So, here’s a weekend adventure I recently got into: I wanted a super cheap, high-torque actuator for a robot joint. Instead of shelling out a loads of money on specialty motors or, like previous projects, spend many weekends putting together 3D printed ones with lots of speciality parts, I thought: “Hey, why not repurpose one of those old car power window motors in the corner?” They’re basically little torque monsters, and they’re pretty cheap if you know where to look.
The Plan: From Car Door to Robot Arm
Alright, so the first step was figuring out how to mount this motor. Normally, these motors are made to fit inside a car door, where they press into a molded spot. But obviously, a robot arm isn’t a car door (unless we’re talking Transformers or GoBots). So I had to design a 3D-printed housing that would hold the motor and turn it into an actuator mount. The housing needed to do a few things:
- Contain the motor and a mount pount for an arm
- Apply a custom shaft adaptor to get meaningful work from the shaft
- Bring the housing together to retain the shaft adaptor
- Create a mount point on the shaft adaptor to mount the other half of the arm, hopefully inline with the original base arm
Adapting the Gears and Mounts
Once I had the motor housing sketched out, I went down the rabbit hole on McMaster-Carr (as one does). I needed a gear that matched the little spline or tine pattern of the motor’s output shaft. After some measuring and a bit of trial and error, I found a gear that was pretty close to a perfect fit.
From there, I designed a slip joint—basically a coupler—that would let me turn that weird car-window spline into a nice, standard D-shaped mount. That way, I could attach a normal arm or linkage to it. The end result is a sturdy, 3D-printed housing that holds the motor and gives me a nice solid joint I can use for a robot arm.
Practical Application and the Fun of Tinkering
In the end, what I’ve got is basically a repurposed power window motor serving as a cheap but effective robot joint. I’ve tested it with a piece of 20×40 aluminum extrusion, and it works surprisingly well. The motor’s got enough oomph to move a small arm, and it only cost a fraction of what a specialized actuator would have.
So that’s the gist of it! If you’re curious, I’ll share the 3D files and some more detailed steps in the next post. But for now, just know that with a little bit of 3D printing and some off-the-shelf parts, you can turn a junkyard car part into a neat little robotic gadget.
