On Friday 10 July 2020 05:34:58 andy pugh wrote: > On Fri, 10 Jul 2020 at 02:00, Chris Albertson <albertson.ch...@gmail.com> wrote: > > Belts can go to about 6:1 at best a double belt reduction only goes > > to 36:1 > > I don't see why there is any limit to the possible reduction of a belt > drive, if idlers are added to increase the wrap. > If I was doing this (and this particular application is something that > I have considered) I think that I would use a rotary variant of the > "servobelt" system: Glue a length of T-section beliting to a circular > component with the teeth pointing out to make a sprocket, and then > have a close-spaced pair of rollers to keep the belt wrapped round > the sprocket except for a short loop that pops out and wraps round the > stepper pulley.
That could work great even for a 340 degree turn. But I'd have the belt teeth pointing inward so the pop-out between the idlers could wrap the little pulley by at least 190 degrees. With the lack of stretch, one end could be anchored solidly to the big wheel, while a heavy spring maintains the belt tension on the belt on an otherwise smooth pulley. A matching belt glued on and teeth facing outward would be optional. With full time tension on the belt from a stout spring, only the idlers would need flanges. Their flanges could straddle the big wheel. That could work for az/el, but the base would need a full turn+ (I think). That could be handled by glueing on an endless belt to make the sprocket teeth, and using another belt facing inward so there would not be a gap at the anchor points. Diameter of the big wheel might need a tweak so theres no discontinuity when passing over the inner belts end gap. Still relatively cheap, no backlash. > > He is doing only > > about 10 Hz. > > In that case I think that a user-space loop in something like Python > would be fine, just monitor the time using an accurate RTC (GPS > module?) and have the loop say "have I made as many pulses as I should > have for this time of day?" and either make a pulse on a GPIO pin, or > not, accordingly. I love playing what if... 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
