Just One More...
Pedaling Composite Materials
Composite replaces aluminum casting
and acetal bushing in drive mechanism
 For marine enthusiasts who desire a lower-body workout,
Hobie Cat, Oceanside, CA, offers a Mirage Kayak with the patented Mirage
Drive foot propulsion system. The drive's pedals connect to supports that
pivot on a stainless steel shaft. Three cables attached to this shaft push
and pull on several chains, driving sprockets that move semi-flexible fins
back and forth. The fins twist and flex like the wings of a penguin, moving
side to side in a circular motion to thrust the boat forward.
Previously, the drive mechanism used cast aluminum supports with an acetal
bushing that lost its stiffness after one or two seasons. The pedals developed
"extra flop" in them, allowing them to slip sideways. Such flexibility
in the pedals produced slack in the cables, which in turn allowed the chain
to skip a tooth in the sprocket. Hobie Cat searched around for alternative
materials, conducting extensive fatigue testing; Verton RF Composite, a
long glass fiber-reinforced nylon 6/6 from LNP Engineering Plastics, Exton,
PA, was found to have wear resistance far exceeding the aluminum casting
and acetal bushing.
Exposure to water did not pose a problem; although nylon tends to degrade
in water, the Verton composite retains its strength under these conditions.
According to Greg Ketterman, Vice President of Engineering at Hobie Cat,
"Once we found that [Verton] was stronger and stiffer and had less
abrasion, we didn't consider any other material." Ketterman also said,
"Once we switched to the Verton composite, the pedals remained tight."
Other companies have replaced metals in such applications as an automotive
shifter base, pneumatic nail gun housings, automotive safety restraint housings,
and an automotive sunroof bracket with glass-filled Verton polypropylene
and nylon composites. The high strength, lower weight and reduced cost per
cubic inch makes this family of composites an attractive substitute for
traditional materials. --SG
For more information:
Circle 705 - LNP Engineering Plastics Inc, or connect directly
to their website via the Online Reader Service Program at http://www.OneRS.net/106df-705
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