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A new hybrid low-inertia SCARA-like machine named "Pythagoras"

Posted by Dmytry 
A new hybrid low-inertia SCARA-like machine named "Pythagoras"
January 17, 2023 11:20PM
I'm working on a high speed / low inertia mechanism, with a side effect of it being well suited to self replication.


(Everyone is always concerned about the wobble, note that this wobble does not impact the position where 2 belts meet, and also that was an extreme test with 50 000 acceleration and moving speed up to 1.41 m/s. I also glued on some foam and that worked to prevent violent banging around which was problematic)

An earlier iteration:


Brief description: position of the print head is controlled directly by 2 tensioned belts, which are controlling two distances to the print head. There is a purely passive SCARA style mechanism which is needed to provide rigidity in the Z direction. (It doesn't have to be rigid in any other direction, allowing very lightweight construction). Alternatively, a hinged Peaucellier-Lipkin linkage, or another mechanism can be used to confine movements to a plane. E.g. an air bearing gliding on a glass plate. Or just a long stick confining movements to a large sphere.

The belts are tensioned by 2 sticks. The sticks are not directly connected to the print head (in the second iteration) and their precision is non critical (I literally use natural bamboo for prototyping since it got surprisingly high specific modulus).

This approach seems new and well suited to self replication, since it has relatively few parts. The only precision critical components in the XY stage are pulleys, belts, and motors.

A lot of variations can be done on this design, that can make it even more self replicated. For example, the arm could be spring loaded at the elbow joint, and the belts can be replaced with winched cable. The Z rail could be replaced with a straight line mechanism (e.g. Sarrus) which can be constructed similarly to the arm.

Less replicably, the sticks I'm using to tension the cable could be replaced with something akin to measuring tape, which can be rolled up in one direction but not the other.

Effective inertia of the Z-stiffening arm can be reduced by attaching a smaller flexure based, foam damped arm at the tip of the larger arm.

It is possible to build a rail-less Delta ish printer, by controlling 3 distances.

I'm hoping to attach an extruder and print the first benchy within the next couple weeks, and resolve remaining issues (add homing switches, add datum points for taking measurements of the machine as built for entering values into the klipper config file, etc). I'll be releasing the whole thing as open source.

edit: I posted it here rather than SCARA forum because it has quite different equations and properties from typical SCARA.

Edited 2 time(s). Last edit at 01/18/2023 12:23AM by Dmytry.
Re: A new hybrid low-inertia SCARA-like machine named "Pythagoras"
January 18, 2023 01:15AM
... yes, an interesting design! smileys with beer

Let me think about other uses of this sort of linear drives cool smiley

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Re: A new hybrid low-inertia SCARA-like machine named "Pythagoras"
January 23, 2023 12:25AM
First print: https://www.youtube.com/watch?v=1AJoZBwP0K4

Still a lot left to do, obviously, the arm structure needs a couple more iterations. I'm semi inclined to change it entirely to use a straight line mechanism attached to a hinge, at least as an experiment. Straight line mechanisms are marvelous.

Edited 1 time(s). Last edit at 01/23/2023 12:26AM by Dmytry.
Re: A new hybrid low-inertia SCARA-like machine named "Pythagoras"
May 22, 2023 03:36AM
really cool work. I haven't seen a new concept in a really long time. Last one was the simpson series of printers. Just out of curiosity wont it be simpler to have the tension rods move inside bushings , thereby eliminating the support arm? Just a though. I would love to make one of these. I have built scara plotters in the past but the inverse kinematics of those are kind of difficult to work with. How is the inverse kinematics of this mechanism ?
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