On July 11, 2006, about 1133 Pacific daylight time, an experimental Velocity 173/RG-XL, N992PC, had a landing gear collapse during a hard landing at Modesto City Airport, Modesto, California. The pilot/owner/builder was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The local personal flight departed Modesto about 1125. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot planned to do a touch-and-go landing on 28L. He stated that the airplane ballooned after initial touchdown due to too much elevator trim. It began to fly again at approximately 57 miles per hour, which was under the stall speed of 63 miles per hour. The airplane then landed "very hard" farther down the runway. The gear collapsed; the rudders contacted the runway, and sustained substantial damage. The pilot reported that the airplane had a total airframe time of 89 hours. It had an annual inspection on November 15, 2005, 9 hours prior to the accident. He said that a hydraulic actuator drives a set of cables, which move the landing gear extension/retraction mechanism. The cables attach to the main gear struts. The cables provide the force to extend the locking mechanism to the over-center position. The pilot/builder does the maintenance on the airplane, and had adjusted the cable tension several times. He surmised that he had the landing gear cables set too tight. Coupled with the hard landing, he felt that this caused the main gear over-center linkage to release from the over-center position.