Simulink single-link robot arm model example.

Hello.

I would like to ask you guys, if you may, to clarify to me the single-link robot arm motion equation presented in Simulink, on Mathworks site and in their toolbox guides.

What I'm refering to is this example.

where u is supposed to be the torque supplied by the DC motor and ϕ is the angle of the arm.

It may sound stupid, but could any of you explain from the beginning how this equation took its final shape?

Thank you in advance, Mat.

[Chuong Nguyen]

-10 (N.m) is the Gravity Force, assuming the arm length is 1m.The torque created by gravity is -10*sin(phi) .

-2 is the friction coefficient. -2\phi_dot is the moment friction.