Hobby servos work great for small robots, but what about if you want to build a somewhat larger bot that needs a motor with a lot of torque? They may not have the controllability of a servo, but for the price ($16.49 from Monsterguts) they might be an attractive option for your next robot. They’ve long been used as the drivers for Holiday props, but I haven’t seen many of them used for hobby robots. Feel free to link to yours in the comments if you’ve built one!
Straight out of the box, you may think that they will take a lot of work to fasten to your device of choice. They, at least the motors that I’m using, come with a wiper motor arm linkage sporting a ball joint on the end. Pretty useless, you might say, why not just a hole for a 1/4 inch bolt? Well, if you have a Dremel tool, Grinder, or milling machine and a hammer, you’re in luck! Simply grind off the back side of the ball joint, then fasten it in a vise. Using a punch (or whatever you have available), put it in the middle of the ball joint, and hammer it out!
You’ll now have a hole that a 1/4 – 20 bolt can go right through, attaching to whatever you like! In my situation, I used some rod ends purchased from Amazon (not the cheapest things in the world). Control will eventually be provided by a servo switch from Servocity that is able to turn a standard hobby PWM signal into a simple on-off relay.
Depending on your situation, the motors can be mounted by the three holes around the gearbox, but I instead opted to mount them using a piece of 2×4 with a hole cut in it large enough for the motor to fit into. This was then fastened down with wood screws as shown in the picture to the right for a tight fit.
I’ve been working on the remote control hexapod (introduced here) that this goes on for quite a bit, and plan to do several more posts on it including how to control these motors with a PWM switch. Hopefully at some point, there will be a post about it actually walking! If you’d like though, you can just check out my first little hexapod robot.