Servo Usage Tips

Below are some tips on using servos in FTC.

  • Do not backdrive servos. Forcibly rotating a powered servo away from its position risks damaging the internal gears.

  • Servo wires usually are black-red-white. Matching the colors is an easy way to check if the servo is plugged in correctly. Servo connectors provide no protection from plugging them the wrong way: if you rotate it 180 degrees, it will still fit - but the servo would not work. (It wouldn’t be damaged, though). Thus, if your servo is not working, first check if they are plugged in correctly. Then check it again.

  • When using servo wire extensions, use retaining clips to prevent the connection from coming apart when someone pulls on the wire. Alternatively, electrical tape will work in a pinch.

  • Do not use socket head screws to attach servos - when tightened, they will damage the plastic. Use button head screws or socket heads with a washer.

  • Servos break very easily when subjected to lateral loads or bending of the shaft. For example, if you mount an arm or a claw directly on the servo without any additional precautions, it is very likely that you will break the servo first time you drive into the wall with the arm extended (and this will inevitably happen).

    To avoid that, use additional supports. The easiest way to do it is by using Servoblocks from Actobotics or goBILDA. These assemblies act as exoskeletons for the servo, providing additional support. They are expensive, but worth every penny. Additionally, REV offers the inside and outside channel servo bracket, which when paired with the aluminum servo shaft adapter and bearing assembly, fulfills the same function.

    servoblock

    A servo in a ServoBlock

There are also some alternative designs of servo supports; one of them, which is not as strong as the original Servoblock but much more compact, is shown below (CAD is also available):

compact servoblock

Alternative servo support block

  • Use linkages. Instead of mounting some rotating piece directly on a servo, mount it so it can rotate around a pivot point and then connect it to the servo using linkage as shown below:

    linkage

    Linkage example, courtesy of team 4137 Islandbots. A goBILDA flat beam is used as the link.

  • If you need more power, use REV Servo Power Module. By itself, REV Expansion Hub provides 5V power to servos, and the current is limited to 2A for each of 3 pairs of servo ports (0-1, 2-3, 4-5). Since stall current on a servo such as goBILDA Dual Mode servo is about 2.5A, it means that if one of the servos in a pair is stalled, the other one will not be getting enough power to maintain its position. The REV Servo Power Module provides 6V and up to 15A current total for 6 servo ports.