ABE Accessibility Mod: Continuous Drive Servo Configuration Windows

["What the hell happened to my feet???]

What’s the deal with drilling holes in your drive servos?

Continuous rotation servos are made by taking normal servos and replacing the feedback pot with a static pot and/or some extra resistors. In essence, when you tell a regular servo motor to move itself to a specific angle, here’s what happens:

1. It reads its current angle
2. It sets the direction of the motor in such a way that the difference between the current angle and the one that you’ve requested will be reduced
3. If the difference is large, the speed of the motor will be set high. If small, it will be set low

[pre-mod: notice the pot onboard and where it should line up to roughly once reinserted]

In a continuous rotation servo:

1. It reads its current angle the angle given by the static pot (usually inside the enclosure). The static pot is usually set such that it reports back about 90°, which is the zero-point of most standard servos.
2. As above
3. As above

[a completed accessibility mod - I see a pot dial!]

So, why are you drilling holes again?

Well, in the not-so-wonderfully-made servos, there is a tendency for the servos to (over time or perhaps with vibration/delivery) have the pot move or the impedence in some way change itself. That means that when you want a continuous rotation servo to STOP, it will often be just moving instead.

Now, this can be fixed by telling the servo to go to the 90° angle and adjusting the pot until the servo stops moving. Doing this is a finnicky operation as the four screws that hold a servo together usually release all the gears, the circuit board and the motor at once. Getting it back together is a pain in my arse.

SO! One simple hole later and we have a feature that some servo makers are charging extra for: Accessible tuning pot. Done!