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Electrical Subsystem

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Electrical Subsystem. Scot Marshall, Staff Test Engineer. Lockheed ... scotmar_at_bellsouth.net. IFI Hardware. 1. 2. 3. 5. 5. 6. 4. 7. 8. 9. 9. Power Distribution ... – PowerPoint PPT presentation

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Title: Electrical Subsystem


1
Electrical Subsystem
  • Scot Marshall, Staff Test Engineer
  • Lockheed Martin Space Systems
  • Michoud Operations
  • Team 1913, Covington High School
  • Covington, LA
  • scotmar_at_bellsouth.net

2
IFI Hardware
3
6
5
9
9
4
5
2
8
1
7
3
Power Distribution
This Schematic is available at http//www.ifirobot
ics.com/rc.shtml
4
IFI Hardware
  • Robot Controller
  • Wireless RS-422 40-Channel Receiver
  • Back-up 7.2 VDC Battery
  • CM2 Camera
  • Operator Interface
  • Wireless RS-422 40-Channel Transmitter
  • Power Supply
  • Tether
  • Power Distribution Panel
  • Resettable Circuit Breaker (20A, 30A, 40A)
  • Robot Controller Interface
  • Cabling
  • Serial Computer Interface

5
1. Operator Interface
  • Inputs
  • 12 VDC Power
  • (4) Joystick
  • Competition Port
  • Team Number
  • Radio Modem
  • Outputs
  • Radio Modem
  • Dashboard (PC)
  • Tether
  • Special Instructions
  • No external power needed when Robot is tethered
  • Diagnostic Indictors for Robot and Operator
    Interface

6
Operator Interface
Competition
Tether
To PC Serial Port
Radio
Joystick
Joystick
Joystick
Joystick
Disable Channel
Robot Reset
Display Select
OI Reset
Team Number
This information is available at http//www.ifirob
otics.com/docs/oi-ref-guide-11-21-2005.pdf
7
2. Robot Controller
  • Inputs
  • Digital Signal
  • Analog Signal
  • Radio Modem
  • Tether
  • Serial
  • Programming
  • Outputs
  • Relay
  • PWM
  • Radio Modem
  • Special Instructions
  • Use Breaker
  • Wire ON when Robot is powered
  • Use Backup battery also

8
Robot Controller
Team Color
PWM Outputs
7.2 VDC Backup Battery
12 VDC Battery
12 VDC Battery
16 Analog Inputs
Program
Black Red Wh/Yel
Ground 5 VDC In/Out
Tether
Tether
18 Digital In/Out
Radio
Relay Outputs
Serial Input
Pgm
Reset
This information is available at http//www.ifirob
otics.com/docs/rc-ref-guide-01-31-2005.pdf
9
3. Breaker Panel
  • Inputs
  • 12 VDC from Battery
  • Outputs
  • Power Distribution
  • Ground Plane
  • Serial to Robot Controller
  • Special Instructions
  • Wire through Main Breaker
  • Terminals Numbered
  • G is Ground
  • 40 is for 40A
  • Wire straight into 40A (Drive Motors)
  • Use Spade lugs for 30A 20A

10
Breaker Panel
40A and 30A Breakers Installed
(6) 40A Breakers
40A wires attach under screw plate Power Ground
30A or 20A Circuits24 places
MainBattery12 VDC
Red/Green/OrangeStatus Indicator
PWM Cable
MainBatteryGround
Terminals use spade lugs
Reset
Serial to Robot Controller
11
4. Circuit Breakers and Fuses
40A
  • Circuit Breakers
  • 20A, 30A, 40A
  • Push/Pull Installation
  • Overcurrent (thermal) cutoff
  • Resets as soon as condition is resolved
  • Fuses
  • 20A for Spike Relay
  • One-time use
  • Look for broken loop
  • Same as for Automobile

30A
20A
Fuse Element
12
5. Wireless Modem (Transmitter)
  • Inputs
  • 9600 Baud RS-422 Data
  • Outputs
  • 902-928 MHz Band - 40 Channels
  • Special Instructions
  • 100-300 ft Range
  • 35 Competition Channels
  • Default (Practice) Channel 40
  • 2 robots on Default will interfere
  • 01, 04, 13, 22, 31 User Settable Channels

13
6. Victor 884 Speed Controller
  • Inputs
  • Digital PWM
  • 12 VDC, Ground
  • Outputs
  • Variable Current
  • Special Instructions
  • Use 40A Breaker
  • Use for CIM Drive Motor
  • Wire fan ON when robot is powered

14
Victor 884 Speed Controller
Fan GND Battery GND Battery 12 VDCFan 12
VDC
Motor GND Motor Power
PWM Cable Wh Rd Bk (Fits Poorly)
Red/Green/OrangeFwd/Rev/ActiveIndicator
Brake/CoastJumper
Cal
15
7. Spike Relay
Fuse
  • Inputs
  • Digital PWM
  • 12 VDC, Ground
  • Outputs
  • Full Fwd
  • Full Reverse
  • Brake
  • Special Instructions
  • Use 20A Breaker
  • Use for Motor Drive

Red/Green/Orange Fwd/Rev/ActiveIndicator
PWM Cable
16
8. CMUcam2 Camera
  • Inputs
  • PWM Power from RC
  • Outputs
  • RS-232 DB9 to Computer
  • RS-232 3-pin Serial to RC
  • Servo Control
  • Special Instructions
  • Use PWM 7.2 VDC Supply
  • Use for Motor Drive
  • Connect Only 1 RS-232 at a time

17
CMUcam2 Camera
Servo Outputs
RS-232 to PC for GUI
RS-232 to Robot for Auto
PWM Cable Connector
Focus by Rotating
Red/GreenLED Indicators
RC Board Connector
On/Off
RC Power
This information is available at http//www.ifirob
otics.com/camera.shtmlCMUcam2_fe manual
18
9. Cables
  • PWM Cable
  • Digital Signal
  • DB9
  • Joysticks
  • Serial Communications
  • RS-232
  • RS-422
  • Tether
  • Digital Signal Power

19
Wires
  • Wire Gage
  • Main Power 6 AWG or larger (4 AWG)
  • 40A 10 AWG
  • 30A 12 AWG
  • 20A 14 AWG
  • Color Code
  • Red/Blue - 12 VDC Power
  • Black/Yellow Signal Return
  • Green - Chassis Ground
  • Safety
  • Insulate all connections

20
Documentation
  • FIRST Robotics Website
  • 2006 Manual The Robot
  • IFIRobotics
  • Robot Controller
  • Operator Interface
  • Breaker Panel
  • RS-422 Modems
  • Victor 884 Motor Controller
  • Spike Relay
  • Camera

21
Robot Controller
  • FRC 2004 Control System Overview(pdf)Installatio
    n Info (pdf) Size and mounting infoFRC 2004
    System Quick Start2004 Reference Guide
    (pdf)2005 Reference Guide (pdf)  1-31-05Analog
    and Digital Input (pdf)  2-17-05
    schematicProgram Port Pin-out (pdf)  4-7-05
    schematic

22
Operator Interface
  • SpecificationsDescription2005 Reference Guide
    (pdf) 11-21-05Installation Info (pdf)2004 FRC
    System Quick Start (pdf)2004 FRC Control System
    Overview (pdf)Competition Port Pinout Guide
    (pdf) RevA 1-12-05Frequently Asked Questions
    (FAQ)Legacy Docs

This information is available at http//www.ifirob
otics.com/oi.shtml
23
Backup Charts
24
Connectors
25
Motors
26
Compressor
  • Inputs
  • Digital Signal
  • Outputs
  • Air Pressure
  • Special Instructions
  • Use Breaker
  • Wire ON when Robot is powered
  • Need Pressure Relief

27
Sensors
  • 123

28
Switches
  • 1
  • 1
  • 2
  • 456

29
Chargers
  • 7.2 VDC
  • 1
  • Main Battery
  • 456

30
Websites
  • 7.2 VDC
  • 1
  • Main Battery
  • 456

31
Adapted from a 2004 Presentation
  • 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

32
Overview
  • Electrical kit and IFI Hardware
  • Layout and Planning
  • Resistance and Ohms Law
  • Electrical Tools
  • Myth-Busting
  • Questions

33
Documentation Example
34
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

35
FIRST Electrical Problem
  • How much voltage is lost in a typical FIRST
    circuit?

36
Ohms Law
By Ohms Law V I R 12 V I 24 W I 0.5 A
_
12 VBattery
24 W
37
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?
38
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
39
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

40
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

41
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!

42
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)

43
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

44
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

45
Other Required Tools
  • Multimeter (DMM)
  • Voltage
  • Resistance
  • Continuity
  • Wire Strippers
  • Re-strip any wires where copper strands are lost

46
Myth-Busting
47
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.

48
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.

49
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.

50
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.

51
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52
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)

53
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
54
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.

55
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.

56
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.

57
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.

58
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.

59
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.

60
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.

61
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.

62
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.

63
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.

64
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.

65
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.

66
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.

67
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.

68
The top ten robot myths of all time!
69
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.

70
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.

71
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.
72
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.

73
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.

74
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.

75
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.

76
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.

77
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.

78
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.

79
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.

80
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
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