I have BTS 7960b 43A motor driver. I am controlling this driver with 18F4520 PIC. When I send the PWM Duty %100 percent then I read 24 volts at motor side.Motor runs very well. But If I send PWM Duty %50 then I read 12 volts at motor side and motor speed and torque is reduced.So as much as I reduce the PWM percentage then the motor voltage reduces to 8 - 5 volts etc.... So I can not keep motor voltage at 24v level and therefore motor torque gets weak as the voltage reduces. How can I keep the motor voltage at 24 Volt level and make speed controlling to this motor? Thank you very much for your helps in advance. Regards.
If you are looking for advice on programming a Microchip PIC microcontroller you are at the wrong Forum. This Forum is for the Arduino system which uses Atmel microcontrollers.
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Torque is proportional to current (less friction losses), not voltage.
The average voltage you measure being in proportion to PWM duty cycle is
perfectly correct, these devices use synchronous rectification (aka active
freewheeling), so the output speed should be a pretty linear function of PWM
level.
For large efficient motors the speed holding is stiff w.r.t voltage, torque (and
current) will depend on the load and not alter speed much. Smaller, less efficient
motors are less stiff so loading will significantly reduce speed. The fundamental
equation for a DC motor is
V = E + IR (V = voltage, E = back EMF, proportional to speed, I is current (prop
to torque). R is the winding resistance. The smaller R the stiffer the speed holding
under load, all else being equal.
Hi, I gather you want constant speed no matter what torque or load is applied to the motor.
You will need to have feedback from the motor representing its speed.
So when you apply load and require more torque, the feedback will show a reduction in speed and increase the power to the motor to keep the speed at a constant level and thus increase torque.
Tom...... 
Hi, Thank you very much MarkT, TomGerge ad Robin2 for your all information and helps. I realized what I am missing and cought the solution with your informations.
Regards,