I’m having a problem with OnShape that when I import an assembled part, they aren’t mated together. How can I fix this other than having to manually assemble an omni wheel?
Don’t worry, this is a feature of OnShape and is supposed to happen. All you have to do is group together the parts. After this, you can constrain the groups of parts together.
Yep. Not just Onshape, but all parametric CAD: it’s because .step files contain only geometry data, but not mate data.