remote control car

[aamir shabbir]

guyz ive made a rc car using a mosfet based h bridge the h bridge is working fine but i have to control speed also i will use pwm from avr microcontroller for it what ferquency should i choose for the motor speed control ? and when we choose high frequency and when we choose low what is the idea behind it plz let me know

 

[audioguru]

Ultra-sound frequencies are used for the PWM speed control in a wheelchair or golf cart so that it is not heard (and so it does not deafen people nearby).
The inductance of the motor will reduce its maximum power if the frequency is too high.

I used 2kHz as the frequency for the motor of a model airplane so I COULD HEAR that it was running.

 

[aamir shabbir]

please mention some detail what do u mean by inductance will reduce power ?? if i use frequency below 100 hertz what will happen and if i use beyond 10 Khz what happens except the fact that human hear can hear till 20Khz what is the fact regarding electronics?

 

[audioguru]

please mention some detail what do u mean by inductance will reduce power ??

An electric motor has coils of wire that have some inductance (I don't know how much inductance your motor has). Inductance in an AC motor reduces its current at high frequencies.

if i use frequency below 100 hertz what will happen

The motor will vibrate violently and the car will jerk along.

if i use beyond 10 Khz what happens except the fact that human hear can hear till 20Khz what is the fact regarding electronics?

The frequency you use depends on the value of the inductance of your motor.

 

[aamir shabbir]

what is the reason that motor will vibrate on low frequnecy the inductor will be short and only coil resistance will be there so y would it vibrate ?

 

[audioguru]

what is the reason that motor will vibrate on low frequnecy the inductor will be short and only coil resistance will be there so y would it vibrate ?

Anything moving at the very low frequency of 100Hz will vibrate. At higher frequencies the inertia of an object smooths out vibrations.

 

[aamir shabbir]

would it be feasible to run the motor on 20Khz or above im using irf3205 mosfet in h bridge

 

[audioguru]

would it be feasible to run the motor on 20Khz or above im using irf3205 mosfet in h bridge

It depends on how much inductance the motor has. If it has high inductance then it will have low power at high frequencies. Try it and see.

 

[aamir shabbir]

it is due to the fact that bcoz of high frequency if inductance is large XL will be large and current will reduce and motor will be slowed is that so ?

 

[audioguru]

it is due to the fact that bcoz of high frequency if inductance is large XL will be large and current will reduce and motor will be slowed is that so ?

Yes.