Fabien,

My approach would be to write an include or macro to calculate the position
of each link and the rear sproket based on the rotational position of the
front sprocket.  There are, of course, a few finer points to work out, such
as:

1. Keeping the two sprockets in sync.  The rear sprocket should rotate at an
exact multiple of the front sprocket (if the front rotates once, the rear
should rotate exactly 3 times, or some whole number like that).

2. For a single speed bike, the length of the chain must exactly fit the
path, and the position of the two sprockets needs to mate with the chain,
of course.  Simple math and trig to calculate that.

Questions I woud ask myself if I were doing this:
1. Do you want the lower part of the chain to be taut, as on a single-speed
bike, or slightly slack, as on a multi-speed bike? (There is a macro for
those kinds of curves, isn't there?)

2.  If a multi-speed, the chain will angle in or out some between the two
sprockets, depending on what gear you are in.  Point #1 would need to apply
to each rear sprocket.

3. The whole rear end gets real complicated to model in motion for a
multi-speed bike.  The tensioner does not remain in a static position as
the speed of the chain increases.  Could this be ignored? (if the animation
is not required to be in great detail or run at multiple speeds it could)

4. The motion of the chain as it changes gears is not easily described.
Perhaps some slow motion video of the system moving would help to model it.

    Randy


HENON fabien wrote:
>I know that there must be several ways to do it.
>
>My question is simple. How would you do to make an animation of links of a
>bicyle chain running on its chainwheel and cogs, (keeping in mind that the
>each link has to be rotated, then translated to its proper place).
>
>Could it be done with an include file ?
>
>Thanks
>
>Fabien H
>

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