Hi Dave, I think the question being raised is whether it's possible to create a zero backlash 4th or 5th axis with COTS hardware for less money than a harmonic drive or the cycloidal gearboxes.
John > -----Original Message----- > From: David Berndt [mailto:ber...@uberwin.com] > Sent: May-15-20 11:19 PM > To: Enhanced Machine Controller (EMC); Roland Jollivet > Subject: Re: [Emc-users] Cheaper than normal FHA-25B > > Why are you particularly worried about that? Cyclodial gear boxes and > harmonic drives are both basically 0 backlash, with potentially some lost > motion. Most are repeatable well under 1 arc minute, which compared to a > lot of rotary tables already out there. And that's something like a .0017" > displacement on a 12" radius. Angular transmission accuracy would seem to > be almost as big an issue that you'd have to start to think about if > you're concerned about those levels of backlash. Also overall mechanical > stiffness. > > -Dave > > > On Sat, 16 May 2020 01:49:58 -0400, Roland Jollivet > <roland.jolli...@gmail.com> wrote: > > > I've been thinking about 4th axes; > > While motorised reduction drives are readily available, the issue is > > obviously backlash. > > > > One way to make a zero backlash drive is to use two identical > > gearbox/drives. Place them at opposite ends of the axis, and pit them > > against each other by a few encoder counts. > > So they will track and retain the zero-backlash. > > > > Of course, the total power available is now less than one drive motor, > > but > > it is an option to use almost any pair of reduction drives that can be > > got. > > But there is also the cost of the second servo amp. > > > > > > On Fri, 15 May 2020 at 14:11, andy pugh <bodge...@gmail.com> wrote: > > > >> The normally appear on eBay at up to 6x this price. > >> https://www.ebay.co.uk/itm/233587431605 > >> > >> The B versions have conventional incremental encoders and hall > >> sensors, so are easy to integrate. Lots of torque, zero backlash and a > >> very strong and fancy big crossed-roller bearing make them an > >> almost-complete 4th or 5th axis just needing a bracket and a drive. > >> > >> I have no connection with the vendor, if you order one and receive > >> dolls-house furniture instead don't blame me. > >> > >> -- > >> atp > >> "A motorcycle is a bicycle with a pandemonium attachment and is > >> designed for the especial use of mechanical geniuses, daredevils and > >> lunatics." > >> � George Fitch, Atlanta Constitution Newspaper, 1912 > >> > >> > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
