It’s kind of important that the belt doesn’t skip in one wheel applications. I’ve skipped a HTD 5m belt before during heavy braking (and that was with two belts), so thought an upgrade to HTD 8m was in order.
Interestingly the specs for a 5m belt seem fine based on this chart (src). Assume motor makes 4kw, with an extreme’ish load factor of two (4kw motor power * 2 load factor = 8kw design power), this still puts us just within the HTD5m band at 2500rpm. Just.
Gearing is a real problem with higher pitch belts/pulleys. The 22t HTD8m motor pulley looks roughly similar in size to the old 56t HTD5m wheel pulleys I ran on my esk8. Even for a kart wheel HTD8m pulleys above 60t get impractical (they’d hit the ground when turning sharp). Found a very nice looking pulley from Jones Racing Products in 49t that was originally intended for a quarter midget race car. Idea with this pulley was that it came in a variety of sizes which would allow be to change ratios in the future, however over the last few years I see they’ve discontinued these pulleys. There are other options, but nothing with the same off-the-shelf bolt pattern that will mount straight up.
Motor pulleys are much easier to come by, in this case I’m using a rather industrial taper lock pulley. I don’t think these are an option for HTD5m pulleys or smaller bores, but they do have one neat benefit. The bushing locks into the shaft when the two grub screws are tightened. To remove the pulley you take them both out and screw one in to the third hole that just pops the pulley off.
So with a large wheel diameter (approx 280mm), and not really being able to get much gear reduction I needed a low kv motor to keep the top speed in a reasonable range. Still wanted an excess of power though, so settled on an APS 80100 50kv, this should absorb as much power as the battery can throw at it. If we plug all these numbers into the esk8news calculator this works out to be a loaded top speed of 46km/h, and that’s just fine for now.
I’d like to have a smaller motor as I felt packaging an 80mm motor somewhere in a one wheel lead to compromises, more on that later. Just not sure if they’ll have the performance I want. It’d also be great to find a better/more available solution for the wheel pulley.
There are obviously other ways to do this. Chains would be off the shelf from kart stuff, give more reduction, and are quite a bit slimmer, but I ruled them out because I just find them too dirty. Gears would work, but with a bunch of extra complexity and need for precision. So belt it was.