On Thursday 29 October 2020 15:02:16 Gene Heskett wrote: > On Thursday 29 October 2020 14:08:37 Chris Albertson wrote: > > If the motor is expensive or hard to get, keep it and use a driver > > rated for more volts. As said, you can buy four MOSFETS and make > > a driver that is good enough for a use-case where A/C mains is > > available and you are not trying to squeeze every drop of power from > > a battery. Homemade h-bridges tend to waste power and turn it to > > heat. But maybe not. Today they sell "logic level" MOSFETS that > > you can drive with 3.3 volts. > > > > If you don't like dealing with low-level drivers they sell > > controllers that work at a high level and will servo the motor to > > some commanded position. But you'd pay $100 for that. or $4 for a > > handful of MOSFETS. > > > > Good 12V motors are really cheap because they are mass-produced for > > the automotive industry. > > But this one wasn't built for car apps, its made to run driveway gates > sliding across estate driveways, supposedly to keep out the riff-raff > like me. :) And it has a builtin encoder so the gate driver knows > where the gate is. That sort of stuff tends to be 24 volt based. Less > power loses on lighter ga wiring etc. The price of copper often drives > that design choice. UL also has vastly different safety rules for 24 > volt compared to 120 volt stuff. But you knew all that. :) > > [...] PS, I don't know if I have a problem or not. I changed pwmgen_type to a 2 just to see what the signals looked like, then downloaded the datasheet. I find its too slow to respond to the narrower pulses the pwmgen can output. Lots of Pgain might overcome the narrower pulse problem by forcing the error response until its wide enough to move the motor, and there is a deadband where no pulses are generated about 70mv wide centered around zero error.
But until I try it next week, thats not a huge concern. The data sheet is for one half-bridge, and these boards use 2 of them to make a full H bridge. And this chip is also pretty ancient, 2004 ack the datashhets history. But the mesa cards output a logic high on both lines when lcnc is not running. Which is effectively anytime F2 is not in the machine enabled state because that is also the main power for all the motors. Because the interface is continuously powered. My own logic says that will send both motor leads to the top of the supply, asserting a near short on the motor, but there is not any motor power until the soft start time delays run out about 2 seconds later. But at release of f2, these pwm lines are sent to a logic one instantly, while the supplies are left to bleed off by whatever means, which could take 30 seconds or more. Can anyone see a problem? Or am I barking at the moon?... My logic says both dir lines high is net zero to the motor, but maybe somebody else has a more experienced view. Plz advise. Thank you. 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
