Yet another mate question - conflict between planar and circumferential mate

les_green

Hi all, yet again I am trying to get to grips with the mate in OnShape

I'm trying to model a universal joint, with a spider and two Y joints (picture below). the spider obviously has a circumferential mate to the corresponding bores on the Y joint, however when I try and set a planar mate with an offset to keep the spider in the correct place in the Y joint, I am getting a conflict with the circumferential mate, with the spider being pushed backwards out of circumferential alignment. The faces I have selected are both perpendicular, and while I know this isn't solidworks, that is what I have used to replicate UJ's in that program. However here something is up

I would like to be able to attach the file to let someone play with it to see what I am doing wrong, is there a way to do that?

NeilCooke

Revolute mate with offset - should "never" be any need to use planar.

les_green

Thanks for the feedback, let me give that a try

Cheers

STEG

For a few joints, revolute with an offset whould do it like @NeilCooke suggested.

For your information, I assembled many universal joints in a complex equipment a few weeks ago and there was too many revolute so the assembly was "stuck" with all the mates to compute. The solution was to use ball mates which are easier to compute. But I had a lot of joints.

les_green

I tried the Revolute with offset and it didn't work either, so I went back again and checked everything to see if there was something about the geometry that was wrong. I found that somehow one of the lines was at 90.00097 degrees. This was obviously making one of the mates conflict. Once corrected both methods worked.

I can see that some of the lines have the symbols denoting horizontal, vertical etc, so will have to pay a bit more attention to that. However on other programs I found it useful that when creating a line it would actually have fields that displayed the angle, length, start point etc. If there is a way to have this displayed I think it would have helped me avoid the error in the first place, so is there a way to display line or entity properties?

eric_pesty

The "correct" way to do this to create an explicit mate connector in the yoke and the spider (in the part studio) that's centered and use a revolute mate (with offset).
Using a cylindrical and a planar is definitely not the right way to do this in Onshape and it will give you trouble!

Also based on your last comment it doesn't seem like you had fully defined sketches in your part studio, which will also cause you trouble later on...

les_green

Thanks, I will remember that.

For the sketch, it was fully defined, but just with wrong dimensions!

I suspect my error was that I assumed that one of the lines I drew was properly horizontal when it wasn't, so drew a line to the end of it, which fully closed the sketch. As mentioned, if there was a 'properties' panel I would appreciate it as it would allow a good visual cross check. As previously indicated, I come from a QCad and Solidworks background, and both these had the properties pane which I would use extensively to help me define the lines and indeed verify the angles of lines. Maybe I'll put that in as a suggestion

Thanks again for all the help, I have to say that despite my little tribulations I am really enjoying using OnShape and the ability to ask when I get stuck is so helpful!

Les