John Kasunich <[EMAIL PROTECTED]> wrote: > Sebastian Kuzminsky wrote: > > I've determined that with no load on the motor shaft, stepping the > > PWM duty cycle from 0 to 100% causes the motor to accelerate from a > > stand-still to the 1200 RPM limit in about 75 us. > > Wow. > > And wow again. > > That is one VERY low inertia motor, or an astonishing amount of torque, > or both. Zero to 1200 RPM in 75uS is 16,000 RPM per millisecond. I > don't know what the top speed of the motor is, but it sounds like it > can get there in at most a couple milliseconds. That's remarkable > performance.
It's a Pittman 8322, overdriven from 19.1 V to 24 V. The rated top speed (at 19.1 V) is 7847 rpm, rated peak torque is 7.4 oz*in. There are excellent manufacturer's specs here: <http://pittmannet.com/series8000motors.html> > You might want to connect it to your actual load and measure the accel > rate again. If it is a very low inertia motor, you might find that the > load inertia gets the accel rate down to something a little less > astonishing, and a lot easier to deal with. Good idea, I bet it'll spin much slower when driving something. > > My plan for trying to limit the motor shaft speed is to run a two-level > > PID controller. The first PID controller tries to achieve the target > > position using encoder.position as feedback. The output from the > > position PID controller goes not to the pulse generator, but to the > > command for the velocity PID controller. The velocity PID controller > > uses encoder.velocity as feedback, and *its* output goes to pwmgen.value. > > > > I'll run the velocity PID controller in a relatively fast thread (no > > more than 75 us period), but the position PID controller can run at the > > usual rate of 1 KHz or so. > > The problem is going to be getting usable velocity feedback. Your > encoder sampling is at 25uS, and your PID is running at 75uS. That > means in any one PID period, you get either 0, 1, 2, or 3 encoder > counts. Not much resolution. That makes sense. If the load doesnt slow the motor down enough, it looks like I'll need to buy a Pluto-P or a MesaNet product. Bummer, I was hoping to do it all in software on the PC using just the parallel port for I/O. -- Sebastian Kuzminsky ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
