How to calculate speed and torque

[webby]

As above, i have 2 wheelchair motors and i will be using 150mm wheels and i was wondering how to calculate the current speed if i was to have a direct motor-gearbox to wheel drive or if the speed is too low (probably) will i need to gear it up or down by how much.
Thanks

[terry]

http://www.technobotsonline.com/robo...alculator.html
Lots of other calculators there aswell.

[webby]

Thanks, Found out i need a 0.2:1 ratio lol what sort of gearing would that be?

[terry]

That looks like you are gearing up which is strange. 0.2-1 would mean for 1 turn of the motor the wheel would turn 5 times that must be wrong. A common gearing is 10-1.

[maddox10]

Terry, if the wheelchair motors still have the original gearing, it's rather normal to gear up if a smaller wheel is used.

On the other side, it's difficult to calculate end speed with only wheelsize known. Somewere we need more information, like RPM of the axle.

Also, wheelchair motors come in a lot of flavors. From 125W from small indoor wheelchairs to 750W from large mobility scooters With worm and wormwheel gear, timing belt, or epicyclic gearboxes. And then the wheelsizes. From 125mm solid wheels, to 26" bicycle wheels, and everything in between.

[webby]

Thanks guys, yes maddox is right, because i have the origional gearbox attached, my motor is a 24v and 10.9 amps so is a 261.6 watt motor, so what gearing would i need? I will be using chains and 2 wheels per motors so what gear for the 2 wheels and what gear for the motor shaft?
Thanks

[terry]

didn't realise you still had the gearbox attached, could it be modded so its not gearing down too much ??

[webby]

Not really as its very compact and would need alot of cnc work, plus its easyier to use chain gears as i would still have to use chain drive to connect the motor to both wheels.

[maddox10]

Let us take 10 km/h end speed -with only 2*250W available, you won't get a speedy machine.

The wheels need to make 400 rpm.

Als long we don't know thet RPM of the motor, it's not easy to calculate the rest.

[webby]

the rpm of the motor is 117

but all i want to know is what sort of gears (tooth) am i looking for, for a 0.2:1 gear ratio?

thanks webby

[maddox10]

You want a 5-1 ratio then.

Meaning the gear on the motor needs 5 times more teeth than the one on the wheel.

That will give you a theoretical end speed of 16.5km/h. A tad fast for the motors.

I would suggest a 3.5-1 ratio. End speed 11.5km/h
If you need more speed, you can always go 36V.

[webby]

wow ok thanks
so like a 50 tooth on the motor and 10 tooth on the wheel? (example)

[maddox10]

Yep. But I would use a few more teeth. Is just that tad stronger.

[terry]

if your motor is 117rpm and you want the wheel to do 400rpm then you will needto gear up 3.42 - 1.

eg- 41t motor gear and 12t gear on wheel.

[webby]

Ok great, thanks