[ODE] Ode modelling

[Jon Watte (ODE)]

You can create your own joint, that only constrains sideways rotation, 
not twist, roll, or position. This isn't well documented, but you can 
probably start with the hinge joint code and rip out the position 
constraints.

To control an object, it's often easiest to add manual torques and/or 
forces each step, based on where you want to go, and where the object is 
currently going. Thus, determine what facing you want, what facing you 
currently have, and what your current angular velocity is around the 
facing axis. Then apply a torque proportional to how much you want to 
turn, and inversely proportional to your current angular velocity in 
that direction (to avoid overshoot). You will have to tweak the 
weighting constants in this formula -- it turns out that this becomes a 
"PID" controller, which you can Google for general information about. 
The axis and reference frame you want here is world space, not object 
space, btw.

For rolling, just add a bit of torque around the local "right" axis of 
the object.

To avoid falling, you can also use a manual controller like that, if you 
don't want to create a joint. Figure out how much you are leaning based 
on some dot products between local and world axes, and apply a torque to 
correct. Again, make sure to subtract out current angular velocity, and 
avoid oscillation.

Cheers,

          / h+


Lucius Crenshaw wrote:
>
> Hi.
> I'm still in need of some serious help on model my rolling "coin".
>
> What I want is this:
> 1.) A "coin" /cylinder standing on its side.
> 2.) Some kind of motor making it roll.
> 3.) Be able to control the direction its rolling in. (the rotation 
> around the global up-axis)
> 4.) It must not fall on it side, it have to be standing all the time.
>
> 1 and 2 isn't really a problem but 3 and 4 is.
> This is viewed form a top-down perspective and the coin is supposed to 
> always roll towards the mouse pointer.
>
> How can an object like this be modelled in ode?
>
> Is there a joint like the hinge2 that can be attached to only one object?
>
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