2007 FIRST Robotics Conference Simple Robot Electrical Design Presented by: Al Skierkiewicz, Broadcast Engineer, Mentor Team #111 Rookie Year 1996

2007 FIRST Robotics Conference

Simple Robot Electrical Design

Presented by:Al Skierkiewicz, Broadcast Engineer,

Mentor Team #111Rookie Year 1996


Outline

Ten things a Rookie Team needs to know. Real world design example. Minimize the losses. What happens with a motor under varying

conditions. Working with a design and layout. Techniques and layout. Tools Questions


Top Ten Things

Rookies Need to Know.


10. The Robot Section of the manual and the Tips And Guidelines Docs are not the only place to get info.• Check the FIRST website (www.usfirst.org) often,

team updates come out weekly and the Q&A allows teams to ask questions and get answers from the GDC.

• The FIRST website (FRC Documents) also will have manufacturer specification sheets and the Tips and Guidelines will also include manufacturer website info.

• Check team websites for suggestions and up to date info on KOP motors

• IFI, Innovation First, has a great website and PDF documents for all it’s products.


9. The main battery is a high current device.

• The main battery is capable of 600 amps for a short period of time.

• This is enough current to burn wires, motors, dangling bracelets, rings, and necklaces.

• This is enough current to weld most metals including the terminals on the battery.

• In a two minute match, it is more than capable of running a robot with a six motor drive.


8. You shouldn’t control two motors with the same speed controller.• I don’t recommend this practice. Rules in

the past have allowed certain motors to be controlled by the same controller.

• Most motors already exceed the current specs for speed controllers.

• Motors rarely need the same drive signal.• Doing so will result in less than designed

operation.


7. A stalled motor is one that is not moving.

• A motor is stalled when no power is applied.• A motor is stalled when mechanically prevented

from turning.• A motor is stalled (near stall) when used in a

tank style drive design without using omni wheels. i.e. the motors will draw max current in every turn.

• A stalled motor draws maximum current, 130 amps for small Chalupa (CIM) and 96 amps for the large. Six motor drives can draw over 500 amps!


6. Snap action breakers do not trip at the rated current.

• All breakers can function with up to 600% over current for a few seconds.

• All breakers can function with up to 200% over current for almost ten seconds.

• All breakers can function with about 150% over current indefinitely (based on internal temperature of breaker)

• Breaker specs are available on FIRST Website• Breakers will “buzz” when repeatedly tripped.


Breaker Trip Curves


5. Motors run at different speeds in opposite directions.

• Motor brush bias causes this difference.• CIM (or Chalupa motors) have the least

difference.• Similar motors on different sides of the robot

will likely run in opposite directions due to mounting.

• Speed controllers will supply the correct input power, when calibrated, for each direction.

• The bias can be overcome in software or by driver practice.


4. Mechanical design does affect electrical design.

• Operating characteristics are influenced by mechanical design. Arms draw max current when parallel with the floor, long wires reduce power to critical motors.

• Placement of components may lead to changes in electrical layout and wire runs.

• Do not place speed controllers in a debris field from exposed mechanical systems (chain sprockets, open transmissions, pulleys bearings).

• Replacement is a critical design factor.


3. Wire does make a difference!

• At the currents encountered, real world voltage drops of several volts can occur in your wiring.

• All wire has loss, smaller diameter wire has greater loss. I recommend #10 for all CIM (large and small), the compressor and all Fisher Price motors.

• Please remember both the positive and negative leads carry the same current.

• Design for short wire runs. Loss is length dependent.

• You can attach motor leads directly to speed controllers and/or cut them shorter.


2. If you use the default software, you must calibrate the speed controllers.• Speed controllers and joysticks are not

matched.• Joysticks are not precision devices.• Calibration will match joystick travel and

center position to speed controller operation.• Without calibration you may not be able to

achieve maximum output from your motors.• Without calibration, motors may not zero

speed or brake when the joystick is released.


1. You are never alone!

• As a rookie, you should have access to a mentor team in your area. They are your greatest asset.

• Team websites like www.chiefdelphi.com can have a lot of useful information. Beware that some answers might not be accurate.

• FIRST Q&A is a valuable resource, check it often.• I can be reached at [email protected]

one person per team please.• At events, any team can help. Your lead

inspector is a valuable resource.

http://www.chiefdelphi.com/

mailto:[email protected]


Real world design of an arm motor.

• Lets take a large Chalupa motor with the following specifications:

• Stall Current = 96 amps• Peak Power Output = 280 watts• Choose operating point of 1600 RPM@225

oz-in., 40 amps, 160 watts out.• If input= 12v@40amps, then • R motor =12/40=.3 ohms


Large Chalupa Motor Curves


StallRPM=0I=96 Amps

Chosenoperating point40 amps, 160 W1600 RPM


If there is resistance in series with a circuit, the current will decrease in direct proportion to the

resistance. A decrease in current will provide less power from the motor.

Ohm’s LawR (motor) =V/I=12V/40A=0.3 Ohms

Calculating for 4’ of #10, 2’ of #6, 0.011 ohms for the battery internal resistance and .002 ohms for

breakers and terminals..3+.008+.0028+.011+.002=0.3238 ohms

I (motor) =V/R=12V/.3238 Ohms=37 Amps


New Point for wiring.20 watts less power40 oz-in less torque

Motor Load Point with Real World Losses


If this is an average system and four small Chalupa drive motors are near stall,

I (stall) =100 amps x 4 motors=400 amps.

The battery is capable of delivering more than 600 amps when fully charged but has an

internal resistance of 0.011 ohms. So for this example 400 amps flows through 4’ of #6, a few connectors and the fuse panel, then the

voltage loss in this robot is:V=I*R=400*0.0238ohms=9.52 volts.

That leaves only 2.5 volts available for all other systems including the RC. In terms of motor current, I=V/R=2.5/.3238 ohms=7.7 Amps (if

the RC were still in control).


New pointOnly 20 watts output60 oz-in. of torque

High current on drive motors


Each intermittent load on a motor reduces the available current and therefore reduces power and RPM temporarily.

• This is why many robots with arms are not able to raise a game piece as designed, other motors are causing losses in the system.

• It is also why a team that raises the arm when not moving may not achieve the same movement while driving.


To Begin Design and Layout of Robot Electrical System, know

your robot system.• It is essential to know the list of requirements

for the system before you begin.• It is essential to have an grasp on the location

of mechanical parts and needed clearance.• Must work with mechanical designer to place

major components in a central location, i.e. battery, main breaker, terminal block and fuse panels.


–You must know how many motors will be used.

– How many and what type of motors for drive and where located.

– How many motors for actuators, are they required to be speed controlled or operated by relay.

– How many motors for steering.– How many servo motors.– Where will all these be located on the

robot?


–You must know what electrical hardware you will be using.•How many Victors and how many Spikes will

be needed?•Will you be using the SLU or crimp

connectors for the mains wiring?•How do I attach cable to the battery

terminals?•Do I need to use insulated or non insulated

terminals?•Do we need to solder?


–Know the installation failure modes of all devices.•How should it react when powered? •Does it have indicators and what do they

mean?– Know the correct handling of all devices.

•Check wiring polarity for all devices before applying power!

•What are the mechanical stresses due to mounting and termination?

•What happens if you drop the device?•What is the correct wiring polarity?•How should it be electrically protected?• Is there a common mistake when installing?


Now, Let’s Begin With a Plan!

• Make a table of controlled components needed

• Add control components (Victor or Spike)• Obtain the control inputs and outputs from

the software team• What Breakers are needed?• Will sensors be associated with the motors?• Other data, color coding


Color code everything, make a list of functions. Electrical and software will need this list.

Motor Control Feedback Speed Controller

Relay PWM Output Braking (A-B)

Current Rating Comp Output

Connection

Chiaphua PWM Distance/Velocity encoder, Current

Blue 1 No 40A Flipped PowerLoc

Chiaphua PWM Green 2 No 40A Flipped PowerLocChiaphua PWM Distance/Velocity

encoder, Current Orange 3 No 40A Normal PowerLoc

Chiaphua PWM Red 4 No 40A Normal PowerLocGlobe PWM Digital Pot - 270 Deg Yellow 5 No 30A Normal PowerLocGlobe PWM Digital Pot - 270 Deg Grey 6 No 30A Normal PowerLoc

Fisher Price PWM Digital Pot - 300 Deg Purple 7 No 30A Normal PowerLocWindow PWM Digital Pot - 270 Deg Brown 8 No 20A Normal PowerLocWindow PWM Digital Pot - 180 Deg Black 9 No 20A Normal PowerLoc

PWM White 10 NoPWM Green/Brown 11 NoPWM Black/Brown 12 No

Relay Relay Output

Air Piston #1 In/Out 1-way Valve On-Off Blue/Black 1 20AAir Piston #2 In/Out 1-way Valve On-Off Blue/White 1Air Piston #3 In/Out 1-way Valve On-Off Green/Black 2 20A

Green/White 2Air Piston #4 In/Out 1-way Valve On-Off Orange/Black 3 20A

Orange/White 3servo or cylinder Red/Black 4 20Aservo or cylinder Yellow/Black 5 20A

Grey/Black 7 20ARed/Green 6 20A

Purple/Yellow 20A

Digital Inputs Port Analog Inputs PortPump Pressure

1 Front Crab Pot 12 Rear Crab Pot 23 Shoulder Pot 34 Forearm Pot 45 Rotation Pot 56 6

Motor Functions - 2007





Connection




encoder, Current Orange 3 No 40A Normal PowerLoc




Relay Relay Output





Purple/Yellow 20A




Motor List

Color code everything, make a list of functions. Electrical and software will need this list.





Connection


reading



encoder, Current reading

Orange 3 No 40A Normal PowerLoc




Relay Relay Output





Purple/Yellow 20A




PWM & Brake Current and Polarity


Electrical Design Begins

• Select a position for the Main Battery and compressor if you are using pneumatics. (The battery and compressor are heavy so they can be used to balance the robot.)

• Select a position for the main breaker and the terminal block near the main battery.

• Select a position for the Maxi Block and ATA Fuse panels near to the terminal block.

• Select positions for the Speed Controllers (Victors) and relays (Spikes).



• Select a position for the Robot Controller and the Radio Modem.

• The RC does not need to be near the outside of the robot but should be easy to see without removing covers.

• The modem should be placed so that the antenna can be placed away from metal objects. Do not bury in the robot frame.

• Use a 9 pin extension for the programming port and tether port if RC is inside the robot.



• The main breaker needs a solid mount and the case is easily cracked.

• Mount the main breaker where it is easy to access but not positioned so that another robot could easily bump the “OFF” button.

• It helps to label the main breaker location so your robot can be turned off if needed.

• The terminals need to be insulated!



• Mount controllers near the motors they will control.• When mounting speed controllers, position so that it

is easy to see the indicators.• Allow some open area so that cooling air may flow

around the controller and through the fan.• Make sure you can access the calibration switch.• Controllers can be mounted in any position but

should be secure.• Don’t place near mechanical parts that will produce

metal flakes.


Primary Electrical Wiring

• Consists of #6 wiring, 50 amp Anderson connector, Main breaker, terminal blocks and wiring to breaker panel(s).– Carries all robot current.– The same current that flows through the red wire

flows through the black wire.– The main breaker is a temperature sensitive device.– #6 wire is about .0005 ohm/ft. At 200 amps, at

least 0.4 volt drop across the KOP supplied wire length, more if the Anderson connector is damaged.


Bad #6 AWG Wiring Long wire runs, shared currents with high current loads.Voltage to RC estimated to be below 9 volts during pushing, much less during stall.

To RC

All robot current flowsthrough these wires.

High Current

Returns


Better #6 AWG wiring Current sharing is reduced, wire runs are shorter. Jumper still taking a lot of current. RC fed at sensitive position on block.Voltage to RC estimated to be max 9.6 volts during pushing, less during stall.

To RC

Drive current only flowsThrough these wires.


Best #6 AWG wiring Current sharing is reduced, wire runs are shorter. Jumper carries less current, reduction in single point failure. RC fed from minimum loss terminal on small breaker panel. Voltage to RC estimated to be at least 9.8 volts during pushing, less during stall.

To RC


Many team batteries are wired this way.Terminals close to battery edge run the risk of abrasive breakdown of insulation.Unequal wire length makes connection difficult and mating questionable.


Best battery wiring. Terminals are turned to inside and are mounted on inside of terminal, allowing battery case to shield them from abrasion.Wire length is equal to allow ease of connection. If battery or mount moves during match, secure Anderson connector with ty-wrap to prevent opening. Terminals (SLA or KPA4C) may be bent to reduce overall height above battery case.


Note battery terminals turned to inside, away from chassis supports.Terminals are well insulated and wires are held out of the way. Battery is securely mounted and cannot move.


Note: Wire is stripped back the length of the terminal, about ¾”. Insert wire between the shell and the terminal. Do not insert wire under screw!The screw pushes on the copper not the wire. When terminated properly, the wire should take on the shape of the shell and cannot be moved. You can solder but insert solder from the terminal side, not the wire side. Stop when solder flows to the insulation. This will keep the wire flexible.

For SLA or KPA4C ConnectorTerminationSoldering isRecommended!Insulation is a must!


Crimp terminals are also allowed. They are easily crimped with the corners of a vise if the correct crimper is not available. Solder these the same way as SLA or KPA4C connectors. There is a solder hole in the terminal side of the connector. Again only add enough solder to prevent it from flowing under the insulation. Pulling the wire should not give any movement. Insulate with electrical tape or heat shrink (A #10 push on shown for reference.)


Various hand tools: Ratchet style crimpers on left, then small wire strippers and cutters, followed by a cutter meant for #6 only.


Common Tools For Electrical

Install


Automatic stripper shown with common T type stripper for 16-24 AWG.


Thomas and Betts crimper on left can be used for both insulated and non-insulated terminals. Ratchet crimper on right will not release the jaws until the correct force has been applied.

The T&B crimper should be used on non-insulated terminals by orienting the slit in the terminal against the concave side of the jaw. When correctly terminated, the slit should remain closed and the wire can not move within the terminal.


• Fluke 77 VOM • Useful for measuring all

electrical on robot.• Measures voltage &

resistance. • Use for troubleshooting. • Fluke 410 Current Clamp• Useful for measuring

currents up to several hundred amps.

• May give inaccurate readings when measuring output of Victor at less than full power but is still useful.


3M Color Wheel contains a few yards of each of the EIA colors (resistor code).Useful for marking all electrical wiring and components. (power wires, Victors, breakers, Spikes, motors, and PWM wiring)


Anderson Power Products

Flag Terminals

¼” uninsulatedTerminals

BentTerminal


Stranded, flexible “zip cord” is available in sizes from 18 – 10 AWG. Source MCM or Newark in rolls of 50’ or 100’


Common Wiring Techniques

• Mount components where practical for lowest loss or replacement not convenience.– Reduces wire length.– Reduces control PWM wiring.– Mount so that component indicators can be seen.

• Split high currents to prevent shared in same wire.– Currents add together reducing available voltage.– Currents shared by same terminals.– Add to wire and breaker heating.



• You should purchase additional 50 amp Anderson connectors and install one on the battery charger. Strip at least 1” from each wire and fold the exposed wire so that it fits in terminal, then solder or crimp.

• Check all terminations by pulling on wire, this includes crimps, screw terminals and the terminal block.

• Use tywraps to secure wires near each terminal to prevent vibration from loosening the connection. Use this same technique for securing PWM cables.


Common Wiring Techniques• When using the Maxi block (40 amp breaker

panel), terminate the #6 by stripping back 1 to 1-1/2” of insulation and folding the wire back on itself(twice). This causes the wire to be the diameter of a #2 wire which is the largest wire designed for that block.

• Solder KPA4C connectors after you have tightened the clamp screw so they don’t loosen up. Heat terminal then apply solder to the end of the wire and inside terminal. Do not allow solder to wick under the insulation. This reduces the flexibility of the wire.



• All exposed wiring and terminals need to be insulated especially the battery terminals.

• You may use uninsulated crimp terminals and solder if you then insulate the terminals. Heat shrink tubing works very well.

• Keep wiring short and direct when possible. Use #6 for all high current primary wiring.

• Use #10 for all high current loads; Chalupas, Fisher Price and compressor.



• When attaching terminals to the battery, use a star washers between the mating surfaces. This will prevent the terminals from twisting.

• All wires used on the terminal block should be stripped back 5/8” for proper insertion. You can use two #10 wires in the same terminal but only one #6. You only need to use as many of the block inserts as your design requires. You may cut the yellow jumpers. All high current loads must return to the terminal block.


Some Rules of Thumb• Wire Foot(WF)

– Equivalent to loss in 1 foot of #10 wire.– At stall current of the three large motors, about

100 amps, this is equivalent to 0.1 volt/wirefoot(WF).

– 1 ft. of #6 wire =0.5 WF– 1 ft. of #10 wire=1 WF– 1 ft. of # 12 = 2 WF– Battery Internal Resistance=11 WF– Victor Series Resistance=6 WF– Bad crimps=1-3 WF each– Remember, there are two wires in every circuit,

positive and negative.


Some More Rules of Thumb

• Murphy’s Law– Anything that can go wrong will…at the worst

possible time.– Robot postulate…It will go wrong in the last

match of the finals on Einstein.– My favorite is Murphy’s Law of selective

gravitation. A dropped tool will fall where it will do the most damage.


MCM ElectronicsDescription Part # Price18 GA zip cord/100' 24-1870 $11.9714 GA zip cord/100' 24-1900 $24.8812 GA zip cord/100' 24-1915 $31.4510 GA zip cord/100' 24-1930 $46.47Solder 21-1845 $14.44WP30 Soldering Iron 96-429 $47.95Iron Tip, Large Flat 96-1565 $5.76Iron Tip, Conical 96-320 $5.7680 Watt Soldering Iron 21-4345 $8.23Large Wire Cutters 96-1309 $24.17General Purpose Cutter 96-235 $20.93Flush cutters 96-1188 $17.21T Stripper 28-2700 $15.50Auto Stripper 10-22AWG 22-3045 $29.95T&B Style Crimper 22-1780 $10.95Ratchet Crimper 22-770 $25.95Needle Nose Pliers 96-1330 $22.75Retracting Utility Knife 22-825 $3.99Color Wheel Tape Marker 108-035 $24.95

TERMINALSNon insulated Female,12-10 108-275 2.99/25Non insulated Female,14-16 108-270 3.89/50Full Insulated Female, 12-10 108-290 7.49/25Full Insulated Female, 14-16 108-285 10.75/501-800-543-4330 www.,mcminone.comfax:1-800-765-6960

WIRE FOOT EQUIVALENTS 1WF@100AMPS=0.1VOLTDevice WF#10 Wire per foot 1#6 Wire per foot 0.5#12 Wire per foot ~2Victor 6-8Spike <1Crimp (good) 1Crimp (poor) 1-3Crimp (soldered) <<1Battery 11Circuit Breaker <1Rockwell Terminal Block (tight) <1Rockwell Terminal Block (loose) 5-2050 amp disconnect <150 amp disconnect (scratched) >10

This is a list of tools, wire, terminals and other parts you have seen pictured in this presentation.Included is also a Wire Foot reference to help you analyze what might be taking place on your robot.Copies are available, please take one.Pictured is a close-up of Victor with push on tabs and color ID tape as well as tools and wire.


Thanks!• Questions?