Today's achievement: a conveyor belt

I'm starting to work on my "Main Menu" screen.  My plan is to have some non-interactive game action going on in the background.  I drew up an idea to implement a conveyor belt.  I had three ideas for this and implemented two of them. 

The first (unimplemented) idea consists of creating a surface that detects collisions.  When an object has collided with that surface, an impulse is applied in the direction of the conveyor belt direction.  I think this would work, but seems kinda kludgy.

The second idea consists of creating several rotating circles (ie. gears).  Here's a picture of that implementation:

It works ok.  It does suffer from objects occasionally getting stuck between each gear.  I've got a 'slop' implemented so the gears aren't fighting each other -- it may take some tweaking to nail that down (maybe add joints or a filter type that prevents gear collisions?)

The third implementation took quite a while to figure out.  It deals with defining a chained set of objects (that I call the ChainLink) and two gears.  I took a bit of thinking to figure out an algorithm to define the chain link lengths and how you can programmatically adjust the width / height.  The biggest sticking point was a snafu I had with drawing the chain to revolve around the gears -- I was using degrees and the (poorly documented) API I was using didn't indicate that my units should have been in radians.  Whoops.  I ran into this before and was a bit frustrated that it was something as simple as that.  At any rate, here's an example of the conveyor belt I made up.

There's still a bit of slop to it, so I added a 'magic' variable that I named 'tension' that allows you to adjust the size of the gears.  This either tightens up a loose ChainLink or loosens up one that is too tight.  I've tried it on a couple of different sized gears / widths between gears and it works pretty well.