FIRST Electrical Design

1
FIRST Electrical Design

• Michael Dessingue
• College Mentor - Hudson Valley Community College
• mdessingue_at_nycap.rr.com
• Team 250
• Steve Shade
• Controls and Simulation Engineer Rolls-Royce
• steven.shade_at_rolls-royce.com
• Teams 1111 7
• Al Skierkiewicz
• Broadcast Engineer - WTTW-TV
• Askierkiewicz_at_networkchicago.com
• Team 111

2
Overview

• Electrical kit and IFI Hardware
• Layout and Planning
• Resistance and Ohms Law
• Electrical Tools
• Myth-Busting
• Questions

3
IFI Hardware
4
Planning Your Electrical System

• Plan, create drawings just like mechanical
  systems
• Create a test bed early
• Use test bed to test all systems before
  integrating
• Communicate effectively with the mechanical
  sub-teams early and often
• Document everything

5
Documentation Example
6
General Layout Tips

• Label and/or Color Code Everything
• Secure wire so a hit from another robot doesn't
  stretch the wiring to a breaking point or pull a
  terminal out of a breaker, victor or spike
• When in doubt, insulate
• Secure the battery so it doesn't fall out
• Leave some slack in wire to allow for swapping of
  parts
• Be careful when running wiring through frame
  members so that mech heads don't drill into it at
  some point down the road

7
FIRST Electrical Problem

• How much voltage is lost in a typical FIRST
  circuit?

8
Ohms Law
By Ohms Law V I R 12 V I 24 W I 0.5 A
_
12 VBattery
24 W
9
Typical FIRST Circuit
120 A Circuit Breaker
Victor 884 Speed Controller
_
40 A Circuit Breaker
VoutMeasured
12 VBattery
Assuming the Victor 884 Speed Controller is given
an input signal of 254 from the Robot Controller,
how much voltage is output to the device?
10
Typical FIRST Circuit
120 A Circuit Breaker
Victor 884 Speed Controller
_
40 A Circuit Breaker
VoutMeasured
12 VBattery
Circuit consists of 8 of 6, 4 of 10, and 2
of 10. 14 Connections in the circuit
11
More Wire Adds More Resistance

• Standard Wire Foot - A 10 gauge wire will drop
  about 0.1 volt per foot at the stall current of
  any of the drive motors.
• There is resistance in every wire
• .001 ohm/ft 10 wire
• .0004 ohm/ft 6 wire

12
Typical FIRST Circuit

• Resistances 8 6 0.0032 W 6 10
  0.0060 W Rtotal 0.0092 W
• Steady State Current 40 A
• Voltage Drop IR 40 A 0.0092 W 0.368
  V
• Max Voltage at Device 12V - 0.368V 11.632
  V

13
Typical FIRST Circuit

• Resistances 8 6 0.0032 W 6 10
  0.0060 W Rtotal 0.0092 W
• CIM Motor Stall Current 114 A
• Voltage Drop IR 114 A 0.0092 W 1.05
  V
• Max Voltage at Device 12V - 1.05V 10.95 V
• At Stall Current of CIM, Max Voltage at the CIM
  motor for the same current path is 10.95V!

14
Reducing Resistance

• Check every crimp to make sure the wires do not
  move or turn when pulled
• Use the correct tool for the job
• Solder all critical joints
• Shorten the length of your wires (also helps in
  keeping things neat and traceable)

15
Crimp Connections

• Buy a good crimper for about 20
• Home Depot, Lowes Electrical Sections
• Many Auto Parts Stores also stock crimpers
• Look for crimper with good handles and can used
  with wire gauges 10 to 24

16
Soldering

• Good Practice to solder all connections where
  high currents exist
• Use Appropriate Size iron for the job
• Use a Rosin Core Solder for all electronics

17
Other Required Tools

• Multimeter (DMM)
• Voltage
• Resistance
• Continuity
• Wire Strippers
• Re-strip any wires where copper strands are lost

18
Myth-Busting
19
The RC, OI, Victors and Spikes need external
components to run (i.e. capacitors, voltage
regulators, etc.)

• IFI has done a good job of designing the power
  and internal circuitry of all the kit electronic
  components. There is no additional circuitry
  required for reliable operation. The fan that is
  mounted on the speed controller is required
  though and most teams will wire this fan to the
  controller power input. The fan then becomes an
  indication of good input power to the controller.

20
The controllers cant go from forward to reverse
quickly.

• The speed controllers do exactly what you tell
  them to do. Your robot cannot make the sudden
  changes you are demanding for other reasons
  related to mechanical design and physics. You
  cannot hope that the control system will overcome
  all other losses. It does not have the power
  resources to overcome the momentum of a charging
  130 lb. robot and change its direction.

21
The controllers and motors are not matched, the
switching is all wrong.

• This may seem to be the case, but the components
  work very well together. All teams use the same
  motors and drive components so there is no
  disadvantage to any team using the supplied
  parts.

22
The OI says my battery voltage is 10.5 but my
voltmeter reads 12 at the battery. It must be
broken.

• Your RC voltage monitor accurately reads the
  voltage that is present at its input. If your
  RC reads 10.5 volts, there is considerable loss
  in the wiring and connections. Check that you
  have connected the RC to the 1 or 2 positions
  on the breaker panel and check that your
  connectors are well crimped and are tight and
  fully engaged on the push on connections.

23
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24
The battery is too small.

• The battery is actually very powerful. Most
  teams have no problem driving a 130 pound robot
  for more than two matches with the kit battery.
  If your robot drains a charged battery by the end
  of a match, the mechanical design is inefficient
  or you are using some form of tank drive. (treads
  or four or more non-steering drive wheels)

25
TYPE ES18-12 CAPACITY 5HR 3.06A 15.3 AH 1HR
10.80A 10.8 AH 1C 18.0A 9.0 AH INTERNAL
RESISTANCE APPROX. 15m MAX. DISCHARGE CURRENT 230
A (5 SEC.) MAX. CHARGE CURRENT 5.34
26
The main battery cannot be used lying down.

• The main battery can be used in any orientation,
  including upside down. It can be charged in any
  direction except upside down. Battery terminals
  must be protected at all times and the battery
  must be secured in the robot. You cant play
  when your battery is lying on the field.

27
A sparking motor is defective

• Sparks are normal in DC brush type motors. The
  magnetic fields in a motor generate high voltages
  that spark across gaps in the brush assembly.
  Motors that are working hard or have worn brushes
  produce more sparking.

28
I can only get 11 volts at my motor running. The
breaker panel is defective.

• This actually is an effect of the some of the
  principles discussed earlier. High currents in
  the wires we use result in some voltage drop.
  Measuring at the motor, is in effect,
  compensating for this loss. Remember the wire
  foot, every foot of 10 at stall drops 0.1 volts.
  A one volt drop is an indication you have 10
  wire feet of loss on the robot between the
  battery and the motor. This could be two 10
  gauge wires, five feet long, or four feet and a
  speed controller or three feet, a speed
  controller and a breaker and some connectors.

29
The backup battery is disconnected when you power
off.

• According to the RC manual, Team LEDs (and the
  backup circuit in the RC) will go out after four
  seconds if the RC has not established contact
  with an OI connected to the arena controller. If
  an arena controller is connected and a link has
  been established, the RC will shut down about
  four minutes after main power has been removed.
  The backup battery supplies current to the RC,
  modem, servos and team LEDs when the main battery
  has fallen below about 7.2 volts. You must hit
  reset to save the backup.

30
My Chalupa is only running a light load but it
keeps tripping the breaker, the breaker must be
defective.

• A current monitor would verify what the motor
  current actually is. Many manufacturers make
  clamp on probes that will monitor current for use
  with you multimeter. If the motor current is high
  check that there isnt a problem in the drive
  system by running the robot with the wheels off
  the ground. If motor current is normal, suspect
  bearing side loads, misaligned wheels, etc. If
  it is high, remove the motor from the
  transmission and try again, if it is high suspect
  a defective motor, if low, suspect a problem in
  the transmission.

31
I dont need to insulate the black wire

• The black wire carries the same current as the
  red wire it is paired with. By insulating both
  wires, you are backing up the backup. If the
  insulation on a wire fails, the insulation on the
  other wire keeps the electrical system safe.
  (backup the backup is a common method used by
  NASA and others to insure safety, reliability.)
  The black wire on the motors are not connected to
  battery negative all the time.

32
Main circuit breaker is vibration sensitive it
needs to be shock mounted.

• This was true of the old panel type breaker, but
  it is not true if the breaker supplied in your
  kit this year or last. These breakers were
  designed to be used in vehicles and boats. A few
  have turned up this season that were sensitive to
  light tapping on the red disconnect button.
  These are defective breakers and should be
  replaced.

33
Protect the radio by putting it down inside the
robot.

• It is important to protect the radio modem and
  the rubber antenna that sticks out the top. To
  mount it down inside all of the metallic parts,
  motors and transmissions, is reducing is ability
  to communicate with the OI modem. The robot
  modem needs to be mounted in a protected area
  with the antenna vertical and as far from
  metallic structures as possible.

34
The antenna on the robot can be anywhere in any
orientation, same with the OI.

• Antenna coupling is greatest when the antennas
  are mounted in the same orientation. Coupling is
  minimum when the antennas are mounted 90 degrees
  apart. The radios still appear to work but the
  margin of good signal is vastly reduced.

35
The IFI control system is awful, my robot keeps
cutting out.

• A robot that cuts out on the field is most often
  a result of input power to the RC falling below 7
  volts. A high current draw when running will
  take the battery voltage down temporarily. The
  RC will go to backup and shut down while the
  input voltage is low. When it returns, the RC
  will act normally. Occasionally a modem problem
  may occur on the field, the IFI reps are
  monitoring every robot and can tell most problems
  from their monitoring station.

36
4 wire is way better than 6.

• This is partly true. If you are running a long
  distance with the primary wiring and you can
  stand the extra weight, then 4 gauge may be a
  good choice. Mating 4 gauge to the Anderson
  connector is a problem for most teams. For short
  runs and the best weight savings, 6 gauge is
  perfectly fine.

37
Soldering is better than crimping.

• Manufacturers crimp contacts all the time and
  the military requires crimping only. The big
  difference is the crimp is made with a very
  expensive crimp tool or by machine. For our
  purposes, a soldered connection adds a little
  insurance to the connection. A good soldered
  joint is one that is mechanically sound to start
  with. Crimp first, then solder, then insulate.

38
A motor will run at free speed if you connect it
to a battery.

• The motor specifications are recorded under very
  strict testing guidelines and using equipment
  that takes away any variables in testing. The
  motor may get you close to tested specifications
  but dont expect to duplicate results in your
  shop with a battery.

39
The electrical rules dont meet electrical
practice. (NEC)

• The electrical rules attempt to follow NEC
  guidelines if you check the open air tables.
  This allows a 12 wire to be used in open air
  where a 10 for the same current must be used in
  conduit. I personally prefer to use 10 for all
  high current wiring on the robot, and 18 for the
  lower current valves and RC.

40
The top ten robot myths of all time!
41
10. The motors do not have large enough wire.

• The wire supplied with all motors is designed by
  the manufacturer for use with these motors. The
  wires although undersized, are fairly short and
  will add very little loss to the system. Put the
  controller close to the motor if you think you
  need to reduce the loss. If you shorten the
  leads and add connectors to get a larger gauge
  wire, you wont gain an advantage. Note The
  Chalupa motor may be damaged if you open it.

42
9. Wire is wire is wire.

• Not really. There are various styles of wire,
  based on your need for flexibility. These wires
  have distinctly different reactions to
  connectors. Superflex wire(137 strands) in an
  SLU70 type connector will pull out making a high
  resistance connection and it is difficult to
  strip without cutting or breaking strands. A low
  strand (9 or 17) wire may be too hard to
  terminate with a manual crimper. It may also
  break with the repeated flexing encountered on
  our robots. The wire sizing rules this year
  allow you to make decisions on weight but in most
  case will be a disadvantage electrically. The
  drawing in the guide is misleading.

43
This is misleading. The wire does not go under
the screw. It goes between the collar and the
tab. Fine strands would be pulled up along the
sides of the screw and very few would be held in
place. The connector supplied last year was
terminated as shown but could not terminate fine
strand wire.
44
8. The battery could electrocute you, why do we
use it?

• The voltage generated by this battery is not
  capable hurting anyone due to direct contact.
  The battery can still cause harm if misused.
  Shorts across the terminals can generate high
  amounts of heat capable of burning anyone who
  touches it. I have seen fires on the field and
  in the pit due to shorting out the battery. Keep
  battery terminals insulated at all times.

45
7. Battery connectors are too small, underrated.

• Although rated at 50 amps, the overall heat
  generated in the connector during a two minute
  match is low enough that teams do not need to
  worry. If the connector is improperly crimped,
  damaged or misaligned, or the robot design is
  significantly inefficient, some heating of the
  connector is possible and damage could be the
  result. I have seen little evidence of connector
  damage. Using alligator clips on the charger to
  connect to the Anderson battery connector will
  damage the surface.

46
6. The main battery cannot be used lying down.

• The main battery can be used in any orientation,
  including upside down. It can be charged in any
  direction except upside down. Battery terminals
  must be protected at all times and the battery
  must be secured in the robot. You cant play
  when your battery is lying on the field. Also
  dont pick up the battery by the wires, as
  internal damage will result.

47
5. My four wheel drive robot eats batteries,
there is something wrong with control system.

• Four wheel or tank drive systems use incredible
  amounts of current when turning using high
  friction drive surfaces like belting or knobby
  tires. When a robot turns it must drag the
  wheels or treads sideways across the carpet. In
  a tight or fast turn, this high friction
  translates into near stall conditions for all the
  drive motors. The result is temporary current
  draw above 200 amps in a four motor drive. That
  may be enough to draw the voltage in the battery
  below RC minimum.

48
4. The backup battery is not used when the main
power is shut off.

• According to the RC manual, Team LEDs (and the
  backup circuit in the RC) will shut down after
  four seconds if the RC has not established
  contact with an OI connected to the arena
  controller. If an arena controller is connected
  and a link has been established, the backup
  battery will still be connected to everything on
  the robot for up to four minutes after main power
  has been removed. With servos and LEDs, a lot of
  power is watsted. Press reset after every power
  off.

49
3. The battery has memory and needs to be
discharged to zero.

• This is one of the most common myths. It arises
  from a particular type of NiCad battery behavior.
  Gel cell batteries do not have a memory that
  needs any special handling. Charge them normally
  with the supplied chargers and never at more than
  6 amps.

50
2. The battery is too small.

• The battery is actually very powerful. Most
  teams have no problem driving a 130 pound robot
  for more than two matches with the kit battery.
  If your robot drains a charged battery by the end
  of a match, the mechanical design is inefficient
  or you are using some form of tank drive. (treads
  or four or more non-steering drive wheels). In a
  hard match or a restart, you may not have enough
  battery reserve to last two minutes.

51
1. You dont need to calibrate speed
controllers.

• The biggest myth of all. Do not believe this
  one. The speed controller has the ability to
  adapt to each joystick you use. Since each speed
  controller is not matched to the joystick you
  were shipped, they must be calibrated.
  Calibration gives the controller the ability to
  match the maximum travel on the joystick to the
  maximum output on the controller.