On Thursday 29 October 2020 13:26:12 Chris Albertson wrote: > You can set the VNH3SP0 to "brake" mode. But this works or not > depending on the motor and gearing. It is very easy to test if it > will work. Twist the leads of the DC motor together.
How do I turn this motor by hand? its output shaft is the bullgear shaft of a worm drive so several thousand armature revs is 220 rpm on the shaft. Most definitely, absolutely, non reversible. Thhe other end is occupied by a quadrature encoder, with which I'll drive a pid.A.feedback for considerably under 1 degree of accuracy. Even under cutting loads. > With shorted > leads, the DC motor should resist rotation, to what degree depends on > the motor. The other mode is "coast" which is simply an open > circuit. Then you have forward and reverse modes as well. Plain and simple, its too slow to do the job with this motor. Looking for a better one, the 43 amp, 27 volt rated "BTS7960 High Power Motor Driver Module 43A H-bridge Current Limit" I found from a us supplier, at $13/copy and will have a pair of them here by next Wednesday. The others might not be here till about Christmas. And I'm more than tired of screwing with this. The BTS7960, rated for pwms up to 25 khz, and can be driven by a software pwm in mode 2. I can put that on the sainsmart bob at a 1 millisecond resolution. Mode 2 should handle any reasonable reversal timing constraints. But before I goto sw pwmgen, I'll try putting the mesa pwmgen.00 is mode 2, which should give the the correct pwm on the stepgen4 outputs of the 7i76D. Doing that puts the pwmgen's beyond the quantization of the 1 kilohertz servo update writes. By that means I can get pwm pulses as narrow as 200ns. Good control of the spindle at 100 rpm in high gear is quite do-able even with only a 2khz pwm. > To handle shoot through, just never switch from forward to reverse or > vice versa without first going to either "coast" or "brake". The signals available from the mesa cards I have do NOT have that dead time. So at 24 volts all it will do is overheat and shut down even at pwm rates way slower than my spindle could tolerate. It for sure did not like 1 kilohertz. It tolerates 2khz, but has been running at 10 for several years. I'll wind up running the mesa hardware as fast as these can tolerate. 5k would be better for the spindle. > Yes, > you can look at the datasheet and count microseconds but if the PID > runs at 1000 Hz you are guaranteed to always remain in one of those > four states for at minimum 1/1000th second. If switching directions > "brake" might even help, depends on the motor. > > As for the design of those internal MOSFETs, just try doing better. > They needed to open the lower side of the bridge and there is no > negative voltage available and they want low on-resistance. This used > to be really hard to do. (But today we have logic-level MOSFETs) Apparently not in this now elderly design & fab. Its over a decade old from what I read. Thats not "today"... Stay safe and well Chris. [...] Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
