On Sunday 02 May 2021 09:29:09 dave engvall wrote: > Hi Gene, > > Your comments on the servo-stepper are interesting. How well would > they drive a BP sized mill?
I can't think of a GOOD reason, other than the mass of the knee would probably need some belt reduction in the knee. 3NM is in the 425 OZ/IN range and drives my GO704 at 70 or more IPM. XY would be std ball screws of course. > > I'm thinking about picking up one to play with. > > Any reason you know of that they could not be used with and external > encoder, eg glass scale for position? None, it would be two different feedback paths that don't need mixing, let the motor and controller be run by the TP, and let the scales tell the TP where its at. PID's optional, all it would be is an additional rubber band in the control loop. I have no PID's in the sheldon config at all. Motion tells the motors what to do and they just do it. Feedback comes from the stepgen, and the motors do as they are told. And if either can't do it, they stop linuxcnc in its tracks, litterally without a mark on the work that isn't springback. Whats not to like? The only problem I can see would be the time lag in the scales, they would have to be real time. Any lag would translate to overshoot and possible oscillation. That would limit the useable accels of the machine as the TP or moiion would have to be able to anticipate the = point before it got there. That is the unmentioned in polite company problem associated with glass scales as even resolvers aren't completely instant. The rssolution of it might include a higher frequency than 1 kilohertz for the servo loop. Stepgen based feedback doesn't have that lag. They report the position they've sent to the motors, no lag other than the quantization of the 1 kilohertz servo loop. And if the motors can't do it, they stop linuxcnc quite close to instantly. You of course have to hook all that up in the hal file. > Dave > > On 05/01/2021 05:51 PM, Gene Heskett wrote: > > On Saturday 01 May 2021 12:34:01 Chris Albertson wrote: > >> Gene, > >> > >> I did a search on the part number to gave and, they look really > >> good but cost $400 per axis vs about $60 for what I have. Yes, > >> they are much better. Did you find a better deal? > > > > Egad, where are you looking? 6 months ago I bought 4 of them in two > > orders thru ebay, 3 3NM's and a 2NM, and paid about $130 USD per > > axis. > > > > <https://www.ebay.com/itm/173853491927?hash=item287a79c2d7:g:mYYAAOS > >wEZdaQa5B> > > > > 85$ copy, but $45 shipping. So $130/axis, discounts for 3 or more. > > > > Cheers, Gene Heskett 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
