IEEE-RWEP Feedback Controlled Faculty-Proj-Desc

8/10/2019 IEEE-RWEP Feedback Controlled Faculty-Proj-Desc

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Faculty Project Description for Brushless DC Motor Project

Project Description The brushless DC motor project has been used for at least two years in a first-semesterintroduction to electrical engineering (EE) course. More than 125 first-year EE students havesuccessfully built the project during that time. The simple-to-construct motor kits provide

exposure to elementary circuits, magnetics, power electronics, and feedback systems.Feedback signals are generated using magnetic and optical sensors. The feedback signalcauses an electromechanical reed switch or a power transistor to actuate an electromagneticcoil. Project benefits are an animated, physical manifestation of electrical engineering and arecruiting tool for future students. Assessment results indicate a high degree of studentsatisfaction with the project.

Educational objectives of the project are to gain an understanding of the operation andapplication of brushless DC motors, particularly in transportation systems; to comprehend theelectrical, magnetic, and mechanical principles of operation of the brushless DC motor; tocorrelate the physical system components and layout with their abstract schematicrepresentation; to use physical sensors as feedback elements; and to compare the use of an

operationally visible mechanical reed switch as a coil commutator with the use of a solid statepower transistor.

An assignment to analyze the potential impact of personal electric vehicles on energy use andcarbon dioxide emissions is included to illustrate a real-world application and its benefit tosociety. This assignment depends on at least two lecture periods for introduction andclarification. The students write a final report that: defines the problem, shows construction andfinal stage pictures of their motor, presents their analysis results, and draws conclusions. Thisreport is a major outside effort for the students. You may want them to work in pairs to reducethe work. Make sure a digital camera is available during motor construction or that somestudents can bring theirs and share.

A schematic of the system showing all electrical components is shown in Figure 1. In this

1.5V

1.5V

1.5V

1.5V

TIP106Reedswitch

1N4001

X

3121E

SW1

k

OPB831W55Optical switch

SW2

SW1 and SW2 areconceptual only.

Implemented as wirehook-ups on breadboard.

Hall-effectswitch

k

C O I L

Figure 1. Schematic of brushless DC motor



system, the position of the rotor may be sensed by a Hall-effect sensor switch, a slotted opticalswitch mechanically configured as a rotary encoder, or a reed switch. The Hall sensor or theoptical switch signal drives the base of a Darlington PNP transistor. The transistor operates asa switch to energize the coil whenever a rotor permanent magnet is facing the coil.

Alternatively, the reed switch may be used to combine the sensor and coil switching functions.The diode allows the coil current to circulate during times that the coil is disconnected from the

battery supply. This reduces voltage stress on the transistor and reed switch. Thefreewheeling diode provides opportunity for further exploration by students.

The motor is built in two laboratorystages. An unassembled motor kit isshown in Figure 2. Although studentsbuild their own individual motors, theywork in pairs to assist each other inassembly.

The first operational stage, built in thefirst-week laboratory, uses a mechanicalreed switch to commutate theelectromagnetic coil. Students can seethe reed switch actuate as they move therotor permanent magnets. During thesecond-week laboratory, the reed switchis replaced with a bipolar junctiontransistor (BJT). The remainder of theconstruction is completed and a fully assembled motor is shown in Figure 3. The transitionfrom the mechanical reed switch to the solid state transistor switch effectively introduces theconcepts of current flow and transistor switching. The students’ physical understanding ofswitch operation provides a basis for understanding transistor operation as a switch. It isrewarding when first-year EE students comprehend the functional operation of the transistoras a switch. The concept of magnetic field attraction and repulsion is also observed.

Having optical and Hall-effect feedbackavailable invariably raises the studentquestion, “Which is better?” This yields agreat opportunity to discuss their relativemerits and applications. Students also cansee the effects of inductive switching byremoving the freewheeling diode from thecircuit and seeing the reed switch arc as itoperates. Students may observe the switchvoltage on an oscilloscope with and withoutthe freewheeling diode in the circuit.

Students may measure the speed of theirmotor using a stroboscope or anoscilloscope attached to the rotor positionsignal. If these instruments are available,speed measurement is a very satisfyingconclusion to the laboratory. Some studentsmodified their motors (e.g., by adjusting encoder phasing or by adjusting the position of Hallsensor) to demonstrate the effects on motor speed.

Figure 2. Unassembled motor kit

Figure 3. Fully-assembled final stage motor



The parts list for the project is shown in Table 1. Cost per kit has been $50 for the past twoyears. The supplier at http://www.simplemotor.com/ has been used for all items except thosewith an asterisk.

Useful tools and equipment:Safety glasses, solder iron, solder, wire cutters, wire stripper, steel cutter, sandpaper,electrical tape

A complete set of motor assembly instructions follows. This is provided to the students. Thestudents work in pairs to help each other build their motors.

OPB831W or eq. Slotted optical switch

A3121E Hall-effect switche.g., Yaskawa R24U Reed switch (1A, 50V)

TIP106 PNP Darlington transistor (2A, 20V)1N4001 Diode (2A)

270Ω, 10kΩ ¼W resistors50 ft, 27 ga. magnet wire4” nail for magnet wire coil4 permanent magnets 0.5” dia. discs5" x 6" press-boardPre-cut 7/8” round PVC pipePre-cut 5/8” square PVC pipe “rotor core”7/8” PVC endcapsOpaque optointerrupter disk 1.3” dia.PushpinT-pinSequins

Adhesive feltRubber cab to protect sharp end of t-pinSuper glue4 AA battery holder¼” round dowel

1.25” long square (3/8” sides) wooden stand24 ga. jumper wire*Male header pins*Female headers*TO-220 heat sink*Heat sink grease*2”x3” breadboard*



Assembly Instructions:Brushless DC Motor

I n s t r u c t i o n s ( r e a d a n d u n d e r s t a n d e a c h st e p c o m p l e t e ly

b e f o r e a c t i n g ! )

1. Insert the T-pin into one of the end caps.

2. Insert the rotor core into the same cap as shown below.Carefully apply some pressure (avoid poking yourself

with the sharp T-pin) to push the rotor core

approximately 1/2" (10-12mm) into the cap.

3. Insert the round wooden dowel into rotor core tube.

4. Insert the pushpin into the other cap.



5. Complete rotor assembly as shown. Carefully push the

caps towards each other until they cannot move anymore. The T-pin must be secured firmly. This process

may require some strength. Be careful not to bend the

T-pin or poke yourself.

6. Carefully open the super-glue tube. Make sure you are working over a protected

surface. Glue the magnets to the flat surfaces of the rotor core with the letter S facing out. Straighten the T-pin if necessary. You will need to press the magnets

onto the rotor for at least 30 seconds to allow the glue to adhere.

7. Cut out the disk.

Poke a hole in the center, which ismarked by a cross. Apply some glue to

the middle of the disk and glue it to thecap with a shorter axle (with the

pushpin). Slide two sequins as shown

below. The sequins act as a spacerbetween the disk and the stand and

work better if their convex surfaces faceoutwards.

8. Insert the rotor into the stands marked with blue

and silver stars as shown below. Hold the stands

and test to see if rotor spins freely. Make finaladjustments to the T-pin if necessary.

9. Position the stand with the blue star on the board.While covering the corresponding star completely,

align the marks on the stand with the line on theboard as shown. Keep in mind that super glue bonds

instantly. Glue the blue star stand to the board.



10. After letting the glue set, insert the

rotor into the stand marked with theblue star.

Note that the star's position and themarks are approximate. You may

need to move the silver star stand

slightly to achieve the lowestrotational friction. Leave a gap ofabout 1/16" (1/32", or 0.8mm on

each side) between the rotor and

the stands.

Glue the silver star stand to theboard. Test again to see if the rotor

spins freely.

Carefully use steel cutters (n o t wire

cutters) to trim the off the sharp end

of the T-pin (shield the free, sharpend to keep it from flying away duringtrimming). Or, secure the rubber end cap on

the sharp end of the T-pin.

11. Insert the nail into the stand with the green

star. Apply glue as shown.

12. Cut two 8" lengths of wire from themagnet wire spool. These will be used

later for connecting the reed switch. Usethe rest of the spool of wire to wrap

around the area between the tape and

the head of the nail. Keep the coil turnsrelatively tight and always wrap in the

same direction.

Tape the end and beginning of the

wire using the same tape andleaving open ends of wire about 6"long. Remove about ¼” to ½” of

the wire ends’ insulation with

sandpaper.

Both leads ends

must be more

than 5” long



13. Solder the two coil leads to the short end of two

male header pins. You may have more success atsoldering if you work with a partner. Ask for

instructor help if you have trouble.

14. Position the coil stand on the board as shown. Turn the rotor slowly to find therotor magnet that comes closest to the coil head. Position the stand so there is a

1/16" (1.5mm)gap between

the coil head

and the closestmagnet on the

rotor. You maywish to mark

this position onthe board to

remember itbefore gluing.

Glue the stand

onto the boardin this position.

15. Attach the green self-sticking felt pad to the reed switch stand as shown.This soft pad decreases the reed switch vibration thus decreasing the sound

it generates.

16. Sand the wire ends of the

two 8” lengths of wire youcut earlier to remove theinsulation. Clean about 1"

to 1.5” (4cm) on one end

and ¼” to ½” on the other end of each wire piece. Be careful not to break the reedswitch, it is very fragile. Wind longer bare ends tightly around outside contacts of

the reed switch as shown. Solder the wires onto the reed switch.



17. Twist the wires as shown.Make sure the reed switch is

kept securely in the positionshown by the twists of wire

on the opposite side of thestand.

18. Make sure the reed switch is oriented as shown in step 15. Solder the ends of the

reed switch leads to the short ends of two male header pins.

19. Position the reed switch holder on the

board. It should be located at a distanceof about 1/8" (3mm) from the closest

magnet. Check the rotation of the rotorto make sure that it does not hit the

reed switch. The three slots cut into the

stand must line up with the rotormagnets.

IMPORTANT: The most sensitive part of the reed

switch is not in the middle of it, but more to the sideas shown to the right. You should hear a clicking

sound when each magnet passes by the reed switch.

Move the reed switch a little closer to the magnetsuntil all four can turn the reed switch on.

Make sure the three slots cut into the stand line up with the rotor magnets.

Glue the reed switch holder to the board.



20. Tin the battery holder leads with

solder. Solder the battery holderleads to the short ends of two

male header pins. Attach the

battery holder to the board in theposition shown.

You may have more success in

soldering if you work with a partner.

21. Set the board aside.Tin the three colored leads with solder. Solder the

three colored leads to the pins of three-pin femaleheader strip. This is the most difficult solder step.

Ask for help if you need it!

The color order is important!Red=right, black=center, blue=left.

Tin the other end of these leads with solder.

22. Get two, two-position female parts. Cutfour 10” leads from the wire in your kit.

Tin the leads with solder. Solder leads toeach of the four header pins.

FINISHED SOLDERING!



23. Tape the 2”x3” breadboard onto the motor base board in the

position shown. You should have three pairs of male headerpins – from the battery pack, the coil and the reed switch.

Connect the circuit using the header pins and the breadboard.Make sure the wires cannot get wrapped onto the rotor. Insert

batteries to verify operation. You may need to reverse the coil.

1.5V

1.5V

1.5V

1.5V

Reedswitch

COIL

Negative

battery

Coil

Positive

battery

Coil

Reed

switch



24. Insert the Hall-effect sensor into the three-pin

female header strip. Holding the sensor with theprinted side up, the left side should insert into the

red-leaded jack. Use needle-nose pliers to carefullybend the Hall-effect sensor to a 90˚ angle with the

printed side of the sensor facing outward .

25. (Optional: Smear a dab of heat-conducting grease to the metallic

tab-side of the TIP106 transistor.) Attach the transistor to theheat sink fin using the small bolt and nut. Use needle-nose pliers

to bend the leads as shown.

26. Insert the Hall-effect assembly onto the reed-

switch stand. The printed-side of the sensorshould face the rotor magnets. It needs to be

close, but not touching the rotor magnets.



27. Connect the Hall-effect sensed /

transistor-switched circuit. You will needto make two jumper wires. If you use

stranded wire to make jumpers,

then tin the leads with solder tomake them easier to plug into the

breadboard. One connects the

TIP-106 to the Hall switch (seecircuit diagram on right), the other jumper wire connects the TIP-106

to the negative battery supply.

Try to get the Hall switch chip as

close to the rotor magnets withouttouching them.

Verify operation!

1.5V

1.5V

1.5V

1.5V

TIP106

X

3121E

Hall-effectswitch

C O I L

Black

Re dBlue

10 k

baseemitter

collector

10k resistor

Hall switch Red

Hall switch Blue

Hall switch Black

Jumper wires



Locate the optointerrupter pins as shown on the following picture. It is very important to

identify all four pins properly. Wrong connection in the circuit will destroy theoptointerrupter. There are no spares of this part. Insert the two pairs of long-leaded

female header strips onto each pair (Emitter and Sensor) of opto pins making sure they

are not touching each other.

28. Glue the opto to the square wooden stand aligned with

the guidelines on the stand. The Sensor side should be

attached to the stand.

29. Position the optointerrupter stand on the board as

shown in the picture. If you rotate the rotor, the diskblades should be in the middle of the slot as deep as

possible without hitting the optointerrupter. Glue thestand to the board. Wait for the glue to dry. You willneed to experiment with it to find the best position of

the disk to provide a good start and the best speed.



30. Connect the Hall-effect sensed / transistor-switched circuit. Verify operation!

31. Clean up the wiring. Arrange breadboard connections so you can demonstrate your

circuit in its three modes of operation.

32. If a tachometer is available, use it to measure the speed of your rotor for itsdifferent modes of operation.

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IEEE-RWEP Feedback Controlled Faculty-Proj-Desc