Modelling the arms was challenging because I had to turn three-dimensional motion into two-dimensional motion to be consistent with the techniques learned in this class. For the purposes of this analysis, I looked at the bear from the side and I said that the arms were a 5 linkage system with a slider joint as shown in the diagram to the right. I did the analysis based off of this diagram and measurements I took while building itthe mechanism. I said that the angle between L4 and L5 (the upper arm and the forearm) was 90 degrees and the input crank moved with a constant w2 = 10 deg/s and a2 = 0 deg/s^2. I also used the position, velocity, and acceleration of L3 that I calculated while calculating the position of the head.
The position and angle of the arms is shown in the following adjacent graph. I looked at the vertical position of the forearms in the same plane as the head (vertical or y) and the forearm's angle from horizontal. The arms move in the opposite direction of the head, i.e. when the head goes up the arms lower to reveal the head and when the head drops back down the arms go up to hide the face.
Next I looked at the linear and angular velocity of the arms by taking the derivative of the positional loop. For the purposes of this graph y is defined as up and down along the motion of the head (direction of head motion) and x is defined as the forward motion (towards and away from the nose). I also calculated the linear and angular acceleration of the forearms as seen below by taking the derivative of the velocity vector loop.
