Mate Limits Question...

larry_hawes

Tried choosing different (slider mate) MC first and got the same results with each choice. Just sayin'...

http://www.youtube.com/watch?v=eCgQu6sE4OA

larry_hawes

...and planar mates. PLEASE do not misinterpret these posts as anything truly negative regarding OS. It's just one user's experience.

http://www.youtube.com/watch?v=A41jkjFcuvU

mahir

Hi, @larry_hawes. The behavior you're seeing is what I would expect. I said the first MC is used as the reference. I didn't say that changing the order would change the observed behavior. I repeat; it's convoluted. The vector math being applied is not intuitive. The gist of it is that selecting the MCs in a different order changes which one is being used as the reference, but at the same time, it's also changing the direction along which the offset is being measured.

I'm not fancy with the videos, but here's a graphic example. Lets call the two MCs created by selecting the highlighted surfaces MCA (RIP) and MCB. In the first scenario, you select MCA first followed by MCB. With a gap in between the surfaces, both Z axes point to each other as seen below. The offset is measured from MCB to MCA. This is important. The offset isn't just a number, it's a vector pointing from MCB towards MCA. Notice how this vector points in the opposite direction as MCA (the first MC)? That's why the offset is negative.

In the second scenario, you select MCB first. Now the offset vector points from MCA to MCB. This is still considered negative because it's pointing opposite to MCB (picked first this time.

In order to get a positive result for the offset seen below, you would need need click the "Flip primary axis" button in the mate dialog and also edit the mate connector definition of whichever one you picked first and flip its primary axis as well. I'm hoping they put a button in that does this last part for you.

mahir

@larry_hawes, here's the improvement request I just created. If enough people vote for it maybe your CAD headaches won't be quite so painful.

MATE OPTION TO FLIP OFFSET/LIMIT DIRECTION

brucebartlett

here's a video of me working in real life adding some slider mate. This some real user experience. 

https://goo.gl/Scw5Z7

larry_hawes

Nice video Bruce and I think it illustrates the initial confusion pretty well. One can get it figured out but it does takes a few stabs at it to remember the paradigm.

mahir

@larry_hawes, btw you can reset both the min and max to No minimum or No maximum just by deleting all text and tabbing away from the box. OS will autofill the No max/min.

larry_hawes

mahir said:

@larry_hawes, btw you can reset both the min and max to No minimum or No maximum just by deleting all text and tabbing away from the box. OS will autofill the No max/min.

BRILLIANT Mahir, never knew that.

bradley_sauln

To add to this for any new users with questions on this same topic I'd like to draw specific attention to our help documentation that I think does a good job of helping understand how the mechanisms of mating works today: https://cad.onshape.com/help/index.htm#mate.htm?Highlight=mates

Looking under the section "Setting mate values for movement" walks through how the order of selecting your mate connectors matters for the coordinate positioning of how the parts will move and where negative values come in to play.

@larry_hawes, @brucebartlett, and @mahir thank you for your input and discussion on this thread thus far.

larry_hawes

Thanks Bradley and look forward to any changes your team might deem necessary for the future.