Requirements(s):

The weights shall be released with sufficient exit velocity to deploy the net.

Design Intent:

There are three basic approaches to shooting something out of a barrel: compressed gas, explosives, or springs. Compressed gas systems are expensive, and explosives warrant safety concerns; springs are the best method for this project. 

Implementation:

Wave springs were used inside the barrel because they provide a higher force per inch than compression springs, reducing the height of the barrel. The barrel featured a recessed area for the compressed spring and a threaded hole to attach a plastic spring retainer. The barrel also has a slot for the line connecting the weight and the net.

Requirement(s):

The launcher shall store the net.

Design Intent:

This should be a simple 3D printed net housing, with a pass-through for the winch line, and the lines connecting the net to the weights.

Implementation:

This print was large but straightforward without overhangs. All of the line pass-through locations were filletted to prevent the line from catching during release.

Requirements(s):

A baseplate shall connect the launcher components to the rest of the structure.

Design Intent:

This is one of our more expensive plates, and we barely have the budget or schedule to replace it if something goes wrong during manufacturing. This interface needs to be locked down early so the baseplate can be manufactured while other parts of the system are in development.

Implementation:

The baseplate wasn't reworked, but we managed to have it manufactured early enough in the workflow that a rework wouldn't have broken us.

Requirement(s):

The launcher shall release weights simultaneously.

Design Intent: 

There needs to be a mechanical linkage between all 6 weights and barrels. A rotating release plate would remove retaining keys from all six barrels simultaneously. The ring rotation will be pushing against the friction forces generated by the barrel springs, so a relatively high torque will be required to release the weights.

Implementation: 

The release plate was made of aluminum, and actuation was driven by a second set of springs. These springs were compressed by rotating the release plate. A linear actuator then secured the release plate in place, storing energy in the springs.

Requirement(s): 

The launcher shall have a disarm feature.

The launcher shall be safe from pinch hazards.

Design Intent:

Safety pins need to be incorporated into the design. These are fool-proof mechanical hard stops that prevent the linear actuator from unlocking the release plate and prevent the weights from leaving their barrels.

Implementation: 

7 safety pins were used to disarm the system: one for each barrel, and one for the linear actuator. These were COTS safety pins, and the COTS actuator already had a pin hole. Pin holes in the weights and barrels were easy to incorporate.

Requirement(s):

The launcher mechanism shall accommodate the assembly tolerance stackup.

Design Intent:

If you can't be precise, add adjustability. The structural rods (specifically, the retaining ring cutouts) that hold the mechanism together will be prone to positional tolerance error. An adjustable solution should be implemented to avoid excess friction.

Implementation:

We rested our release plate between a set of shaft collars and the retaining rings. By moving the shaft collars up and down or swapping washers under the retaining rings, we were able to adjust the perpendicularity of the release plate.