Miura Fold in Onshape

matthew_mueller537

Hello. I'm interested in creating an assembly in Onshape that can move like the Miura Fold pattern. I've tried making the parallelograms with rounded edges, and mated the edges with pin slot mates and one revolute mate to keep all of the parts together, but it's not fully constrained. Here's what I have so far. Any ideas about a better way to do this? 

EvanReese

I saw this fold years ago and it stuck with me, but I haven't come up with a search term to find it since so thanks! Pin-slot isn't what you want. it's for things like this: 
I used a combination of revolute and cylindrical mates to get it working. When i used all revolute it would become overconstrained, which I assume has something to do with Onshape's internal tolerance since it should work in a perfectly precise world. Using some cylindrical constraints loosens it up a bit.

romeograham

I made a quick working version to try out a couple things. I think you'll find success with these tips:

• use surface bodies at first to get the mates correct. When using Mate Connectors for mates, Onshape doesn't care about your rounded edges, but they may make it difficult to select the right edges for the Mate Connectors. Surfaces will make the early work of figuring out the Mates much simpler
• use the least-restrictive Mate types possible. For my sub assembly (4 panels, like yours) I used 3 Revolute mates and 1 Ball Mate. 
• When you assemble the sub assemblies together, continue to try to use the least-restrictive mates where possible....
• When placing new sub assemblies into your Main Assembly - use the Group to (temporarily) freeze your sub assemblies so they can't fold while you're trying to apply mates to the existing parts. Remember to delete the Group before you add all the mates, or try to drag your assembly to check the motion. You can also suppress/unsupress a Group on your first sub assembly while mating - this will effectively freeze all motion while you apply mates.

See Branch B1 in the link above for a version using just mate connectors, which would make it quite easy to swap out the surface bodies for other parts later.

Good luck!

NeilCooke

Can you make the doc public?

matthew_mueller537

Sorry about that. It's public now. I think the issue is there's not one point of rotation with the rounded edges. If I make edges then I can use revolute joints for all the connections. But any other thoughts would be appreciated!

EvanReese

I saw this fold years ago and it stuck with me, but I haven't come up with a search term to find it since so thanks! Pin-slot isn't what you want. it's for things like this: 
I used a combination of revolute and cylindrical mates to get it working. When i used all revolute it would become overconstrained, which I assume has something to do with Onshape's internal tolerance since it should work in a perfectly precise world. Using some cylindrical constraints loosens it up a bit.

romeograham

I made a quick working version to try out a couple things. I think you'll find success with these tips:

• use surface bodies at first to get the mates correct. When using Mate Connectors for mates, Onshape doesn't care about your rounded edges, but they may make it difficult to select the right edges for the Mate Connectors. Surfaces will make the early work of figuring out the Mates much simpler
• use the least-restrictive Mate types possible. For my sub assembly (4 panels, like yours) I used 3 Revolute mates and 1 Ball Mate. 
• When you assemble the sub assemblies together, continue to try to use the least-restrictive mates where possible....
• When placing new sub assemblies into your Main Assembly - use the Group to (temporarily) freeze your sub assemblies so they can't fold while you're trying to apply mates to the existing parts. Remember to delete the Group before you add all the mates, or try to drag your assembly to check the motion. You can also suppress/unsupress a Group on your first sub assembly while mating - this will effectively freeze all motion while you apply mates.

See Branch B1 in the link above for a version using just mate connectors, which would make it quite easy to swap out the surface bodies for other parts later.

Good luck!

EvanReese

@romeograham
way better than mine!

romeograham

A mesmerizing view with more complex panels (Branch "Solid Panels" in the document).
https://youtu.be/yOJSx71PEEs

steve_shubin

@romeograham

NICE WORK !