I have 6v rated motors and a 8.4v maximum voltage source (2 series lipo battery) and would like to skip the voltage regulator part.
I would assume that as long as i dont do a 100% PWM the motor would never see the 8.4V. if i do ratio and proportion the maximum i should go is 71% (at 8.4v) that should make it that the motor see 6v. am i right?
Whst motor driver are you using?
Im not really sure... no model number. i know that its an H-Bridge driver though. Does the type of driver matter?
let's assume the internal resistance of your motor is 5 Ohm (ignoring induced resistance when it starts turning).
at 6 volt you get a current of 6 Volt / 5 Ohm = 1.2 Ampere. 1.2 A x 6V = 7.2 Watts
at 8.4 volt you get a current of 8.4 Volt / 5 Ohm = 1.68 Ampere. 1.68 A x 8.4 V = 14.1 Watts
So by increasing the voltage from 6 to 8.4 you double the power load.
With PWM the motor will see the voltage of your power source for a certain duration of time. So PWM dutycycle at 60% means that your motor will see 8.4V for 60% of the time and 0 volt for 40% of the time
Would I try it if I were you? Yes, I would, but start at 50% PWM and regularly feel the temperature of the motor and H-Bridge driver, until you are sure it does not get hotter than before.
Some drivers have built-in current limiting. Adjust that to your max. working motor current and your PWM signal is at the safe side.
A driver like the ancient L29x motor drivers have a large voltage drop. So with a motor power supply of 8.4V the motor would only see about 6.5V or less. That is why i asked.
I do not recommend those old inefficient drivers, but in this case, if that is what you have and the motor stall current is less than the driver max current they may be OK.
Hi, @drakejest
Can you please post some images of your project, in particular the motor driver?
If you are using a driver board, then you should be able to read the number on the IC doing the job.
Thanks.. Tom.. 
Brushed DC motor voltage ratings are nominal, not "absolute maximum".
It is OK to apply a larger voltage, but the motor shaft will spin faster and the motor will have a shorter lifetime. The motor does more work in that time, though.
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