In my experimentations with building a robot platform I have had a similar experience. I started out using a pair of Vexta PK245 stepper motors as drive. These require about 1 amp per phase which is 2 amps per motor with two windings excited for max torque. So with 4 amps as a current requirement I had to go with a sealed lead acid battery. Even a small one weighs a lot! Performance was very disappointing (it barely moved on a hard surface!). I eventually switched to 1/4 scale RC servos. These make for very inexpensive gearhead motors when modified to rotate freely. I removed all the electronics and drove it with PWM from a PIC. The ones I have will put out 150+ oz-in of torque and typically draw 100mA no load to 500mA loaded heavy. They cost about $30 each. Now, I did not have a requirement for precise positioning. So you still need to tackle that problem. Let me know if you want further info. Thanks Scott ----- Original Message ----- From: "michael brown" To: Sent: Monday, February 10, 2003 7:12 PM Subject: Re: Stepper drive methods.... On Monday 10 February 2003 02:08 pm, you wrote: > Chris:- > > If you really need high performance, you might want to look at DC > servos rather than steppers. With a built-in optical encoder (and > some drive circuitry) they can "look" just like a microstepping PWM > stepper controller to the driving software. Steppers have issues with > resonances and such like, as well as the obvious one of getting > enough drive current due to winding inductance. Spehro, When I first read this, I thought you were talking about R/C type servos. ;-) Now I realize that you must mean something a little more industrial. This sounds like a really good way to do it. To put it mildly, my experiences with using various cheap stepper motors in my little robot project have been less than satisfactory. Much of it being virtually no torque when running at any speed and not much at slow speeds either. Plus the noise and vibration are quite irritating. I've been thinking about switching to gearhead motors and using PWM, but didn't like the idea of losing the dead reckoning ability of stepper motors. I realized that by using an optical encoder or some other feedback mechanism I could get some good acuracy, but didn't think of just adding another layer of processing to get a PWM encoded wheel to look like a stepper. Thanks for the information. michael brown -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu