Rope(s) jerking & destroying - v2.1.0

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Rope(s) jerking & destroying - v2.1.0

Postby middle_road » Fri Oct 25, 2013 6:59 pm

I've created a simple scene with a lever, two idlers and a 'ball' connected with a rope.
No matter how I run it the rope goes into spasms and destroys itself.

I've tried a number of things like setting Tools.ChainTool.springConstant=1e4, ETC,
re-creating the scene from scratch, different materials for the idlers, lowering friction,
basically just shooting in the dark.

It's as if the rope is jumping, snagging, jerking, all sorts of unexpected behaviour ending
with the scene destroyed.

One other thing I noticed is that the idler 'pulleys' spin in a direction opposite of the
direction that the rope is traveling during the lever stroke - odd.
If I set 'showForceArrows' to 'True' on the idlers the arrows are flying all over the place.

I haven't had a chance to use Algodoo since v1.8x, but I had several scenes like this with chain
and such and never had these results.

Sizes:
Idlers: 1M
Ball: .75M - Steel - Mass 4kg
Rope @ .2 link distance. (tried .1 - .75)

_mr
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Re: Rope(s) jerking & destroying - v2.1.0

Postby middle_road » Sun Oct 27, 2013 6:20 pm

I may have figured out a partial fix for this problem.
I made up a chain/rope from scratch using links and axles, it still came apart no matter the size.
Then, under scripting, I tried setting 'autobend' to TRUE, and it's working fine, low & high.

_mr
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Re: Rope(s) jerking & destroying - v2.1.0

Postby middle_road » Mon Nov 04, 2013 5:52 pm

So, I take it that there is no way in v2.1.0 to create any type of 'chain' that simulates an axle, shaft or a pin.
What I am attempting is just a roller chain. I've been playing around with what suggestions there are in posts,
but no matter what I try the entities just fly apart or stretch ridiculously.
I thought that autobend would do it and it did work for awhile and then started failing.
I don't understand why an axle isn't an axle...
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Re: Rope(s) jerking & destroying - v2.1.0

Postby jon_joy_1999 » Tue Nov 05, 2013 7:27 pm

because you haven't offered a scene that replicates your problem, I took the initiative to use all of the information you provided in your OP and made this
Rating: rated 5
Filesize: 67.16 kB
Comments: 0
Ratings: 1
download
hopefully it solves your problems!
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Re: Rope(s) jerking & destroying - v2.1.0

Postby Xray » Sat Nov 16, 2013 2:08 am

Jon_joy_1999 - You made a scene with shows a stable rope but you neglected to explain what you did to prevent it from flying apart (the OP's problem). I've had this same problem also in some of the scenes that I've made which have a chain or a rope. At times, the chain or rope goes unstable and literally explodes, and I never figured out what causes that. An explanation to go along with your scene would be very helpful. Thanks!
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Re: Rope(s) jerking & destroying - v2.1.0

Postby jon_joy_1999 » Mon Nov 18, 2013 5:49 am

I followed the Op's information, and added no new, non-default information for the scene.
the steps to reproduce my scene are:
  1. Grid on
  2. Delete bottom plane.
  3. Create bar on left side, mine was 4x0.25 meters
  4. add center axle to bar
  5. create two 1 meter radius circles (instructions were not clear if circles were 1 meter radius, or diameter, chose radius because it's what is used in Algodoo)
  6. add center axles to both circles
  7. add one .75 meter circle below the two 1 meter circles. Do not add center axle to 3rd circle
  8. create chain that passes around all three circles and closes back on itself. Chain parameters: link distance: 0.20;
    Strength 1.0 * 10^5;
    Rope
really the only thing that I can think of that would make a rope go bizonkers is having it interpenetrate another object, have it weak for its capacity, or have a config problem. I don't know what kind of config problem would cause this though
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Re: Rope(s) jerking & destroying - v2.1.0

Postby Xray » Mon Nov 18, 2013 6:11 am

I wasn't asking for details on how you reproduced the OP's scene! I was just interested in what you did to prevent the chain from going bonkers. Your detail #8 explains the chain parameters which is really all I needed. So, it sounds like if the strength is kept very high, then that's the trick to keeping it from flying apart. One thing that I've found empirically is the fact that it's not good to make the strength +inf because that just creates more problems. I'll play with it some more to see what works and what doesn't work.

Thanks!
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Re: Rope(s) jerking & destroying - v2.1.0

Postby jon_joy_1999 » Mon Nov 18, 2013 6:31 am

strength +inf means that there is no wiggle room for when things get tight, there's no margin for calculation errors that accumulate in the positions as the scene progresses. conversely if the strength is too low then there is too much wiggle room, which causes the chain to stretch excessively and creates larger calculation errors, I think.
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Re: Rope(s) jerking & destroying - v2.1.0

Postby Xray » Mon Nov 18, 2013 9:50 am

I think you're right. Thanks again. :thumbup:
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Re: Rope(s) jerking & destroying - v2.1.0

Postby middle_road » Sun Nov 24, 2013 5:42 pm

Oops, should have posted samples - my bad.
What I ended up doing is taking on of my chains/belts/conveyors from v1.7 or 1.8 and importing it into the v2.1.0 scene.
And it works for some odd reason.
The old ones were made from scratch, links put together with axles and such.
When I tried that method with v2.1.0 it would just self destruct.
When I get some free time I'll dig back in the previous files and find the examples and upload them.

_mr

*EDIT* : added file
Attachments
Lever_Chain_Lift_01_Bugged.phz
(449.62 KiB) Downloaded 17 times
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Re: Rope(s) jerking & destroying - v2.1.0

Postby jon_joy_1999 » Sun Nov 24, 2013 9:59 pm

middle_road wrote:Oops, should have posted samples - my bad.
What I ended up doing is taking on of my chains/belts/conveyors from v1.7 or 1.8 and importing it into the v2.1.0 scene.
And it works for some odd reason.
The old ones were made from scratch, links put together with axles and such.
When I tried that method with v2.1.0 it would just self destruct.
When I get some free time I'll dig back in the previous files and find the examples and upload them.

_mr

*EDIT* : added file
the issue here is you have a frictionless rope, if you give a little bit of friction then it doesn't jump and jerk
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