[ODE] dBodyGetForce returns zero force

Jon Watte (ODE) hplus-ode at mindcontrol.org
Thu Jun 28 15:11:51 MST 2007

If you go this route, beware that, because of the way the integrator 
works, certain joints may be very jittery from frame to frame, but be OK 
in the averaged case. I would recommend returning a force value averaged 
over at least the last four frames to get a de-jittered value. Also, a 
leaky integrator only has 6 dB/oct rejection for jitter, so it may be 
better to integrate some known number of steps each time, rather than 
trying to keep a running average. (Illustration of the bad, 6dB/oct, 
running average method:  blah = oldBlah * (1-lambda) + newBlah * lambda)


          / h+

Gazi Alankus wrote:
> I think that only returns the forces that you applied to the body. I
> had to modify my ODE source and add a dBodyGetPrevForce() to get the
> force that was used in the last iteration.
> -Gazi
> On 28/06/07, PKS123 <prashant.coder at gmail.com> wrote:
>> Hi
>> I am using the dBodyGetForce() function to find out the force on a body
>> which is in free fall.
>> The function is returning a zero vector.
>> I noticed from the ODE Documentation that the force accumulators are set to
>> zero after each time step. So, I put the function both before and after the
>> dWorldQuickStep() function but the value was zero in both cases.
>> The Body has a mass of 100, and so the minimum force that I should be
>> getting is m*g ie. 100*9.8
>> But I get a zero force. Could anyone suggest what might be wrong.
>> Thanks and Regards
>> PKS123
>> --
>> View this message in context: http://www.nabble.com/dBodyGetForce-returns-zero-force-tf3993241.html#a11339547
>> Sent from the ODE mailing list archive at Nabble.com.
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