# ME 321 Homework

## hw2 #3

Does anyone know how to relate points D and C to the loop closure equation in question #3? I have the loop closure equation as L1i+L4i4=L2i2+L3i3
As we discussed in class today, points D and C are not part of the loop closure equation. However, once you solve the loop closure equation for the angles (and likewise the velocity equations for the angular speeds) you can use these to go back and determine the position and velocity of any point in the mechanism.

I guess I’m confused on how to solve for the velocity. I found the angles and angular speeds through position and velocity analysis, but am not sure how to relate that to the velocity of D and C. I am trying to go off of problem 6 from hw#1 where the velocity of B was found in the i and j directions, but I’m not sure where that came from. is it always distance times angular speed in the j directions?

Once you have the angles and angular speeds from the position and velocity analysis, then go back and find, for example, the position of D with respect to a point fixed in the ground. Knowing all of the angles you can find this vector. Likewise, the velocity of D is found by evaluating the change in position (taking a derivative) and then using th known angles and angular speeds.