Team 24 - Manufacturing & Assembly

Link Adaptations

The links went through a few adaptations for the mechanism. The first design for the links is seen below.

The links were designed to reduce out-of-plane movement with a large surface area. At the bearing joints, the links would slide along each other, and the extra material increases the sturdiness. 

Unfortunately, once wired to the motor, the links were too heavy for the motor to move in full rotation, so the team had to adapt to a lighter alternative, re-designing the shape of the links to have a bone-like structure.

This bone structure heavily decreased weight, the T joint decreased from a weight of 64 g to 16 g allowing the motor to rotate the system. The team also lasered the same parts in 1/8" wood and 1/4" acrylic in case they were needed for further weight loss or structure. 

In order to maintain the mechanism alignment in-plane, spacers were added between each joint. Each joint hole was sized for a bearing press fit. These bearings were flanged and facing each other so any axial forces would further push them into the links. In addition, press-fit spacers were printed for any links that needed additional support. 

Base Adaptation

Since the mechanism’s rotation goes below the ground link, a slot had to be created to allow for the movement as seen in the figure below. 

The first iteration is on the left, and the final version is on the right. Some differences are the slot’s dimensions are bigger to allow for more clearance and adjustability as we built the mechanism. Secondly is that the right side of the slot was increased in thickness for stability. 

Additional custom parts

The motor mount was adapted and printed with inspiration from the Pololu motor mount. The original mount did not fully enclose the motor, it provided bolting holes but once tested it did not keep the motor from vibration when run at full speed. So a new design was printed that kept the mount holes and added a hood over the motor to restrict vibrations. 

Secondly, a motor shaft converter was printed. The one ordered did not arrive on time, so the team printed the same design on PETG to resist the torque from the motor. 

Dart Housing and Attachments

In order to house the dart while the mechanism is moving we designed the following dart holders. The dart needed to be held horizontally or slightly higher than horizontal so that when it slides out of the housing it is in the correct orientation for flight. Housing version 1 and mount version 1, were designed to be used on the original mechanism design with the thicker links. They would be oriented in specific positions to hold the dart horizontally throughout the motion.

Version 1-Dart Housing and Mount

Once we shrunk the size of the links, both of these pieces needed to be redesigned. The dart housing now had to be placed at the joint where we would like it to release. This placement required the housing to add a roof so that the dart does not fall off of the mechanism. Version two was quickly designed but it did not have the clearance for all of the fletchings to be upright and it did not hold the dart still throughout the movement so we had to further iterate the design. 

Version 2 - Dart Housing and Mount

In version three, we were able to successfully hold the dart in position throughout the motion by using an additional guide originating from the roof of the housing. This guide worked a little too well and the dart struggled to leave the housing at all and would eventually be thrown out at random orientations and fall quickly to the ground. 

Version 3 - Dart Housing

The housing was adjusted one more time resulting in version 4. In this iteration, the dart smoothly fell out of the housing and stabilized the dart through the motions. Once attached to the mechanism, we had to sand it down a little bit for the dart to consistently release at each loop which can be seen in the videos included in the final prototype. 

Version 4 - Dart Housing

3D Printed Housing Prototypes