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How to Calculate the RPM of a Motor and Speed Reducer

Sunday - 09/07/2017 16:47
Write down the rated RPM of your motor; for example, 5000 RPM.
Write down the ratio of the speed reducer; for example, 12:5.
Calculate the reduction by dividing 12 by 5, which equals 2.4.
The RPM of the assembly is the RPM motor divided by the reduction. In our example, it would be 5000 RPM/2.4 = 2083 RPM.

The ratio of a reducer will always be in the form of A:B, where A>B.

The RPM found should always be lower than the base RPM of the motor. If it is not, either redo your calculation or make sure you did not get a speed multiplier instead of a reducer.

This calculator determines the top speed of the vehicle with no margin for mechanical, rolling, or wind resistance. These resistance factors could make the top speed slower than the calculation.

The amount that the top speed will be reduced by resistance depends on many factors such as the power of the motor, weight of the vehicle and rider, size and air pressure of the tires, incline degree that the vehicle is going up, and headwind.

The top speed could also be increased above the top speed calculation by riding down hill, or riding with a strong wind against your back.

When riding on flat ground the top speed is usually only reduced by a small amount.

his guide is for modifying, designing and building custom electric; scooters, bikes, go karts, ATVs, wagons and other similar light electric vehicles.

Motor Types

There are two types of electric motors; standard motors and gear motors. Standard motors have shafts directly attached to the motor windings with shaft output speeds commonly between 1800-3000 RPM. Gear motors have gear reduction transmissions built into them with shaft output speeds commonly between 400-550 RPM.

Standard Motors (Electric Scooter Motors)

Standard motors are made for electric scooters, go karts, and other similar vehicles with 6"-12" wheels. Standard motors should not be used for electric bicycle projects unless a gear reduction transmission such as a jack-shaft is used with them to lower the gear ration so they can operate near their top RPM while the vehicle is in motion, otherwise they will run at too low of an RPM which will cause them to overheat and possibly burn out along with not allowing them to produce the full amount of power that they have the potential to.

Gear Motors (Electric Bicycle Motors)

Gear motors are made for electric bicycles with 16" through 26" wheels. Gear motors can also be used on vehicles with smaller wheels if a slow top speed and a high amount of torque for uphill climbing or driving through sand or mud is required.