Question

A vehicle needs to run continuously at 60 kmph and should have a peak torque of 150 Nm. A motor gives peak torque of 25 NM at 3000 rpm. What should be the time radius of the vehicle in m.

Answer 1

The torque required [Nm] at the wheels is Maximum force[N] x radius of the wheel{m]

T(wheel) = F x r

This has to be converted to the torque required at the machine side, which is a ratio. Ignoring all losses, power in = power out, but one can generally allow for a loss of about 2% therefore,

T(motor) x w(motor) = T(wheel) x w(wheel) where T is in Nm and w (angular velocity) is measured in radians per second.

To include gearbox efficiency of 98% this becomes

0.98 T(motor) x w(motor) = T(wheel) x w(wheel) (you will need more torque at the motor side to overcome the inefficiencies)

To convert rpm to radians per second: w = rpm x 2Pi / 60.