Pulley system that can go slack

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Pulley system that can go slack

Postby Esharc » Tue Mar 14, 2017 12:50 am

Good morning

I work for a company that makes mining simulators and we use Newton dynamics for our physics.

We have to make a simulator of the Marion 8750 Dragline, and we have run into an issue with the pulley system attached to the bucket.

https://www.youtube.com/watch?v=onUbhQ85efs

One thing to notice about the attached video is the fact that the pulley system can go slack. I have attached a picture of the pulley system that we are trying to simulate.

BucketWithPulleyMarked.png


I did see that you have a CustomPulley joint, but I tried modifying it to see if it will be able to work, but I have had no joy.

Do you think something like this will be able to be simulated with Newton, and if so, do you have any guidelines that I could follow?

Thanks in advance
Etienne
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Re: Pulley system that can go slack

Postby Julio Jerez » Tue Mar 14, 2017 8:55 am

oh, that an interesting a challenging project. and yes newton that can be simulated that.

first thing is to determine if you are using latest version for the engine.
We have made large progress since we adopted the exact solver for all joints as oppose to for 3.xx to 3.13 when with move to iterative solver for performance reason. Now the joints are exact and can be even faster without solving. With 3.14 we went back to our mission statement
"Newton Dynamics implements a deterministic solver, which is not based on traditional LCP or iterative methods, but possesses the stability and speed of both respectively. This feature makes Newton Dynamics a tool not only for games, but also for any real-time physics simulation."

but this time we are adopting it for bilateral joints instead of for the entire scene.
that's first thing.

The second is what to you mean by pulley system that can go slack? I do not understand what that means. I see you overlaid red lines over the image, is that what to are referring to?
anyway I can make a small demo to show you how to do it.

Now that we are using a unity plugin It can be modeled in there an exports a serialized version to the
sand box.
anyway can you elaborate more about this?
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Re: Pulley system that can go slack

Postby Esharc » Tue Mar 14, 2017 11:20 am

That is great news :)

Yes, the red overlay in the image is the pulley system I am talking about.

In the Youtube video of the machine that I posted between 5 and 10 seconds in, you can see that when they place the bucket on the ground, there is no tension in the rope between the bodies and the pulley. Then he drags the bucket to collect whatever they are mining, and when he lifts the bucket again, the rope is pulled tight again. This is what I mean with "slack"

So maybe if I can put it simply, if we have two rigid bodies connected with a fixed length rope around a pulley body. Then if the pulley body is lowered and the two connecting bodies are on the floor, then the rope will not have the tension from the two bodies anymore.

I am currently using Newton version 3.13. But I can upgrade to the newer version if I have to to get this pulley system working.
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Re: Pulley system that can go slack

Postby Julio Jerez » Tue Mar 14, 2017 1:31 pm

Oh I see now, the wheel in the center slides and move the change from one side to the other.
That would required a better model of a change than a single rigid link.
Yes that can be done easy and with the help of some fiddling tricks to make it practical.

The first step for you to upgrade to newton 3.14, the version committed is very close to final stable release candidate for 3.14 and it should be easy to migrate from 3.13
Then what can do is that we can add a new demo to the sandbox calling it excavator, and there we can try few ideas.

The pulley joint in the custom joint, is not going to model a rope or a change, I believe that will required a series of joints so that it can model the effect of the rope losing tension.

For that we may need to make a dedicated joint that combines the functionality of the pulley and a universal joints into one. But that's the specialty of the engine.

The reason you need to upgrade to Newton is that like I explained before, when I move to the iterative solver, in 3.xx modeling contractions of articulate bodies in newton became a black art like in many other engines, but that bothered me a lot, so I decided to take a another pass at the original solvers and see if I can adapt it to solve errors in the joint solver.

It took me several iterations and with the help of people like Joe that provided me with challenges to resolve, now we do have a true exact solver that removes the biggest uncertainty people get when something does not work as expected. which is that we never know if the errors come from a bad design or from the solver been incapable of resolving the articulations errors.

We still have to deal with other uncertainties: numerical errors, condition numbers, non holonomicity, integration errors, and so on. but we do not have to deal with solver errors which is the hardest to deal with and why physics engine modeling is a black art, and thrust me it is a black art, some people try to pass hankered and kludge like "Long distance Constraints and Joint duplication" as "brand new breakthrough in the laws of Physics"

Anyway once you update to 3.14 and we get the basic of the functionality in the sand box you can take it up from there an elaborate all you want on your own, and we can use that demo to share new issues as the come up.

Does that sound reasonable?
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Re: Pulley system that can go slack

Postby Esharc » Tue Mar 14, 2017 3:07 pm

Thank you very much.

I will update my Newton release when I get to the office tomorrow morning and take it from there.
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Re: Pulley system that can go slack

Postby Esharc » Wed Mar 15, 2017 6:02 am

Ok, after quite some time and effort (mostly to my own mistakes), I have the latest version of Newton from Github and the Unity plugin installed on my machine.

I am using Unity 5.5.0. I think this will be easier to test development.

The Unity demos look good by the way :D
Last edited by Esharc on Thu Mar 16, 2017 1:43 am, edited 1 time in total.
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Re: Pulley system that can go slack

Postby Julio Jerez » Wed Mar 15, 2017 11:16 am

ha that was fast.
can you make a 2d sketch of how the model should look like?

This will be a good test case to test the Unity plug in, and using eh plugin will be very easy to determine the configuration by simply checking out the inspectors.
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Re: Pulley system that can go slack

Postby Esharc » Thu Mar 16, 2017 3:23 am

I have attached a couple of pictures.

If any of them are unclear, let me know and I will make more.

There are two ropes in the whole system and can be seen from the top down view screenshot that I have added. That helps with the stability of the bucket. If you want I can make a drawing of the front (or top view) like I have with the left view.

DraglineDrawing.png


Dragline Left View.png


Dragline Top View.png
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Re: Pulley system that can go slack

Postby Julio Jerez » Thu Mar 16, 2017 2:56 pm

excellent, I will paly with that this weekend in unity

can you make a large resolution of the screen shoot so that I can see better detail in Paint,
when I open the image the picture is too graining and all detail is lost.
I like to see how you guys are modeling the part around the bucket in a view that is more 3d.
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Re: Pulley system that can go slack

Postby Esharc » Fri Mar 17, 2017 1:16 am

Here are a couple more images. I hope they are better. Let me know if there is another angle that you would like it from. These are 3 views from the bottom. I cannot attach more than 3 images, so I will add another three from the top in another reply

Dragline Bottom View 1.png


Dragline Bottom View 2.png


Dragline Bottom View 3.png
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Re: Pulley system that can go slack

Postby Esharc » Fri Mar 17, 2017 1:18 am

Here are the three from the top

Dragline Top View 1.png


Dragline Top View 2.png


Dragline Top View 3.png
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Re: Pulley system that can go slack

Postby Esharc » Sat Apr 08, 2017 12:59 am

Hi Julio,

I was wondering if you have made any progress on this pulley yet?
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Re: Pulley system that can go slack

Postby Julio Jerez » Wed Apr 12, 2017 1:58 pm

Oh, yes sorry I was absent for few weeks, and I forget about this.

Yes, I was looking at the diagrams, and I can see this present a challenge if we what to make using joint tricks, is it better to just grad the bull by the horn and do it the right wait, beside si some I alwat want to do.

I would be simple to make a special joint that implement the sliding effect but very soon you will find pout that it will do a very small sub set of what is support to do.

I believe is better to implement a realistic rope or change joint, that will be capable to do many of the sing that a rope can do: flexibility and strength
It will not be able to do role but I do not think you are ling for that kind of functionality.

Fortunately the engine is cable to realized that joint without don any changes since a rope joint is a superset of a generic rigid body.
Basically a rope joint is just a joint that connect tow particles tow a particles to a rigid body,
and a particle joint is a body with infinity inertia.

I will start doing the prototype in unity, and make the joint in unity the you can take for there a use it in your engine. That way this will be you own custom version of the engine, I have help many people to do custom stuff like that in the pass.

I starting the prototype now, you let me know if you have objections.
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Re: Pulley system that can go slack

Postby Esharc » Mon Apr 17, 2017 3:04 pm

Sorry for the late reply. I have no objections at this time.
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