Greetings Sam; I'm working on an all printed, miniature version of the loose belt harmonic drive and am about 90% done in a unit sized to work with the A axis supplied with a 4 axis 6090 gantry mill. 21.5mm thick, and about 85mm around. Rather than bolted, the inner facing splines are keyed to prevent slippage, and I'm using the same recipe in openscad to generate the two rings with the only diff being the number of splines. One at 60, one at 62 teeth, loose belt is 60 teeth. Simple, eccentric by 2mm armature, with 2 printed race ball bearings on the armature to drive the inside of the loose spline, also printed but in PETG as its enough more flexible that at 2mm eccentricity, has not failed even for long enough my fingers are numb from around 3500 rpms at the motor. Repeatedly. PLA broke in seconds.
All this on the cheap as the bearing balls are crosmann bb's. They aren't all that precise but neither is the printer, but I can tweak the sizes quite well in openscad to .005 mm's. So they are interchangeable. AIUI, interchanging them will reverse the direction the output turns while also changing the gear ratio. So a 30/1 going backwards becomes a 29/1 turning forwards. Or something like that. So my question is: Is there, since lcnc can do both just as easily, a preferred, mechanically better direction? I'm currently driving it, without an alu hub for the armature by making a Dflat hole in the armature for the 8mm shaft of one of the new 3 phase stepper/servo motors (after I ground a much wider Dflat than supplied with a CBN wheel, those are magic) and have a box of 1NM's on order as they have the same size shaft but are about 3+" shorter. And should still be able to spin the input shaft up to 3+ grand or so. With a 23 tooth sprocket on this drives output, and a 83 tooth sprocket on the axle with a 3" chuck on the other end, it should make over 500 rpm at the chuck. With arc-minute accuracy. All from less than half a small bottle of bb's and about a 1/4 kg of plastic filament. $15 total. Cheap, if you break it, make another. 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
