SIMONS ARRAY POLAR BEAR TEAM:
PB-2B RECEIVER CRADLE
MAE 156B | Spring 2022
Team: Shannon Lo, Nathan Han, Stephanie Cote, Ray Nunez
Sponsored by: Dr. Sean Casey
Embedded Files
Figure 1.1: One of the Simon's Array Telescopes
Figure 1.2: PB-2B Receiver lifted into telescope
Figure 1.3: Receiver hanging after lifting failure
Overview of Project
Check out our full report here
Background:
The Simons Array is a suite of three telescopes stationed in the high Atacama desert of Chile (Fig. 1.1). The telescopes and associated receivers are designed to detect and characterize the fluctuations in the Cosmic Microwave Background (CMB). The objective of the Simons Array is to obtain and analyze data about the earliest phases of the Big Bang.
Problem Definition:
In each telescope, there is a Polar bear (PB-2) receiver that weighs 1600 lbs (Fig. 1.2). Thus, this requires a hoisting mechanism that not only lifts this weight onto the mounting fixtures inside of the telescope, but prioritizes easy-to-follow installation instructions and the safety of the people installing it. In the original design, the hoisting mechanism experienced failure (Fig. 1.3) where the the wrong fasteners were used, causing the threaded holes to strip (Fig. 1.4) and the receiver to fall as the straps lost its tension (Fig. 1.5).
This caused various damages in the receiver and its optics tube. The goal of this project is to understand the current issues with the Simons Array Hoist Assembly and recommend any alternative approaches to improve safety and reliability concerns. For the mechanical design, the team's goal is to create a cradle that will support the receiver on all sides by minimizing major stress points and will contain lifting points for chains and straps, while also avoiding interference with other parts of the telescope (Fig. 1.6 and Fig. 1.7).
Figure 1.4: Stripped threaded holes, post-failed lifting procedure
Figure 1.5: Lost tension of straps, leading to the tipping and hanging of receiver
Figure 1.6: Initial stress-concentrated mounting point for lifting the receiver
Figure 1.7: Interference Area above the Reciever
Functional Requirements of the Cradle:
Figure 1.8: Receiver on existing cart
Must support the weight of the receiver (1600 lbs.)
Must be able to be built around the support cart shown in Figure 1.8
Cradle must not interfere with extraneous hardware that will be attached to the receiver and telescope
All components must have at least a Factor of Safety (FOS) of 5
Avoid collision with connecting support truss on the telescope
Considers the off-axis center of mass of the telescope
Durable in potential extreme weather and environmental conditions of the Atacama Desert
Lightweight (less than 50 lbs. per side; less than 100 lbs. in total)
Final Design Solution and Hardware Performance
Overview:
The final design decided upon by the team is a truss structure that attaches to an existing I-beam on the Simons Array receiver. The structure will be referred to as a “cradle” as agreed upon by the sponsor and the project team. The cradle is split into two halves that are mirrored and built on both sides of the receiver opposite its optical axis. On each half, there are hook attachment points that provide rigid points to lift up the cradle, and as a result, lift up the receiver. The final dimensions for one side of the cradle are approximately 40in X 15in X 15in with a weight of 40 lb, leading to a total weight of 80 lb.
Figure 1.8: Isometric view of final cradle design
Figure 1.9: Full assembly and PB-2B Receiver on cart
Copy of [21] Powell Labs TestingTesting 875 lbf of weights on the PB-2B Cradle at Powell Labs
Manufactured Cradle and Hardware Performance
The Simons Array Polar Bear team was able to successfully manufacture and test the cradle as shown in the video to the left. During manufacturing, several challenges included machining large parts to tight tolerances and working around these tolerances when assembling. Overall, the team was able to navigate through these obstacles and was able to build a cradle that underwent successful testing.
The results of testing are as follows: one half of the cradle was able to withstand a 875 lbf load without deforming or yielding. Some sliding of the 80/20 slots occurred during to improperly fastened joints, but this was resolved by adding additional fasteners for additional security.
Final Poster
Check out our final poster to see a summary of our entire project!
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