The Wobble Ring Stepping Motor MK1
by Ndrew, published
This is my humble start on an actuator that could be mostly printed on a 3d printer. Incomplete as it is, I thought I'd post it as it developed.
It is based on this:
Instead of air chambers, I plan on rolling my own solenoids, eventually.
It also uses hypo-epicycoidic gearing, based off this:
And it should move like this:
But instead the outer ring 'wobbles'.
The wobbleRing is 1 tooth larger than the drivenGear(51/50). This allows for 2.4 degrees between solenoid steps(360 / (50 * 3)). But that's with just one of the 3 solenoids pulling at a time.
Now why did I use cycloidic gearing? Well, I understand they wear a little slower for this application. Also I was really having a time getting the MCAD library to work. Please correct me if there is a better gear profile for this application.
I do also appreciate any constructive critism, as this is my first openscad project.
BEWARE: I have not printed this thing yet!
I really wish I could but I am still waiting for mine.
BEWARE: There be snakes in dem codes; look at the openscad code at your own risk!
I really do intend to add more paramaters too, just working out the basic form first.
Oh and for now there are no solenoids included. At this point I really don't know enough yet to design capable ones.
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Wow I am having a hard time picturing that. I think I've got it though. Correct me if I am wrong then: each vertex of the 3 original rectangles is connected by an edge to the rectangle 1 size bigger. So that the smallest rectangle would form 4 trapezoidsÂ when connected to the middle one, and the middle sized rectangle would form 4 again with the largest rectangle. The middle rectangle would not be filled. Is this about right?
Nope googling doesn't seem bring up anything that looks like my third option. What I meant is to make the inner walls from a (hollowed out) sequence of expandingfrustum-cylinder-reducingfrustum-cylinder-expandingfrustum-... and so on.
Still there are the chamber seperation walls blocking flexing a bit.
So now that I think of it in more detail the best solution would be to start with three (or more) concentric rectangles projected from the origin outward onto one chamber wall. Pull the wall with the outer two radially outward while holding the center part of the wall with the innermost rectangle in place. (translate into openscad-fu). Only the inner rectangle will be in contact with the "wobble ring". If the flexing force is consderably smaller than the pneumatic force: (pressure*areaOfInnerRectangle) the the motors torque can be precalculated more precisely.
I think it might be a good sign if the design is so sensitive that it would be destroyed if pressured without the "wobble ring" in place.
Then again If you make the motor very small chamber hight Increasement might be the only option.
Maybe print some pickle-jar-lid-style bellowchambers for testing-purpouses
One more thing: Maximize Toothcount to minimize necessary amount of flexing.
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I don't pretend to know enough to instruct anyone else when I've not built anything myself.
If someone were to print just one or two pieces, I'd think that the "wobbleRing" and the "drivenGear" would be the most illuminating. Really curious how they mesh IRL...
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