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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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Try using the spline tool for the path of a single link. A second spline
would be used for the rotation. Then using the clamp to wrap the spline T
value based on the number of links needed and the spaceing. One you find the
difference between each link this is added to the T value. It should place a
link all around the spline which would be in the shape of the normal path of
a chain around the gears.
I hope this makes sence.
"HENON fabien" <fab### [at] caramail com> wrote in message
news:web.3e7a16dbf3ebf8221fafdf9d0@news.povray.org...
> 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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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 ?
Good ol' memory still working even with no sleep ;-)
http://news.povray.org/povray.binaries.images/12630/
http://perso.wanadoo.fr/mops/atelier.htm
Povingly,
Philippe
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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).
>
You have to separate the chain in portion:
- tight parts
- slack parts
- constrained parts
It is simpler if all your measurement use a link as the unit.
Tight parts are the simplest: it's a straight line and it transmit the
power.
A Tight part is connected to a constrained part at each end, always.
The length of a tight part is an entire number of link.
A slack part is the hanging part which allow the length of the chain to
be an entire number of link, as well as give it the needed elasticity.
The form of a slack part is a catenary (chainette), and you need a
gravity vector.
You can use the slack part to adjust the offset of the link on the other
parts as well as the number of links. (But having more than one slack
part introduce a non-deterministic issue). No power is transmitted on a
slack part.
A slack part is connected to a constrained part at each end, always.
Constrained parts are the parts where the chain is in contact with the
gear (whatever the form of the gear!!!).
Assuming a circular gear with no offset (a well centered gear, the one
you want on your classical bicycle), you can use the tangency of circles
to fix the line of a tight part, that give you the angle from the center
where the constrained part begin.
You then add more links around the gear until you reaches the angle of
exit (if the next part is also tight or constrained).
The hard part of that process is the two borders of the slack part moves
with the offset of the link (but on a bicycle worth it, you have the
tending mechanism which allow you to get the slack part straight (and
not the low part between the tender mechanism and the drive, but shorter
right after the sliding-mesh gear), so it's not really difficult for a
bicycle.
> Could it be done with an include file ?
Yes.
The simplest way is probably to generate a spline for the path, and use the existing
facility to
distribute regular point along that path (that should be fine: no link
the slack part so as to have a perfect chain, if you have a One-speed
children bicyle,
or previously adjust the path length with the position of the tending
gears for a fixed length chain. (that's a little of math, but only with
circle and straight lines, no catenary here!).
You might want to perform the distribution for each offset of an initial
link.
At worst, your bicycle is a 'top-racing' one, with an ellipsoid drive,
and you will have fun adjusting the tending gears according to the
position of the drive (but again, no catenary, simple math !(ok, with an
ellipsoid :-P)
The real headache comes when you use 'strange' gears (ellipsoid,
irregular, heart shaped, ...) and there is no mobile gear to keep the
parts straight...
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Philippe Debar wrote:
Merci pour la macro, c'est exactement ce que je cherchais.
Thanks for the macro, that's exactly what I was looking for.
Fabien
> 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 ?
>
>
>
> Good ol' memory still working even with no sleep ;-)
>
> http://news.povray.org/povray.binaries.images/12630/
>
> http://perso.wanadoo.fr/mops/atelier.htm
>
>
>
> Povingly,
>
>
> Philippe
>
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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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