Having seen various tracked robots on Thingiverse and especially this amazing one, I thought we should try and implement Wall-E’s tracks ourselves.
We could have gone with a simple rubber band or timing belt (and in retrospect that would have been MUCH easier), but I really fancied seeing how far I could push 3D printed parts.
So I had a long browse through thingiverse looking at lots of track designs and started to draw up my own. The FPV rover design had an interesting idea for fine adjustment – they used 2 different sizes of 3D printed pins to join the tracks together to make the whole thing slightly tighter or looser as needed.
In the end I settled on a design which had sprocket wheels mounted on either side of a supporting frame (to avoid nasty torques on the frame). Obviously the layout of the sprocket wheels on the frame had to match the ‘real’ Wall-E, but I decided to make the sprocket teeth larger (and therefore stronger).
Then the track elements needed designing. I went with a design which used the links between the tracks as the raised sections and the sprocket teeth sat in a deep well, but did not protrude from the other side. Like this:
A matching pin is shown too. After a few trail and error prints to fine tune the pin diameter, well depth, we got something that worked. And then we needed to print about 36 of them per set of tracks (3 x 4 hour sessions of printing).
The final problem was how to connect these to the motor. We wanted a fair bit of speed, so I’d ended up buying pololu motors with a 4:1 gearbox. Having seen these run, I was a bit worried about the high speed, so wanted to gear them down a touch. I found a bevel gear generator plugin in Onshape and ended up with this:
And that worked!
In fact running these is slightly terrifying – fairly sure if you got your finger in there it’d get a nasty nip…