Deltesian Update: Got the big bed mounted and I was able to do a test print, 160mm x 380mm. It’s pretty wild seeing this thing actually functioning after months of work.
Still a long way to go before I can fully open source everything, but personally, it’s a huge milestone to hit after months of working on this concept.
…that really messes with my head
One quick observation, you should be able to get away with just 3 connector rods versus 6. The key would be to not use ball joints. Use simple planar pivotals. I assume this prototype is reusing components from a Delta, hence the current pivot style.
That is some pretty wicked reverse kinematics.
@Jim_Powers That was his exact reason for building it that way – reusing delta parts.
@Jim_Powers Ball Ends are not necessary, but only 3 connectors will not have enough rigidity.
This isn’t without precedent, in 2007 the Chinese built a 12’ tall machine tool using the same principle. https://imgur.com/jLqK993
That updated picture is inline with what I was invisioning. With the upper links bound together that mechanism is effective 4 links. On the left hand side you could mount the upper bound pair (effectively a single) at the vertical center of the end effector and drop the bottom link (redundant). Boom, 3 links.
@Jim_Powers downside I see to the 3-link approach is that the stability of that parallelogram element will vary with arm position. Say you have the parallelogram arranged with joints more or less vertical as Rob has done — when the whole arm is near vertical, the parallelogram is in a pose with very low stiffness. (There’s a constraint singularity when the end-links are parallel to the arm links.) So both sides need parallelograms to ensure stability in both near-tower regions.
You could largely resolve the issue by placing the end-effector joint positions at about a 40 degree angle so the parallelogram doesn’t go wonky at either extreme.
@Ryan_Carlyle I hadn’t considered offsetting the joints further. Currently I have them at ~9deg offset, but it sounds like a great idea; experimenting with some more exaggerated offsets to see it there are noticeable improvements. I would only need to print a new Effector and 2 Carriages, so it’s a not huge deal to test a few configurations.
@Rob_Stuart_bornity People have proposed regular deltas with over/under parallelograms (rods stacked vertically) in the past, which is why I thought of changing the angle on your Deltesian arms linkages. The over/under Delta is kinematically unstable if the joints are directly above/below each other.
Putting the joints on an angle off vertical resolves both these issues for the over/under delta. The Deltesian obviously doesn’t have #2 because of the upper hinge linkages.
@Ryan_Carlyle you hit the nail on the head, the larger offset allows the effector to get closer to the side of the build plate.
Though it would involve notching the Effector around the timing belt.
