Re: More torque One word "Chopper"

Nearly every commercial stepper motor driver I have ever seen uses a 
chopper circuit. This is because torque is related to current (actually its 
related to magnetic flux but that's related to current :-). The operation 
of a chopper is pretty simple, you slam a "huge" voltage on your motor with 
a circuit the measures the current through the motor, (voltage comparator 
across a .1 ohm resistor is good for this) and then when it gets to the max 
current you "chop" the voltage off. (usually by turning off a MOSFET) When 
the current gets a bit below where you want it you turn the voltage back 
on. (this provides "holding" torque) It is all a simple feedback circuit 
and requires no software at all.


--Chuck

At 11:31 PM 4/11/00 -0600, Sean Verret wrote:
>Is there an easy way to get more torque out of a stepper motor?  Upping the
>voltage is not an option at this time.  I've already decreased the width of
>the pulses enough (so that it has enough torque to start on its own without
>a push) that it goes rather slow.  Speeding up the pulses doesn't allow it
>to start - maybe my wheels are too slippery?  Maybe putting some sort of
>grip on them....  I'm just throwing out some ideas here - please throw out
>some more if you've tried anything like this before...  oh yeah - setting up
>a gear box is most likely out of the option due to my current time
>constraints.
>
>Thanks in advance for all your help.
>
>Sean Verret
>B.Sc. Electrical Engineering 2000
>University of Alberta
>mailto:verret@ee.ualberta.ca
>http://www.ee.ualberta.ca/~verret/
>Phone: (780) 439-0329
>Fax: (206) 493-2713



