Background

Designed and created in 1995 by previous MAE 156b students, and completed by the Finisher's Club, the nine foot tall clock uses a weight and pendulum to tick accurately at a two second period. Over time, weathering has bested the clock inside and out. Through a series of improvements, the team worked towards bringing the Jacobs Hall Clock back to it's former glory. 

As mentioned above, the energy from the weight is transferred through the differential system, to the main gear train to turn an escapement wheel. While the pendulum swings, the escapement pallets regulate the escapement wheel's motion while regaining lost energy from drag and friction. When the weight falls completely, a mercury switch activates a motor which rewinds the weight to the start height. During this phase, a differential allows the pendulum to continue to power the clock. 

At the start of this project, the clock had minimal functionality as friction brings the system to a half after only a few minutes. As the team studied the gear box, one gear on the differential gear train became loose, causing the weight to free fall without any useful transfer of power. When solving this issue, the team discovered that the pin holding this gear was fractures, and only worked from accumulated dirt and grease holding it in place previously. This piece was improved and replaced, bringing back functionality to the gear box. To improve runtime and accuracy, key aspects of the system were identified and prioritized. These components include the warped suspension spring, the chipped escapement pallets, corroded bearings, and worn differential. Due to time constraints, enclosure refurbishment and self-correction implementation remain incomplete. However, the team has high hopes that TRI continues these endeavors with the foundations that have been laid. 

The changes made before reassembly include replacement of frame spine, bearings, pallets, differential, a full cleaning, and re-anodizing of all frame components. The frame spine was remanufactured to improve the bearing slots, since the original spine required bushings to create an accurate hole size. Bearings were replaced with stainless steel shielded bearings to balance low friction with dust protection. The complicated pallet shape was digitally probed to allow for simple reconstruction and simple periodic replacement. The differential replacement, cleaning, and re-anodizing were all completed to reduce friction and improve aesthetics of the gearbox.  A deeper look into these changes, as well as our maintenance plan and self-correction proposals can be found here.

The performance results of these changes can be seen below;

With minimal testing and adjustments, the restored Jacobs Hall Clock successfully achieved a runtime over 19 hours before being manually stopped due to time constraints. The system now operated with a tick accuracy above 90%, marking a major improvement from initial testing which show a mean runtime of 3 minutes and a tick accuracy below 50%. One remaining issue is the off-center alignment of the escapement wheel, which introduces a high point at each revolution. This misalignment makes it difficult to consistently set the correct pallet distance, which causes ticking inconsistencies that the low minimum runtime and high standard deviation can be attributed to. However, once this and the final pallet positioning are resolved, the team is confident the gearbox will be fully prepared for integration into the newly refurbished enclosure. 

University of California, San Diego

Department of Mechanical and Aerospace Engineering 

MAE 156B: Senior Design Project

Sponsored by Dr. Nathan Delson and TRI 

Jonathan Dela Cruz | Irving Ding | Fatima Fazli

Fernando Gochicoa | Lacey Potter