1. Servo-Finger Linkage as Parallelogram
With a parallelogram linkage, the finger will move through the same angle as the servo arm. For example, if the finger needs to open 120 degrees, the servo needs to move 120 degrees. The servo mounting must allow the servo to move the required angle.
Link length
Link
part
Servo
arm
length
Finger
Hinge
part
Hinge pivot
(Link attachment point)
Parallelogram
Servo
pivot
Finger
arm
length
Servo
For a parallelogram linkage, the Servo arm length must equal the Finger arm length (as shown), and the Link length must be the same as the Pivot center to pivot center length. The Link length is the sum of the Link part and the Hinge part lengths.
Finger
hinge
pivot
Pivot center to
pivot center length
The Servo arm length determines how much of the Servo torque will be applied to move the Finger. The Link attachment point (here the Hinge pivot point) must be at a Finger arm length from the Finger hinge pivot, to match the Servo arm length and form the parallelogram.