I computed potential well and resonant frequency of Roberts Linkage.

Both results were made by material point model.
Potential well of Roberts Linkage of which depth is 250mm was only attached. Beacuse relationship between COM position and depth are same.

Resonant frequency of Roberts Linkage of which depth are 108mm and 250mm wrere attached.
Some measuremet results of which depth is 108mm are far from material point model's ones.
Actually, I don't know certain reasons. I just wrote down some suspicious points I thought.

• When I computed COM position,  there were mistakes.  I think it is most suspicious.
• Material point model was made by some approximation.  That maked some gaps?!
• I confused frequency for angular frequency.
• Basically, results' resonant frequency are wrong.
• Basically, material point model are wrong.