FlyWheelz said:
I am using a geared motor from an electric wheelchair. Its a 2-pole brushed motor. Would 4-pole be better?
The 4pole will probably be better--it certainly was for CrazyBIke2, especially for startups, which had been weak and waobbly with the 2pole but really torquey and fast on the 4pole.
For one thing, the 4pole on mine is a heftier motor, capable of more power output just from it's windings/etc, leaving out the 4 vs 2 poles. But you may also destroy the Shimano hub with the power the motor can create, if you slam on the throttle at any point.
Apply throttle slowly or use a controller with a ramp up input and it should be ok.
Yours might already be ok, though, if you just up the voltage on it. Catch is that I doubt the wheelchair controller can go higher than 24V.
You could test by simply taking out the controller temporarily, then wiring in a switch to engage the power--but you need to have a safety cutout that you can yank out of the circuit in case the switch welds shut (it might happen!). I'd put such a safety cutout in regardless, since if a brushed motor controller fails it could fail in a way that leaves the motor on full throttle, with no control over it.
For electronic I am using the original wheelchair 80amp controller and joystick.
Right now the trike gets about 8mph in Shimano low gear. In high gead the motor/controller over heats.
My first suggestion would be to try a higher voltage, first by just adding another battery or two, but a set of questions before you do:
What is the motor-gearbox's shaft RPM, without a load on it, at 24V? This is probably printed on the gearbox or motor, and it's usually 100-140RPM.
What is the RPM the pedals would input at the same place the motor is doing so, in order to get that 20MPH you're after? This is a little harder since you probably can't measure this directly and I'm sure it's not marked anywhere, but you can calculate it backwards from the wheel diameter, the ratio from the wheel sprocket to the Shimano's output sprocket. If I did it right below, the ratio from input to wheel to output of motor with 40T should be about 2.14, not including the wheel diameter in that. (but I am bad at math concepts so I sometimes make serious mistakes in figuring out formulas and stuff, so check everything yourself. :lol
THese questions matter because the original RPM will be multiplied by the change in voltage. If it was 100RPM, then it will be 200RPM if you double the voltage. So then the whole system would double in speed. But that might not be enough, so to figure out how fast it needs to be at the input to the Shimano hub, you can take the speed it needs to be there and divide by the speed it already will be at the motor. Then figure the sprocket you need on the motor based on that and the sprocket already on the Shimano.
The torque is really bad at the moment with 40 tooth.
The motor was designed for good torque at a certain RPM, and now you're asking it to do that at a different effective RPM (much different gear reduction). It's original RPM would've been whatever the wheels directly mounted to the axle gave it. It's new effective RPM is the ratio from the sprocket mounted on it's axle (40T) to the one on the Shimano (19T), then whatever ratio the Shimano is set to by it's shifter, then the ratio from the Shimano's output sprocket (22T) to the wheel's input sprocket (28T), then the diameter of the wheel.
So that's 40:19, then say 1.3:1, then 22:28, then the wheel.
So 2.11:1 x 1.3:1 x 0.78:1, then wheel.
Or, 2.14 times as fast as it was originally meant to go, before considering wheel ratio. Now you have a 24" wheel, originally it directly drove a 14" wheel. That's about 1.71:1 ratio. So ultimately 3.668 times faster, meaning really it's little more than 1/4 of the torque it originally had.
So a 4-pole motor will by nature double that torque, assuming all else is identical. Since the 4pole will probably also be a higher power rating (you'd want to check that) then it'd probably be more than double. Should still be more than enough to go up those hills, but it might not be able to sustain full speed while doing so.
It'll take at least
I also tried a 18 tooth sprocket on the motor and while the torque seemed ok the speed was around 5mph.
Which means that you either need a sprocket 4 times the teeth of that 18T, or you need a voltage 4 times as high. Or a sprocket twice as big and a voltage twice as high.
Meaning with a 40T it's a bit more than double the 18T, so you can double the voltage to 48V and theoretically get 20MPH out of it. That particular motor may or may not be able to do it by itself, so you can try either using a pair of them in parallel, both outputting to the same chain (whcih can just wrap around the sprockets on each one), or use a bigger motor.
I really have no idea what I should do to accomplish my goal. For starters, I would like to buy another controller and throttle. The one from the wheelchair requires a second motor plugged in. Extra weight for nothing.
Well, you could mount and use the second motor, putting it into the same chain as the first, so the chain wraps around both sprockets, one from each driveshaft.
I am using a Curtis golf cart controller now, and I have also used a 2QD controller from http://4QD.co.uk . The only reason I switched was because I SEVERELY overloaded the 2QD (about 3500W!) and while I was working out some alternate ways of setting it up in a box and heatsinking it, I fixed a Curtis 1204 that had been donated to me. The 2QD works fine, too. Both can work up to 36V and with mods at least 48V. Some versions of either work at 48V out of the box, and I think even higher, but I think 48V is all you need.
In theory a hub motor might be "simpler", but might not work as well over the hills as the geared system, or at least not as power-efficiently (forcing you to carry more battery to do the same work). However, the hub motor could possibly perform regenerative braking down hills and such, regaining a few watt-hours here and there, making up for the other losses, perhaps. It would be difficult to know the regenerative effects until you had the system operational and in use. The freewheels in the chain system prevent using regen with the wheelchair motors.
I am biased towards fixing up the wheelchair motor system, because I know they *can* work, and they are a creative way to solve a problem, where a hub motor is more commonplace.
I use both, but I like the idea of the w/c motor better. Which one you should use depends on which is more practical for you, though.
