Revolute connectors, breaking

olivier_benoit

I cannot find a way to solve the connections of 4 parts linked with 4 revolute connectors.
This is supposed to be easy but I have tried for hours all options without success.

https://cad.onshape.com/documents/22eb8f99d7e3e06f78902120/w/0c35ca4e6d26c9e708ce6871/e/04c744e30db0c1a6878d0f51

Any help would be appreciated

mahir

Fixed it. Turns out the circled faces on Part1 weren't parallel. You should definitely better constrain your sketches. That particular sketch was completely free floating.
https://cad.onshape.com/documents/fa757a0758b1935d14c14743/w/a3d3d08df76549f4b1cd7872/e/39065cf933ff6379c290219d

philip_thomas

FWIW - the advice @mahir gave was spot on. 
I do a lot of assembly work and i have learnt to identify visually 'closed' systems (where the last part mates to the first part) and have trained myself to add that one extra degree of freedom (usually a cylindrical mate) to make the assembly far more resilient.
(of course, non parallel faces will mess you up (if you weren't expecting them)).

There are newbies that will find this thread and so please forgive me for this quick diatribe.

Onshape's high level mates are between two and three times as productive/faster than traditional low level mates.

• If you are trying to add a SECOND mate to a part, stop. You are probably using the wrong mate type.
• 95% of the time, any two parts or sub-assemblies can be mated with one mate
• When importing - group mate is your friend
• Fixing a part applies ONLY in the (sub)assembly in which the fix is applied.
• To reinforce - a fix added in a sub-assembly WILL NOT be respected in any higher assembly (intentional)
• Onshape mating can be broken down into a simple hierarchy (from low level to high level)
•    Mate connection points are automatically generated points to which Mate Connectors may be attached (or offset from).
•    A Mate connector is a local coordinate system that may be generated explicitly, or implicitly (as part of the creation of a mate)
•    A Mate is a definition of the degrees of freedom that exist between any two Mate Connectors
•    A Mate Relation defines the relationship between a single degree of freedom from each of two Mate Connectors (gear ratio)

I hope this helps

mahir

I'm having issues with this, too. I would expect 4 revolute mates to break because you're it would overconstrain the assembly. You have to leave at least one pair free to translate along X. So setting the fourth mate to a cylindrical mate should do the trick... but it doesn't. Maybe a more savvy person or an OS employee will figure out what I can't.

mahir

Found something. Haven't fixed it yet. For some reason, not all your mating faces are parallel. Somewhere in there you have a draft or and almost-right angle that is hosing it all.

mahir

Fixed it. Turns out the circled faces on Part1 weren't parallel. You should definitely better constrain your sketches. That particular sketch was completely free floating.
https://cad.onshape.com/documents/fa757a0758b1935d14c14743/w/a3d3d08df76549f4b1cd7872/e/39065cf933ff6379c290219d

philip_thomas

FWIW - the advice @mahir gave was spot on. 
I do a lot of assembly work and i have learnt to identify visually 'closed' systems (where the last part mates to the first part) and have trained myself to add that one extra degree of freedom (usually a cylindrical mate) to make the assembly far more resilient.
(of course, non parallel faces will mess you up (if you weren't expecting them)).

There are newbies that will find this thread and so please forgive me for this quick diatribe.

Onshape's high level mates are between two and three times as productive/faster than traditional low level mates.

• If you are trying to add a SECOND mate to a part, stop. You are probably using the wrong mate type.
• 95% of the time, any two parts or sub-assemblies can be mated with one mate
• When importing - group mate is your friend
• Fixing a part applies ONLY in the (sub)assembly in which the fix is applied.
• To reinforce - a fix added in a sub-assembly WILL NOT be respected in any higher assembly (intentional)
• Onshape mating can be broken down into a simple hierarchy (from low level to high level)
•    Mate connection points are automatically generated points to which Mate Connectors may be attached (or offset from).
•    A Mate connector is a local coordinate system that may be generated explicitly, or implicitly (as part of the creation of a mate)
•    A Mate is a definition of the degrees of freedom that exist between any two Mate Connectors
•    A Mate Relation defines the relationship between a single degree of freedom from each of two Mate Connectors (gear ratio)

I hope this helps

olivier_benoit

Thank you all for your help.
I love onShape, I think it is an amazing tool and I am glade I got quick help on that one since I spent many hours on it on my own before reaching out to the community.