I'm being pedantic.
La = gc + lw * ka / kp
where
La is the total arm length,
gc is the constant distance between gear centres,
lw is the length of wire that the stepper moves
ka is the mechanical disadvantage of the arm (these arms are third-class levers)
kp is the aggregate mechanical advantage of the pulleys
The real difference here is gc.
Not quite. I mean, it's close enough to make little difference, but I think it's an important distinction. The PGJD has an additional term:Quote
nicholas.seward
The Annirak Drive or the Proportional Gear Joint Drive both make the relative rotation of one of the steppers proportional to la, lb, or lc.
La = gc + lw * ka / kp
where
La is the total arm length,
gc is the constant distance between gear centres,
lw is the length of wire that the stepper moves
ka is the mechanical disadvantage of the arm (these arms are third-class levers)
kp is the aggregate mechanical advantage of the pulleys
The real difference here is gc.