On Wednesday 22 September 2021 14:48:55 dave engvall wrote: > Hi, > > Fully recognizing that nothing is impossible to the person that > doesn't have to make it work. With that proviso I will open > mouth and insert foot. To wit: a sine for acceleration should give a > more gentle startup and approach to end point. Of course > implementation is left as an exercise for the student. ;-)
Which will probably involve a limit3. ISTR I've already got one in there. > Now I'll shut up and go away. > > Dave > Chuckle. Thanks Dave. > On 9/22/21 11:28 AM, Chris Albertson wrote: > > So you are driving it with something like this? > > amazon.com/HiLetgo-BTS7960-Driver... > > <https://www.amazon.com/HiLetgo-BTS7960-Driver-Arduino-Current/dp/B0 > >0WSN98DC/ref=asc_df_B00WSN98DC/?tag=hyprod-20&linkCode=df0&hvadid=198 > >090929431&hvpos=&hvnetw=g&hvrand=9099973595926304313&hvpone=&hvptwo=& > >hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031026&hvtargid=pla-4036 > >76040447&psc=1> > > > > One possible mistake is if even for a short time the both enable > > inputs are active you will get "shoot through" and short the power > > supply. Can you verify this NEVER happppens using a scope or > > logic analyser? Do not bother with a software "hal scope" You > > need to look at that is actually on the wires with a device that > > samples the actual metal pins. Real pins have riseand fall times > > and they can't intersect. > > > > I would also just use one PWM generator and connet it to both LPWM > > and RPWM. A safer why to handle L-EN and R_EN is to make 100% > > certain that they go through a state where BOTH ARE OFF. Don't flip > > them instantly as there is a finite rise and decay time. There needs > > to be soome number of microseconds where both are off. > > > > I bet LCNC flips both L-EN and R_EN on eht same software cycle. If > > so then the supply is shorted via the controller board. > > > > There boards are cheap and another way to fix this is to used a > > boaed with a "forward/Reverse" pin rather then two pins sothere is > > no chance of enabling both pins. > > > > Or using a "smart" controller with a serial interface where the > > speed and direction are sent as a digital command message. Then > > the acceletaion and such is handled by the controller. > > > > The sounds like an short in the h-bridge to me but I could be wrong. > > You can test this with a digital scope. on the control pins. > > > > On Wed, Sep 22, 2021 at 10:21 AM Gene Heskett <ghesk...@shentel.net> wrote: > >> On Wednesday 22 September 2021 11:44:51 John Figie wrote: > >>> Gene, > >>> > >>> I would like to better understand your problem and have been > >>> thinking about this. I have some questions. > >>> > >>>>> I don't think the fact that there is a worm gear matters. The > >>>>> problem, I bet is the large inertia of the system. > >>> > >>> Hmm I am not sure about the inertia. I think if you have a large > >>> gear reduction then the inertia reflected across the gears should > >>> appear low from the motors point of view. > >>> > >>>>> Aside from proper tuning of the PID gains you could change the > >>>>> system to use a nested or "cascade" PID. THis allows the > >>>>> velocity setpoint to be controlled by the position error > >>>>> see the section "cascade" in the wiki article > >>>>> https://en.wikipedia.org/wiki/PID_controller > >>>>> > >>>>> I think you want a very fast loop i=for the inner PID. LIkely > >>>>> it wouldbe in external hardwarelike a microcontroller or FPGA. > >>>>> (does MESA > >>>> > >>>> do > >>>> > >>>>> the PID algorithm in the FPGA? It should.) > >>>>> > >>>>> > >>>>> > >>>>> On Sun, Sep 19, 2021 at 3:39 PM Gene Heskett > >>>>> <ghesk...@shentel.net> > >>>> > >>>> wrote: > >>>>>> Greetings all; > >>>>>> As most of you know, I built a servo from scratch for a BS-1. > >>> > >>> BS-1? What is this? Is this like a Grizzly BS-1 dividing head? Did > >>> you mount the servo motor to this? > >> > >> Not a grizzly, a Chinese clone. > >> > >>>>>> But I am not at all happy with its performance. > >>>>>> It is a motor with a worm output, driving the worm of the bs-1. > >>>>>> And it has an A/B quad encoder in it. > >>> > >>> So you have a 2 worm gear reduction. Where in this system is the > >>> encoder mounted? > >> > >> On the rear of the motor. > >> > >>> What are the encoder counts per rev of the encoder? > >> > >> DNK, no index in it. So I measured the encoder for 100 turns of > >> the BS-1 as verified by the home switch, divided that by 360000 to > >> get a count per degree scale value. Thats about 666.something per > >> degree of the BS-1 > >> > >>> What are the motor characteristics? > >> > >> Brushed PMDC, rated a 100 watts, 24 volts. Intended to run estate > >> gates by chain drive similar to garage door openers. I assume its > >> OEM controller has a homing switch, and counts encoder pulses to > >> open so many pulses when the approaching driver punches his access > >> button. > >> > >>>>>> But I must rather severely limit its run speed because the PID > >>>>>> doesn't see the null coming near fast enough to slow it and > >>>>>> stop a couple > >>> > >>> When you say null coming what do you mean? Is this the point where > >>> the desired position is reached according to the motion planner in > >>> LinuxCNC? > >> > >> Yes. I'd assume so. Motion has its own version. > >> > >> Null in this context is when the encoder output equals commanded > >> position. > >> > >>>>>> arcseconds early. I can't allow it to use reverse to stop as > >>>>>> the motor seems to be a near short circuit then, crowbarring > >>>>>> the power supply, > >>> > >>> How do you prevent the PWM from reversing the voltage on the > >>> motor? Is the motor driven from a PWM in only one polarity? How is > >>> the PWM and the switches arranged? > >> > >> Control is by a LCNC PID, fed by the lcnc encoders position output > >> feeding the PID feedback, with a pwmgen running in mode 2 where it > >> has two pulse width modulated outputs, one fwd, one reverse, which > >> are fed to a BTS 7960 board containing 2 of the Infineon half > >> bridges for a full bridge control. This IC is rated at 45 volts, 43 > >> amps. Fed by a 24 volt supply good for nearly 20 amps, intended for > >> automotive seat position controls, it runs this motor with zero > >> heating. But if it overshoots the commanded position and goes into > >> reverse to bring the motor back by more than a 1 or 2 % drive while > >> the motor is still coasting fwd, it will crowbar the psu, getting > >> it hot instantly, causeing the psu to do a shut down until it has > >> cooled for 2 or 3 minutes. Even then, no heat in the BTS IC's. > >> > >> The net result is that I must limit its cuising speed and > >> accelleration in order for it to coast to a stop using its own > >> friction while avoiding the use of reverse to stop, usually a quite > >> small fraction of a degree early. And that is about 10 to 15% of > >> the speed it can move with the full 24 volts applied. > >> > >>> Regards, > >>> > >>> John Figie > >>> > >>> _______________________________________________ > >>> Emc-users mailing list > >>> Emc-users@lists.sourceforge.net > >>> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > >> 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 > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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
