On Wednesday 22 September 2021 14:28:40 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/B00W >SN98DC/ref=asc_df_B00WSN98DC/?tag=hyprod-20&linkCode=df0&hvadid=1980909 >29431&hvpos=&hvnetw=g&hvrand=9099973595926304313&hvpone=&hvptwo=&hvqmt= >&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031026&hvtargid=pla-403676040447 >&psc=1>
Precisely. In mode 2 for what you want below, there is a setable deadband so both inputs are never on at the same time. > 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? The best sampling scope on the planet at the moment has not found both signals high at the same time. > 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. Mode 2 does that. > 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. > That is the case. I could post pix but John K. won't let me. > 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. Not that I've caught with a $3400 350 megasample scope. > 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. Link? > 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 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
