To accomplish (1),(2) and (3), a modular gearbox implementation seemed obvious.

Since the crank of the Jaw mechanism only needs a torque input, any power transmission that gives this torque would be acceptable. (1) is accomplished by making the gearbox modular, and it powers the jaw mechanism via a timing belt.

The gearbox can be mounted anywhere so long as the L-brackets can be fixed. The belts can be tension by simply moving the gearbox mounting point on a slot. The output of the gear is coaxial with the pulley of the gearbox. 

(3) is accomplished using a unique type of geneva mechanism. In essence, the final output of the gear is modified such that a) it is spring loaded somehow and b) it has missing gear teeth to decouple the input from the motor and let the spring "fire" the output gear.

This unique gear configuration enables the mechanism to "snap" at any desired configuration since the start and end of the "snap" motion is dictated by the position and number of missing  gear teeth.

The idea was that (4) was accomplished by the virtue of the design. After the mechanism snaps, the mechanism is reloaded again since the teeth of the gears would re-engage with the input gear. However, the design did not enable this action.

(5) is accomplished In this design by having a wheel with holes for the extension spring. The idea was to have multiple holes that go out radially which the extension spring can mount onto. This enables changing the preload force of the spring to provide more snapping force if needed. 

Manufacturing 

Only requires a band saw, a laser cutter, and a lathe. The band saw is to cut the aluminum shafts, the laser cutter is to cut the two gearbox plates and gears, and the lathe is to make the standoffs that rigidly connects the gearbox together

Design Issues

There are two main design issues. The first is that (3) and (4) had design issues so the snap motion and its reload capability was not achieved at all.

The second was that even if (4) worked, the snapping motion would cause high impact on the output and input gears.

In this design, we tried to address the issues of (3) and (4) not working. We still use the missing teeth method to control the starting and ending snap points of the mechanism. However, the way we load the mechanism is completely different.

We now utilize a lever (light wood color in the image) that has a toggle position. When the toggle position is passed, the mechanism is ready to provide the snap force and motion. The snap force is provided by the extension spring.  The extension spring is connected to one end of the lever and its other end can be mounted to different locations on the gearbox.

Manufacturing and Assembly

We still use the same manufacturing method as in version 1.

To ease assembly, we locate the gears and fix the different components using shaft collars. We also use 3/8" delrin bushings on the shafts to alleviate friction.

Finally, the laser cutter provides the accuracy we need to axially locate the shafts for minimal friction misallignment.

Design Issues

While now all design objectives have been obtained, the output and input gear are still undergoing high-impact after the mechanism has snapped.

In this design, we address the issue of the gear integrity. We also improve and simplify the manufacturing and assembly of the gearbox.

To address the gear integrity we separate the spring loaded output and the missing gear teeth into two separate gears.

The missing teeth is now an idler gear. The output gear is always loaded and will fire when it is no longer engaged with the gear with the missing gear teeth. Since we have full control of everything but the preloaded output gear, we can choose to engage the output gear whenever we desire.

The last final design change is using T-slots as standoffs. The laser cutter is quite accurate so here we use it to create custom and accurate standoffs for the gearbox.