The Project

To build a tiny brushed Ant Weight motor system that is lighter and smaller than typical 16mm motors and more powerful than typical n20s.​

Design Goals

Should use brushed motors. I like their simplicity and start up torque. There are some brushless options out there (and I'll be exploring those later).

Should be light.  An n20 weighs around 9g and a 16mm (BotKits) motor weights around 27g.

Should be cheap.  Spending money on motors for combat robots can be painful. $5-$10 for a normal n20 is hard. If you are doing 4wd, that is a lot of money in motors that will break, it's just a matter of time. I want to build a lot of fun cheap robots and I'll spend a lot of time and money to figure out how to do that! (yes there is irony there).​

Things required

  • An n20 motor with neodymium magnets and carbon brushes.
  • Some kinda gear box
  • A Torque Tester
  • A Tachometer
  • A Current meter

The story​

Browsing Ali Express I discovered there were some very very fast looking n20 motors (sans-gearbox) with carbon brushes and neodynium magnets – and they were cheap, about 50¢ each.  

I ordered 12 and then waited a few weeks. ​

The mounting holes on the spicy n20s are different from on the basic n20s. The simplest way to see how these would work would be to swap the motor shells. ​
I dismantled both, popped the magnets out of the spicy one and transplanted them into the basic n20 motor shell, then reassembled everything. ​

After I had done that I cut down the motor shaft to the right length and re-inserted the pinion. With pinion reattached I was able to attach the gear box. ​
The whole process took about an hour, but now that I know what I'm doing it would only take about 15 minutes.​

Reinstall pinion:

Of course I forgot to take photos of reinstalling the pinion but it was relatively simple. I simply lined the pinion up on the shaft and then using my small vise just gently pressed it in.​
After I got that all assembled I gave it a quick spin.  Everything seem to work. I cleaned up the gears and gave them a little bit of lubrication.​

I put the newly minted gear motor on my little homemade test bed consisting of a current meter, a tachometer, and a torque meter (which really is just an arm that pushes down onto a scale).​

What I saw was very impressive.​

The motor drew 0.7 A at idle and was running at 787 RPM. When I hooked it up to the torque meter it stalled out at 7.2 A and the gearbox exploded at 3.2 kgcm. ​

For comparison my Valkyrie Nerf motors attached to a 22 mm 84:1 planetary gearbox stalls out at 9.8 A and runs at 410 RPM and produces 9.75 kgcm at stall. Note that while the nerf box produces about 3x the torque, it is spinning at nearly half the RPMs and is much heavier and bulkier. If we were to put that Valkyrie on a lower reduction in gearbox and had it running at 800 RPMs (the same as the spicy n20) we would likely be seeing torque of a round 4.8 kgcm​

We really don’t know what this is spicy n20 is capable of! From the specs I've seen, n20 gear boxes can only handle around 3 kgcm.​

For more context see the motor results spreadsheet:

​Dec 1, 2021​:

Spicy n50 on an 84:1 22mm gear motor.

Dec 2, 2021

Making a turducken: I wanted to put a spicy n50 (sn50) on a 16mm gear motor, but I didn't want to have to build a mounting plate. So I did the next obvious thing – I removed the guts of the 050 motor on the 16mm gearbox, and jammed a sn50 into it and shimmed it into place.

The 16mm gearbox pinion expects a 1.5mm shaft.  I took some of my 2mm brass tube, and using my drill press, ground it down to 1.5mm to make a pinion shim.