Lagrange equations in Control Design and Simulation

[spalinowy]

 Hello,

I'm trying to make the Lagrange equation from the kinetic energy in Control Design and Simulation. However I must first calculate derivate by the speed and then after a time. Derivate by the time is easy, but how to calculate the derivate by the variable?

[jozef.liptak]

I am not really familiar with mechanics but: You can solve it analytically, and then program the solution into labview 🙂 or just do a little investigation and if I am right, then Lagrange equations are second order partial differential equations, so you can try to find ready to go VIs in LabVIEW to get this solved. Most probably something from here will help you:

http://zone.ni.com/reference/en-XX/help/371361G-01/lvanlsconcepts/solving_daes/

http://www.ni.com/example/31306/en/

http://zone.ni.com/reference/en-XX/help/371361M-01/lvanlsconcepts/solving_daes/

http://zone.ni.com/reference/en-XX/help/371361M-01/lvanlsconcepts/solving_odes/

http://zone.ni.com/reference/en-XX/help/371361M-01/lvanlsconcepts/ode_solvers_in_labview/

or a more general crossroad:

http://zone.ni.com/reference/en-XX/help/371361L-01/TOC115.htm

and finally the VIs:

http://zone.ni.com/reference/en-XX/help/371361M-01/gmath/ode_solver/

http://zone.ni.com/reference/en-XX/help/371361M-01/gmath/dae_radau_5order/

Those VIs can be used also in Control and Simulation loop, but maybe you can calculate the parameters outside, and then just wire them to the C&S loop. Depends what you want to achieve (except doing home work 😉 no offence)... 

B/R

[spalinowy]

Thank you for your answer.
However, the analytical approach is very easy for a simple mechanism, but the coordinates junction and a few lumps of it is already difficult issue. That is why I am looking for a different approach.