Jeshua Lacock wrote: > It felt like I wanted to get P set as high as I could. Is that correct? Or as > long as P is high enough to command the machine to move is that adequate? > > You want the P as high as you can get it while still having stable response. Low P will lead to "sloppy" positioning, ie. large following errors that don't get reduced. But, there is always a limit on how high you can turn P when instability develops. Then, you use FF1 and FF2 to reduce the error further. These compensate for finite gain in the rest of the servo system. >> Of course. You should ground the shield at the control end only, so >> either the USC or the Gecko interface. >> > > Thanks! So I use the ground from either the USC or Gecko? > Yes. > I see. Currently, since I am only using pulleys with timing belts (no gears > or lead screws per se), I was under the impression that backlash is nearly > non-exisistent. Is that true? > > The only thing left is stretch of the belt. Long belts may have some stretch, which is somewhat different from backlash, but can still be a problem in servo response. At the middle of travel, it produces a springy effect, but less at the ends of travel. And, at the ends, the sprinigness could become asymmetric. > My z-axis is pulleys with a ballscrew. > > Of course as soon as I install the 5:1 gearbox on my X (hopefully here > tomorrow) then it will have some backlash (see below). > > > Actually the gearbox is rated as 6 arcmin backlash. I did the math and that > seemed quite negligible to me, at least for my purposes. Thoughts? > > WOW, yes, that is quite small! Some of the crap that is out there for smaller machines have simple spur gear reduction on Pittman motors and the backlash in in the several degree range at the output shaft. I would think this level of backlash is indeed negligible. > Do you recommend any tricks, like springs or semi-flexible drive shaft? > > Ugh, no, you want to avoid adding any springiness in the system.
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