Create your comp and one Link layer along the chain bar, with the anchor point at the bottom of the link layer
Create your Bar layer in its hero position
Position the Link layer below the bar layer
Reveal the path of the Bar layer by pressing UU with the top bar layer selected to reveal the path, change to the Selection Tool (v) and select the path, draw a selection around the vertex on the Bar Path you want to use as the starting point, then right click or use the Layer Menu/Mask and Shape Path Menu to set the First Vertex
With the Bar Path selected in the timeline set a single keyframe for Path, then cut it Ctrl/Cmnd + x
Select the Link layer, press Alt/Option + p to set a keyframe for position and then Paste (Ctrl/Cmnd + v)
Turn on Auto Orient to Path on the Link layer.
If needed, select all Position keyframes and use the Keyframe Assistant to Time Reverse the keyframes so the Link layer moves in the right direction
Check to make sure that the link rotates around the path and adjust the position of the last Position keyframe to set the maximum speed that you want to use for the moving link
Duplicate your link layer (Should now be Link 2)
Add a Null to the timeline, name it Ctrl, then add a Slider Control to the Null and name it "Time Offset"
Go to the Link 2 lyer, press "p" to reveal the position and delete the eyframes then press Alt/Option and click on the Posiition property to add an expression
Copy and paste this expression to Link 2's position property l = thisComp.layer(index + 1);
ofst = thisComp.layer("Ctrl").effect("Time Offset")("Slider")/10;
dly = thisComp.frameDuration * ofst;
p = l.position.valueAtTime(time + dly);​
Adjust the Time offset slider to move Link 2 down the path until it is in the perfect position relative to the the first Link layer
Duplicate the Link 2 layer as many times as needed to fill the bar with links
Fine tune the Time Offset Controls on the Ctrl layer to make sure the first Link and the last link lineup properly
Check to make sure that the complete chain moves around the bar correctly
Select all layers and Pre-compose the entire comp and give it a suitable name
Open the Pre-comp, set a guide or take a screenshot so that you can tell when one or two links have move to the exact position as they were at the start of the timeline and then press N to set and out point for the work area
Trim the comp to the work are using the Composition Menu/Trim To Work Area
Return to the main comp, select the Pre-comp and enable Time Remapping using the Layer Menu or the keyboard shortcut Alt/Option + Ctrl/Cmnd + t
Move to the last Time Remapping keyframe, then go back one frame (Ctrl/Cmnd + <) and set a new keyframe, then remove the last keyframe
Alt/Option click the Time Remapping effect in the timeline and add a simple loopOut() expression
You are done. You can control the speed of the chain links by moving the last Time Remapping keyframe up or down the timeline
I have attached a AE-23 and an AE-25 sample comp. This is what it looks like:
The low frame rate of the GIF makes the movement look jerky, but it's fine in the sample compositions.
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