On Sunday 09 June 2013 18:59:56 andy pugh did opine: > On 9 June 2013 23:05, Gene Heskett <[email protected]> wrote: > > With my limited understanding I'm assuming the with FF0=100, and all > > the other trimmers setp'd to 0.0000, that it should have a straight > > thru transfer function, ignoring any feedback from the encoder > > velocity pin. > > Yes, you should. > > > However, with the motor driver disconnected so there is no input from > > the encoder, the output voltage steps at the C41 output aren't truly > > linear either. > > What is the PID output doing? That should be completely linear, which > suggests that the nonlinearity is in the pwm-voltage stage (and I > would be astonished if that circuit was actually linear). > As a CET, it being really linear, like a charge pump, would blow me away too.
> > I am beginning to get the impression this controller might need a > > buildout resistor in the control voltage wire. > > If you do have active PID then the nonlinearity is a non-issue. If all > plants had linear, well characterised response curves then there would > never be any need for PID control. > > If you do want to linearise the transfer function, you could look at > the lincurve hal module. Designed for just this sort of application. > http://www.linuxcnc.org/docs/devel/html/man/man9/lincurve.9.html Thanks Andy, I hadn't been aware of that module. Not in my sim install here either, but in the devel branch of the wiki. That looks pretty complex to setup as it might need 13 or 14 values to fully comp what I am seeing. Speaking in terms of practicality, what I am seeing, both in motor rpms and in the pwm-voltage stage, is a combined, quite positive transfer function after the usual s curve in the first half of the range. The last click on the + button that pins the tach needle, is about 2x the rpm change I'm getting for the first 3 clicks on the plus button. And this is with Pgain at about 40, but there is a speed instability, an almost random 50 rpm wandering that doesn't go away if I turn off the pwm dither, most obviously audible at about 600 rpms, or 10 rps. The motor controller apparently has its own PID like function built in, with an adjustment pot that can actually cause a rise in rpms under heavy load if its turned up, but that pot is turned to minimum. Whether that takes it completely out of the circuit I won't know till I call the maker tomorrow. I suspect that I'll wind up using the buildout resistor to linearize, effectively converting the control voltage to a current source, which is what it took to properly control the OEM controller in that 7x12, which when opened up, had a 250 watt rated controller running a 400 watt labeled motor. IMO the fuse could have safely had another amp, maybe 2, added without endangering that controller. The devices used could handle nearly 10 amps. Thanks Andy. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Detroit is Cleveland without the glitter. A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ How ServiceNow helps IT people transform IT departments: 1. A cloud service to automate IT design, transition and operations 2. Dashboards that offer high-level views of enterprise services 3. A single system of record for all IT processes http://p.sf.net/sfu/servicenow-d2d-j _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
