Window Motor Modification - Is it legal?

Team 2219 is considering using a swerve drive this year, but our problem is where to mount the encoder on our steering motor. We are using the Window motors and right now our design does not leave any room for the encoder.

Our thought is that we can cut away part of the plastic housing on the Window Motor transmission where the other side of the output shaft is, drill a small hole, tap it and put in an assembly to mount the encoder.

Quoting the rules:

<R54> So that the maximum power level of every ROBOT is the same, motors and servos used on the ROBOT shall not be modified in any way
A. The mounting brackets and/or **output shaft/interface **of the motors may be modified to facilitate the physical connection of the motor to the ROBOT and actuated part.

My question is, does the opposite side of the output shaft still constitute an interface? Does modifying the plastic housing where the output shaft sits result in a violation of this rule? I will be posting this on the Q&A tomorrow but wanted to get your opinions first.


Wouldn’t the output of the motor be the input to the transmission? I know that that interpretation is true with FP and the old Globe motors.

I’m fairly confident if i remember correctly that the denso is a dead axle system, with the shaft mounted to that plastic. The output plastic rides on this shaft so by cutting away the back plastic you’d be removing the mount for the shaft altogether.
(someone correct me if im wrong)

The window motors are an odd case, the transmission is much more integral than the transmissions on the Globe and FP motors.

I would not even try to guess the answer to this one, wait for the QA response.

The problem is that you have to modify the casing (which is not allowed) to get to that end of the output shaft. If it were already sticking out, you could modify it, though.

Can you provide a sketch or cad drawing of what you wanted to make? I’m sure we can help wedge an encoder in there somewhere.

Also, the encoder does not have to be directly attached to the motor. there are other places to put them, and having it mechanically further away from the motor can have some benefits to absolute positioning accuracy (for example compensating for system backlash)

From Team 2219:

We have confirmed what most of you are saying…there is no way to access the shaft in the Denso motor through the case…we took one completely apart (for an old kit) to draw that conclusion.

Thank you for the input.

Team 2219: The Megahurts

In the past using the same rules quoted above, the modification you are describing would have been deemed illegal. The rule refers to the fact the mounting holes may not facilitate mounting the motor on your robot using the provides holes. The rule allows you to modify so that the motor can be mounted to your robot without changing the operation or power output. In the case of the window motor, the transmission is considered an integral part of the motor.

In the configuration shown, I don’t see a need to modify the motor mounts. Please be advised that the bearing in the plastic housing that is supporting the output shaft does not contain a thrust bearing to support any force supplied by the module. Damage will result should there be excessive vertical movement in the module while driving.

actually, looking specifically at <R54> part B:

B. The gearboxes for the Fisher-Price motors are not considered “integral” and may be separated from the motors.

It would appear that I was incorrect in comparing it to the FP since it is explicitly stated that the FP is not considered integral. I have seen window motors with encoders mounted that way in past competitions on the old window motors, but obviously this is a new year and asking on the Q&A forums would be appropriate.

Not legally. Modification of window motors has been and remains illegal except as indicated above.

Our team is using a different form of encoder - we are making a laser-printed “tape” of lines that is wrapped around the axle. I haven’t decided if I’m going to use the provided sensor or make my own, though.

Put your encoder on a separate idler sprocket that is the same size as the motor drive sprocket. This can be anywhere on the steering chain/belt.