## Variables of the double inverted pendulum

I am trying to model the following in a computer simulation:

The Acrobot

However I am struggling to understand which variables stand for which. In particular, the variables not defined are:
• d1 and d2
• phi1 and phi2

Another problem is which order are these calculated in to update the system? d1 and d2 first (as the angular acceleration relies on these).

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 Recognitions: Homework Help Science Advisor d1 is the total moment of inertia, d2 is some part of it related to link 2. phi1 and phi2 are linked to the potential energy of the system. Those variables just simplify the equations, you could insert their definitions in the first two equations and get rid of them - but that would give very long expressions. The angular acceleration needs all 4 of them. Therefore, after each change of angles, re-calculate them.