Servo Legality

Hello CD,

Our team is looking into using a servo on the robot this year. Our team has never done this before so we looked into all of the rules regarding their legal use. The two primary rules that we have found that pertain to which servos we are allowed to use are R18 and R19.

R18 The only motors and actuators permitted on 2015 FRC ROBOTS include the following:

PWM COTS servos with a maximum power rating of 4W each at 6VDC
Per the Servo Industry, Servo Max Power Rating = (Stall Torque) X (No Load Speed)

R19 The integral mechanical and electrical system of any motor may not be modified. Motors, servos, and electric solenoids used
on the ROBOT shall not be modified in any way, except as follows:
A. The mounting brackets and/or output shaft/interface may be modified to facilitate the physical connection of the motor to
the ROBOT and actuated part.
B. The electrical input leads may be trimmed to length as necessary.
C. The locking pins on the window motors (P/N: 262100-3030 and 262100-3040) may be removed.
D. The connector housings on window, door, windshield wiper or seat motors and Bosch motors (P/N: 6004 RA3 353-01)
may be modified to facilitate lead connections.

We have been looking for servos with a relative high stall torque (>200 oz-in) that are less than 4 watts as calculated by “servo industry standards”. We have been verifying our calculations using the spreadsheet provided here.

We were unable to find a standard servo that meets these requirements so we began looking into gearing a servo to get the stall torque desired. We found a geared servo on servocity that would accomplish what we would like to do that also has a rating of less than 4 watts. Here is the link to the servo:

The reason we are questioning the legality of this servo is due to how the potentiometer is wired into this servo. The potentiometer is mounted on the output shaft and appears to be wired into the servo.

We think this may violate R19 and we were looking to see what the CD community thought before we posted this to the Q and A.


I believe the particular servo linked meets the definition of a COTS servo, so per R18, it should be legal as long as it meets the power rating.

I believe R19 is trying to prevent TEAMs from modifying motors/servos/solenoids to give themselves an advantage. You’re not making a modification, you’re buying a COTS component. If it meets your need and you have reservations, ask for clarification on Q&A, otherwise, bring documentation to the competitions proving its COTS and meets the power rules in the event someone has a question about it.

Note, if you do end up posting to Q&A, dont ask if that particular model/part is legal. You likely wont get an answer. You need to phrase your question in a way that asks for clarification on the rule.