Let's Make Robots!

Hacked some servos for fun


I had a GWS S03TXF 2BB servo that I had previously released the magic smoke from. It's been sitting on my desk, labeled "bad" for some time. I took it apart and could see that the board shows visible signs of frying.

I also had a GWS S03N STD servo that I had butched for the brains, in order to try to create a mongo-sized servo for steering YardGnome (a work in progress).

So I decided to hack them both for their motors and gears, to make two gear motors. This worked well enough, but because the motors and gears of the two servos don't match, they turn at different speeds. Soooo...

I decided to butcher another perfectly good S03N STD servo, so I could get matching gear motors. This worked well, and will probably form the basis for another project. In fact, I have seen on this site previous attempts to add optical encoders right inside a gear motor. With the electronics and potentiometer gone, these servos have lots of room inside the case. I'm thinking of trying to find some small quadrature (also known as rotary) encoders, and jam them in there where the potentiometers usually go. We'll see how that goes.

In the meantime, I now had some spare servo parts including:

  • One perfectly good motor from the S03TFX servo
  • The case and gears for the S03TFX servo
  • One perfectly good servo board from the S03N servo

What to do? What to do? (Evil laugh from Dr. Frankenstein...)

A little more work, and we have a S03TFX servo running with the brains of the S03N servo inside. Due to the mismatch of gearing and programming, the servo only turns about 90 degrees instead of 180. However, I'm sure I can make use of this at some point.


I just bought a few of these rotary encoders.

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Usually the pot inside the GWS servos has a 5mm shaft. Those rotary encoders have a 6mm shaft, so I am curious how you're going to fit them inside the servo. I've tried to find encoders with a 5mm shaft but couldn't. Good luck!

I actually could have ordered 5mm shafts or 6mm shafts. I opened up the servo and it looked like 6mm, so that's what I ordered. They were only 75 cents each, so it is not a huge loss if I can't make them fit. I may have to get creative with a dremel tool.