Resistance pulley - Does this exist?

[verticaljim]

I am in the process of inventing a new water sport that uses a rope rigging system. I am trying in vain to find a mechanism that applies resistance onto a rope that is passing through the system.

What I have now is a pulley that allows the rope to pass through freely, with no friction or resistance. I want the rope to pass through the pulley at a slower rate, perhaps 35% slower. Is there such a pulley (or other mechanism) out there that simply applies resistance on a rope? What comes to mind is what you see on a chairlift, where the wire cable passes between two sets of wheels. I need a miniature version of this (one wheel on top, one below) with the rope passing through and getting squeezed to slow its movement either direction. Right now, with the rope free flowing, the system is fouling up due to un-regulated rope movement. Does anyone have an idea of where to look for this type of item? I've been searching now for 2 weeks with nothing found in the climbing or safety gear industries. Any help would be greatly appreciated.

 

[plasgears]

An adaptation of a cam lock similar to that used in sail boats may help. The cam lock may be controlled from full lock to slip if the cam is relatively smooth. The usual cam lock is grooved with small teeth to lock the rope.

 

[Warpspeed]

Another way would be to pass the rope one full turn around a pulley, so there was minimal chance of slip, and then use some sort of brake built into the pulley hub.

This brake could be a fluid or viscous arrangement as well as centrifugal/frictional. This brake might apply significant torsional loads to whatever it is attached, but two similar contra rotating pulleys could balance this torque out.

One problem I can see, is you mention water-sports ? Braking a rope or anything else requires friction to be developed somewhere. Things might change rather dramatically and suddenly between the wet and dry condition.

 

[Pekelder]

Try an adjustable rotational damper as is used in automatic closing firedoors etc. It utilises a fluid with shear-speed dependend viscosity, and allows you to set the friction-effect within certain limits. With slow speed, there's little friction, with high speed, there's a lot.

Related: thread406-55486

See

http://www.dictator.de,

look for rotational dampers. There are more suppliers like this.

Regards,

Pekelder

 

[Cevennes]

I have been looking for similar items and came across this site. Look under permanent magnet clutch/brakes. I think this just micht work for you.

http://www.ogura-clutch.com