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Robot Inspection and Build Rules - Electrical - Answer Thread

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  • #16
    Linear Servo Legal?

    Originally posted by FTC9958
    We'd like clarification if a Linear Servo assembly such as the one in the link below would be considered legal as:

    1. Servos (and not a motors)
    2. Legal COTS Part
    3. Only 1 degree of motion (Likely rolled into #1)

    Thanks for your help,

    A: No. This linear servo requires a connection to an external 12v power source and is not driven purely by the Servo Controller modules. Allowed servos must be controlled and powered by an allowed Servo Controller.


    • #17
      Sensor Legal

      Originally posted by FTC4631
      A lot of the color sensors are on backorder now. We found this one still available:

      This seems like a "manufactured sensor" that will plug into the Core Device Interface Module once the header and leads are soldered onto the board. That is all explicitly allowed, but I still would be a lot more comfortable with an official approval on this sensor.

      A: In general, it is not possible for the GDC to rule on the legality of all sensors. In this particular case, yes, this sensor appears to be an example of manufactured sensor as allowed via <RE06>.b.i


      • #18
        Sensor Clarifications

        Originally posted by FTC4029

        We've got several questions regarding the legality of interfacing with various types of sensors using the new control system.

        1) Is it now legal to use a LEGO Mindstorms NXT sensor with a spliced LEGO connector cable if it interfaces directly with the Core Device Interface Module? These could be considered "sensors from any manufacturer" as per <RE06>bi, but would this be in violation of the ruling on "legacy sensors" in <RE06>bii?

        2a) Is it legal to use passive components in conjunction with sensor connectors, such as filter capacitors (necessary for using many IR rangefinders), or resistors (for creating voltage dividers to power lower-voltage sensors)? We feel that this could be covered under <RE05>g, as these components could be physically integrated into a sensor's connector, which we are free to modify. Since many manufactured sensors call for these components as part of the sensor's spec, could they be considered part of the manufactured sensor itself in that case?

        2b) Is it legal to connect a level shifter such as between a legal manufactured sensor and the Core Device Interface Module? Many manufactured sensors require 3.3v power and signal, which the Core Device Module cannot provide without one of these shifters. We believe these could also reasonably be considered part of the "connector", which we are free to modify per <RE05>g.

        3) Would an integrated sensor package that includes a programmable microcontroller, such as, be considered a legal "manufactured sensor"? There are many more sensors beyond this that feature integrated microcontroller units with varying degrees of programmability. This includes practically any sensor that interfaces over I2C, such as some Modern Robotics sensors. Could we have some more clarification on what constitutes a legal "manufactured sensor"?

        Thank you very much!
        FTC 4029

        A1: No. LEGO NXT Sensors may only be connected to the Legacy Module per <RE06>.b.ii. The Legacy NXT sensors require non-standard I2C support (as provided by the Core Legacy Module)

        A2: Yes. Passive components, as required by sensor manufacturers are allowed.

        A3: No. <RE06>.e.iii limits power for allowed sensors to come from either the Core Device Interface or the Core Legacy Module.

        A4: No. Sensors combined with programmable systems are not allowed with year.


        • #19
          Vex 393 Motors and Optional Gearsets

          Originally posted by FTC10126
          The Vex 393 motors come geared for high torque and also come with a set of replaceable gears that will change them to high speed, and now there is a third gearing you can buy to change them to "turbo speed". Is it legal for the teams to change these gears as these motors were designed for these gears to be changed by the user?

          A: Yes. The replacement gearsets and optional gearsets for the Vex 393 motors are allowed.


          • #20
            Connectors for Sensors

            Originally posted by FTC8881
            Our team has a Parallax L3G4200D Gyroscope breakout board. We want to connect it to a breadboard for the sole purpose of attaching the I2C wires that will go directly into the Device Interface Module. In essence we will be doing nothing with the gyro other than extending the pins so that we can plug it into the DIM (like connecting the switch in one of your earlier posts). Would this be allowed?

            Using the provided com.qualcomm.robotcore.hardware I2cController interface class, it appears that we can easily obtain the information from the Gyro by writing a simple API/Driver. Would this be allowed?

            We will not be using any external processors, controllers, etc. for the Gyro and the only power source would be the I2C power lead coming from the DIM.

            Team 8881
            Pirates of the Pacific

            A: Yes. collections of simple connectors and breadboards to allow easy connection of sensors to the Code Device Interface are allowed per <RE05>.g


            • #21
              Sensor Legal?

              Originally posted by FTC8548
              Hello. Our team was wondering if we could use this chip since the ZTE phone doesn't have a built-in gyro sensor. Thanks for clarifying!


              Team 8548

              A: In general, it is not possible for the GDC to rule on the legality of all possible manufactured sensors. This sensor is an example of a broad class of sensors that are legal within the limits imposed by <RE06> and other rules.

              All questions about similar sensors will be mitigated to the "duplicate questions" forum.


              • #22
                Alternative Configuration for Matrix Support?

                Originally posted by FTC9958
                With support for Legacy Matrix motor controllers not yet available, our team has adapted a working robot with the following configuration:

                New Modern Robotics Core Power Module
                New Modern Robotics Motor Controllers
                Legacy Matrix 9.6v Motors
                Legacy Matrix 9.6v Battery
                Standard ZTE Speed Phones for Driver Station and Robot
                Standard Driver Station & Robot Apps, with custom op mode

                Note: This configuration does not provide motor encoder use/feedback, we are using power leads only on motors.

                As per current rules RE01 (control modules), RE03 (power) and RE04 (motors & servos), the described configuration would only be legal for competition if we were using Legacy Matrix Motor/Servo controllers.

                As support for the Legacy Matrix Motor/Servo controllers is not yet available, no firm release date has been announced, and as we have no other options available, we are requesting that the applicable rules be adjusted to allow our team (and potentially others) to use the described configuration for the 2015/2016 season.

                Thank you for your time and consideration,

                Redfish Robotics
                Team 9958
                "We're Hooked on FIRST"

                A: No. This alternate configuration is not allowed. Matrix Controllers are now supported in the SDK.


                • #23
                  Servo Controller Current Limits

                  Originally posted by FTC7172
                  <RG04> says that "Any compatible servo is allowed"; Q&A Forum update #9 says "Make sure to pay attention to the stall current ratings."

                  Does this mean that the TETRIX Quarter Scale Servos (#W39904 and #W39905) are no longer legal if used with the ? Both of these servos list a stall current rating of 1800mA; the MR Core Servo Module says individual servo power is 6 volts DC 1.5 amps max.



                  A: Both the Legacy HiTechnic Servo Controller and the Modern Robotics Servo Controller have the same 5 amp total current limit. The total stall current rating for servos attached to a servo controller must stay below this 5 amp limit.


                  • #24
                    Sensor Clarification

                    Originally posted by FTC5385
                    It is not clear to me why the sensor referenced in Post #18 is not allowed while the sensor in Post #21 is allowed. Both appear to be sensors that offer on device processing. Perhaps the distinction is that the sensor in Post #19 has a micro controller which appears allow full customization? As opposed to Post #18 where the micro controller and firmware is is provided by the vendor (Bosch). I am just looking for a way to distinguish between the two types of sensors so we can apply this to other sensors we might select.

                    Post #19 -
                    Post #21 -


                    A: The Sparkfun sensor includes a on-board processor that is user programmable and is effectively an Arduino board with sensors included. The Adafruit sensor is not user programmable, only configurable.
                    Last edited by Buckaroo Banzai; 10-19-2015, 03:17 PM.


                    • #25
                      Parallel Motor Connections

                      Originally posted by FTC4644
                      (This question was previously addressed for the legacy Motor Controllers:

                      With the shift to the new hardware, is it acceptable to wire 2 motors to a single channel of Modern Robotics Motor Controller?

                      A: Yes. It is acceptable to wire up to 2 motors in parallel to be driven by a single motor controller. Care should be taken during the electrical design process to avoid overloading the motor controller. The internal thermal breaker takes significant time to cool and reset once tripped.


                      • #26
                        Alternative Encoders

                        Originally posted by FTC2887
                        Is it possible to use an optical encoder on Tetrix motors which is different from the one sold by Tetrix, (I believe this one is produced by US Digital), assuming that the alternate has input power and output quadrature which are the same as the Tetrix encoder (5V TTL compatible)? The encoders sold by Tetrix are expensive, and we have found them in the past to be quite fragile and somewhat lacking in reliability. It seems there are several other encoders out there that would be less expensive, more rugged, and compatible with the motor controllers.

                        A: Encoders compatible with the Modern Robotics Motor Controllers and Legacy HiTechnic are allowed. Care should be taken to match the specifications of the Tetrix encoders exactly as the PID code that runs within the motor controllers relies on the characteristics of the encoder. Encoders not compatible with the Motor Controllers may be used as connected to a Core Device Interface.


                        • #27
                          Tetrix Encoders

                          Originally posted by FTC7503
                          My team has two tetrix motor encoders from previous years, it appears they will not work with the new system. Is this accurate?

                          FTC 7503

                          A: There is nothing in the rules that would prohibit the use of the above encoders. They are compatible with both the HiTechnic motor controllers and the Modern Robotics Controllers.


                          • #28
                            Power Splitter Usage

                            Originally posted by FTC10131
                            In previous seasons, teams had electrical troubles when their power was daisy-chained through the HiTechnic motor and servo controllers. This is because when a lot of current was drawn by a motor (e.g., if it was stalled, or changing direction, etc.), the large current passing through the small trace on the printed circuit board inside the controllers resulted in a downstream voltage drop which could affect the electronics. The FTC Robot Wiring Guide, released by FIRST, specifically identified this as a problem and proposed the solution of using external power distribution terminal/splitter/network which bypasses power being distributed through the controller's printed circuit board traces. See for example, page 18. of the FTC Robot Wiring Guide.

                            This year, the game manual states that we must route all power through the new Power Distribution Module. This essentially requires that ALL power now go through traces on the Module's printed circuit board, which again can result in the same problem identified in the FTC Robot Wiring Guide.

                            So, our question is, may we use an external power distribution terminal/splitter/network as suggested in the FTC Robot Wiring Guide instead of or in addition to the power distribution option in the Power Distribution Module? Please consider that a lot of time and trouble was spent by FIRST in making the FTC Robot Wiring Guide to address previous chronic power distribution problems, and we humbly suggest that the recommendations in that document be at least permitted as an option for teams concerned about the same issues.

                            A: Power splitters are explicitly allowed per rule <RE05>.f. They may only be used downstream from the Core Power Distribution module ... i.e. the battery must connect to the Power Distribution module with nothing more than a (recommended) single power switch between.


                            • #29
                              Resistors Inline with DC Motors

                              Originally posted by FTC6137
                              We're concerned about possibly burning out motors or motor controllers, so we want to insert a 1 ohm resistor in series with the motor controller 12 volt input to limit the current. Is this allowed or is it a violation of RE06 or another rule? We noticed passive components are allowed for creating voltage dividers for sensors. Thank you for your help.

                              A: No. Resistors are not allowed to be placed inline with DC motors per <RE06>.d


                              • #30
                                Storage of Static Electricity

                                Originally posted by FTC9107
                                Hello I have a question about preventing our robot from being affected. Can we have our robot store static electricity in a battery as long as we don't use it for our power source? Thank you!

                                A: No. Per <RG10> and <RE03>.