symbolic derivative of lagrangian & kinematic coefficient

Question

Young Lee 2020-5-7

回答： Guru Mohanty 2020-5-11

Hi

II am working on some mechanical problems.

basically trying to take symbolic derivative of kinematic coefficients for the purpose of checking my hand calculations..

so here is the position scaler ; r2 cos(th2) - r3 * cos(th3) = 0

taking derivative with respect to th2 (theta2) , Vx = -r2 *sin(th2) + r3 *sin(th3) * d(th3)/d(th2) - cos(th3)*d(r3)/d(th2) = 0

and differentiate again for acceleration with respect to th2

Could you please explain on how this can be achieved using matlab?

Answer 1

Guru Mohanty 2020-5-11

Hi, I understand you want to find the first and second derivative of the following expression. You can do this by the following steps.

Here is a sample code for it.

syms th2 r2 th3(th2) r3(th2)
disp = r2*cos(th2) - r3*cos(th3);
vel=diff(disp,th2);
accel=diff(vel,th2);