Code broken by commit 4db76ac32aee6a562f2d928313f44db4d8809b75

[nerian-vision]

Commit 4db76ac seems to have broken the code. The sign changes for the wrist, shoulder and elbow position initialization in Hexapod::Setup() causes the math to always result in very large positive or very small negative servo angles.

[i-make-robots]

This code is for the RSPv1, which has not been used in a very long time. Are you sure this is the one you want? Our current model uses the https://github.com/MarginallyClever/Rotary-Stewart-Platform-2-firmware code. We're working to roll that firmware into https://github.com/marginallyclever/makelangelo-firmware so we have fewer projects and less maintenance.

[i-make-robots]

also I'm very eager to see your machine and learn about it's applications. please & thank you.

[nerian-vision]

I was just looking for a starting point for an Arduino and servo-based Stewart Platform. The v1 firmware looks nice and simple, but I haven't gotten far with the built yet.

[i-make-robots]

Aha. Well, looking at the commit in question... it seems to flip the direction of each motor. You're saying it produces impossible angle values. Does the commit before that work ok?

[nerian-vision]

I reverted the sign flips from this commit and now the angles seem reasonable (though I haven't yet finished building the platform for testing). For now I have been using the default parameters for everything, so it shouldn't be a misparameterization.

The angles I get with the current head are always at +90° or -90°. If I output the angles before they are clipped to this minimum/maximum, they are about +160° and -160°. This is also the case if I send:
G00 x0 y0 z0 a0 b0 c0;

[i-make-robots]

Pretty sure the starting position of the head has a non zero z value. Try an M114 command to get the head position at the start.

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On Feb 27, 2018, at 12:34 AM, Dr. Konstantin Schauwecker ***@***.***> wrote: I reverted the sign flips from this commit and now the angles seem reasonable (though I haven't yet finished building the platform for testing). For now I have been using the default parameters for everything, so it shouldn't be a misparameterization. The angles I get with the current head are always at +90° or -90°. If I output the angles before they are clipped to this minimum/maximum, they are about +160° and -160°. This is also the case if I send: G00 x0 y0 z0 a0 b0 c0; — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or mute the thread.

[michimichi123]

Hello everybody,
i reverted the sign flips and now my stewart platform is working.

I changed the servos to Dynamixel XM430 which are quite expensive but they do a great job.
To use them i slightly changed your code.
I used your old code because the transformation to Dynamixels seems easier than in your Stewart V2.

But know i am facing the following issue:

when going to:
G00 Z1 X0 y0 A0 b0 C0;
and after that going to
G00 Z1 X0 y0 A0 b0 C20;

The Platform should just rotate, but it also makes a Z move.
In my opinion the z height it should stay the same.
Can you give a hint why this happens?

regards michael,
and thanks for your effort dan!

edit:
I solved it, the problem was due to wrong Z direction movement of my Dynamixel Setup.
By changing the Rotation Direction of the dynamixels i got rid of the problem.

[i-make-robots]

Can you share with us some pics? I want to confirm it's built to match my design. I notice there's no assembly guide here. :(

[michimichi123]

Hello Dan,

It´s the Platform from Robotis Friends - Stewart:
(https://emanual.robotis.com/docs/en/platform/openmanipulator_x/friends/#openmanipulator-stewart)
Since i had issues with their code i decided to use yours instead.

I rotated the Motor pair to be parallel and fit your design.

[i-make-robots]

The openmanipulator turns the servos so they are not in parallel. this would be... bad for my code. What are the major dimensions? Here's a picture for reference.


A and C are to the plane that passes through the center of the ball joints.

[i-make-robots]

because these numbers are hard-coded in the the stewart platform IK and must be adjusted to your platform size.

[i-make-robots]

partially related: https://www.youtube.com/watch?v=ysVzRRzQXTc