Lateral springs in Mechanism

[gpommeranz]

I have a helical coil spring that supports a cradle.  The cradle catches a structure and supports it when not in use.  The question I have is in reality there are 6 dof of how this spring moves.  It operates in torsion, extension, and laterally.  So it's a complicated scenario.  My question is whether it is possible to simulate this in mechanism.  I started with a 6 dof connection so the cradle could move freely but I'm unable to make the torsion spring connection because there are not co-axes to select.  If I change my connection to a cylinder then I can create the extension and torsion springs but lose the lateral movement.  

My question is if it is possible to write the equations of motion between the two points so that I can create all 3 types of springs?  Basically can I made a UDF for the springs?  

[ChrisKaswer]

This can be done with the idealized joints provided in MDO. The effort will be in defining the spring as a combination of individual "simple" joints between spring segments, similar to what it looks like you started with. I created a very accurate model like this many years ago, so I may only be able to share a movie clip of the result if I can't find original models. Your 6 DOF should be possible, but would require more overhead to make these behave properly. Using cylindrical joints should do it. If you select the correct division number for each full coil, you can capture the behavior well, and it will offer lateral movement too. My original application was high-speed valve trains to model the spring surge characteristics, so I only used pin joints and this worked excellent for this application (and provided lateral movement too - in the directions dictated by the selection of coil segment lengths). I'll share the movie clip if I can find it...

Of course, equations of motion should be possible as well, but might take a bit more effort unless you already have these handy and can be patched into your MDO model without much issue.

Cheers