Good work Gen! I originally tried to do the chopping by hardware using a single 324 quad op amp as the comparators, but it was too unstable. Glad to see your's work so well. Software chopping chews up too much cpu time.
One thing to note is that at high stepping rates, the inductance of the motors become the limiting factor and the current never reaches the point where the chopper would kick in. So the acid test is to use a low step rate and a higher voltage, 20 volts or more. Make sure you monitor the current in case the limiter don't work. Keep in mind that the current flow in the sensing resistor is bi-directional, so a simple voltage measurement might not give a true reading. A scope is best.
Also keep in mind that the voltage across the mosfets is TWICE the supply voltage.
To avoid resonance problems, micro-stepping is extremely desirable. In theory, it would be easy to use 6 MCU pins to make two 3 bit resistor ladder D/A converters to feed varying references to each of the two comparators.
Keep us posted on your progress!  |