Ozzzz said:
I'm thinking of attaching a big cog and using the mtr mounted on the rack with a small cog via a chain or belt. I'm thinking a smaller wheel would just still spin faster so a bigger wheel may be better? I found q 50T 'extender' cog but would it be better to break down a cassette (not a lot of experience with what can be done with cassette clusters)
Before you go finding cogs or sprockets, you need to determine the gearing ratio that will get the motor's speed at the voltage you're going to run it, down to the wheel speed of 2-3mph.
Then you can find stuff that will give you taht ratio without eitehr end being impossibly large or small.
So if you know what speed the motor went in a wheel of a certain size, you can calculate it's RPM. THen you can calculate the RPM of the wheel size you are going to use, when it's at the speed you want. Divide the one by the other, and that gives you the ratio of the two, to figure out the gearing.
I recommend the largest wheel you can fit, because it will be easier to pull or push over unsmooth ground. Smaller the wheel is, the harder it is to do that. If it's a tall wheel like 26" or 29", then make side panniers mounted really low to carry your load, or make it like a BOB trailer that has the wheel at the far back end, and a load carrying tray between that and you.
You will probably also want the fattest ballooniest tire you can get, so it will roll over mushy ground and stuff easier.
I'd use a brake handle type throttle, rather than a grip or thumb type, if you need more than on/off control, so you can easily squeeze it as you pull or push. TO make one you use the cable from the brake lever to operate one of the cable-oeprated throttles found around the internet.
If you only need on/off operation, you can just use an ebrake lever and use the switch in it as the control (you'll probably have to use a voltage divider from 5v to ground, to create the specific voltage you want, or a potentiometer, and then put one wire of the lever on the center tap of that, and the other wire of the lever on the controller's throttle input.
If the motor is a hubmotor, is it a front or a rear? Does it have disc mounts you can bolt stuff to?
Or are you going to use the cassette freehub on the motor itself (assuming it's a rear)? Remember that you'd have to lock the freehub to do that driving it normally, *or* you'd have to lock the motor's clutch inside so you can run the motor in reverse.
The latter won't work if it's a freewheel instead of freehub, because the freewheel cluster will unscrew.