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Mate Connector Directions NOT Intuitive
marten_hutchison
Member Posts: 29 EDU
The axial (Z) behavior of mates, except maybe Fastened, doesn't seem to have any logic, which can't be true because its software. This has been frustrating the crap out of me for the past 3 years I've been using OnShape (the first 2 I thought it was just my ignorance). Its a total crap shoot what the directional behavior of any mate with motion is going to be. Its pretty irritating to have to create air cylinders with negative strokes (most of the time, but not always). A scan of posts shows that its not just me. You can't look at two mate connectors on your screen and reliably know how they'll orient themselves. Venting... having to correct the orientation of virtually every mate gets tedious.
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Comments
I can't give you any wisdom.
I will add though, once you get into assemblies and the fact that they can inherit mates correctly from sub-assemblies, I stopped complaining. Try pulling sub-assemblies into higher level assemblies and watch how everything works. I've never seen this before and it really helps creating a library of working sub-assemblies. Hopefully soon, we'll be able to download robots, and stages that actually articulate and we don't have to create sub-assemblies that work. When I download a pneumatic cylinder from mcmaster carr, why do I have to make it work? What's wrong with this world?
A word of warning, limit mates are confusing also. Just remember that the lower limit mate always has to be a lower value than the max limit mate. When limit mating a lot, you'll find some go from negative infinity to zero and others go from zero to infinity. I can't tell you why and I've tried to figure it out.
For this reason I find it is bets to pick the part you are mating (i.e. the "free" one) before the part you are mating to (i.e. the "fixed" one). This is especially helpful when setting offsets as if you pick a "fixed" one first and apply an offset it will try to move the fixed one, which is impossible so in order to achieve the correct relative motion it will move the free part in the opposite direction.
My advice is to create a basic assembly of two parts. fixing one of them and try different things (selection order and offsets), starting with "fasten" mates and moving on to ones with more DOF. That's how I can now predict (about 90% of the time at least!) what I need to do to get the desired result.
It's also helpful to keep in mind that the mate dialogue applies relations between the two mate connectors, but you can also edit each (implicit) mate connector individually (by expanding the mate after creating it), which can be a cleaner way to get what you need. I did submit an IR to add the mate connector icon (like in features that allow a MC as an input) so that they can be edited during the mate creation process as I find this would help get what you need more quickly (rather than having to exit the mate creation to go edit them).
There are definitely a few cases where the "Solidworks-style" mates are easier but I find the vast majority of the time the Onshape way is much better, it's also a lot easier to fix any broken mates or mate errors (although I find it really helps you name your mates, especially since we can't group them in folders yet)!
OS assemblies solve reverse kinematics:
You can mate an effector and OS will tell you the robot's angles. If you're designing automated equipment, this is a huge benefit. The last time I used SW, it wouldn't do this.
And then there's assembly inheritance where you can take a switch assembly that toggles, add it to a panel, add it to a chassis, add it to a rack, add it to room, add it to a building and then the switch still toggles in the building assembly. The explode state (whatever its called) in SW doesn't work and forces you to build crazy assembly structures that are meaningless.
I don't understand why not understanding the mate orientation would stop someone from switching when the OS assemblies are superior.
I'm thinking online sales doesn't work, this is a simple objection that should be handled easily.
I'm hoping with cloud cad, vendors get wise and build onshape models to distribute. A vendor could push current pricing and availability to your design. You could easily look at a BOM and see if the next build has any issues. The vendor could derive a usage count and supply demand.
I'd simply like more predictable orientation behavior when I mate parts in assemblies. I've realized that I unconsciously cringe when I have to hash through a large assembly because I have to contend with guessing the mate orientation for virtually every mate and then correct them. For small assemblies its not a big deal, but larger ones where I have to place 20+ components, it gets old. I can understand its a difficult challenge for developers to create software to guess the local coordinates of a part. I'd be happy if just the Z's of the mated parts always did the same thing.
I'll refine my statement... OS's mating concept overall is intuitive, but the initial behavior of the two part's local coordinate axes, when the mates are selected is not.
Adding the mate connector editing launcher (whatever it's called) in the mate dialogue would go a long way as it would make it a lot quicker to fix the MC themselves rather than adding offsets/rotation in the mate!
Something like this:
I already raised it as an IR but from the "contact support" menu so there is no forum post to vote for... feel free to make one as well!
@eric_pesty I've submitted this enhancement 3 times and each time support tells me I've already submitted it. I've been waiting for this for a while now and asking multiple times doesn't seem to help.
Right, I don't think an individual submitting the same IR multiple times help, but they do keep track when multiple people ask for it so that's what I meant!
Mate option to flip offset/limit direction
I would also argue that any of the Limit options should have the current value in the dialog. I know it shows up on screen, but why not in the dialog too? (this is what Solidworks does)
Haha.
How about, as a user, it seems weird to have the limits but not the value itself all in the same place. When I'm first creating one of these types of mates, I often want to play with all three values.
I'd be happy to read a short description of the programmer's design intent with respect to the mate's coordinate axis behavior when they're selected. Maybe that would clear up my question.
tks MH
I can't tell without seeing the document but I believe you are trying to offset the moveable part which is on the right relative to the fixed part which is on the left. If you switch the order of the mate connectors it should give you the expected result.
Remember the offsets are trying to move the first selected MC in the axes direction of the first MC.
That could be the usability improvement. Whichever coordinate system the movement is based on could be made much bigger or highlighted, etc, so its easy to figure out what will happen. If you switch the selection order, the bigger/highlight goes to the other coord system.
I got a bit frustrated by the apparent "randomness" one day so I created a basic test assembly and played with mates to try to figure out how it worked but there are probably still some more subtle points I am missing! That's how I figured how to apply offsets to fasten mates in a predictable manner, but it gets more complicated as well when you throw in rotations, or have more degrees of freedom, etc
I started another thread about the need for a "tips/webinar/tech brief" type of material as this really isn't explained properly anywhere in the training, but that hasn't gotten any traction!
If the devs are reading this (@NeilCooke is pretty active around here!) and looking for topic ideas for tech tips or webinars, I would be really interested!