Ho do I calculate what size/power/speed etc DC motor is required to drive a variety of vehicles?

Question

What considerations are required such as
-weight of the vehicle
-direct drive vs pulleys or gears
-anticipated maximum speed
-vehicle shape
-wheels/tyres
-expected terrain
etc etc etc

Is there a mathematical formula that I can use to calculate what motor is required for eg. 2kg or 10 kg or 100kg vehicle to travel at various speeds, and how can I calculate the effect of other factors of the vehicle. How much extra power is required if some form of alternator/generator is added?

Answer 1

Motors are rated by the amount of power they supply. The formula for power is P = Fv, where F is applied force and v is velocity. F, in turn, needs to be greater than the force of friction acting on the vehicle. Since coefficients of friction will vary, a good assumption would be that the force provided by the motor must equal the weight of the vehicle; that guarantees it will be greater than the force of friction.