Limits on mates

Jean-Robert

Hi all,

For my first post, I would like to congratulate all the Onshape team for this great work.
I'm very impressed by the already done job !

I've created and make public 2 models using mates :

https://cad.onshape.com/documents/48a3f2e6f67a4aea9d6d097b/w/b6f4ee9e22e04c7394369f41
https://cad.onshape.com/documents/154ce2da51284e048f6177f9/w/5d6c05c499e846d2b2b36429

If you play with the assemblies, you can see that the limits are missing, and the parts can move infinitly.
Do you plan to implement limits the features like SW or something else ?

Regards

Jean-Robert

joe_dunne

Jean-Roberts

thank you.

Yes our plan is to do exactly that. Because of our approach to Mates as more of a mechanism style joint. The idea of a zero point, and the concept of limits can be applied to any mate.

So this is coming, as with a lot of stuff.

I do have a question, there are 2 ways to tackle this problem that are obvious. I wonder which you would find more useful

1. One is to add settings a mate so that is only allowed to move through a start and end value (limit)
   
2. Another is to use a collision detection method. Where movement stops when something hits something else. In Solidworks they have a few ways to do this, like dynamic collision detection.
   

Which of these would you find more useful to start?

Jean-Robert

Hi Joe,

The collision detection method is smart but from my point of view, add settings to specify a start and an end values is more useful.
Most of the time, our models are simplified. If you check the url of the cylinder I gave in my first message, in the true life the rod extension is limited by the inner geometry which is not modeled in this case. The best is to use limit values for this model.

So the 1st solution is more useful to start.

caradon

JoeDunne said:

...
One is to add settings a mate so that is only allowed to move through a start and end value (limit)
...

I would prefer this solution.
It allows to add design intent as well. (That could be used downstream: configurations, drawings, documentation, manuals...)

Dries

kevin_quigley

Ditto. Settings. Collision detection has uses but tends to be a bit flaky.

brian_11

I was hoping that the assembly would do collision detection so that I would know if I have a problem before I make parts.   I guess I need to visually watch for collisions?

jakeramsley

Brian Carlson said:

I was hoping that the assembly would do collision detection so that I would know if I have a problem before I make parts.   I guess I need to visually watch for collisions?

Yes, however if you do a section view we mark collisions in solid red rather than a cross-hatching for the cap face.  This can be a way to inspect collisions.

brian_11

JakeRamsley said:

Brian Carlson said:

I was hoping that the assembly would do collision detection so that I would know if I have a problem before I make parts.   I guess I need to visually watch for collisions?

Yes, however if you do a section view we mark collisions in solid red rather than a cross-hatching for the cap face.  This can be a way to inspect collisions.

Thanks, I did not notice that feature because my math all worked out and my parts did not collide!

Edit:  I just sectioned and then intentionally over-rotated and see the collision marked in red.  That meets my needs just fine for new.  I'd still love for collision detection to eventually limit the movement of the parts

andrew_troup

I think specified limit mates (linear and rotary, latter with the option of degrees or turns) would do the job best for me, 90 times in 100

The highlighting in section views would cover two thirds of the balance.

luiz_otavio_zorzella

I take it you never got to implementing collision detection, right?

andrew_troup

@luiz_otavio_zorzella
Given the latency inseparable from computation of collisions in the cloud, I can't see how this could ever be a realistic, real-time option, except for those whose geographical location yielded round trip ping times more normally associated with Ethernet LANs.

Unless or until we repeal the limits on the speed of light   I'm guessing irreducible latency for the great majority of cloud users is like death and taxes. 

billy2

Webgl has collision between bodies. No round trip necessary. One of these days..... 

andrew_troup

@billy : I stand corrected: I thought WebGL was unacceptably slow for mesh-based collisions, so that it was usual to substitute bounding boxes or spheres.

billy2

Not sure how they do it, I was reading the webgl manual and saw that they can report collisions. Thought it was interesting.