# DC motor

1. Jul 2, 2015

### Shravan N Agni

I have a 24V, 1500rpm bldc motor.The power output will be around 400W. We are using it to electrically drive a tricycle. How can I calculate the gear ratio to decrease the rpm and increase the torque? The transmission system includes an intermediate shaft with 22 teeth sprocket and 44 teeth sprocket. Motor is connected to the 22 teeth sprocket and 44 teeth sprocket is connected to the 26in(dia) wheel with gear cassette.

If the motor is used as generator, how can I know the voltage and current generated by it?

2. Jul 2, 2015

### EverGreen1231

So far as the gear sizing, I cannot say...I've had no experience with such things.

But to the second question, the voltage that is generated at the terminals of the motor when used as a generator is proportional to the magnetic flux produced by the rotor and the speed at which the rotor rotates. There's also consideration to be given to the number of pole pairs there are. The workings of a DC generator and an AC alternator are basically the same, accept that one uses splits rings while the other uses slip rings. \

The current produced will depend upon the load connected, this value will also affect the other values of the generator (i.e. rotor speed, terminal voltage)

Here's a link that will give you an idea of the basics: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemot.html

This is just a high level view and probably not what you're looking for since I didn't give you a "fast and dirty" equation. Others will be able to explain more eloquently than myself.

3. Jul 3, 2015

### insightful

The basic calculation goes like this:

26" dia wheel has a circumference of pi*26"=81.7"=6.8'/rev
Say max speed of tricycle is 10 mph=15 ft/sec
15*60/6.8=132 rpm at the wheel
total reduction = 1500/132 = 11.3 to 1 to be divided between intermediate shaft gearing and final gearing

Example:
22 teeth on motor shaft to 44 teeth on intermediate shaft = 2 to 1.
22 teeth on intermediate shaft to 124 teeth on wheel axle = 5.64 to 1.
total reduction = 2*5.64 = 11.3 to 1.