WallyKins

WallyKins

Postby cdsteinkuehler » Thu Mar 13, 2014 9:30 am

I got my first prints out of Wally tonight, so I thought I'd start a "buildlog" thread. Everyone seems to be giving their printers names, so I'm calling mine WallyKins. Mostly because I plan on implementing real-time kinematics using LinuxCNC. And it's a cute name. :)

The first print was done using trivial kinematics and the segmentize.py program, to make sure everything works.

cdsteinkuehler
 
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Re: WallyKins

Postby Nicholas Seward » Thu Mar 13, 2014 2:08 pm

TSA loves to break Wally's. I would suggest unmounting the xy arms. Everything else after being taped down should survive.

Awesome work. I love the name.
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Re: WallyKins

Postby cdsteinkuehler » Thu Mar 13, 2014 2:23 pm

Thanks, I've been meaning to ask you about the best way to box a Wally. Do you just remove the arms at the shoulder joint (meaning I have to re-string when putting back together), or pull the whole arm/shoulder assembly off the backboard?

I also have to take at least one flat-screen monitor with me (fingers crossed). At least it was a $10 state surplus special if it turns back into sand. :)
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Re: WallyKins

Postby Nicholas Seward » Thu Mar 13, 2014 2:30 pm

Restring is the way I would go. It gets much easier as you do it over and over.
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Re: WallyKins

Postby cdsteinkuehler » Fri Mar 14, 2014 1:13 am

UPDATE: I just got the inverse kinematics working with LinuxCNC. It's way too much fun to do coordinated jogs in X and Y and watch both arm motors move! Video to come in a bit...
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Re: WallyKins

Postby cdsteinkuehler » Fri Mar 14, 2014 3:43 pm

cdsteinkuehler wrote:UPDATE: I just got the inverse kinematics working with LinuxCNC. It's way too much fun to do coordinated jogs in X and Y and watch both arm motors move! Video to come in a bit...


False alarm. I did pretty much get this going, but there seem to be some issues with either my math or the LinuxCNC support for inverse only kinematics. So I took an unexpected detour and had to code up forward kinematics. I gave up on a closed form solution, my math mojo just isn't up to the task given the available time. Instead, I'm using "simple" wally kinematics, where I assume the arm position doesn't affect the motor drive (as if the motor was mounted on the shoulder arm). Then it's just intersect the two circles to get a predicted XY, use the predicted XY to calculate the arm positions, calculate a the new effective drive command based on the current arm position, lather-rinse-repeat until the error from one step to the next is below your threshold. So far it's taking about 25-30 iterations to get below 0.05mm error.

Now I've got to pack, so Wally with full kinematics looks like a show-floor activity. Nothing like working in demo mode! :)
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