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Miscellaneous Robot Electrical Parts and Materials - Answers

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  • #16
    Originally posted by FTC2844

    Subject: Replacing Bottom Plate of REV XT30 Distribution Block

    Question: Can we replace the bottom of the REV XT30 PDB with a 3d Printed replacement that includes 2 mounting holes for more secure attachment to the robot? No Electrical Modification has been done, with only the plastic casing being switched. Here is the 3d Printed part in question:
    Originally posted by FTC2844

    Answer: No.


    • #17
      Originally posted by FTC4634

      Subject: Other Light Sources

      Question: Since the ruling that disallowed using the phone's camera flash has been reversed (thanks!) would it also be allowed to use a bright 12v LED like this or the Andymark Targeting Light in conjunction with a webcam, since the webcam does not have a built-in flash?

      Answer: Both appear to have lenses to focus/concentrate their light sources and are not allowed.


      • #18
        Originally posted by FTC4634

        Subject: Relay Use Exception?

        Question: Most digital servos will continue to hold their position even after the PWM signal from the controller is stopped. One of the great features of the REV Expansion Hub is that once your program stops and the SDK sends the "failsafe" command to the Hub, the Hub will actually turn off the 5v power to the servo ports altogether. Thus, even digital servos will cease operation. This can be a huge safety plus at the end of the match, as a servo-controlled arm on the robot which is caught on something at the end of the match would be de-powered, which would otherwise cause the servo to be stalling, overheating, and possibly become a fire hazard while field personnel perform their post-match duties.

        Unfortunately, when using the REV Servo Power Module, this feature is lost. Would the GDC consider making a single-case exception and allow a relay to control the 12v power to the SPM in order to re-create the aforementioned safety functionality?

        Answer: No.


        • #19
          Originally posted by FTC6762

          Subject: Slip Ring Connectors

          Question: Hello! The team is really enjoying the challenge this year! We have seen this answered in a previous year clarification but would like clarification that slip rings are allowed as long as they abide by the wiring gauge requirements. We are actually planning on two slip rings, one slip ring for four servos (4 servos x 3 = 12 wires) and another for the servo power block power (20 amp). Our assumption is that we would not be able to only transmit the PWM signal and that we would need to do all three wires for each servo in this case and is what we have planned for. Thank you!

          Answer: Yes. Make sure that everything meets the wire gauge requirements/equivalents and that everything is well insulated


          • #20
            Originally posted by FTC4634

            Subject: Powering a USB Hub from the 12V Supply

            Question: The current rules state that if a powered USB hub is used, it must be powered from the 5v port on the REV Expansion Hub or a COTS USB battery pack. However, our initial testing has shown that using a standard powered USB Hub dramatically reduces ESD tolerance compared to connecting the phone directly to the REV Hub and frequently causes the REV Hub to pull the FTDI reset line when ESD occurs from contacting the Lander, causing temporary loss of control. Would the GDC be willing to expand the rules to allow USB Hubs to be powered from the main 12v battery, so that Industrial USB Hubs with 15kV ESD tolerance such as this one could be used?

            Answer: There are no current plans to approve 12v powered USB hubs


            • #21
              Originally posted by FTC8565

              Subject: USB LED Light

              Question: During our Vuforia testing, our programmers reported that it was too dark for Vuforia to recognize any of the three minerals during the autonomous period. They then decided to add on an LED light to brighten it up in order for Vuforia to work. We were just wondering if this kind of light was legal? (Heres a similar light:

              Answer: No. Take a look at <RE12>.d for the allowed methods of powering LED lights that are a part of your robot


              • #22
                Originally posted by FTC9999

                Subject: Robot Grounding Strap


                says "Electrically grounding the Control System electronics to the frame of the Robot is only permitted using a FIRST-approved, commercially manufactured Resistive Grounding Strap. The only Resistive Grounding Strap approved for use is the REV Robotics Resistive Grounding Strap (REV-31-1269)..."

                As of this wriing, the REV Robotics Resistive Grounding Strap (REV-31-1269) is not available with no indication as to when it will be available. The published specfications of the strap are:
                • Length: 30 cm
                • Resistance: 470 Ω 1/2 W 5%
                • Wire Gauge: 22 AWG
                • Terminations:
                  • XT30 - Male contacts
                  • Ring Terminal for #6 or M3 stud

                We request a rule change that would allow teams to use a team manufactured grounding strap since a commercially manufactured grounding strap is not readily available to all teams. We recently registered to compete in the Rover Ruckus season.

                Answer: There appears to be stock available as of this reply. The rule stands as written for this season. We will consider updates as we develop the manuals for next season.


                • #23
                  Originally posted by FTC9999

                  Subject: RE10 REV Servo Power Module and VEX EDR Motors

                  Question: The game manual says "A REV Servo Power Module can provide up to 15A of current across all output servo ports for a total of 90 Watts of power per module."

                  The stall current of the VEX EDR 393 is 4.8 amps at 7.2 volts (35 Watts). So at 6 volts the stall current would be roughly 4 amps (24 Watts). Moreover, the required VEX Motor Controller 29 draws a maximum 3 amps at 8.5 volts (26 Watts). So at 6 volts the controller can only draw 2.1 amps (13 Watts) from the Servo Power Module (SPM). Thus it appears that the SPM can safely power six VEX EDR 393 servos.

                  Also, the Modern Robotics Core Servo Controller is rated at 36 Watts maximum power across all output ports. If the Core Servo Controller can safely power two VEX EDR 393 servos, then with an output rating of 90 Watts, and considering the over-current protection feature of the SPM, the SPM can safely power at least four VEX EDR 393 servos.

                  We request to remove the <RE10> restrictions on the number of VEX EDR 393 servos that may be controlled/powered by the REV Servo Power Module.

                  Answer: We are not anticipating changing this rule for the current season. We will re-evaluate as we begin work on next season's rules.


                  • #24
                    Originally posted by FTC12833

                    Subject: Electrical Connector

                    Question: Would these be considered "any compatible connector" per <RE14> part f?

                    Answer: Yes, as long as the individual conductors within the connector meet the gauge requirements for the circuits being connected.


                    • #25
                      Originally posted by FTC5202

                      Subject: Splitters for Motor Wiring

                      Question: Tetrix Robotics sells a Y connector for servos, part 39082, "for connecting two servos to one channel" which we assume is FTC legal. On our robot, we have created our own Y connector with wire and Anderson Powerpoles to drive two motors from one motor port of a Rev Expansion Hub. In application, the motors face each other and thus need to run in opposite directions, which we have taken care by reversing the black and red wires on one of the legs of the Y connector that we made. Is this setup legal?

                      Answer: There is nothing in the rules that prohibits controlling multiple motors with one motor controller port. Care should be taken to ensure that the operation of the paired motors does not exceed the rated current limit for the motor controller. Additionally, all connections should be appropriately insulated.


                      • #26
                        Originally posted by FTC15254

                        Subject: Electromagnets

                        Q: We were thinking to use parts of a solenoid (coil of wire and rod) to act as an electromagnet. It will not interfere with another teams robot or the playing field. We were going to attach the rod to our team marker and at the start of the match, the coil to be powered to hold our team marker to the robot temporarily, then to drive to the home base in the corner and deactivate the coil which would drop our team marker. After that, the coil would not be used for any other purpose.
                        We would be removing the spring and E clip and only use the rod and the solenoid coil.

                        Would this be allowed?

                        A: No. Electromagnets would fall under <RE17> and are not allowed.


                        • #27
                          Originally posted by FTC1999
                          Subject: Resistors w/ LEDs

                          Q: My team would like to use an LED that doesn't contain an internal resistor. In order to use this LED, we need to build a circuit containing the LED and a resistor. We will use a legal power source per rule <RE12>d. IS this allowed or is it an illegal custom circuit?

                          A: No. This would fall under custom circuits and not be allowed. The allowance for passive electronics (RE11.c) is specific to sensors.


                          • #28
                            Originally posted by FTC10138

                            Subject: Spark Mini Motor Controller and LEDs

                            Just being careful although we believe this is pretty straight forward. The current rule <RE12>d explicitly states that lights can only be powered by: (i.) internal source, (ii.) Power ports on CPDM, (iii.) Motor control ports on CMCM, or (iv.) REV Hub Motor-control ports, spare XT30 ports, 5V aux Power ports, and I2C sensor ports.

                            Q1. Can one use power from the REV XT30 Power Distribution Block (and if so, can this block be connected directly to the feed from the main power switch or does it have to be cascaded off a hub XT30)?

                            Q2. Can they be powered by a Spark Mini controller? Control is already allowed via <RE12>b and <RE12>c, but power is the grey area since these motor control ports not directly on the REV Hub?

                            A1: See Miscellaneous Robot Electrical Parts and Materials #13
                            A2: Yes. The Spark Mini Controller is essentially and additional motor control port.


                            • #29
                              Originally posted by FTC13499

                              Subject: Light Power Sources

                              Rule <RE12> states Light Sources - Functional and/or decorative light sources (including LEDs) are allowed with the following constraints:.....

                              The rule does not allow "focused" lights, but permits "functional" lights.

                              Sub section d. states

                              "The only approved power sources for lights are as follows:

                              i. Internal (as supplied by the Commercial off the Shelf manufacturer) battery pack or battery holder."

                              I read this as an off the shelf product like a flash light or headlamp is allowed as long as they are not focused. In this respect,

                              Q1. Can a flash light or some other LED light source independently powered by a battery pack be considered as "functional" light under this?
                              Q2. If an independent light is not allowed, can I connect an LED strip light to the Rev Power Distribution block to light up the area?

                              A1: Any light source that includes focusing is not allowed. Most (if not all) flashlights include a parabolic reflector behind the bulb to focus the light. This makes most (if not all) flashlights violate RE12. For other light sources the independent power source (batteries) needs to be manufacturer provided (e.g.. a part of the LED system)

                              A2: Yes. See Miscellaneous Robot Electrical Parts and Materials #13