SIn waves are there own derivatives and integrals, except for phase. So a sine wave acceleration works if the gaol is a sine wive velocity curve. But I assume the goal here is maximum change in velocity. You get that by running the motor is full reverse.
I doubt we are seing back EMF because the worm cn not be back driven by a wheel. My guess about the root cause if the power supply current spike is a shoot-through in the double h-brige because the direction owas reserved instantly with no though to the gate driver rise and fall times. (I actualy hope it is this because the fix then is easy and can be done on software. If I'm wrong th fix is harder. On Wed, Sep 22, 2021 at 11:51 AM dave engvall <dengv...@charter.net> 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. ;-) > Now I'll shut up and go away. > > 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/B00WSN98DC/ref=asc_df_B00WSN98DC/?tag=hyprod-20&linkCode=df0&hvadid=198090929431&hvpos=&hvnetw=g&hvrand=9099973595926304313&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031026&hvtargid=pla-403676040447&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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
