# Two torqued and hanging constrained rods

1. Jan 28, 2010

### pc100

1. The problem statement, all variables and given/known data

This is a general situation that I'm trying to figure out. Say there are two massless rods connected with a revolute joint, and one of the rods' other free end is connected to the wall with a free pin joint. There are two point masses in the system (see attachment), so the system is in a double pendulum configuration.

Now a torque τ appears between the rods only. What are the equations describing the motion of the two masses?
There's no gravity (i.e. this is sideways in a plane, for example)

Intuitively both the bottom and top masses will rotate and displace around some pseudo-center-of-mass point (the green dot P?), and with different displacements. I drew this guess onto the figure as well.

2. Relevant equations

These are not correct:
where I(m2 about P) = m2 * r(b to P)^2
and
where I(m1 about P) = m1 * r(a to P)^2

3. The attempt at a solution

The problem is that the wall is causing some strange behavior of the system, and I don't know how to approach this in closed form due to the constraint of the wall... Hints?

#### Attached Files:

• ###### torqued rods.GIF
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2. Jan 28, 2010