E-bike fail

So actually I’d consider this project a bit of a fail and a success. I was able to mount the motor on a bike frame and even get a decent tension on the belt. At 18v there was very little torque, so I put a second battery to make it a 36v pack. Doubling the voltage would then double the current, thus doubling the torque. That still didn’t do much, so I swapped the sprockets on the bike front to rear to again double or triple the torque (and slow down the speed). With that it was able to move on level ground, but on the second trial run the sprocket came off the aluminum pulley (it wasn’t a well fabricated part). I also managed to short out my battery, DOH! Worse, it was my 3.0aH battery that new is $100. Fortunately I had gotten it for $13, but it doesn’t make me feel a TON better. At some point I will try taking it apart to see if I can fix it somehow. Not sure if it is a fuse or if the circuits are fried.

Still, at this point I’d have to get up to 80v or more just to have any sort of usable torque with the current setup. The only way it would be usable is if I increased the size of the pulleys or changed up the sprockets. I think the perfect thing would be a worm gear reducer, they can do 30:1 or better reduction ratios. Unfortunately, they are difficult to make and pretty expensive ($100ish) to buy. The whole point of this project though was that I had all the components on hand.

I think I will take a break for a while, but when I re-start I am thinking I may try to take the flywheel / pulley off and make my own. A v-belt pulley would have less slip, and I should be able to make one of those easily. A 1.5 or 2″ on the motor and then a 6-10″ on the drive would get me a somewhat better reduction ratio. Currently, I was doing 2:1 motor to aluminum pulley, then about 2:1 from the sprockets (17 teeth to 36 or so teeth). So I had 4:1. If I could go as small as 1.5″ up to 10″ then I would get a 6.7:1 ratio. Not a LOT better, but a bit. If I used an intermediate shaft and used the same 17:36 ratio then I should be able to get enough torque at 36v. If one were making this project from scratch and willing to put money into it, the BEST would be to buy a lower voltage, lower RPM motor that develops good torque at a more usable range.

The other thing I am considering is changing this from a bike project to more of a cart. Unfortunately though, I am not sure how workable that is since I don’t have much in the way of steel tubing or fabrication ability. What it would allow me to do though is use lead acid batteries to get the voltage up and be cost effective. I’d be looking at too much weight and volume to get up to 36-48v for a small bike. The small bike was desirable though since it would be small and light enough for my wife to put in the back of her car so she could take it places to use (I have not talked about it much, but my wife has had severe foot pain for almost a year now that has severely limited what she can do on her feet). A full sized bike or cart we wouldn’t be able to do that with.

I’m not sure when I’ll start the next try of this project. Given the time of year, lots of things will be coming up. I need to put away the ice skating rink, start planting some stuff for a garden, and I am looking at starting work with rabbits. Then come warmer weather I need to plan out and do some more concrete work on the pole barn (getting a ramp and door track put in), get a permanent door made, fix the driveway concrete that the concrete truck broke, pour another pad along the driveway for backing up, constructing rabbit cages if I do go that route, etc. I also want to get my transfer switch installed, wire the pole barn for electricity (and even better, wire it to backfeed the transfer switch so I don’t have to have the tractor in the driveway), and get the wood furnace installed for the coming winter. Oh, and start cutting down trees and firewood for use next year! All while juggling family responsibilities with the wife not feeling well.

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