No announcement yet.

Motors and Servos - Answers

This is a sticky topic.
  • Filter
  • Time
  • Show
Clear All
new posts

  • Motors and Servos - Answers

    Answers to questions about Motors and Servos can be found in this section.

  • #2
    Originally posted by FTC1000

    Subject: TETRIX TorqueNADO motor legal?

    Q: Hi Game Design!

    Can you confirm that the TETRIX TorqueNADO motor is a legal robot component?

    Thank you!

    A: Yes. The TETRIX TorqueNADO motor is an allowed motor (RE09.a allows TETRIX 12V DC Motors)
    Last edited by Buckaroo Banzai; 09-28-2017, 10:15 PM.


    • #3
      Originally posted by FTC13539

      Subject: Servo Power Module Wiring

      Q: If we are using a REV Robotics Expansion (not hybrid MR) control system, and we would like to add a REV Robotics Servo Power Module, can we power it from the extra XT30 on the Expansion Hub?

      Based on RE05.a the answer appears to be yes, but the second sentence of RE05.c (emphasis mine) seems to disallow it.

      <RE05> a. Allowed electronic devices may only be powered by power ports on the Core Power Distribution Module or the REV Expansion Hub [...snip].

      <RE05> c. A second REV Expansion Hub is allowed to be connected to and powered by the extra XT30 power port on a Robot's first REV Expansion Hub. No other devices are allowed to draw power from the XT30 power ports on a REV Expansion Hub.

      A: <RE05>.a allows any allowed electronic device (not explicitly excepted in i through iv) that requires 12V power to be connected to the power ports on a REV Expansion Hub (the XT30 port). Additionally, <RE14>.j allows a team to custom make power wiring, including the use of "splitters" or "y-cables" to allow for fan-out of power connections.

      We agree that the wording in <RE05>.c is a bit confusing. There is a pending update to Game Manual Part 1 that should help eliminate the ambiguity.

      Note: Care should be taken when custom making cabling to follow the wire gauge constraints listed in <RE14>.j. All connections should also be appropriately insulated to protect against possible short circuits


      • #4
        Originally posted by FTC5187
        Subject: Motor Gearbox

        Q: Hello, we are wondering if it is legal to use a motor without a gearbox. We would like to use a vacuum pump and found one that would work if we took off the illegal motor it came with and attach a NeveRest motor minus the gearbox in its place. Thanks.
        A: Yes, teams may use a legal motor without a gearbox.


        • #5
          Originally posted by FTC11541

          Subject: Servos with feedback wires

          Q: Rule <RE10> requires that "Servos ...must have the three-wire servo connector." Are servos with additional sensor feedback wires like this ( ) Adafruit servo allowed as long as they don't violate any other rules?

          A: There is nothing in the rules that would prohibit the use of the above servo. Be aware that the programming to read the the sensor may be challenging as the feedback signal is a 910 Hz PWM signal and encodes the speed of the servo by varying the duty cycle of the feedback signal from 2.7% to 97.1%.
          Last edited by Buckaroo Banzai; 10-16-2017, 03:19 PM.


          • #6
            Originally posted by FTC8424

            Subject: Is the REV-41-1097 Smart Robot Servo a legal component?

            Q: Is the REV Robotics configurable servo ( a legal servo? We think it is, because we are allowed to make changes to gear boxes on motors and such, but given that it is "programmable" to make it a continuous rotation / 180-degree / setting specific limits on movement, we wanted to be sure.

            Thank you!

            A: Yes. The REV Robotics configurable servo mentioned above is an allowed servo


            • #7
              Originally posted by FTC5501

              Subject: Servo Potentiometer

              Q: According to rule RE15 we are allowed to make modifications to make electronics more useful. Are we allowed to extend wires from a servo to an external potentiometer as long as the servo is able to be programmed in Android Studio and hasn't been modified in a way that affects its safety?

              A: No. Adding a potentiometer either inline w/ the internal circuitry of a servo or inline in the control lines would fall outside of the scope of the modifications allowed under <RE15> as well as violating the <RE17> with respect to being a custom circuit.


              • #8
                Originally posted by FTC11722

                Subject: Servo cable extender electronics

                We would like to know if using these servo cable extender boards are permitted:
                - CAT6 Sending Board
                - CAT6 Receiving Board

                A: No.The Sending Board is essentially just a connector, but the Receiving Board has active electronics and would fall under <RE17> as additional electronics and is not allowed.


                • #9
                  Originally posted by FTC7549

                  Subject: Modifying Servos into Continuous Rotation

                  Q: Aloha-

                  I know this topic comes up every year, but I would like an official ruling for this year's game. The question is to what extent can we modify an existing servo so that it becomes a continuous rotation one.

                  Game Manual 1, RE15, can be interpreted in favor or against the modification. Servocity has a good write-up on how easily modifiable their servos are. Is a team allowed to modify a servo accordingly?

                  Or is it better to purchase a servo from a vendor already modified to be continuous?

                  Thank you!

                  A: No. Modifying a servo internally to change it into a continuous rotation servo is an example of a modification not allowed by <RE15>


                  • #10
                    Originally posted by FTC1999

                    Subject: Servo Power Compatibility

                    Q: When <RE10> requires that the servos individually and together on the same servo controller do not exceed the manufacturer specifications for the controller, to which the specifications is this referring?

                    Specifically, would the HS-805 MG servo be legal, when attached to the REV Servo Power Module?

                    A: The specification of primary concern in <RE10> is the stall current rating for the servos. For the REV Expansion Hub, there is a 5A total and 2A per pair limit to the current available through the servo ports. The stall current for each servo driven by a module should each be below the max rating for the module and the sum of the stall currents for all the servos drive by the module should be below as well.

                    The HS-805MG servo shows a stall current rating of 6A and would not be directly usable with the REV Expansion Hub. However, by utilizing a REV Servo Power Module, the servo could be utilized safely. Teams following this approach should be careful to manage the overall power budget. The REV Servo Power Module supports up to 20A across the available connections. Remember as well that the main fuse in the battery is rated at 20A.
                    Last edited by Buckaroo Banzai; 11-01-2017, 01:58 PM.


                    • #11
                      Originally posted by FTC12687

                      Subject: VEX Power Expander

                      Q: According to Relic Recovery Rules <RE10> VEX EDR 393 motors must be connected using the REV Servo Power Module.


                      However, the REV Servo Power Module is out of stock and unavailable for purchase. (At REV and

                      Given that this module is out of stock, I would like permission to use the following Servo Module from VEX Robotics EDR:


                      The VEX Power Expander has the same purpose and function as the REV Servo Module and these are readily available for teams.

                      We would like to use the VEX Power Expander in place of the REV Servo Module for the meet on November 11th. Is this allowed?

                      A: No. The only allowed Servo Power Module is the REV Servo Power Module. The VEX Power Module would fall under <RE17> as Additional Electronics and is not allowed.

                      We do understand the frustrations that come with equipment back-orders and hope that supplies will be available soon.


                      • #12
                        Originally posted by FTC6183

                        Subject: 180 degree servo modification

                        ServoCity has an option when ordering servos to extend the range of travel to 180 degrees. For example, when ordering the HD-625MG, they have a ordering option for "rotation" where you can select "stock rotation", "Increased rotation" or "continuous rotation".


                        In previous years, modifications to servos were not allowed. However, I cannot find a rule prohibiting such modifications in this year's manual. In addition, since this modification is commercially available (i.e. being done by the supplier), rather than being done by the team after purchase, it is not clear whether this is considered a modification to a COTS part or not.

                        Would a servo that was ordered with the "increased rotation" option be legal?

                        A: No. Modifications of the internals of electronics are not allowed (RE15), even if done by a vendor.


                        • #13
                          Originally posted by FTC4634

                          Subject: 12v Servos?

                          Would a servo such as this one that uses external 12v power to boost the torque be allowed?

                          A: No. <RE10> clearly limits the power for a servo to come from only an allowed Servo Controller or the REV Servo Power Module.


                          • #14
                            Originally posted by FTC4224

                            Subject: Legal Servos

                            Q: Are the following HiTechnic servos legal:

                            HS-645 MG
                            HS-785 HB
                            HSR-2645 CRH
                            HSB-9380 TH

                            Thank you

                            A: It is not possible for us to rule on the legality of all servos. <RE10> indicates that any servo that is compatible with an allowed servo controller is allowed. Compatibility is best understood in a couple of forms: voltage and power. I.e., does the servo operate with the voltages provided by the servo controller and does the power consumed by the servo in operation fit within the power constraints for the controller.


                            • #15
                              Originally posted by FTC11594
                              Subject: Extra Motors

                              Q: Are extra motors allowed to be used as counter weights? We are still under our 8 motor limit and they will not be attached to power. However, they will be secured to the robot.
                              A: Motors may be used as counterweights but the limit of 8 motors still stands, regardless of whether the motors are connected to power or not.