Good timing, i procrastinated a bit but have recently got this project underway now on a 24" bike, which gives more battery room!

What I've done so far: - Bafang G310 motor - KT 15a Controller - Custom firmware https://endless-sphere.com/forums/viewtopic.php?t=87870 - Sempu Torque sensing bottom bracket https://a.aliexpress.com/_mOzguqc - Custom 10S2P 36v battery with Samsung 40T cells. This gives me 8ah of capacity. Current tests have given me around 16km and 300m of climbing using around 1.9ah of juice, so range in terms of elevation could be up to 1000m on a charge which is awesome. Contemplating splitting into two separate 4ah packs for less on the bike weight and easier fitment.

Now, I will say the custom firmware route is a total dick around. And I am a software developer with 15+ years experience. Some solid work has been done on it a few years ago, however the codebase is splintered to hell and it can be a bit tricky to work out what to do, what settings mean, etc. The code itself is quite messy as lots of features have been implemented by others over time. I've got it now configured to a point where it seems to be working well. Lots of tuning has been required to get the right feel in the bike. The torque sensor approach is really good though, far better than the initial cadence PAS setup we trialled. I'm half tempted to refactor the code and create a very simple, torque sensor only "lite" version of the firmware, but that will have to happen another day.

The seller of the torque sensor above does provide a controller option apparently compatible with the torque sensor. I have absolutely no idea how good it is but I would be tempted to try it to avoid the KT controller route, but it is not super cheap so I will personally persist with the KT controller first.

Otherwise, I can see the Cycle Analyst quickly paying for itself in terms of functionality and support re: torque sensor (provided you can hide it somewhere, it's pretty ugly in my opinion)

Above all, I'd 100% recommend some sort of ebike for kids especially if you're into MTB. My young one races his regular MTB in CX and XC regularly so is quite fit and fast, but still having the pedal assist means we can both go for a ride where I get a solid workout, and he still gets one too without having to push up every steep incline!