Break joint at certain torque/moment

[misho]

Hi all!

Is there a way to set some kind of a threshold/limit on a joint, over which the joint breaks?

I have a situation where I have 2 bodies, connected by a joint (hard joint in this case, but it could be any type). In my case, it is a space capsule with a solar array attached. If the space capsule's solar panel hits something in space, say, a part of the space station, I would like this solar panel to break off from the space capsule. How can I do that?

Thanks!

[Julio Jerez]

Yes, you just delete the joint if any of the forces pass some preset value.

[misho]

Yes, you just delete the joint if any of the forces pass some preset value.

Thanks Julio - but how do I find out what the forces are on the joint itself? Is there a value that I can read somewhere? Because, I suppose, I can calculate moment/torque, but I was wondering if something like that is already calculated within the joint class/structure...

[Julio Jerez]

I will post a code fragment later.

[misho]

I will post a code fragment later.

Thanks Julio, that would be great!

[misho]

Hi Julio, I was wondering if you had a chance to look at this?

thanks,
Misho

[Julio Jerez]

are these the panels you are taking about?
https://www.youtube.com/watch?v=-wA-RlEnCNI

there is a naïve was of doing that and a more sophisticated way.
the naïve way is just liek I said before, ther are only thing to find out when do you determine of the joint broke so that you delete it. this has to be outside a new top update, becaus eteh engine does no support deleting objects from with in a update. it is sort of supported but it is better not to mess with that.
because for that the naïve way may no be too good, and I explain.

imagine your solar panel that is attached to the far more massive body of the space ship.
imagine some impact hit the solar panel,
because the solar panel is attach rigidity to the massive body. the entire thing act as it is was one one solid massive body, therefore the impact is it was with a really massive body will apply a very strong torque and force to the ship because the body was deleted. it will brake but it will be the wrong physics.
If may be fine with, but very soon the more knowledgeable people will figure out that any attachment like a feather will be strong enough that a collsion can alter the trajectory of the capsule.

the more correct way is to do as fallows.
I have to add a funtionality to teh bilateral joint name brake force and break torque.
this value will be set to the max that is set already. but can be over wrote by the application.

then the solver will check is the partial solution is larger than the brake limit, it is was throw out the partial result and solve the joint again this time using the iterative solver and flag that joint as broken,
the effect now is that the light object will only be able to apply the max brake torque and it will be update the app to delete the joint in the next update.

let us try that this weekend, please send me a post so that I remember.

[misho]

Yes - the panels in the shape of "X" on the space capsule docked onto the space station - that is exactly the panel(s) I am talking about. Actually, one panel is comprised of 3 sub-panels that are articulated with hinges. The spaceship has 4 such panels, so a total of 12 sub panels. I implemented the deployment using hinge motors and it worked, but there were some instabilities I encountered with that approach due to the high velocities the spacecraft is moving at (If you remember, we chatted about this about a year ago). For now, I have one large piece representing the panel (and the collision) and I'd like for it to break off the main body

Excellent - I will do that, Julio. I can even set up the test case if you'd like me to.