Petal System

Component Design

PETALS:

The defining feature of the iris box is the opening and closing mechanism for the petals. The petal system was first designed in SolidWorks, by dividing a 5" diameter circle into five evenly sized, curved triangular petal faces and a collision simulation was run to verify unobstructed opening. Notably, the petal opening dimension was limited to 5" due to limitations in 3D printer bed space for the printing accompanying 9" in track. Taking inspiration from Evan's design, a simliar petal subsystem including a support, shaft, arm, dowel, and ball shown below was implemented and fitted for a five petal approach.

TRACK:

The opening-closing (OC) and rising-falling (RF) mechanisms of the petals are entirely governed by the petal ball riding along a cam track. To design the OC motion, an arbitrary acute angle between the petal and petal arm was fix in SolidWorks and the tangent point of the ball was traced in the open and closed orientations to generate two circular paths. A 90° section of the circles was cut and an arc was used to connect the two rings, creating a path from the open radius to the closed radius. Next, the path was divided into threesections: 1) 22.5° for lowering the petals, 2) 22.5° for opening the petals, 3) 45° for keeping petals open & allowing space for the bowl to rise. Notablity, these angles were selected to balance motion speed with motion smoothness.

To design the RF motion, a depth profile was created on a diagonal plane intersecting the the starting and ending points of the track. Next, a Sketch-To-Sketch Projection was used to create a 3D Sketch combining the OC surface profile with the RF depth profile. A slot was then Sweep Cut along the 3D Sketch and Circular Patterned for five total grooves.

Material Selection

Material selection was critical both to the functionality and visual aesthetic of the project. From early prototyping with only 3D printed pieces, two major challenges were identified for for the petal subsystem: 1) Friction and 2) Rigidity and alignment.

To overcome friction, the interaction between the balls and track was targeted. Slippery PTFE balls which have one the lowest coefficients of friction of any solid were used. While the team originally planned to machine the track from UHMW Polyethylene, lack of a 0.5" diameter, 0.75" LOC ball-nose endmill forced the team to pivot to 3D printed alternatives with extra fine layer lines. To futher reduce friction, the track and balls were lubricated with cutting fluid from the Machine Shop.

To overcome issues with rigidity and alignment, the petal subsystems were made of aluminum and steel. Moreover, set screws were used in the petal supports and arm componets to ensured the orientaion of these components remained fixed relative to each other during use.

Assembly & Integration

In terms of assembly, the pressfit components like the petal / petal support and the ball / dowel / arm were connected first. Next, a custom alignement block set to the required height was used to set the height of the arm along the petal shaft. Lastly, the petal shafts and petal face were aligned in the cage and setscrews were used to lock the pieces in the correct closed orientation.

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