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23/06/2008
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Researchers working for NASA have devised a simple mechanism that makes descent rate limiting mechanisms run at constant speed, instead of slowing down as the rope or cable is paid out
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Conventional mechanisms use an unwinding spool coupled to a centrifugal brake, so that as the spool unwinds, the effective radius becomes smaller and the payout speed reduces, but a team led by Tommaso Rivellini at NASA’s Jet Propulsion Lab in Pasadena has devised a way of making the payout speed constant.
As the cord leaves the spool, it passes into an assembly wherein its direction is changed by the first of three idler sheaves, and it is then routed into the first of three grooves on a capstan, which is attached to the centrifugal brake instead of the spool The spool is attached to a constant slip clutch. After completing less than a full circle in the first groove, the cord passes over a second idler sheave, which is positioned to enable the cord to make the transition to a second groove on the capstan. Similarly, a third idler sheave enables the cord to make the transition to a third groove on the capstan. The total wrap angle afforded by the capstan and idlers is sufficient to prevent slippage between the cord and capstan.
Tommaso Rivellini is the lead engineer responsible to ensuring that the various NASA Mars landers made it safely onto the surface. NASA says it intends to post more information as a Technical Support Package at http://www.techbriefs.com/tsp
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Author
Tom Shelley
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