Gear spin test

I mounted the gears on a piece of 2×4 today using 1/4″ threaded rods (1/4″ 20) for axles. They seem to spin really well. I only have a 3:1 ratio with these, but it’s a good proof of concept and not a bad place to start for the coil-winding device.

Here’s a video:

New coils?

I’m going to wind some new coils and see how they compare to the old ones. These will be superior in a couple of ways: better cores, and better winding technique.

The cores will be these ferrite rods (replacing the hot-galvanized nails I used the first time. These are the rods:

For the winding technique, I’m working on building a winding jig out of plywood. The idea is to make a gear system out of wooden gears using the approach detailed here:

A crank handle will turn the gears, which then turn a cheap drill chuck that will hold the workpiece (in this case one of the ferrite rods mentioned above). Wire feeds onto the rotating workpiece from a spool after a tensioning device applies tension to the wire. I’m not sure what I’ll use for a tensioning device yet, but it could be as simple as a series of holes or pegs for the wire to pass through or a clamp that squeezes the spool of wire. Having a set of gears allows me to get several turns of the workpiece for each turn of the crank.

I used a different template generator the create the gears than the one provided on It creates involute gears, which aren’t as easy to cut out, but transfer power more efficiently:

I drilled and cut out the gears using a drill press and scroll saw. They’re not perfect, but they may answer the purpose. If these don’t work well, I may try again with the template generator, which creates less complicated geometries for the teeth.

Gearing up

My gears arrived today. I ordered three packs of plastic Stevens International hobby gears from :

  • Crown gear set (SVM-101)
  • Pinion gear set (SVM-102)
  • Worm gear set (SVM-103)

All of them say they have an inner diameter of 1.9mm, so I also bought some 2mm steel rods on Amazon (pictured, left). Sorry about the quality of the mise-en-scène; I got excited and opened them before I remember to take the picture. Anyway, the crown and pinion gears mesh really nicely together. The worm gears have three different pitches to them, and only one of them meshes with the other pieces, so that’s a little odd. But they fit snugly on the 2mm rods, so I’m hoping they will be the solution to the problem of how to transfer power from the vertically-rotating motor shaft to the horizontal axle.

I’m also currently moving all the coils to a new plywood engine block that has the appropriate hole in the center for the 2mm shafts (the Erector set shafts I was using are 4mm).