Calculating speed by rpm and wheel diameter
Calculating the speed of any machine is quite a simple task if you know the diameter and revenues per minute (rpm) of your motor or other power source spinning the wheel. Other variables might be gearbox or other rpm transitions between motor and wheel, for example, bicycle gears. For those, you need to know the gear ratio.
In this example, we have an electric motor that has a maximum rpm of 5000. The motor is a rotating gearbox with a gear ratio of 64:1, which means the gearbox will lower down the rpm by transforming the rotation to one time for every 64 revolutions of the motor.
Formula to calculate rpm after gearbox
- motor_rpm / gearbox_ratio
In this example: 5000 rpm / 64 = 78.125 rpm
Formula to calculate wheel circumference from diameter
- wheel_diameter * π
Formula for kilometres in an hour (km/h)
- rpm_after_gearbox * circumference / 1000 (meter: 1000 millimetres) = meters_per_minute
- meters_per_minute * 60 (one hour) / 1000 (kilometer: 1000 meters) = km/h
Formula for meters in second (m/s)
- rpm_after_gearbox * circumference / 1 000 (meter: 1 000 millimetres) / 60 (seconds in minute)
The π value used in the calculator is 3.1415926535, which gives slightly different while more accurate values than in examples with a π value of 3.14.
|Gearbox ratio||(min value 1)|
|Rpm after gear:||0||rpm|