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A project log for Arcus-3D-C1 - Cable 3D printer

3D printable, Open Source Hardware, tripod kinematics, cable driven 3D printer

Daren Schwenke 11/11/2017 at 04:133 Comments

The tripod kinematics is giving me a headache.

Machinekit tripodkins is modeled as struts, not cables.  This means that reducing all the struts lengths is a move which goes down, not up.  I need the other direction.

So what I really need is inverted tripodkins.  

Running inverted looks like it is already handled in the code, but it's not something you can just select.  You just have to present it with the right situation, and it happens.

Well that's all good in theory.  Starting below the XY plane, which according to the source looks like the trigger, results in the machine going into estop with joint following errors.  Many hours of flipping signs and switching directions on everything has yielded no results yet.  Many 22kg test lines have been snapped in the process.

There seems to be zero examples online of using tripodkins in Machinekit in this way.  My googlefu is strong, so I've really, really looked.  I know it's been done.  I've found many projects which did it.  Problem is apparently none of them committed their configurations to the ether.

Then there is homing.  I had it sorted.  Of course this was before I realized the entire machine was upside down.

I'll just have to figure it out.

Discussions

Daniel Kruger wrote 6 days ago point

Another link. This person was using Marlin.  https://www.thingiverse.com/thing:1024307

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Daniel Kruger wrote 11/11/2017 at 19:07 point

I assume you've looked at this but I thought I would put a link just in case. https://designmakeshare.wordpress.com/2013/09/16/introducing-skydelta/

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Daren Schwenke wrote 4 days ago point

Yeah.  I've been back and forth with Brandon a few times in email and pulled many of his github repos local for searching as well.  No tripodkins configs seem to have survived.  That fact previously delayed this and my other cable printer by 6 months at least.

It's all good now though.  I have a working one, it is on github, and I'll keyword bomb it enough that future versions of me can find it.

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