Hi Curtis, There are a few major hurdles to doing rotary axis blending:
1. Blends between circular motions (that also have motion in other axes) are not geometrically possible with the blending technique we use (circular arc segments), except for some special cases. This IS possible with line segments, however. 2. The blend arcs are parameterized using arc length; the distance in ABC has to be included in the arc length calculation, or the blends won't match velocities properly with the segments they're blending. The current TP assumes in many places that "progress" along a segment means XYZ motion, and UVWABC motion is indirectly tied to this. 3. It's difficult to define blend tolerances for ABC motion in a useful way. For example, with 4th axis engraving program, the effective blend tolerance depends on the diameter of the part. All that said, a while ago I extended the 2.7 TP to handle 6 linear axes (which avoids problem 3, and doesn't try to blend any circular motions). The branch is here if you want to try it out: https://github.com/robEllenberg/linuxcnc-mirror/tree/feature/uvw-blending-2.7 This might help if you don't actually need rotary axis motion and can pretend your 4th axis is linear. Best, Rob On Thu, Mar 14, 2019 at 12:56 PM Curtis Dutton <curtd...@gmail.com> wrote: > I don't mind doing the G93 calculations. The problem for me is no lookahead > when using x,y,z,a > > Does anyone know why n-axis lookahead isn't easy to accomplish with the > new TP? (I'm sure its complicated ! :-) > > On Thu, Mar 14, 2019 at 12:47 PM Gene Heskett <ghesk...@shentel.net> > wrote: > > > On Thursday 14 March 2019 09:12:51 Les Newell wrote: > > > > > That does not help the trajectory planner lookahead problem. It just > > > tries to correct the feed rates for each movement segment. > > > > > > Les > > > > No, it doesn't, so in that sense you're correct, Les, but its certainly > > one way to solve the problem in terms of production time. This is > > something I encountered about 4 years back when I attempted to make a > > ship auger type drill bit on the G0704 while I was building us an > > entertainment center. And again with a similar auger bit when I was > > converting part of our front deck to a wheelchair ramp alittle over a > > year ago so I could get the missus in and out of the house. In the > > latter case I needed it capable of drilling a hole at a low angle into > > the side of a 4x4 about 15" high, to anchor it solidly to the deck so I > > could drop a 46" tall plastic rail post over it and make the safety > > rails on one side of the ramp. Very solid feeling rail, it doesn't move > > with my 165 lbs leaning on it as hard as I can. That was the general > > idea. But it took many many hours with a 1/4" ball nose carving a 3/4" > > piece of cold roll that needed sharpening about 4 times a hole. Cold > > roll is not the ideal to make a drill bit from, but it got the job done. > > > > I should have done something like calculating the speed by translating it > > to radius, then to inches a minute. But TBT, I was much more interested > > in getting the job done, between the rapid dulling and time > > resharpening, it took about a day for each of the 3 posts to get them > > planted in a puddle of tightbond. Needless to say, I downloaded this > > conversion utility. On of the things I intend to do with this big gantry > > is make a copy of a thumbhole gunstock I carved by hand for a 50 cal BP > > rifle. Someday I'd like to find some purtier Maple. It shoots very well > > the way it is. > > > > My thanks to the author, apparently Shawn E. Gano. > > > > > > https://www.ganotechnologies.com/cnc/rapidrotary/ > > > > > > _______________________________________________ > > > Emc-developers mailing list > > > Emc-developers@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > > > 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) > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > > > _______________________________________________ > > Emc-developers mailing list > > Emc-developers@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
