"ility of the syste# would "e affected "y the

saturation nonlinearity due to the finite availa"le thruster tor7ue and the 16

fre7uency of the valves, nu#erical si#ulations of the control syste# were carried out

using atla" and *i#ulink software produced "y &he athworks D%9E. &he relevant

"lock diagra#s are shown in ?igure $)and a ti#ehistory of a si#ulation involving

"oth a static distur"ance tor7ue Bdue to thrust vector #isalign#entC and rando#

fluctuating distur"ances is shown in ?igure $+. &his si#ulation predicts that the

controller descri"ed a"ove would sta"ilise the syste# even in the face of

nonlinearities and distur"ances.

II= 1ro>ect ?inal &echnical eport %% !avid 6yatt


25/52

Figure 17: &he ?imulink block diagram used to simulate the beha"iour of the system #ith nonlinearities from actuatorsaturation and )M3 thruster acti"ity. For sim!licity, the ma!!ing from controller out!ut to thruster beha"iour #asencased #ithin a subsystem and further di"ided into t#o )M3 generators and a!!ro!riate interconnections. *isturbance

tor%ues acting on the "ehicle include a 1cm misalignment bet#een the thrust "ector 5significantly greater than e/!ected6 andthe centre of mass and a fluctuating tor%ue to model #ind loading.

Figure 1: A simulation of the beha"iour of the nonlinear system under the influence of the disturbances in the block diagramabo"e, #hile attem!ting to maintain an attitude of -L. t is obser"ed that the actual angle fluctuates around -.(rad 511.7L6#ith a fre%uency of a!!ro/imately (8 and an am!litude of u! to -.1rad 5L6 !eakto!eak4 this #ould not be a !roblem for

the rocket, es!ecially since the disturbance conditions are likely to be o"erly harsh.



26/52

(.# Soft'are structure

&he controller descri"ed a"ove was

i#ple#ented on the rocket's on"oard L1(%$

processor. 2verall the flight control softwareconsists of several co#ponents:

Launch se7uencer: this waits until the rocket

has "een placed on the pad Bi.e. until the

launch detect switches are closedCA it then

resets the rate gyros' 4ero point and

configures the digital filter, activates a

warning "u44er and waits for one of the

launch detect switches to open. 2nce this

occurs, execution switches to the:

(ontrol lawKdatalogger loop: this is

executed at a preset fre7uency. In each

execution of the loop, the current angular

velocity readings are read fro# the rate

gyrosA these are integrated to update the

esti#ated orientation of the vehicleA and the

control law is applied to derive duty cycle

co##ands for the thrusters.

Lowlevel peripheral driver functions: these

allow the highlevel functions #entioned

a"ove to access the processor's on"oard

peripherals and, through the#, the sensors and actuators that for# the control

syste#. In particular, drivers were written for:

&he processor's *1I interface

&he functions supported "y the rate gyro's digital control electronics

&he L8!s, !I1 switches and "u44er on the avionics "oard

&he processor's 16 outputs

II= 1ro>ect ?inal &echnical eport %0 !avid 6yatt

Figure 1;: A flo#chart sho#ing the se%uence ofsoft#are states during a launch attem!t. &he

NE*s are used to indicate the success or failureof stages in this se%uence, and an audible alarm

sounds to indicate the "ehicle is #aiting forliftoff or e/ecuting the control loo!.

3nitialise SD card

;ro8nd contact

maintained-

Comp8te attit8de

Command thr8sters

Delay 8ntil next cycle

'es

(o

Delay #s

?og data to SD card

>ait for

gro8nd contact

>ait for

liftoff

.light control

loop


27/52

&he processor's analogue inputs

&he processor's "uiltin ti#ers

&he interface to the *! card for datalogging purposes #ade use of code fro#

D;E./ flowchart illustrating the se7uence of software states during a launch is

shown in ?igure $-.

(.( *evelopment environment and toolchain

&he #anufacturer of the processor "oard D%$E provided a develop#ent

environ#ent for the processor. 1rogra#s were written in the highlevel ( language

on a 6indows 1(, co#piled with the 3F ( crossco#piler for / processors

D$E and downloaded to the processor's "uiltin flash #e#ory over an *%%

connection. &he sa#e *%% connection was the pri#ary #eans of testing and

de"ugging the code.

( Construction and testing

+.1 Time and e,penditure

/ co#parison of the pro>ected schedule Bas of January %;;-C and the actual

schedule is shown in ?igure $. (onstruction of the vehicle took significantly longer

than anticipated, due to overopti#istic esti#ation of the extent of the practical work

to "e carried out. /s a result of this, the 1hase % airfra#e design was #odified to

function as either a "enchtop test #odel or a flying vehicle with #ini#al

#odification, eli#inating #uch of the work associated with 1hase . It was thus a

si#ple #atter to switch "etween "ench tests with off"oard power and co#pressed

air supplies and an on"oard gas supply and "attery for final testing and launch.

?ew specific set"acks were encounteredA the principal ones were initial

difficulty in o"taining key co#ponents, leading to a late start on construction, and

the need for repairs after the first test flight Bsee section -.+"elowC.

&he approxi#ate total cost of the #aterials and parts used in the pro>ect was

U$$%;, of which U+; was in the for# of car"on dioxide cartridges donated "y

II= 1ro>ect ?inal &echnical eport %) !avid 6yatt


28/52

(atering < Leisure *upplies Ltd and the re#ainder was generously contri"uted "y

icrosoft esearch.

Cambridge weeks #)@0#@0(

"!@0#@0(

0#@0"@0(

0)@0"@0(

#!@0"@0(

""@0"@0(

0#@0&@0(

0)@0&@0(

#!@0&@0(

""@0&@0(

"%@0&@0(

0!@0$@0(

#"@0$@0(

#%@0$@0(

"'@0$@0(

0&@0!@0(

#0@0!@0(

#(@0!@0(

"$@0!@0(

@0!@0(

0(@0'@0(

#$@0'@0(

"#@0'@0(

")@0'@0(

(eek o!" #$%S &aunch days

Planned ('anuary ))*"

6ardware constr8ction 9mo8nting loc1:

Software and control law implementation

2hase " in*laoratory "Do. stailisation s8spended from centre of mass

Airframe design B constr8ction


2hase & flying "Do.

2ne8matic system modification to C" cylinder s8pply and testing

2reparation and s8mission of report to +=A Safety B Technical Committee

Eattery power s8pply constr8ction and testing

Airframe modification for roc1et motor


3ntegration and testing

7xtensions

Constr8ction of f8ll 'Do. inertial na5igation system 9electronic and software:

3n5estigation of alternati5e prop8lsion methods

3mplementation of position control

3n5estigation of alternati5e controller types

>riting final technical report

$ctual (up to May ))*"

6ardware constr8ction


2hase " in*laoratory "Do. stailisation s8spended from centre of mass

Airframe design

Airframe constr8ction

-odifying airframe to sa5e mass


2hase & flying "Do.

2ne8matic system modification to C" cylinder s8pply and testing

2reparation and s8mission of report to +=A Safety B Technical Committee

Eattery power s8pply constr8ction and testing


3ntegration and first test flight

=epairs and modifications

>riting final technical report

2hase # in*laoratory enchtop #Do. stailisation on a t8rntale

7lectronic interfacing 9gyro and " solenoid 5al5es to microcontroller:

.8rther electronic interfacing 9gyro and " solenoid 5al5es to microcontroller:

2hase # in*laoratory enchtop #Do. stailisation on a t8rntale

7lectronic interfacing 9gyro and " solenoid 5al5es to microcontroller:

.8rther electronic interfacing 9" gyros and $ solenoid 5al5es to microcontroller:

Figure 1>: Gantt chart for the !roDect, sho#ing breakdo#n into )hases 1 and e/tensions.

+.2 $hase 1- Turntale tested

/ singleaxis test rig was "uilt to test the feasi"ility of the concept of cold gas

>ets for attitude sta"ilisation. &his took the for# of a turnta"le with a "all"earing

pivot, "earing a pair of solenoid valves Bthe ?esto H8 #odel was used for this

experi#entC and thruster no44les connected to the la"oratory co#pressed air supply,

a single rate gyro with its sensitive axis vertical and the processor #odule on the

supplied develop#ent "oardA the apparatus is depicted in ?igure $9. / #anually

tuned 1I! controller was a"le to de#onstrate sta"ilisation of the turnta"le's angle

and re>ection of distur"ances, as shown in ?igure %;.

&he concept was thus considered to "e validated, and design and construction

of the vehicle proceeded.

II= 1ro>ect ?inal &echnical eport %+ !avid 6yatt


29/52

Figure 1: &he turntable testbed. &he aluminium turntable 5(;cm / cm6 su!!orts a cardboard bo/ on its left sidecontaining the !rocessor module on its de"elo!ment board 5at left, in red6, the small yello# gyro carrier board and a circuitboard #ith !o#er transistors to allo# the !rocessor to control the solenoid "al"es. &he right half of the turntable su!!orts

the t#o solenoid "al"es #ith attached thruster no88les, connected to the #orksho! com!ressed air su!!ly "ia the red!neumatic hoses and the blue hose at the to! of the frame. )o#er is also su!!lied from offboard, "ia the red and black #ires

#ound around the blue hose.

0 " $ ' ) #0 #" #$

*%0

*)0

*(0

*'0

*!0

*$0

*&0

*"0

*#0

0

#0

"0

&0

$0

!0'0

(0

)0

%0

*##

*0%

*0(

*0!

*0&

*0#

0#

0&

0!

0(

0%

##

Angle 9left y axis:

Thr8ster command

9right y axis scale:

Time 9s:

Angle9degrees:

Figure (-: A trace of the angle of the turntable 5as integrated from rate gyro readings, on the left hand "ertical a/is6 and thecorres!onding thruster duty cycle commands 5on the right hand "ertical a/is6 against time, using a manually tuned )*controller. m!ulsi"e disturbances #ere deli"ered to the turntable at tO(s, 2s and s 5a!!ro/imately6. &he initial thruster

acti"ity u! to tO(s #as due to torsion of the air su!!ly hose im!arting a disturbance tor%ue to the turntable. &he ma/imumobser"ed angular acceleration of the turntable as a result of thruster acti"ity #as 1(>degs(.

II= 1ro>ect ?inal &echnical eport %- !avid 6yatt


30/52

+.3 $hase 2 / 3 airframe construction

&he construction of the rocket took place over the period ?e"ruary @ ay %;;-.

(o#ponents were sourced and fa"ricated as follows:

*olenoid valves were supplied "y (a#"ridgeshire Hydraulics and1neu#atics Ltd. and 6est 3roup plc BD%EC.

1neu#atic and electronic co#ponents and #echanical fasteners were

supplied "y ?arnell BDEC and * (o#ponents Ltd BD0EC.

&he processor "oard was supplied "y 8#"edded /rtists /= BD%$EC.

&he rate gyros were supplied "y /rrow 8lectronics BC Ltd BD)EC.

(o#pressed gas cylinders and fittings were donated "y (atering < Leisure

*upplies Ltd BD$)EC and supplied "y 6iggle Ltd BD+EC.

3?1 and (?1 rod was supplied "y /ir =orn ites Ltd BD-EC and /ctive

&oys BDEC.

ocket #otor #ounts were supplied "y Hesperis &echnology Ltd BD9EC.

Lithiu# poly#er "atteries were supplied "y *kyLine odels BD0;EC.

&he plastic electronics housing was supplied "y J *ains"ury plc BD0$EC.

?our thruster no44les, and a pivot and du##y #otor for "ench testing of the

attitude control syste#, were fa"ricated "y echanics La" technicians.

&he panels for the central alu#iniu# fra#e were fa"ricated in the Instru#ent

6orkshop using a (F( a"rasive>et #achining centre.

1rinted circuit "oards were produced "y the 8lectronics !evelop#ent 3roup.

/sse#"ly was carried out in the echanics e44anine La" and the Instru#ent

6orkshop.

/ photograph of the asse#"led 1hase % < airfra#e is shown in ?igure %$.



31/52

Figure (1: &he )hase ( P airframe,


32/52

*u"stituting the gas cylinder adapter for a lighter e7uivalent, #odified with a

custo##ade outlet port to fit directly to the downstrea# pneu#atic

co#ponents Bsaving: 0;gC

e#oving parts of the central alu#iniu# "ox fra#e that did not contri"ute tostructural strength Bsaving: %%gC

+.# 0ench tests

2ne of the unusual aspects of attitude thrusters co#pared with other #ethods

of active sta"ilisation is that the control syste# is entirely decoupled fro# the rocket

#otor. ?ull advantage was taken of this to allow the control syste# to "e tested on a

"ench, with the task of "alancing on a pivot Ba steel spike in a conical alu#iniu#

socketC placed in the #otor #ount, close to the vehicle's centre of #ass.

*uch testing was perfor#ed #ultiple ti#es during integration of the vehicleA

initially all the avionics were off"oard, "ut as co#ponents were constructed they

were attached in place on"oard the airfra#e. It was also invalua"le in identifying

crucial "ugs in the flight control software. / photograph of an earlystage "ench test

is shown in?igure %%A later "ench tests integrated #ore of the co#ponents onto the

vehicle, and used on"oard gas cylinders rather than off"oard co#pressed air due tothe distur"ance tor7ue, spring constant and da#ping produced "y the pneu#atic

hose.

II= 1ro>ect ?inal &echnical eport ; !avid 6yatt


33/52

Figure ((: Bench testing of the airframe and control system. n this image the!rocessor, !o#er su!!ly and air su!!ly are all offboard 5at left6, attached "iaan umbilical su!!orted by the retort stand4 the s!ike is "isible underneath the

airframe. ?uch an earlystage bench test #as not used for trialling controlla#s but for integrating and testing the "arious !neumatics and a"ionics

com!onents.

1erhaps #ost i#portantly, "ench testing allowed the testing of control laws

without the issues associated with the use of rocket #otors. &his syste#, with the

dyna#ics of a short pendulu#, approxi#ates the real syste# Bwith dou"leintegrator

dyna#icsC.

However, when tested with the control law derived in section +., the airfra#e

was o"served to oscillate unsta"ly even at reduced pneu#atic syste# pressures

Bcorresponding to reduced overall gain, which should serve to #itigate insta"ilitiesC.

/ sa#ple ti#e history fro# such a "ench test is shown in ?igure %, showing clearly

the increasing a#plitude of oscillations until a li#it cycle is reached. It is nota"le that

actuator saturation is not reached on either axis, i#plying that the thruster

nonlinearity is not to "la#e for this oscillation B"earing out the results of the

nu#erical si#ulation descri"ed in section +.0CA instead, other un#odelled dyna#ics

of the syste# #ust "e causing the oscillation. 2ne o"vious explanation is coupling

"etween the rotation axes, shown "y the synchronisation of oscillations "etween the

two axes. &his was neglected in the syste# #odel "ut #ay have arisen through one

or #ore of:



34/52

isalign#ent of the gyro sensitive axes

isalign#ent of thrusters

2ffdiagonal ter#s in the #o#ent of inertia tensor

?urther investigation is necessary to deter#ine the cause and to i#ple#ent anappropriate #ultiinput #ultioutput BI2C control law.

Figure (: Nogged data from a bench test using an onboard gas cylinder #ith a dual ??9 lead controller. &he angles abouta/is - and 1 are !lotted against the left hand y a/is, the thruster duty cycle commands on the right a/is.

+.( Maiden flight

/lthough the control syste# was not fully functional, as descri"ed a"ove, it was

decided to take the opportunity to testlaunch the vehicle, na#ed estrel, to gain

experience of the pheno#ena that #ight "e expected in flight. &his took place at the

8ast /nglian ocketry *ociety B8/*C D$$E =ig 8/* launch event near 8lsworth,

(a#"ridgeshire, on + ay %;;-. &he vehicle was launched on an 8stes 891 #otor

fro# a flat alu#iniu# "aseplate Bwith no launch guidesC in a sheltered area to

#ini#ise wind effects.

&he audi"le alar# was heard "efore launch, showing that the launch se7uencer


0 0! # #! " "! & &! $ $! !

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)

%

*#

*0)

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*0$

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#Axis 0F Angle 9left y axis:

Axis 0F Thr8ster command9right y axis:

Axis #F Angle 9left y axis:

Axis #F Thr8ster command9right y axis:

Time 9s:

Angle9degrees:


35/52

routine was active and waiting for launch detection, "ut on liftoff the rocket rapidly

veered away fro# the vertical and crashed into the ground near"y within $ second of

ignition. / se7uence of photographs of the launch is shown in ?igure %0.

Figure (2: &he launch of the rocket. A: &he rocket on the launch !ad. B: ?hortly after liftoff the rocket begins to "eer offcourse. 0: &he rocket continues rotating and after reaching a height of about -.7m turns back to#ards the ground. *: &he

rocket as it landed. 5)hotogra!hs: A,B,0: Qane 0handler4 *: Ed 3oore6

!ue to the #alfunction the rocket crashed upside down, with the electronics

housing hitting the ground first. *uch a failure #ode had not "een anticipated,

#eaning that the electronics housing was not designed to resist the i#pactA the

housing fractured and da#age was caused to the processor "oard and one of the

gyro "oards. /s well as re7uiring repair, this and the fact that the datalogging

function had not "een integrated into the flight control software #eant it was not

possi"le to ascertain whether the control law loop had "een active during the flight

or what its outputs were. 8vidence relevant to esta"lishing the cause of the failure

includes:

In previous "ench tests, following the audi"le alar# and si#ulation of launch

B"y releasing the ground contact switchesC the flight controller had always



36/52

"een activated.

/ drop in supply voltage to the processor during the flight would reset the

control software, returning it to the 6ait for ground contact state.

8xperienced o"servers noted that the "ehaviour of the vehicle in flightrese#"led that of incorrectly"uilt #odel rockets with low or 4ero passive

sta"ility #argin.

/ slow gas leak could "e heard for a nu#"er of #inutes after the flight. &his

suggests that a su"stantial 7uantity of car"on dioxide re#ained in the

cylinderA since "ench tests indicated that a cylinder was e#ptied after a few

seconds when the control law was active, it it likely that the solenoid valves

did not operate significantly.

Fo o"servers reported hearing the loud "u44 associated with operation of the

solenoid valves or seeing distur"ances of the s#oke plu#e fro# the #otor

that could "e ascri"ed to the thrusters' exhaustA however, it is not certain

whether either of these effects would have "een o"serva"le under the

circu#stances of the launch.

It was later discovered that a software fault had #eant that a different control

law fro# that intended had "een activeA this incorrect control law had "een

shown to have a definite effect on the rocket's dyna#ics in "ench tests,

although it was not fully sta"ilising.

&he "alance of evidence suggests that the flight control loop was not triggered

Bpossi"ly due to a transient voltage drop resetting the processorC and thus the vehicle

"ehaved as an inert #ass under the influence of the rocket #otor's thrust and

gravity.

1ositive outco#es fro# the test flight included experience gained with

launching the vehicle using rocket #otors and the highlighting of a nu#"er of issues

with the rocket's design to i#prove:

&he i#portance of a #eans of #easuring hidden state of a control syste# in

order to find out the cause of a failure was highlighted. / datalogger interface

was integrated into the flight control software with the highest priority.



37/52

&he screws securing the top plate of the central alu#iniu# fra#e, which had

to "e re#oved to access and replace the gas cylinder and "atteries, were very

difficult and fiddly to re#ove. &his #ade it ti#econsu#ing to replace the gas

cylinder "etween tests, and #eant that the "atteries could not "e re#oved7uickly to #ake the rocket safe. &hese were replaced "y #etal pins that could

"e inserted and re#oved rapidly.

5isual or audi"le confir#ation that the processor is operational and the

progra# is running was i#ple#ented using the on"oard L8!s to signal the

state of the launch se7uencer.

It is i#portant to protect the electronics housing "etter in case of #a>or

#alfunction @ for exa#ple using roll "ars. &his consideration will "e taken

into account "efore the next flight test.

) Conclusions

.1 $roect achievements and validity of concept

/n attitude thruster sta"ilisation syste# for a s#all rocket was designed and

constructed using #ostly co##erciallyavaila"le co#ponents, for a cost of aroundU$$%;. ?unding to pursue the pro>ect was contri"uted "y icrosoft esearch.

Fu#erical si#ulations indicated that the control syste# would sta"ilise and

control the vehicle appropriately. However, "ench tests of the real syste#'s dyna#ics

B#ade possi"le "y the initial choice of an attitude control syste# that was

independent of the rocket #otorC showed insta"ilityA it is suspected that this is due to

crossaxis coupling that was neglected during controller design.

/ trial launch was conducted to gain experience and test the control syste# in

flight. &he test did not appear to show any control activity, possi"ly due to resetting

of the processor at the instant of launch.

/lthough the pro>ect has not yet de#onstrated a sta"ilising control syste#, the

underlying hardware and software functions correctly and in principle the ai# could

"e achieved "y appropriate redesign of the control law facilitated "y "ench testing on

the real syste#. It is hoped that develop#ent will continue and future test flights will

II= 1ro>ect ?inal &echnical eport ) !avid 6yatt


38/52

"e a"le to show a fully functioning attitude control syste#.

.2 $roect significance

2ne of the ai#s of this pro>ect was to develop an active sta"ilisation syste# that

could "e applied to #ore conventional a#ateur rockets to control the ascent

tra>ectory despite crosswinds and other distur"ances. It was con>ectured at the

conceptual design stage that attitude thrusters were not the #ost applica"le #ethod

in this regard, due to the considera"le additional #ass and volu#e they occupy, "ut

they were chosen for their suita"ility in other respects Bease of design and

construction as well as independence fro# the rocket #otorC.

&his is vindicated "y the experience of constructing the vehicle estrel.

/dding the hardware of the control syste# to a conventional rocket would likely

outweigh the "enefits of active sta"ilisation, especially given the #ass of the gas

supply needed for a longer flight andKor higher thrust levels. / control syste# such

as this one would likely "e of #ost value in a lowvelocity rocket where aerodyna#ic

sta"ilisation Bactive or passiveC is ineffective and #anipulating the direction of the

rocket exhaust is not practicalA this is very si#ilar to the situation of or"iting space

vehicles where attitude thrusters are co##only used.Fonetheless, the attitude deter#ination and co#putational hardware and

software developed for this pro>ect could well "e used to control other types of

actuators for attitude sta"ilisation syste#s. It would "e particularly straightforward

to adapt the software to control conventional ho""y servos, since they are also

controlled "y pulsewidth#odulation signals BD0%EC.

.3 valuation of approach

&he construction of the vehicle re7uired significantly #ore ti#e than given in

the initial plan. &his was due to overopti#istic esti#ation of the ti#e

re7uired for practical tasks and neglecting to consider design iteration, rework

etc.

&he i#portance of a #eans of #easuring hidden state during tests in order to

find out the cause of a failure was highlighted "y its lack in the first flight of

II= 1ro>ect ?inal &echnical eport + !avid 6yatt


39/52

the vehicle.

/t several points, #odels of the vehicle's dyna#ics were used that were later

found to "e inaccurate @ "oth #athe#atical #odels that neglected i#portant

dyna#ics Be.g. crossaxis couplingC and physical test setups that have externaldistur"ances Be.g. forces fro# u#"ilical connectionsC. It is i#portant to

recognise for what purposes a given #odel is sufficiently faithful and when it

is appropriate to switch to a #ore co#plex and accurate #odel.

&he choice of a sta"ilisation concept that could easily "e tested under

la"oratory conditions aided syste#level integration considera"ly co#pared

with a concept that could only "e tested in flight.

!uring integration, pro"le#s with su"syste#s were fre7uently resolved

successfully "y a #ethodical reductionist approach of testing the functioning

of every co#ponent in isolation prior to integration.

6hen undertaking field work, it was found to "e difficult to predict which

ite#s of e7uip#ent would "e necessary under a given set of circu#stancesA

thus, as #any ite#s as practical should "e kept to hand.

.4 uture 'or5/s noted a"ove, in order to achieve the ai#s of this pro>ect the control law

should "e redesigned using an approach that considers the true #ultiinput #ulti

output BI2C dyna#ics of the vehicle for exa#ple, I2 pole place#ent or HV

opti#al controller synthesis Bdescri"ed in D0EC. &he latter #ethod can "e used to give

a control law that is guaranteed to "e ro"ust against variations in the plant

para#eters up to a certain level. *o#e #odifications to the airfra#e Bparticularly the

electronics housingC could also "e #ade to increase its physical ro"ustness to i#pact.

?ollowing this, a nu#"er of enhance#ents could "e #ade to the vehicle to

enhance its capa"ilities. &hese include:

8xtended flight duration : =y using a #ore powerful #otor Be.g. the /erotech

3$%(& BD$0ECC and a larger gas cylinder, the duration of the flight #ight "e

extended fro# s to 9s.

1osition control: =y controlling the vehicle's attitude, the actuators give

II= 1ro>ect ?inal &echnical eport - !avid 6yatt


40/52

indirect control over position in a hori4ontal plane. In order to i#ple#ent this,

sensors would "e re7uired to #easure the vehicle's attitude in all + degrees of

freedo# B!o?C @ for exa#ple, an extra rate gyro and three orthogonal

accelero#eters @ and an additional pair of thrusters would "e necessary tocontrol the roll axis.

2n"oard autono#y: &he vehicle could "e e7uipped with sensors to allow it to

execute si#ple tasks while air"orne Be.g. following a white lineC.



41/52

* Ackno'ledge#ents

I would like to thank #y supervisors, !r Hugh Hunt B(8!C and 1rofessor

(hris =ishop Bicrosoft esearchC, for providing resources, advice and assistancethroughout the course of the pro>ect. I a# particularly grateful to icrosoft esearch

for contri"uting the #a>ority of the funding for this pro>ect.

I would also like to thank the nu#erous other people who have helped #e with

the design and construction of the rocket, in particular:

3ary =ailey B(8!C

*i#on =ox Bicrosoft esearchC

ane (handler

(ai4en (heng B(8!C

ichard (hrist#as B(8!C

arco (ostan4i B(8!C

Helen (raig

Jason (rick B(a#"ridgeshire Hydraulics and 1neu#aticsC

!a#ian Hall B8/*C

Henry Halla#

/ndy Hughes B*ilicon *ensingC

1eter Long B(8!C

Ji# acfarlane B8/*C

o" acfarlane

!avid iller B(8!C

Jon oney B(atering < Leisure *upplies LtdC 8d oore

=rendan 2'!onoghue

ike o"erts B8/*C

/lastair oss B(8!C

Jere#y < *ylvia 6yatt



42/52

1+ References

D$E W/ctive 3uidanceW, http:KKwww.ukrocket#an.co#KrocketryKgi#"al.sht#l

Baccessed $)K;$K%;;-CD%E W*tudio di veicolo con sta"ili44a4ione attivaW,http:KKwww.criscaso.co#Kra44i#odellis#oK(asi#iroK Baccessed $)K;$K%;;-C

DE F/*/, %;;0: W&he 5ision for *pace 8xplorationW Baccessed viahttp:KKwww.nasa.govKpdfK)))#ainXvisionXspaceXexploration%.pdfC

D0E WF/*/ (entennial (hallengesW,http:KKexploration.nasa.govKcentennialchallengeKccXchallenges.ht#l Baccessed$)K;$K%;;-C

D)E WartletW, http:KKwww.cuspaceflight.co.ukK#artlet.ht#l B$)K;$K%;;-C

D+E (a#"ridge niversity 8ngineering !epart#ent, %;;: W1roperties of theInternational *tandard /t#osphere at /ltitudeW, in &her#ofluids !ata =ook

D-E (ornelisse J 6, *chYeyer H ? , 6akker ?, $9-9: Wocket propulsion ointed analysis this gives:

&%N $;;FKsinB%$OC N %-F

&$N &%cosB%$OC N %)9F

&he struts were then si4ed to withstand yield failure in tension and 8uler

"uckling in co#pression. /lthough reversi"le elastic 8uler "uckling on landing

would not "e pro"le#atic for the structure, it was assu#ed it would represent a

lower li#it on the failure load. &he #aterial assu#ed was glass fi"re reinforced

poly#er B3?1C kite spar of circular crosssection, with properties 83?1N $)31a and

^y, 3?1N $$;1a Btaken fro# D00EC. &he results are shown in &a"le +.


Str8t #

Str8t &

Str8t "

G#

G"


46/52

(trut Length$mm%

Load $'% #inimumdiameter $mm%

Actualdiameter $mm%

$ $) S%)9 $.-

% $-- %- ).9 +.)

$) _); Besti#atedC .+ 0

&able : ?i8ing of !rimary truss struts. &he ect ?inal &echnical eport 00 !avid 6yatt


47/52

Appendi, . Truster no//le final design

Figure (: *esign for the 1J, 7bar inlet thruster no88le 5all dimensions in mm6. &he 37 thread on the inlet acce!ts astandard !neumatic fitting4 the flange and holes are for mounting to the "ehicle@s structure.

II= 1ro>ect ?inal &echnical eport 0) !avid 6yatt

Figure (;: &he !rototy!e no88le.


48/52

Appendi, C Re0uire#ents for rocketry avionics

/vionics re7uire#ents for generalised rocketry pro>ects are shown in &a"le -

Bco#piled in colla"oration with =rendan 2'!onoghueC.

)unctionEstimatednumerical

speciications

Presentor uture

need*Processor re+uirement

orthogonal gyroscopes p to ;;Ks eachaxis

% present,$ future

analogue inputs or *1Iinterface

+ solenoid valves %05 $/ 0 present,% future

+ 16 digital outputs

/r#ing switch 1resent $ digital input

Liftoff detector 1resent $ digital input

Fonvolatile data logging $); "ytes at );H4 1resent Fonvolatile #e#ory or*1I interface to *! card

ealti#e control up to $;;H4 controlloop

1resent ?ast floatingpointcalculations

*ignalling avionics state 0 L8!s, $ "u44er 1resent ) digital outputs

&i#ing ;.;$#s resolution 1resent &i#ers

ploadingKdownloading data *%% 1resent /&

orthogonal accelero#eters p to )g each axis ?uture analogue inputs or *1Iinterface

0 radiocontrol servo#otors 16, );H4 update ?uture 0 16 digital outputs

=aro#etric pressure sensor $ #=ar resolution,range ;.=ar to %=ar

?uture $ analogue input

al#an filteringKI functions + !o?, $% states ?uture ?ast floatingpointcalculations

ecovery syste# deploy#ent B%electric ignitersC

%;/ for %;;#s ?uture % digital outputs

6ind velocity sensor B axesC p to );;#Ks ?uture analogue inputs

&able ;: nterface and other re%uirements for a"ionics systems for rocketry !roDects, di"ided bet#een !resent needs 5re%uiredby this !roDect6 and future needs 5!otentially re%uired by other !roDects6.

&he re7uire#ents on the processor in particular are: $; analogue inputs ?ast floatingpoint calculations BInterface toC nonvolatile #e#ory $$ digital outputs B+ 16 capa"leC, % digital inputs *%% co##unication *1I "us &i#ers

II= 1ro>ect ?inal &echnical eport 0+ !avid 6yatt


49/52

Appendi, Avionics circuit diagra#s and circuit board

layouts

/ll circuit diagra#s and printed circuit "oard B1(=C layouts were produced

using 8agle 8(/! software fro# (ad*oft D0)E except where otherwise stated.

Main avionics oard

Figure (>: ?chematic for the main a"ionics board.

Figure (: )rinted circuit board layout for the main a"ionics board. &his is a doublesided )0B #ith handsoldered "ias4red denotes traces on the to! of the board, blue denotes traces on the bottom. &he board is ;-mm s%uare.

II= 1ro>ect ?inal &echnical eport 0- !avid 6yatt


50/52

"alve driver oard

Figure -: ?chematic for the "al"e dri"er board. &he original circuit for this board #as designed by Gary Bailey.

yro oard

&his circuit "oard was purely a "reakout "oardA the 1(= layout, designed "y

3ary =ailey, is shown in ?igure %.

Figure (: &he gyro mounting board, designed by Gary Bailey using Easy)0B E0A* soft#are. &his is a doublesided)0B #ith handsoldered "ias4 red denotes traces on the to! of the board, blue denotes traces on the bottom. &he gyro is

mounted u!side do#n in the centre of the s%uare of !ads4 #ires then connect it to the traces on the board.


Figure 1: )0B layout for the "al"e dri"er board.&his is a singlesided circuit board, 7>mm /

>mm.


51/52

$hotographs of assemled circuit oards

Figure : &he "al"e dri"er board 5left6 and main a"ionics board 5right6, fully !o!ulated. &he t#o ranks of header sockets onthe a"ionics board acce!t the !rocessor module.

Figure 2: 9ne of the t#o gyro boards installed on the rocket. &he label is amnemonic to record the direction of rotation that gi"es a !ositi"e out!ut.



52/52

>riting the report

To do

ZZZZrecovery syste#ZZZZlist software used in appendixZ

Control of trans5erse translation

?or a rocketpowered vehicle that is re7uired to #ove transversely

Bperpendicular to the direction of the rocket thrustC, there are two #ain #ethods to

achieve this:

$. /pplication of one or #ore forces whose resultant is a force in the desireddirection at the centre of #ass. *uch forces could "e applied "y s#all attitude

thrustersA the vehicle is treated as a 'free' #ass since the rocket #otor negates

the gravitational attraction, analogous to a puck on an airta"le.

%. /pplication of tor7ues to tilt the #ain thrust vector such that it has a

co#ponent in the desired direction. If the #agnitude of the thrust is not

increased, its reduced vertical co#ponent will lead to a loss of altitude of the

vehicle. &his is analogous to a helicopter or to a "oat on a fastflowing river.

/pproach % has the pro"le#s "oth of loss of altitude during traverse

#anoeuvres and of increased difficulty in the control of the vehicleA however, it has

the advantage of approach % that it can "e i#ple#ented using no additional

actuators co#pared with approach $. &hus to the extent that transverse translation

was considered in the design of the vehicle, approach % was taken.

Documents

Active Stabilized Rocket Wyatt