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Dan_Harlan1-Visitor
1-Visitor
May 7, 2013
Solved

MDX Linked Chain Model

  • May 7, 2013
  • 1 reply
  • 6101 views

All, I've put together a linked chain model (like a bicycle chain) and have put in all the individual links with connections (slots and pins) but I've got 2 problems;

  1. Regen time; if I add a planar constraint to each link (which would be redundant) will this help or hurt? Othe suggestions or techniques for modeling this? I need to be able to animate this in the end for a video (and the chain has cleats and other special links on it)
  2. How do I add a motor to this? What I really need is to be able to apply linear velocity along the guide curve (chain centerline)

Thanks


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Best answer by TomD.inPDX

As I will gladly admit, I am no expert at MDX but I know how to make the system work for me if I give it a good nights rest.

Not knowing if it is directly possible, you could think of making a linear motor this way:

1: define a servo motor and control the -position- with either cosine curve set to 0 - 180 - -180 - 0 (this is hidden part A)

2: define a -generic gear- that is linked the servo motor "part A" as a linear slide (see the infamous meter tutorial). This is the slot servo motor carrier (hidden part part B).

3. Constrain the "slot follower" servo motor to the linear slide "part B". Set the timing of part A and the slot servo motor identical.

To smooth out the motion, you will likely need to create a define the motion graph for the slot follower servo motor. It shouldn't be hard to get a relatively smooth velocity throughout the motion. For instance, use position and hold it in position (0 and 180) while traversing the linear distance.

WARNING: ...and disclaimer; I might be making this a lot harder than it needs to be. I don't know if I can make a linear motor with core Creo (or WF for that matter). I also don't know if you are using the Advanced Mechanism Extension which should have a lot more power, like slot motors. I welcome anyone to set me straight if I am overlooking some basic core functionality and show us how to use it.

1 reply

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TomD.inPDX17-Peridot
17-Peridot
May 7, 2013

This sounded like an interesting challenge and I was close in my 1st attempt. I didn't realize you can define multiple constraint sets to control motion. This video should do the trick to get the constraints set up. Remember to size the curve to fit the final link. Not yet sure how to drive this but a slot motor comes to mind or maybe the belt method.

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TomD.inPDX17-Peridot
17-Peridot
May 7, 2013

I learned a few things when trying to follow the video. The two points used for the links -must- be separate datum point features. If they are 2 points made in the same feature, the assembly constraints will fail (drive me nuts!).

I could not figure out how to drive the 1st link as a servo motor. Although I had a logical solution, it would not run through the analysis. It stopped every time it reached the straight line.

Therefore, I added a "drive wheel" consisting of a line. I then added an additional slot constraint to the 1st link to pull the chain along. Obviously, the velocity is not constant as the drive wheel moves the chain. A few behind the scene tricks can compensate, such as a custom motor curve or even moving the motor with another motor. It can get complicated. But for basic Creo's mechanism, I am happy with this result. See if it works for you.

Video Link : 3981

...and if you don't want your links to reverse themselves, I might recommend adding a limited angle range in the Pin constraint.

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Dan_Harlan1-VisitorAuthor
1-Visitor
May 8, 2013

Antonius, thanks. My model already used the same connection types as shown in the You Tube video (some different references). Good to know the datum points have to be separate features. My were already separate simply by luck.

The idea onb the limits on the pin is a really good idea, the flipping problem is very annoying.

I've not had trouble when I only have a few links, but when I put the whole chain together (104 links total) is when performance becomes a problem.

My path has relatively complex geometry, it only has two sprockets, but it does have a couple of glide paths that change the profile. I think that would make the rotational motor give me fits to get close to a constant speed.

Funny, yesterday my search in the forums showed no similar topics, today I see several others. None have the solution for the performance issue though.

Files uploaded as document; http://communities.ptc.com/docs/DOC-3642

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