MAIN_ASSEMBL_TRANS.mpg

[JohnF]

I am learning how to animate, this is my first attempt, however I cannot get the chain to move as there is no chain in mechanisms.  I am sure a belt would animate but this old gearbox had to transmit a large amount of torque hence the duplex chain. Anyone with any ideas please comment.

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[TomU]

Take a look at this tutorial:  http://support.ptc.com/cs/cs_24/howto/apm11043/apm11043.htm

Here's another really old one:  http://www.ptc.com/carezone/archive/newsletters/071702.pdf

[TomU]

Here's another good discussion:  Mechanism flexible wire tray issue, similar to a chain

And several product ideas requesting this:

• PTC Creo-Dynamics Mechanism for Chain
• Chain Connection
• For Gears Avoid Cams and Manage Multi-contacts

[TomD.inPDX]

Very nice work, John.  I remember discussing this when you posted the drawing.

If you can get one link to drag along a path and somehow link it up to a servo motor, you can get the chain to move.

My earlier attempts at this did not allow me to control velocity.  Only the Mechanism dynamic extension has a slot motor which would be perfect for this application.

[JohnF]

Hi

Find posted my, and Tim Brotherhood’s, completed chain assembly, if you can do anything with it let me know.

Cheers JohnF

[JohnF]

TomD its posted as Duplex Chain.zip

[TomD.inPDX]

I can look but it is probably academic version, right?

Somewhere I have a small file where the technique is illustrated.

It looks like a 1:1 drive which makes it easier.  The part I never finished was managing the "draglink" to manage a constant velocity.  there's got to be a clever way to manage a servo motor and a racetrack path.

[TomD.inPDX]

A little more thinking may have a solution that is easy and lightweight on the model.

Quick math:  What is the frame-rate of the video in relation to the gear the chain rides on?

For instance: what if the cycle of 1 tooth on the sprocket to it's next neighbor is only 3.5 frames; and the chain has to move 6 frames to account for the innies and the outies (bike speak).  Therefore, the timing of the mechanism should be such that you can have a whole number of frames for one tooth of the chain sprocket to traverse to it's second neighbor.

Now assemble 5 chains each moving forward only the amount the sprocket moves in each frame.  You are probably already seeing where I am heading with this.

In the animation module, you can swap out the chain visibility for each frame.  You cycle visibility through the 5 chains throughout the video (lots of entries, I know!).

For all intent, this chain is moving exactly as you would see it.  For this example, I am using 5 frames for a 2-tooth transition.  The 6th is the same as #1.  You can use any whole number you wish and backtrack you chain model to account for the correct displaced angle.

It's all math, but using this technique forces you to time the entire video based on the number of frames you will see during this transition.

The Belt feature cheats.  It really doesn't move, it just makes sure the perimeter maintains a certain length based on a free mechanism constraint.  Fairly basic, really.  Energy chains is a much more challenging this.  All chains are just CPU hogs.

Let me know what you think.