Has anyone tried using universal RC joints for deltas? Pros/cons?
How much backlash do they have? In theory, the magnetic ball couplers I’ve seen have zero backlash.
Not sure, haven’t tried them yet. I agree magnets are better, but I am not looking to necessarily compare the two. Just interested to know if this alone would work.
Sorry, I have no pragmatic advice. There’s no reason they couldn’t work, depending on their quality and the precision you’re after. One other thought, they might be heavier, which will impact acceleration (and therefore print speed). How much are they compared to other solutions? If cheap enough, might be worth trying!
Shai, started with ujoints, and many still use them.
Do kit kid yourself on magnets either. Look at delta mechanics. The more you shove that head in into the right places, the fastest the forces spike. Read thru the Delta forms, and more then one reached a point where magnets gave up, and things get ugly quick after that.
Looks to be about $3-4 a piece. Probably cheaper with bigger quantity. Made of metal. So yes, could be heavy. But rigidity could compensate for it being heavy in acceleration.
The joint diameter seems to be around 9mm based on some specs on aliexpress. Not sure how big the whole setup is though…
I have a good feeling that they are probably loose and probably have ~0.3mm tolerance deviation across 100 pieces (wild guess).
@James_Hutchinson Yep, aware of those and a bunch of other joints. We currently use traxxas joints, but they can be improved upon. Trying to figure out how good these are though.
@Dustyn_Roberts wrote a great book called “Making Things Move”: http://www.amazon.com/Making-Mechanisms-Inventors-Hobbyists-Artists/dp/0071741674 that has a lot to say about joints and movement-coupling. Totally worth reading. U-joints have a potential problem in that as the angle increases, the phase relationship between the driving and driven axles starts to change. (This is why constant-velocity joints were invented.) Beam or bellows coupling joints can have lower inertia and essentially zero backlash, so they’re pretty attractive.
@John_Bump The phase angle issue doesn’t matter for Delta joint applications as long as the effector joint and carriage joint are mounted in the same orientation. The phase errors from the two joints cancel out.
@Shai_Schechter I’m building a tripod bot with printed U-joints (with 4x 623 bearings) right now – no parallelograms. I’m very pleased with the stiffness so far. I’ll post about it on the Deltabots forum after I get the motion mechanism built.