Joints - the building option

Since I haven't seen a lot of people discuss them as anything other than 'don't attempt to use them' I decided to collect some data.

Firstly, some information on what they do:

Hinge: A hinge will rotate around the z axis when the child joint prim is physical.

Point to Point: A point to point will rotate along any axis when the child joint prim is physical.

Limited point to point: don't know yet, too insanely bugged to use. Testing showed that when the child joint prim was set physical (from a height of about 30m), it set the prim to be both simultaneously -113m and 30m. This data was recorded by turning off surface patch, turning up view distance, and actually sitting on the prim. If you try to walk into it, it's still there, but invisible and uneditable (I had to select it at the -113m location). So while it's interesting to make something that exists in two locations at once, it's horribly bugged and I can't discern it's original purpose.


How to set up:

Hinge: Create your point that you want your hinge to rotate around, then create your object you wish to have rotate about that point. I was testing with default cubes with similiar axial rotations. So your experience may differ if you use other objects. Anyway, take the object you want to rotate around the point (it can be a linked set of it's own), then select the rotation point object. Next go to the tools->make joint->hinge. This will draw two little spheres on the objects and a line between them. It is important to note you will only see this when you select the child joint prim (the set selected not last, just like normal linked prims). Now deselect everything and select the child joint set and make it physics. You should be able to push the child set around the parent now along the z axis. Further, the child set will stay the same distance and such from the parent all the time. Also it will rotate to match the parent's rotation and stay with it if you move the parent.

Point to Point: Set up the same way except select point to point. Works pretty much the same way except that the point to point setup will allow the child joint prim set to rotate around all the axises. Oh it should also be pointed out that both Point to point and hinges will allow their child joint prims to clip through their parent joint prims even though their children are physics and the parents aren't, just like in any other linked set.

limited point to point: do not use or go ahead and try and then bug report it. Set up same way as point to point as far as I know.


Limitations: You can only have 1 joint. Meaning you cannot link a jointed set to another jointed set. So you can't have this: Group A-Hinge-Group B-Point to Point-Group C. Or anything like that. It seems a serious limitation to me, but possible to work around.

Applications: I anticipate being able to make a 'physics rag doll' by combining a lot of point to point sets with following scripts. Then maybe implement the 'stair dismount' game in SL lol. It would also work well for revolving doors (entirely unscripted ones), windmills(if designed properly), and probably a bunch of other stuff.

Enjoy.

Even the lindens tell us not to rely on joints for anything. They have a tendency to come apart, crash sims etc.
They are very buggy on Havok1. Havok2 will allow us to have better joints, and native support for ragdolls.

Further reading: /111/58/1577/1.html
This info was also edited and put in a notecard that is/was available at the Ivory Tower... haven't been there too recently so not sure if the card or the tower is still there.

My personal experience: I've gotten one or two very very simple physical objects that use a hinge to work somewhat reliably and that's about it. However, I tried making a very rudimentary physical swing once and the longest it ever lasted without any sort of drift at the hinge was about 24 hrs. So pretty much that type of stuff is collecting dust in my inventory, anxiously awaiting news of a preview grid showcasing a new physics engine. It will be fun to see what springs forth once joints are reliable and can be used in more complex ways.

-Meiyo

as a note on reliability, a blockgrab status script within the physics portion of the joint may help. I've noticed that on hinges you can drag them away from their control point (this is a bug). Preventing people from being able to grab it should fix that.

I just want to make a door. Can someone explain to me, in basic terminology, how to keep my door from swinging around like a rotation stall?

Apparently I need a hinge. I have the door script in the door prim.. along with all the proper sounds, etc. When I click the door, however, the whole thing swings around.. not attached to any door jam, etc. I created a cylinder, attached that to the door part, linked it and now they swing around together. lol. So... I've concluded I've missed a step.

Please help. I read the above posts but I'm uncertain which is the child and what "make physics" means.

Thanks

For doors, just make the script rotate the prim. IM me in-world and I'll give you a simple, open-source door that is very clean and easy to use. It does NOT use hinges or joints. You really don't want parts of your home to be physical...

Trini do listen to the wise Tiger. You have a door, you have a menu that says "hinge", "aha" you think "that must be what I need". The next thing you know, your house is swinging wildly around the door handle. Comical for the first 30 seconds and then a day or so to rebuild your house. I speak from humble experience.

Do's and Don'ts of using Joints in SL:

DO use joints for making turnstyles

DO use joints for making swings (the pg fun kind)

DON'T use joints for making normal doors (free scripts and examples are readily available at the megatower library.)

DON'T make both sides of a joint physics unless you never want to see it again.

DO make the side you want to move physics (by selecting the physics checkbox in the edit menu).

DON'T expect to do much with joints outside a sandbox.

Darn and I was seriously thinking of using this to make a spotlight.. There goes my hopes and dreams again..

It will kill your hopes and Dreams........


Until the DAYS OF HAVOK 2 are upon us. Then there will be Joint fun for all...Hopefully

Ah, and when that happens, combine a good set of linked prims into a flexible chain and voila, a nice pony tail for the laides.

I tried this once and got a pony tail that beat the crap out of the person wearing it every time she moved lol

So my boat with a gun turret is just not going to work...?

Crap!

I am successfully using a joint prim in a planet mobile in my building at Taber(1,1)[ish]. However, IIRC, none of the prims have physics enabled, and it works anyway.

I'll have to jump back on SL to verify that, alas.

That can be done through scripting I believe.

For a door, the best way I've seen done is to make a box twice the
size of the door and use cut to shape back down to size. Takes some
experimentatio,. but then a simple rotate works beautifully.

My favorite way to make a door is with the Deluxe Door script at the wiki. Just drop the script into a normal cube prim and viola! A working single-prim door.

Hinges tend to be bad for anything thats meant to work outside your inventory for long periods of time. I made a crane that used them but it didn't go over well. I used it to make two part vehicles in the past. Once a small zeppelin that had its balloon and cab seperated. And the second time a fully working tank. Both worked extremely reliably and could cross sims without much issue (they'd occasionall "fall through the world" -- more often the normal vehicles do. But just like normal vehicles they would reappear undamaged).

I tried to make a hinge swing as well. Would break over time. I'm real tempted to make a ragdoll now though.

EEEHEHEHEH! Dude, you like, just said "There will be Joint fun for all". HEHEHEHEHE!

Seriously, everything I've seen mentioned here, I.E. "I guess if joints don't work I can't make my _____", can be done with child rotation or some other form of scripted movement. When I first started I played around with joints for a few days, and then after learning about the terrible side-effects I swore off them. ;P

And any sort of rotation and movement I've needed to do since I've scripted, and I haven't looked back. I actually wish they would get rid of joints entirely and make it so you can manually set the axis for scripted rotation, so that I didn't have to make invisible prims to counterbalance swaying trees and moving arms.

is there a script like this I can drop on an existing door and have it work with minimal tweaking?

Joints get messed up when one sits on the moving prim(s). Other than that they are fine, so long as you keep in mind Havok's 10cm collision buffer...