3D Printing Parts

To mix up the LTRT work a bit and take a break from circuits, I decided to go back to the problem of the turret ring.

The turrets of the toy tanks are limited to a rotation of 350° or so. This is accomplished with both a tab underneath the turret and by,  on the turret ring, a solid section in place of teeth. Because I want my turret to rotate 360°, I filed away the tab with a Dremel and I cut crude teeth into the turret ring.

The turret ring as installed in the tank. At bottom, the driving motor and gearbox is seen. I have two Hall-effect sensors installed here. One detects rotation of a magnetic disk that is installed on the motor shaft and is intended to as a rotational encoder. The other sits below where a magnet attached to the turret will pass and will be used to determine when the turret is sitting at its 0-degree position.

A closeup of my crude Dremel work. Surprisingly, this still works.


So, anyway, though my Dremeled turret gear DOES work, it's a pretty dodgy operation. It is way too easy to cut away too much material and render the gear useless. One option was to develop some sort of jig or template so that I could cut proper teeth into the ring. The other option was to get a turret ring 3D printed. About a month ago, I spent some time measuring a turret gear and attempting to recreate it in Blender. Blender isn't designed for mechanical drafting, though, so constraining actions to a single dimension or a precise measurement is not easy. Also, I'm far from an expert at Blender.

I used the excellent gear designer at geargenerator.com to make an vector file of the gear profile. There was a brief detour into gear design theory but I was quickly overwhelmed and decided to be satisfied with "involute teeth are best teeth". 

So I tried some other CAD software options, including an attempt using a free trial of Autocad but I ran into one problem or another. I finally downloaded Freecad, which I had assumed was a less-than-half-formed package, but it turned out to be a really decent program. It had some quirks and did crash a few times but, after a few false starts, I figured out the basics and soon had a turret ring designed.

I looked around at a few on-demand printing services and settled on Shapeways. 

So in a week or so I'll see if it works [I keep thinking about how I did not triple-check measurements]! Though this would raise the price of a single tank by about ten dollars, it might be worth it to have smooth turret rotation. And it will be much easier to throw in a new turret ring than to modify the existing ring.

As a postscript, this is the turret gear of the previous generation of tank that I purchased. At the bottom of the gear, you can see where I ground away an extra bit of stopper plastic, which was all that prevented the turret from a full rotation. This was a much easier gear to modify! I recently searched for and found this model of tank on AliExpress, so it's still possible to obtain. The newer model of tank does have the advantage of being slightly larger, and thus easier to fit all the new components in.