DIY Electric Mountainboard

If you're unfamiliar with what a mountainboard is, it's essentially an off-road skateboard. A mountain bike is to a road bicycle as a mountainboard is to a skateboard. I first learned about mountainboards from this youtube video I was linked to while watching snowboarding videos:

It was immediately interesting to me, but when first discovering this around 2018 it was such a niche market that pretty much all electric variants were custom made by builders online, or by one of 2 companies charging 3-5 grand per board. I decided to make one myself as well, and started with this base mountainboard; It's a Trampa HS11 deck with MBS trucks, foot bindings, and wheels.

The first major hurdle was making the battery pack. Here I am spot welding Samsung 30Q 18650 batteries together into parallel groups, for use in a 12 series 6 parallel battery configuration.

All parallel groups put into a pelican case for test fitting. The extra space at the front will be used for a battery management system for balanced recharging.

I made each series connection out of 4 lines of flat braided tinned copper wire. Each of the lines are rated up to 40A continuous, so since I want my pack to be able to discharge up to 100A continuous I made these internal connections rated up to 160A for extra safety. There is at least 2 layers of kapton tape between each of the parallel groups as well as the entire exterior of the battery coated in it as well.

Here is the full assembly put into the pelican case, with charge ports installed and connected to the balance charger. This was the first charge test to verify the pack would charge correctly and it was really nerve-wracking; if it went wrong it could have been a MASSIVE battery fire.

Here are some 3d printed holders for xt 90 connectors. I drilled some holes in the pelican case to make room for them. They act as power switches for the board. The 3D files can be found here.

The assembly is getting much closer to being finished! The battery and ESC are mounted to the deck as well as the motors mounted to the rear trucks. I still need to make motor pulleys, connect power lines from battery to ESC, and solder the right bullet connectors to the motors to fit the ones on the ESC

Going through the motions of flashing the ESCs, setting FOC and input configurations. Nearly all Electronic Speed Controllers (ESCs) run on open source firmware called Vedder ESC, and it comes with a desktop application to calibrate your controllers to your specific hardware setup.

I 3D printed some 72 teeth gears to mount to the wheel hubs. The gears are PLA at 95% infill with a giant 0.5mm layer height

The board is 'finished'!! Ready for first test ride!

It handles very well, except for a little issue with belt skipping. Because the gears are so close and have drastically different tooth counts, the motor pulleys only ever have 3-4 teeth in mesh. Asphalt handles fine but higher torque needs like off-road and deep gravel struggle with belt skip. At this point I begin to look into adding an idler pulley

This was second sign that my drivetrain needs a re-work. Besides belt skipping, 3d printed gears are just not strong enough for the job. Layer separation would occur if the gears took any non-trivial impact. Printing again with nylon filament might work and I considered reprinting in ABS, Nylon or PETG.

The third and final sign that the rubber belts weren't going to cut it anymore for the project. Too much torque, too much belt skips, too brittle parts for what I need. The torque after only about 20 miles begin to cause the internal fibers of the belts to tear. This is when I begin to replace the belts with chain.

I bought some 66 tooth sprockets and 25H roller chain. This is me drill pressing adapter holes along the spokes to adapt it to the wheel hubs I used.

The inner diameter of the wheel sprockets weren't wide enough to fit over the trucks so the inner part had to be increased in size, so a friend and I used a lathe to make enough clearance on the inner diameter of the sprockets to accommodate the skate trucks.

The drivetrain now completely overhauled to use chain!

Here's the completely functional board but now with chain drive

There's a popular open source 'dashboard' floating around the Internet called DaveGa, and it uses a 177 x 220px screen. I put in effort to rewriting it's display drivers to work with larger format touch screens and a more powerful microcontroller to drive the screens at a sufficient refresh rate. You can find my modified version of the DaveGA library here.

Here's the the finished result fully installed! It's a 3D printed enclosure to hold the display and microcontroller, as well as a few tactile buttons to navigate the menus and adjust the configuration

And after all this effort, it was finally done. Sometimes building things is more rewarding than actually using them, but this was definitely an exception to that; It's one of my favorite things to use that I've made! It handles very well at bmx tracks, only struggling at the tightest of the embanked turns.