James Bruton is in the process of multiple robotics projects. One thing that would be helpful for him (and others) in these pursuits is a standard force-controlled gripper, and he shows how he built such a thing in the video below.
His device uses a three-finger design that would be ideal for gripping a variety roundish parts, and is held open by default with bungee cords attached to the outside like tendons. When he needs it to grip something, a trio of metal gear servos pulls on cords attached to the inside of each of the three gripping fingers. Tuning the servo/gripper assembly is accomplished with an Arduino and a potentiometer for user interface.
To figure out force requirements, he inserted a spring in between the lengths of cord used to pull the device closed, and added a bend sensor that allows him to correlate servo input to finger output. With this feedback, the gripper can be made capable of control not just by position, but can react to how much force is placed on an object as well.
While he sees a few design flaws in his current iteration (hinting at a part 2), it’s a great start and the concepts he used could be applied in several situations. Code for the build is available on GitHub.