[ODE] Setting a joint to only apply force to one body

ChrisC zppz at yahoo.com
Sat Dec 2 07:37:44 MST 2006

Correct me if I'm wrong, but when a joint tries to
correct its 'joint error', it applies forces/torque to
both its attached bodies right? I would like to have a
joint which only applies force/torque to one of its
attached bodies to correct the joint error. Is it
possible to do this already somehow?

On the other hand, maybe there is a better way to
solve my problem:
I have a platform joined to the static environment
with a hinge, the axis is vertical so the platform
revolves like a merry-go-round. Another body is
attached to the platform by a slider, and slides in
and out from the center of the platform as it
revolves. When this second body is close to the
platform everything is pretty much ok, but when it
slides further out, it starts jittering around. Since:
a) sliders attached to the static environment are
always rock-solid
b) reducing the mass of the second body improves the
I'm guessing that what is happening is the second body
is being pulled down by gravity, and then the slider
joint tries to fix the error by acting on both of its
attached bodies, ie. each body only gets part of the
fix. However since the first body is attached to the
static environment it will not be affected, so the
error fixing only gets done on the second body, which
is not enough. 
I guess the only way to solve this would be by looking
at each body attached to a joint and if one of them is
attached to the static environment (or closer to the
static environment in a chain of joints), the entire
error correction will be applied to the other body.
Hope this makes sense...
(although what I've described is pretty much a hinge2
situation, I want to have other and longer
combinations of joints chained together so the hinge2
would not suffice in those cases)

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