UVU Pendulum

Steve Koski and Dave Erhart (Clark Planetarium volunteers) were given the opportunity to help with UVU’s pendulum. The UVU Pendulum is Academy Pendulum Sales 47th pendulum, built 1989. It is a generation newer than the Clark Planetarium (APS #18, built 1967). In early 2026 the UVU pendulum was behaving badly, precessing faster than 24 hours (should be about 37), then stalling completely, making double tap and clunking noises, and other irregular behavior at the top. On 1/24/2026 Dave and Steve adjusted the two driver settings, magnet current amplitude and time on, but without any real success. From a distance, it appeared that some of the O-rings were missing. On 4/29/2026 with a scissor lift we found that four of the five O-rings were missing entirely, and the fifth was split with a significant gap. After replacing them, the pendulum is performing like new, with barely visible minor axis ellipsing that may be removable with further tuning, and is precessing near the expected 37 hour rate. The O-rings give a gentle consistent contact with the upper surfaces, which suppresses minor axis ellipsing, which if allowed to persist adds to or subtracts from the major axis precession that a Foucault pendulum is supposed to demonstrate.