DC Motor for Miniature Car

[hobbybuilder]

Hello all,

I'm building a miniature vehicle and plan on using a DC motor that supposedly spins at 12800 rpm (1340 rad/s) for the engine. However, I'm a little confused as to what the car's acceleration would be. The DC motor on its own would instantaneously have an angular velocity of 1340 rad/s upon turning it on, but once I connect it to the back wheels, the weight of the car combined with friction from the ground obviously wouldn't allow the car's wheels to jump to 1340 rad/s instantly, but rather they would have an angular acceleration.

I've calculated that the car should theoretically have a max speed of ~97m/s (ignoring the car's weight), since the tires would have a max angular velocity of 1340 rad/s, but is there any possible way I could use the given angular velocity of the DC motor to calculate the angular acceleration of the car's tires after they've been connected to the motor? (factoring in vehicle weight) This would allow me to calculate the car's speed at any given moment.

 

[Drakkith]

Without knowing much of the specifics of the motor I don't think there's any way to calculate the acceleration. Also keep in mind that motors never reach their maximum speed instantly, they take a finite amount of time even without a load. Do you have any other information on the motor?

 

[David Lewis]

You will need to know how much torque the motor produces. Torque is inversely proportional to speed.

If I understand correctly, 1340 rad/s is the no-load speed of the motor. (At no-load speed all of the torque generated by the motor is consumed by bearing friction and windage -- no useable net torque is available at the output shaft.)