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Thread: Miscellaneous Robot Electrical Parts and Materials - Answer Thread

  1. #21
    Game Design Committee Member Wil Wheaton's Avatar
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    Matrix Power Switch Concerns

    Quote Originally Posted by FTC12224 View Post
    Hello,

    As recommended by:

    <RE01> Main Power Switch - The Robot Main Power Switch must control all power provided by the Robot main battery pack and it must be used in one (1) of the following configurations:
    a. FIRST strongly recommends that Teams purchase a separate Main Power Switch, either TETRIX (part #W39129) or MATRIX (part# 50-0030). This is the safest method for Teams and Field personnel to shut down a Robot.

    We purchased a MATRIX (part# 50-0030) switch. However, the MATRIX switch comes with 18 gauge wire (FTC rules say power wire should be at least 16 gauge) and is only rated for 6 amps (whereas the battery and core controller are both fused to 20 amps).

    So, it appears that the MATRIX (part# 50-0030) that we are required to buy does not meet the FTC rules (for power wire gauge) and is substantially under-rated (6 amps vs. 20 amps) for the entire system.

    Given this, can we use a 3rd party switch that is rated for 20amps?

    If not, what are we suppose to do (we cannot use the core controller switch, as cannot make it accessible):
    - Install the MATRIX (part # 50-0030) switch - It seems it will probably melt (has anyone used this switch? Does it melt?)
    - What are we suppose to do with the illegal wire that came on switch? (has anyone competed with this switch/wiring?)

    Thanks,
    FTC BlueSmoke Team


    Answer: The switch you have purchased is selected by Modern Robotics for use with the Matrix system and is safe to use. The current ratings you are reading from the switch are AC ratings (6A@125V) not DC ratings.

    The only two legal external power switches are the two explicitly listed in <RE01>

    The wire gauge rules in <RE14> are for use by teams in modifying, extending, custom making, etc., wiring within the robot (i.e. anything your team makes or modifies should follow the guidance in <RE14>).

  2. #22
    Game Design Committee Member Wil Wheaton's Avatar
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    Additional Battery for LEDs

    Quote Originally Posted by FTC9794 View Post
    Is it legal to attach an additional 12-volt battery to the robot to provide power to the undirected LED lights on the robot?


    Answer: No, unless the battery is an internal battery (as supplied by the LED manufacturer) as listed in <RE12>

  3. #23
    Game Design Committee Member Wil Wheaton's Avatar
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    Grounding Robot Frame

    Quote Originally Posted by FTC0542 View Post
    <RE03> states "Robot main power is provided by exactly one (1) battery pack that connects
    directly to a single Core Power Distribution Module or through a switch that connects to a single Core Power
    Distribution Module. Voltage and/or current sensors are allowed to connect between the battery pack and the
    Core Power Distribution Module."
    Our robot still has the battery connected to the PDM but we have an additional wire with a ring at the end (to attach to the chassis) branching off the negative PDM wire.

    Question: Is it legal to ground the negative PDM wire to the chassis of the robot?


    Answer: No.

  4. #24
    Game Design Committee Member Wil Wheaton's Avatar
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    LED questions

    Quote Originally Posted by FTC10432 View Post
    We have some question about LED lighting.

    1. It is our understanding that you can not power low voltage (~2v) LED's from the 5v outputs on the CDIM (these outputs are current limited and work great). Could this be considered next year?

    2. If we use the core power distribution module and a motor controller to power them, we would need a current limiting resistor in the circuit. Is this allowed?

    3. Would the following lights be allowed?
    https://www.amazon.com/dp/B00IR23JGA...ding=UTF8&th=1

    4.Can you use common cathode RGB LED's
    https://www.amazon.com/uxcell-Common...ywords=rgb+led
    and wire the common to the core power distribution module and pick up the positives from separate outputs on a motor controller?


    Answer 1: We cannot comment on what will or won't be considered for next year's rules. In general we are always trying to find ways to allow teams to express their creativity in a safe and manageable manner.

    Answer 2: Yes. A current limiting resistor would be allowed.

    Answer 3: We are not able to comment on the legality of each individual possible LED. Be aware that very bright LEDs are likely to raise concerns at the playing field.

    Answer 4: It is not safe to cross wire between a motor controller and the CPDM. If an LED is being controlled by a motor controller, all connections to the LED should come from the motor controller. Furthermore, it is not safe to cross wire multiple motor controller outputs to a single device of any sort.

  5. #25
    Game Design Committee Member Wil Wheaton's Avatar
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    More LED Questions

    Quote Originally Posted by FTC8045 View Post
    We'd still like some clarification of the use of decorative or signal common cathode LED light strips as questioned in part 4 of post 24. http://ftcforum.usfirst.org/showthre...ll=1#post33859


    Certainly we could plug in one cathode/anode pair into the CDM or a motor controller port, and physically change the colors between matches, this seems perfectly legal, but not very interesting.

    We had tried cross wiring between the CDM and Motor controller, but see in the above post that this not legal.

    1 - Another option is to use transistors or relays to control the power via a port on the DIM, but wonder if that would be considered a circuit rather than 'passive' electronics, and thus not allowed? (Or if passive electronics even apply since the LED's are not sensors?)

    2- If we used diodes (passive) to prevent back feed and wired two motor outputs to the common cathode, would this be legal, or is this considered cross-wiring?

    3- If both of the above answers are no, Is there any legal way to control the colors of a common cathode LED strip other than physically changing the inputs?


    Answer 1: This does not fit the passive electronics that are allowed by <RE11> and is therefore a custom circuit and not allowed per <RE17>

    Answer 2: This does not fit the passive electronics that are allowed by <RE11> and is therefore a custom circuit and not allowed per <RE17>

    Answer 3: Answers to robot design questions are outside the scope of what we can provide.

  6. #26
    Game Design Committee Member Wil Wheaton's Avatar
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    LEDs Controlled with Transistors

    Quote Originally Posted by FTC9794 View Post
    Are LEDs that are fully powered by the 12 battery on our robot controlled by the PWM ports on our core device interface module using transistors allowed?


    Answer: No.. Transistors fall under <RE17> "Additional Electronics" and are not allowed.

  7. #27
    Game Design Committee Member Wil Wheaton's Avatar
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    Non-Powered Electronics

    Quote Originally Posted by FTC6566 View Post
    We were wondering if we are allowed to mount an unpowered beacon circuit board on our robot for aesthetic purposes, or if it would fall under additional electronics.

    Thanks,
    6566 - Circuit Breakers


    Answer: No. All electronics within the robot must comply with the robot electronics rules. The unpowered beacon board would indeed fall under <RE17> "additional electronics"

  8. #28
    Game Design Committee Member Wil Wheaton's Avatar
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    Grounding Chassis Frame w/ Current Limiting Resistor

    Quote Originally Posted by FTC7026 View Post
    If we used a current limiting resistor of 47 ohms @ 0.25 watt between the negative terminal on the Core Power Distribution Module and the chassis, we can limit the grounding of static charges to the chassis to be 0.02 amp max. Please find attached circuit diagram.

    Since the robot frame is not used as a connector in this circuit, please advise if this allowed?


    Answer: No. Any electrical connection to the chassis or other non-electrical parts of the robot is not allowed.

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