Rigging IK sliding joint

[smb]

Is it possible to rig this so it can be animated with inverse kinematics?

[video]

The center joint is a piston and must slide and not bend. I don't have a lot of experience animating and am stumped.

Current animation uses a combination of constraints and driven keys. Works but I think IK would be simpler to handle in a real scene.

Would appreciate some guidance here. Thanks.

Steve

[santd]

Hello,

Thank you for posting to The Area Forums.

I played around with this and was not able to accomplish this using and IK chaing with joints. However, I was able to get it work like an IK chain using some constraints.

I have attached my Maya file for you to take a look at.

I have also created this video showing what I did:

https://screencast.autodesk.com/main/details/db96adcb-c5b2-4159-b36c-25609a1268f5

Cheers,

[smb]

Hi David,

This looks like what I was looking for. Thanks for taking the time to put this together.

I haven't had much time to spend on this lately but was able to set up my file according to the steps in your video. I'll give it a run-through and will let you know if I have any other questions.

Didn't see the link to your file. Do you mind reposting that? I'd like to compare it with mine.

Steve

[santd]

Hi Steve,

It seems that I forgot the attachement. I have attached the file to this response. Hope it helps.

Cheers,

[smb]

Thanks for sending the file.

It keeps giving me a cycle check warning, though. The upper leg seems to be getting conflicting inputs and doesn't always resolve its rotation correctly. It's not an issue with gradual moves, but large moves (made by setting the values in the channel box) can cause the joint to become misaligned. 

To avoid this I've tried combining my original approach with your example, using an expression to calculate the rotation of the upper leg and an aim constraint to keep the lower leg aligned.

See attached. Is this an OK solution?

[santd]

Hello,

I am not seeing a problem with the your setup, I think that should work just fine. One thing I noticed about my setup is that if the controller strays from the plane that the leg is in, then it can break. This can be resolved by creating limits and locking certain axis.

Cheers,