On Sunday 29 January 2017 12:40:21 Alan Corey wrote: > I wonder why there's so much noise. Are you using something like a > light dimmer for speed control? And what kind of noise, continuous or > spikes when events happen? If you turn on an AM radio in the vicinity > you'll probably hear your lathe noises, which might be helpful. I was > thinking lathe = induction motor with belts for gearing, but you're > probably got some nasty SCR or Thyristor causing trash. Are you doing > pwm of the lathe motor from the Pi? Optoisolators might help. Got a > schematic? I'm a ham and electronics technician with some machine > shop experience. Never attempted anything like this though.
Alan, ALL of the motor drivers are switchmode, with the current regulation running at or above 20 KHz. And these noise spikes are ringing at nominally 100 MHz. I have managed to get the xy motor noise under control by takeing out the switchmode psu's, and putting in tordoid transformers, bridge rectifiers, and the biggest electrolytic I had in the drawers that had sufficient withstand voltage. Its a star ground system, and the output cables to the motors are shielded, and the shield grounded as it goes by this single bolt ground on its way out of the box. The shielding extends both ways from that point but is not connected either at the motor, or at the driver, just at the bolt. This is std in such noisy machinery. Also, std in the drivers, is the control inputs are all by opto-isolators, so only the few pf's there, but the length of the wire from the interface card to the driver makes a good enough antenna (plans are afoot to change those wires out for shielded, also grounded at that bolt) that its blown two of the Mesa 7i90 interface cards i/o ports, so I've had to enable the last 2 step generators code modules in the 7i90's currently loaded firmware and rewrite my .hal file accordingly. When everything is finally nailed down, I'll replace that card as its only $60 bucks for 72 pins of i/o, more than enough to run a full turret tooled lathe which this is not. But with ball screws and LinuxCNC running it, accuracy is in the .0005" range and repeatable. You can see what I am dealing with, using run what ya brung stuff, at the link in my sig + /lathe-stf/lathe-noise-pix/ <http://geneslinuxbox.net:6309/gene/lathe-stf/lathe-noise-pix/> Its not purdy, but its what I have on my SS determined budget. :) 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) Genes Web page <http://geneslinuxbox.net:6309/gene>
