# [ODE] Hinge angle convention

yyd_iris@yahoo.com yyd_iris at yahoo.com
Mon Jun 25 11:21:00 MST 2007

```I have the same problem. The joints are left-handed. I
temporarily set axis to be [0, 0, -1].

--- "Ross L. Hatton" <rlhatton at cmu.edu> wrote:

> Hi all,
>
> Is there documentation on the handedness of the
> angle used by hinge
> joints? I have a chain of bodies connected by hinge
> joints:
>
>
> for (int i = 0; i < NUM_SEGMENTS - 1; i++)
> {
>
> //create the joints
> Joints[i] = dJointCreateHinge
> (World,snake_joints_group);
>
> //attach joints to the body
> dJointAttach (Joints[i], Body[i], Body[i+1]);
>
> //place the joints
> dJointSetHingeAnchor (Joints[i], (i+1) *
> (link_length), 0.0, 0.0);
>
> // joints are vertical
> dJointSetHingeAxis (Joints[i], 0.0, 0.0, 1.0);
>
> //allow large torques when setting velocities
> dJointSetHingeParam(Joints[i], dParamFMax, 1000);
>
> }
>
>
> My expectation would be for the joints to follow a
> right-hand rule, as
> I'm connecting from Body[i] to Body[i+1], and have a
> positively oriented
>   hinge axis.  When running my simulation, however,
> ODE seems to be
> using a left-hand rule.  Is this the expected
> behavior, and if so, is it
> documented somewhere?  All I've been able to find is
> the manual entry
> for dJointGetHingeAngle:
>
> "Get the hinge angle and the time derivative of this
> value. The angle is
> measured between the two bodies, or between the body
> and the static
> environment. The angle will be between -pi..pi.
>
> When the hinge anchor or axis is set, the current
> position of the
> attached bodies is examined and that position will
> be the zero angle."
>
> which gives no information about the sign
> convention.
>
> By right-handed, I mean that if I take Body[i] as my
> reference with my
> hinge axis as [0,0,1], then counter-clockwise
> rotations of Body[i+1]
> with respect to Body[i] should be considered
> positive angles.
>
>
> Thanks for any help,
>
> -Ross Hatton
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> http://ode.org/mailman/listinfo/ode
>

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