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Miscellaneous Robot Electrical Parts and Materials - Answer Thread

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  • Miscellaneous Robot Electrical Parts and Materials - Answer Thread

    Answers to questions posted pertaining to Miscellaneous Robot Electrical Parts and Materials.

  • #2
    Legal Batteries

    Originally posted by FTC2844
    The battery in the following link is the exact same battery as the W39057 Tetrix Battery, according to Customer Service.. Is it acceptable to purchase this battery to save money?

    Answer: No. Only the batteries listed in <RE03> are legal for use in FTC Robots

    Legal, approved batteries can be purchased through the following vendors:

    Pitsco: The FIRST Tech Challenge Storefront (access via FIRST’s Team Registration System) – click “How to Order Extra Parts” on the left menu of the Support section. You will receive your team’s discount code to order additional parts.

    Modern Robotics:

    REV Robotics:
    Last edited by Pierluigi Collina; 11-03-2016, 11:44 AM. Reason: add links to sources for legal batteries


    • #3
      Focused Light Sources

      Originally posted by FTC3785
      Are you allowed to use something like to help you aim? Obviously lasers would be inappropriate but ...

      Answer: No. <RE12> disallows light sources that are focused or directed in any way


      • #4
        Legal Batteries

        Originally posted by FTC6981
        I know the question was already asked, but here is a point to consider regarding the battery at :

        Not only is there NO difference between this and the "official" tetrix battery, but the biggest issue is that there is NO way to tell them apart. Neither one, including the Tetrix battery, actually has a mfg. part number on it. I think the rules group may want to rethink this because frankly, MANY teams are already buying the Servocity battery because is cheaper, and is actually identical to the Tetrix battery. We have one ourselves, and there is frankly no way to determine which one it is.

        Just food for thought, and there is no reason to post an answer unless you want to. Thanks!

        Answer: The only legal batteries are those listed in Part 1 of the Game Manual. The ServoCity battery, while similar to the TETRIX battery, is NOT in the approved list.
        Last edited by Pierluigi Collina; 10-10-2016, 06:19 PM.


        • #5
          Use of Arduino for decorative lighting

          Originally posted by FTC7468
          We were wondering if we would be allowed to use an Arduino board with its own power to create decorative lighting patterns on our robot. The lights would serve no operational purpose, and would be purely for decoration.

          Rule <RE12> states "Light sources (including LEDs) are allowed; these may not be focused or directed in any way (for example: lasers and mirrors are not allowed). Approved light sources may include an internal (as supplied by the manufacturer) battery pack or battery holder." And <RE17> states "Electronic devices that are not specifically addressed in the preceding rules are not allowed. A partial list of electronics that are not allowed includes: Arduino boards, Raspberry Pi, relays, and custom circuits." However, we were wondering if <RE17> only applied to functional robot electronics, and not decorative lighting. Also, is it the intent of the GDC with <RE12> to allow only pre-manufactured light strings that provide their own power, and not for teams to be able to roll their own systems, except for using the main 12V battery?

          Answer: No. All aspects of the robot (including purely decorative aspects) must abide by the robot construction rules. Arduino boards (and similar systems) fall into the "Other Electronics" class that is disallowed by <RE17>.


          • #6
            RE17 - Solenoid Actuator

            Originally posted by FTC5828
            Are Solenoid Actuators legal parts?
            A: Solenoids fall under "other electronics" <RE17> and are not allowed.


            • #7
              Limit Switch Inline w/ Motor

              Originally posted by FTC9791
              Our robot has a gear rack that is pulled back under spring tension by the motor. However, if the motor runs past its limit, then it will break the gear rack and potentially release the springs, creating an unsafe robot, as we can't ensure that other pieces will not fly off. In order to prevent this, we have installed a limit switch inline with the motor power line, automatically tripping the power if the gear rack extends too far. This works extremely well from our tests.

              However, the current rules against "other electronics" render this illegal for a competition robot, as the limit switch is not a "sensor" because it does not connect to the DIM. We do not want to run the limit switch into the DIM and use the phone to control the motor based on this feedback because of the program's failure modes. We know that the phone's software is subject to various freezing and disconnect issues. We also know that during these failures modes, all motors will continue to run regardless. Since this could both break our robot and cause somewhat of a safety hazard, we are asking that an exception be made for such cases. We are still adhering to the requirements for minimum wire gauge, and the limit switch is rated for 10A at 120VAC, which is well over the 5A, 12V max draw of the motors. In addition, from our tests, the motor rarely draws more than a few amps, meaning that 5A is more of a peak condition.

              Thank you,

              Answer: The limit switch inline with a motor indeed falls under the "Other Electronics" category and is not allowed per <RE17>.


              • #8
                LEDs Illuminated during Robot Initialization

                Originally posted by FTC5559
                Are LED's allowed to turn on after initialization to signal the drivers what Auton mode was selected?
                LED's would be controlled by a motor controller port.

                Answer: Yes.


                • #9
                  Using Robot Frame as Electrical Connection

                  Originally posted by FTC7203
                  My team would like to know if it is legal to "Chassis Ground" the robot. They want to wire the negative leads of the modern robotics controllers and of the motors to the metal of the robot. The positive leads would connect to the positive poles of their sources as usual.
                  There doesn't seem to be a rule allowing or forbidding this. Is it a legal way to wire the robot?

                  Answer: No, using the robot frame as an electrical connector is NOT allowed. In addition being unsafe (grossly increases risks of short circuits) and violation the wiring rules for appropriate wire gauge usage, the scheme as described would not work.

                  Hint - It is important to remember that the motor connections are NOT fixed polarity. The M+/M- connections on the motor controllers switch polarity based on the motor directions. Under your scheme, the first time you reversed your motors, you would likely trip the thermal breaker in the motor controller, if not the one of the fuses in either the Power Distribution module or the battery.


                  • #10
                    I2C PWM/Servo Driver to Control LEDs

                    Originally posted by FTC11190
                    Can we use the adafruit PWM driver ( to control LEDs as long as all power comes from the Device Interface Module.

                    Answer: No. The module you referenced falls into the "Additional Electronics" category and is not allowed per <RE17>.

                    TIP - The module you referenced is very similar in function to a Motor Controller. Similar control of LEDs can be accomplished with a Motor Controller.


                    • #11
                      LED Questions

                      Originally posted by FTC8745
                      <RE12> Light Sources states that light sources may be powered by an internal battery. Additionally, they may be powered by power ports on the CPDM and or a CMCM port.

                      Can a light source be powered by a port on the Core ServoController or by a USB hub port?

                      <RE11> Sensors states that sensors may be connected to the Core Device Interface Module. Can Light Sources be connected to the CDIM? For example to control RGB LEDs.

                      Do Lighting Sources have to be simple? Or is a unified module that can be controlled for signaling purposes acceptable? (

                      We are thinking of using something like this as a device for the robot to signal the drive team.

                      Answer 1: No. Light sources may not be powered via Servo Controller or USB hub

                      Answer 2: No. Light sources may not be driven by the CDIM

                      Answer 3: The LED backpack module you reference would fall under the category of "Additional Electronics" and is not allowed per <RE17>


                      • #12
                        Multiple motors per Core Motor Controller port

                        Originally posted by FTC2856

                        Is it permissible to attach two legal motors to a single Motor Controller port by soldering the two wires to make a "y" splitter? Please see the attached picture. Thank you.

                        Answer: There is nothing in the rules that would prohibit the connection of two motors to a single motor controller port via a splitter cable.

                        Note: Care should be taken to pay attention to the current driving limits of the Core Motor Controller. The CMC has internal thermal breaker that will open when excess load is drawn from the controller resulting in the controller being inoperable until the breaker resets. Two motors under stall conditions would likely exceed the CMC current limit!


                        • #13
                          Custom LED Controller

                          Originally posted by FTC5957
                          Our FRC team uses Adafruit DotStar & NeoPixel individually addressable RGB pixel strips for both decoration and status feedback. We would love to be able to use these on our FTC bots for the same reasons.

                          1 - Would a COTS LED controller that plugged into the CDIM via I2C and controlled Adafruit DotStar & NeoPixel individually addressable RGB pixel strips be legal without running afoul of <RE17>?

                          2 - If the answer to (1) is NO, is there a process upon which an appeal can be made to allow individually addressable RGB pixel strips via mechanism like a COTS LED controller that can plug into the CDIM via I2C?


                          Answer 1: No.
                          Answer 2: There is no process for appeal.


                          • #14
                            Power Switch Requirements

                            Originally posted by FTC7172
                            At the beginning of the 2015 (Res-Q) season the game manual (and a Q&A Forum post) stated that standalone main power switches "must be either TETRIX #W39129 or MATRIX #50-00300."

                            Since then the rule wording has been changed so that <RE01>.a now states: "FIRST strongly recommends that Teams purchase a separate Main Power Switch, either TETRIX (part #W39129) or MATRIX (part# 50-0030)."

                            Q: If using a separate Main Power Switch, are teams still constrained to the TETRIX and MATRIX switches listed or can other (appropriately sized/rated) switches be used as Main Power Switches?

                            (This question came up during robot inspections at an event yesterday.)


                            Answer: <RE01> allows teams to choose either of 2 configurations for main power control:
                            1. A separate switch (either of two specific TETRIX and MATRIX part numbers)
                            2. The switch on the Core Power Distribution Module

                            If a separate switch is used, it must be one of the specifically listed switches.

                            Tip: Teams are only required to abide by the rules in THIS YEAR's game manuals; last year's game manual has no bearing on this year's game. In general, rules change year-to-year. Constraints from prior years may be relaxed or tightened in the current year. Teams should ALWAYS take the time to read and understand the ENTIRE game manual.


                            • #15
                              RE12 - LED Control Via Motor Controller Ports

                              Originally posted by FTC9925
                              Is it legal to use a spare motor controller outputs to control a series of LEDs to visually indicate specific states or sensor values on the robot during the teleop period?

                              Delta Robotics #9925
                              Cedar Rapids, Iowa
                              A: Rule < RE12> specifically allows for the use of motor controller ports to control LEDs. Teams may use these LEDs to signal specific states or sensor values.