Sebastian Kuzminsky wrote: > The next step was to spin the motor, and that's where I'm running into > issues. At 0% duty cycle the motor is stopped, and at 100% it runs fast, > so that's good. However, the mapping from duty-cycle to rpm is confusing. > Duty cycles from 0 to about 55% give me increasing whining from the > motor but no movement at all. 55 to 100% gives increasing motor speed > and torque. > > I'm using a driver circuit basically identical to the one published by > Jeff Epler (thanks Jeff!). The only power supply I have access to right > now is an ATX one scrounged from some dead computer, so I'm driving > the motor at only 12 V; it's rated for 19.1 V so that's probably part > of my problem. Just like in Jeff's example, I run a PDM pulse train > into the H-bridge enable pin, and direction and not-direction signals > into the two H-bridge inputs. The resolution of my pulse generation > is 100 us, so the pulse train has transitions at no more than 10 KHz, > well below the 25 KHz nominal commutation frequency of the L298 H-bridge. > > So my main question is: What, if anything, can/should I do about the > dead band from 0 to 55% duty cycle? Live with it and tune it out in the > PID loop? You need a lot more voltage supplying the H bridge. At 55% duty cycle, you are getting 12 * 0.55 = 6.6 V at the motor. I am a little surprised the motor doesn't start to turn before this, it must have a lot of friction. Have you measured the motor current just before it starts to turn? That would be interesting to know.
Umm, 1.6 Oz-In continuous torque? What kind of machine are you planning on making with this? You might be able to run an etch-a-sketch with it if you provide sufficient belt reduction, but you couldn't even drive that directly! Do you know how LITTLE 1.6 Oz-In is? The Bridgeport guys use 640 Oz-In motors and up. Jon ------------------------------------------------------------------------- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
