The ingredients are:
- A cheap (used) kickboard form eBay
- Better wheels
- 63mm 3kw outrunner + cheap “100A” ESC
- a cheap servo tester
- a horribly expensive potentiometer
- cogged belt pulley
- drive belt
- Two used 3S 5 Ah Li-Po batteries (from his previous 60 km/h RC car build)
- some wire
- A day of CAD work (more, GitHub)
- A day of milling aluminum (and some minutes on a lathe) (more, more, more, more)
- A day of assembly
It’s a pretty bare-metal job. Instead of adding a microcontroller and programming some firmware he opted for a simple push potentiometer to control the motor speed (video of first motor test)
A first try to build a belt tensioning mechanism by sliding the motor mount looked nice enough but didn’t manage to hold up to the torque and had to be re-designed.
Once that was sorted out it was time for a test ride. Impromptu as always the two battery packs went into his trouser pockets (don’t try this at home) and were connected via a long Y-cable to the motor controller. He’s currently in the process of building a new battery pack from used Makita battery packs with 18650 cells.
Check out the video of the first test drive:
If you’re planning to built your own e-something, Maedler has a nice online calculator for dimensioning the drive train.
For this build the no-load RPM was measured at 1285 rpm which would yield a theoretical maximum speed of 26.85 km/h. Actual measured speed was 22 km/h using 6S Li-Po cells or around 25 km/h using 7S cells.
Mind you, on a kickboard this is scary fast and quite literally brings tears to your eyes from the cold winter wind draft.