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Message from discussion Regarding dJointGetFeedback()
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Daniel K. O.  
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 More options Feb 23 2012, 3:06 pm
From: "Daniel K. O." <danielko.lis...@gmail.com>
Date: Thu, 23 Feb 2012 15:06:52 -0500
Local: Thurs, Feb 23 2012 3:06 pm
Subject: Re: [ode-users] Regarding dJointGetFeedback()
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On 02/23/2012 01:55 AM, Mayank Barnawal wrote:

> I am having a little issue with dJointGetFeedback(). I have simulated
> a modular robot, where every alternate joint servo is made to rotate,
> leaving the other set of servos static.

ODE does not have a joint called servo. You have to tell us precisely
what ODE entities you are using, so we can tell you what to expect from
them.

> However, when I use
> dJointGetFeedback on those static servos, I get some torque values
> (though they should be zero).

A joint doesn't have to be motorized to apply torques. In fact, most
joints have to apply torques to interact with the bodies.

Just a guess here: are you using a hinge joint to keep the axis
constraints, and trying to power it up by using its built-in motor
params? If so, your feedback will contain a combination of forces and
torques, from both the axis constraints and the motor powering it up.
You;'ll have to project the torque along the axis to obtain only the
motor component. Or use a separated AMotor joint to apply the motor part.

> Moreover, if I need to get jointtorque, should I add the values from
> 't1' and 't2'? (Since, if a joint applies t1 to body 1 and t2 to body
> 2, it should experience an equal and opposite torque which can be
> added component-wise)

Newton's third law of motion, the forces and torques will be of equal
magnitude but opposite. So adding t1 and t2 should cancel everything to
zero.

--
Daniel K. O.


 
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