To provide a better view of the action on high school and college football fields, Endzone Video Systems (EVS), Sealy, Tex., developed a portable tower system that lifts a video camera 25 to 35 ft. above the action. To keep the operator from cranking the camera past its stop at the top of the tower and damaging the mechanism, the company incorporated a Polyclutch slip clutch from A&A Manufacturing Co., North Haven, Conn., into its design.
The video systems, first developed by football coach Dan Walling for fellow coaches, are now used by more than 1,200 teams across North America, as well as in Canada, Great Britain, and Australia. Towers are constructed of machined aluminum parts, stainless steel rivets, bolts, cables, and pulleys. To raise the camera and provide a better viewing angle, the operator turns a crank handle that operates a winch that is equipped with an aircraft cable to elevate the camera. If the operator kept cranking once the camera reached the top of the tower, the mechanism or the cable could be damaged.
To prevent damage and prolong the mechanism’s life, EVS incorporated a slipper clutch into the drive mechanism. When the camera reaches the top of the tower, the force exerted on the crank exceeds the limit of the clutch, which slips harmlessly and protects the cable and mechanism. A typical slip clutch consists of two assemblies — cartridge and housing. The cartridge is set screwed or keyed to the input shaft. The housing may be either set screwed or keyed to the output shaft. It also can be attached to the output gear or pulley, with a bronze bearing to allow relative motion between input shaft and output gear or pulley. Compressing the springs with the adjusting nut controls the torque level.
A continuous slip clutch can provide a surprisingly long life in a range of applications. They are available with torque ranges from several oz/in. to more than 1,000 lb/in. Clutch capacity is dependent on torque, rpm, and duty cycle, all of which are interdependent. The friction plate design, when running within design limits, will generally operate for more than 30 million cycles. In most applications, the clutch will outlast the mechanism in which it is installed. For more information, visit www.polyclutch.com.