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Unread 01-02-2009, 19:51
writchie writchie is offline
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AKA: Wally Ritchie
FRC #2152 (Team Daytona)
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by Akash Rastogi View Post
I was thinking, what if there was a way for teams to have a touch sensor near their fan mounts, like really really really close, so that if the propeller moves even like .125" from its original mounting position, the motors to the fans shut off when the limit switch or touch sensor is touched? Seems simple enough to me.
A 12 inch prop rotating at 7500 RPM has a wing tip speed of about 120 meters per second. It stores considerable energy. Even if you could anticipate ALL of the possible fault scenarios and detect when they occur, removing the energy source is not going to change the mechanical energy much over the short term. It's too late to have any effect.

IMHO The only realistic measures are distance from the hazard (used in R/C flying) and containment and only the latter is available to us. For the containment scenario, I think that teams will have to demonstrate that their containment materials and configuration can easily contain a prop failure at max RPM.

There are tradeoffs. Using steel mesh wire, the open area drops dramatically as you increase wire size and reduce mesh spacing. Engineering a mechanism that is both effective and safe is a challenge and either one without the other is just not acceptable.