Tdr19730 said:
I want a front wheel 500 or 750 watt motor and either 36 or 48 volt battery with a thumb throttle.
Installing on a 1970's Gobby trike.
If your trike looks like the attached images I found in a google search, then a front motor with a rim the same size as what you already have is the only easy option, and as noted, you wouldn't want to run that trike very fast. 10MPH is about the fastest I'd recommend, unless you're on a path that guarantees you don't need to swerve or turn even a little bit without slowing way down (to about 5MPH for any kind of turns, unless you're good at riding it on two wheels, based on my experiences).
If you can bring the COG way down, putting all the weight down low under the trike frame for batteries, etc. preferably out towards the sides next to the rear wheels, you'll be able to turn faster on it, but not by a lot. If you can rebuild the cargo area in back so it's floor is below the axle as far as possible without scraping the ground, curbs, etc, then whenever it's loaded up with stuff it'll also be able to turn at faster speeds. Once I got the SB Cruiser trike's COG low enough and spread out wide enough, I've been able to turn at 16-18MPH safely, and faster on certain wider turns.
You can't use a rear hubmotor on the trike, unless you change out the front fork for a wider (fatbike) fork. The rear wheels are single-sided axles, so the hubmotor would have no support on one side, and would probably break the axle quickly. If it is a "live axle" design, then a hubmotor wouldn't work at all on the rear, because the axle is part of the trike, not part of the wheel, and a hubmotor's axle is integral to it.
If you use the original fork, I also recommend a torque arm on each side of the front fork for the hubmotor, because the kind of dropouts that fork has are not very strong, or deep, and even low torque, with repeated accelerations, can spread them apart and the motor axle can force its' way out of them (or spin out and rip the cables). Been there, done that. :/
I also recommend a "slow wind" motor, but you can use a faster wind at a lower voltage, or if you can limit your speed either yourself by throttle, or a speed limiter in the controller or something like the Cycle Analyst, it should be safe enough.
FWIW, Grin Tech http://ebikes.ca has controllers that run at multiple voltages, as do other places; some versions of the Sunwin controller have jumpers (see the Sunwin thread somewhere here on ES). Some of them are "auto detecting", meaning you plug in the fully charged battery and turn on the system, and it "knows" what voltage it is, and sets it's LVC accordingly. (but if you plug in a nearly dead 48v battery, it may think it's a 36v battery, and if the battery's BMS doesn't work right or it doesn't have a BMS, the controller won't shut down and it will damage or destroy the battery). Some use a jumper inside the controller, somewhere on the board, that you solder across to tell it. Some are programmable from a computer via USB-serial cable, like the KunTeng KT series controllers.
Mostly it depends on your needs for what you want the trike to do for you; we need to know that to really recommend specific items.
The one thing I wouldn't cheap out on, though, is the battery. Everything else can be uber-cheap and still work fine for years, but cheap batteries have a tendency to not be as reliable.
