Really nice project - respect :)
Got two questions: 1. How fast it can ride ? If I good estimate (based on max 2750 RPMs for electric motor MY1016 350W 36V, gear ratio ~100:1 and height of rear wheel ~0.5m) it should got about 0.8 m/sec. So really safe for kids and dad :)
2. How long does the battery last ?
I think it goes about 6mph. I agree with your maths though, so probably my estimate of the gear ratio is wrong.
I don't know how long the battery lasts, we have never driven it for long enough to flatten the battery.
While I was building it I used it for about an hour doing several laps of dragging a "trailer" full of rubble from the top of the garden to the bottom (the easy direction - empty load on the way back up) and it became noticeably slower towards the end but still got me up the hill. So I'd say it lasts over an hour.
Thanks for info. And once again really nice project :)