Question

A small motorised vehicle, a child’s ‘ride-on’ car, is powered by a unit connected to its two front wheels. The unit contains a d.c. electric motor.

a. Suggest to possible mechanical alternative for driving the vehicle and state five(5) reasons why a d.c electric motor is a good choice for this application.

b. When the car is lifted off the ground, its front wheels spin freely at 132 rpm. The motor itself is rated as having a no-load speed of 450 rad s^-1. Ignoring efficiency losses, what approximate gear ratio (to the nearest whole number) has been used in the motor unit?

c. Once the car and its small passenger load are in steady motion along a horizontal pavement, the wheels rotate at 60% of their ‘no-load’ speed.If the stall torque of the geared motor unit is 9 N m, what torque is generated by the unit in maintaining this lower steady speed?

d. When one of the child’s parents climb in as well, the total force against which the motor has to work increases 5-fold. Explain what happens and why.

Answer 1

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