The direct drive motors on 'mini bumble' the little bus state that at full power they turn at 117 revolutions a minute. Now my rusty GCSE maths come into play I believe if multiply the rpm (117) by the wheel size (13") by Pi (3.147) and I then multiply that by 60 I should get the total distance in inches per hour, then divide that by how many inches to a mile should get me MPH. So...... 117 x 13 x 3.147= 287,195.22 287,195.22 / 63,360 = 4.53 MPH If I have done my maths right then mini bumble travels at 4.5 MPH at full speed. If I wanted to increase that I'm guessing I would need to change the gear ratios, so theoretically if I use a large diameter cog on the sprocket geared down to a small sprocket driving the wheels I could increase the speed, would that also mean I loose torque as well?
yep Pi is 3.142 (to 3 d.p.), although if you read the text books on engineering calcs (when calculating fatigue etc) they recommend using the Pi button on your calculator rather than 3.142 as this will lead to discrepencies in your final answers!
I think you will need to look up motor formulas to check out the working torque ,breaking torque etc using horse power etc etc. Long time since i done all this stuff but using ft/lbs you should be able to work it out easiest i would think and not metric??
you will lose torque, you really need the motor output to work out how much though. you could just load up the bus to see how much weight it takes to stop it and work back from that
Ah come on it was 16 years ago and I've never needed Pi yet, not bad memory. I can work out the torque by Amp draws under load versus free load but was musing if I change the gearing ratios surely that would diminish the torque, bare in mind this is a wheelchair motor designed for high torque low speed
you need motor speed and voltage, maybe the diameter of the 2 gears would help, im pretty rusty on this stuff though
Is this a real bus, or a toy one? If real, you need to calculate the rolling circ of the tyres, not the wheels, of course. For that you'd need to know the tread width and profile. Gearing down to reduce revs increases torque proportionally, and vice versa. Pi is 3.14159, as any fule no. Or 22/7, if you're in a hurry. Pay attention at the back, homework in by Wednesday, please.
Search for mini bumble on here snotty, you'll see what I'm talking about. 117 is the rpm of the spindle coming out of the motor at full chap.
Are you still using the controller from the original wheelchair? The reason I ask is legally the wheelchair can't exceed 4mph unless its one that can be used on the road it can then do 8mph. The controllers can be tweaked to allow the wheelchair to go faster not sure how much but maybe speak to your local mobility shop... My mate has his own mobility business and I told him to offer people tune-ups for their scooters but he said he can't because of the law etc. etc. I thought it was a great idea, lol...
Yes, still using the controller. As you said the law only allows 4mph on pavements. The motor is 24v 10.6A load, 117 rpm. Ignoring the controller for the moment (I'll rig something else up for that later) I wanted to know if I can speed it up. Obviously I can go and buy a faster motor but as I have two for free it makes sense to fettle what I have.
In answer to your question yes if you change the gear ratio you will have to up the umph of the motor at some point. You need to check your motor formulas. You wont make one that goes very fast with what youve got AND for that reason IM OUT.!!
