Unclejake Posted June 8, 2010 Share Posted June 8, 2010 Soooo. I have a wee project about to start that requires me to fabricate a stainless steel sled to carry a diver down to 400 feet. The sled will travel down a previously deployed fixed weighted rope and needs to be controllable for speed. I will be making a diver operated rope brake to slow the sled's descent. The brake itself is fairly simple and is a rotating cam applying variable friction to the fixed descent rope. The brake will be sprung to be 'usually on'. Activating (releasing) the brake is where I need your advice. Basically I need to remotely manipulate a lever on a clevis pin. Cable operation is easy but for various details I shall not bore you with hydraulic operation would be much better. Could a motorcycle hydraulic mastercylinder work reliably if it was rotated as if the front wheel of the bike was on the ground and the back wheel was straight up in the air? Are motorcycle M/Cs sealed to the atmoshere? What would happen if some water got into the hydraulic fluid (remember there is no heat in this braking system)? Could presure be a problem (this guy is going to 14 atmosheres)? Gah!! Quote Link to comment Share on other sites More sharing options...
eke_zetec_RWD Posted June 8, 2010 Share Posted June 8, 2010 they as sealed as you make them. will work as long as the master is below the resivour. stainless cable? Quote Link to comment Share on other sites More sharing options...
isnowi Posted June 8, 2010 Share Posted June 8, 2010 Most MC's that i have seen are vented to atmosphere to accommodate for pad wear... Mind you i haven't paid close attention to many lately... Also 14 atmospheres would probably be a problem for anything hydraulic or pneumatic, I would imagine that unless the seals of the ram or piston or whatever mechanism you use are designed specifically for the purpose you could run into hassles. I'm open to being corrected.... Quote Link to comment Share on other sites More sharing options...
Unclejake Posted June 8, 2010 Author Share Posted June 8, 2010 Fluid is incompressible so I am thinking that if there is no air in this system the pressure of depth may not be a problem? I really don't know Any advice super welcomed Quote Link to comment Share on other sites More sharing options...
bubblegoose Posted June 8, 2010 Share Posted June 8, 2010 the reservoirs are sealed via a diaphragm that is vented on the other side (air/fluid) so as you descend the pressure should equalise if water did somehow get in there youd have no issues as there is no heat. some corrosion maybe but that is all edit, i take no responsibility if somebody dies due to brake failure Quote Link to comment Share on other sites More sharing options...
peteretep Posted June 8, 2010 Share Posted June 8, 2010 couldnt you just use an ascender or descender like a climber uses? just pull a string and it will release, let it go and it will stop Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted June 8, 2010 Share Posted June 8, 2010 magnet activated device? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted June 8, 2010 Author Share Posted June 8, 2010 Too savage Retep. We need more control and less friction when the brake is not being 'used' (p.s. I took a good look at Treetools before I decided I needed to build my own brake) This is a very interesting and challenging design project. Russell - talk more about magnets! Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted June 8, 2010 Share Posted June 8, 2010 Russell - talk more about magnets! something along the lines of those gauges you use on a lath etc for rotating parts with the dial to activate it. iv got no idea what your trying to make or how this could be applied however http://www.indiamart.com/newindianeleva ... rakes.html http://www.ndttech.com/Papers/FluxLeakageWireRopes.pdf neither are a solutions just something to try get ideas Quote Link to comment Share on other sites More sharing options...
David Posted June 8, 2010 Share Posted June 8, 2010 Is it possible for you run some non expensive tests? Drop something down to try it. As already mentioned water cannot be compressed. As far as I know hydraulic brake fluid used in automotive situations is basically water with some anticorrosive additives. So brake fluid would have a slight lighter specific weight compared to salt water. A simple test maybe to fill a small plastic bottle say a soft drink bottle about 330ml with brake fluid with no air. Attach a weight and lower it on a rope to the desired level and then raise it for inspection. A very basic but cheap test. Due to the soft membrane of the container any change in pressure would directly act against the fluid within. Any unequal pressure during this test that courses a rupture, venting or shrinkage of the bottle would most likely guaranty a failure in a hydraulic system using a similar kinetic fluid. It would also be recommended to use an extra bottle for a control and fill it with salt water. (No air) This would test if the plastic bottle was even suitable for test in the first place. I would anticipate that the test would come out fine however the bottle may be slightly shrunken. This would depend on the temperature of the brake fluid at the time when the bottle was sealed. If the ambient and the fluid was about 12degC and the bottle was dropped to 400 feet is would significantly cool the fluid within. At a guess standard DOT4 brake fluid would be at it densest (compact) at about 4.2degC making it shrink. This would likely be so minimal at a volume of 330ml that you couldn’t tell. Over a couple liters of fluid and you may start to see an affect. Quote Link to comment Share on other sites More sharing options...
David Posted June 8, 2010 Share Posted June 8, 2010 Aside from this, make sure you build in some fail safes into you design. Even making a custom system out of stainless steel fittings to prevent any corrosion, I would still be skeptical about the person’s safety. Quote Link to comment Share on other sites More sharing options...
Mike-e Posted June 8, 2010 Share Posted June 8, 2010 As far as I know hydraulic brake fluid used in automotive situations is basically water with some anticorrosive additives. So brake fluid would have a slight lighter specific weight compared to salt water. Tis closer to vegetable oil Quote Link to comment Share on other sites More sharing options...
racepics Posted June 8, 2010 Share Posted June 8, 2010 Could you use compressed air? Along the same lines as hot-air balloons? Add air to slow or ascend - bleed air off to descend? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted June 8, 2010 Author Share Posted June 8, 2010 Good thinking Racepics but variable ballast would be too slow to react. I need the sled going to be capable of 4 meters a second but the diver will probably go slower most of the time (2.5m/s?). When his ears hurt he will need to almost stop the descent to equalise the pressure in his ears and then pull the lever and descend again. David - the brake will be "usually on" and should therefore stop the descent if the diver gets off or if this system we are talking about fails. Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted June 9, 2010 Share Posted June 9, 2010 Quote Link to comment Share on other sites More sharing options...
sentra Posted June 9, 2010 Share Posted June 9, 2010 can you just remove the resoviour and block its port in the cyl afer its bled? Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted June 9, 2010 Share Posted June 9, 2010 Can you even buy a normally on brake caliper in anything smaller than fucking huge? If its going to be a custom setup then you can make it do whatever you want, most brake masters are open to atmosphere because when the piston extends it would otherwise create -ve pressure behind it. please ignore this if you know this im just thinking out loud. The vacuum you will pull in the stroke of a piston will be fuck all you will just need a half decent seal which is required anyways at the depths you are talking. If you are rolling stainless it will need to be completely flushed out if any water gets inside as stainless doesnt like to be underwater/wet for extended periods of time. youd almost want to have an extra failsafe in there. Davy Jones would love to add you to his locker [/useless rant] Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted June 9, 2010 Share Posted June 9, 2010 You could poss modify a mountainbikes slave into something, they are nice and small Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted June 9, 2010 Share Posted June 9, 2010 Oh lol, I read this soooooo wrong. You are only using the master to hydraulicly activate a brake you already have. That should be sweet remove top cap off master cyl. and replace with a custom non vented one and try and assemble with no air at all in the system, testing is essential hah. Make it and dive down to 50 odd feet and use the system and then check for water. Fucking around with lever lengths will get throw/effort right. Roll some sweet seals on the actuator end and you shouldnt get water inside. bleeding all the air out will be a bit of a cunt, but once youve done that it should be sweet. Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted June 9, 2010 Share Posted June 9, 2010 Oh lol, I read this soooooo wrong. DITTO LOL Quote Link to comment Share on other sites More sharing options...
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