Spring Arm Cam design spreadsheet

Regarding new Vex products thread “Cam”, I have a sample spreadsheet for cam shape design, and 3 pages of power point description and drawings in the attached zip file. MarkO requested I post this in Vex Code, but I assume he means Vex CAD, since it is HW design, not SW.

Goal: make a “balanced weightless arm” using a spring and cam instead of a counter weight.

Overview:
Assume a point mass m at end of massless arm length L, and availability of spring with constant K. As the arm raises and lowers, the change in PE(mgh) of the mass can be coupled to the change in PE(Kxx) of the spring displacement x. This spreadsheet example shows a discrete solution for appropriate cam shapes.

Weaknesses in current model:
Assumes non-stretching tensile cam wrap, connected to perfect spring.
Does not yet account for changes in angle of the cam wrap vector.
springarmcam.zip (38.6 KB)