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This Floating-Opposing-Arm (FOA) Centrifugal Clutch, developed by the BYU CMR lab, utilizes compliant mechanism technology to produce a high performance clutch with only two components. The clutch shoes are fabricated from a single piece of material and the flexible segments connecting the shoes eliminate the need for springs. The two parts of the FOA clutch can be seen below.
What is a centrifugal clutch?
- A clutch that uses centrifugal force to engage two concentric shafts.
How does it work?
-The torque is transmitted from the central drive hub through the floating clutch shoes to the outer drum. Since centrifugal clutches rely on centrifugal force to actuate, there is increased engagement and friction between the shafts at greater speeds. Likewise, as the drive hub slows down, the floating clutch shoe retracts and disengages from the outer drum.
-low part count
-easy clutch assembly and replacement
-symmetry that allows for use in either rotational direction
-higher torque than non-aggressive shoes
-smoother start than aggressive shoes
-low probability of self-locking
-adaptable to a variety of materials and loads
Printed with PLA
Inside Piece (central drive hub, blue) - 50 to 100% infill
Outside Piece (floating clutch shoes, green) - 40% infill
Cylinder Wall (outer drum, orange) - 20% infill
If not printing for actual use, 20% infill on all 3 parts is okay.
This FOA clutch (originally milled out of steel components) was designed to work in a chain saw. The clutch replaced the original 4 piece clutch while allowing for a reduction in part count and assembly. The FOA centrifugal clutch has also been used in weed wackers, which are usually equipped with two 1/8" thick s-clutches. A single FOA clutch 1/8" thick replaced the two s-clutches. This device shows potential for other lawn and garden equipment as well.
The FOA Centrifugal Clutch (steel) on a chain saw
Original 4-piece centrifugal clutch (left), and the FOA clutch without the nested driveshaft (right)
FOA Centrifugal Clutch (steel) customized for this weed wacker
Experimental setup on a dremel. Central drive hub (blue), floating clutch shoe (green), and the outer drum (orange).
Slow motion capture of the clutch shoe expanding and engaging the outer drum. Taken at 2000 frames per second as the dremel goes from 0 to 5000 rpm.
Water jets, laser cutters, and milling equipment could also be used to produce the FOA Compliant Centrifugal Clutch.
Milled out of steel (left) and cut with water jet out of polypropylene (right)
By Howell, L.L. , Crane, N.B.
U.S. Patent No. 6,736,249