Help...Anyone ever use a set of hydraulic motors for pedal drive?

[Guest625101138]

Originally Posted by riverliver2b

Rick W.....very cool propulsion! did you adapt an off-the-shelf weedeater shaft or is it completely scratch-built?

The shaft is just a 4ft long 8mm OD piece of 2011 T8 aluminium rod fixed to a larger steel tube that mounts on the right angle drive. The prop and water stabilises the whole thing when you go forward. In reverse the prop wants to dive so it needs to be restrained. It will also clip the hull if you get into waves while turning so again there is need for restraint to limit how far it moves.

Point is you can make a very simple flexible shaft that will bounce over logs or rocks without incurring damage to the prop.

Rick W

[TeddyDiver]

Originally Posted by alan white

The problem is that when any liquid gets compressed, it heats up.

This is not totally true. It's true for gases, but liquids only theoretically becouse they don't considerably compress through pressure. The heat still is the way how hydraulic transmissions lose energy, but it comes from the fluid friction (eddies) and pressure reliefed throw pressure valves.
Some hydraulic systems can be up to 90% efficient when it normally stays in 70% in closed circuit and less in open circuit systems. Best effiency can be gained in such "man powered" system where fluid velocity is moderate (large diameter piping) and pipes are short and straight..

[TeddyDiver]

Originally Posted by jeremy360

Whats the best smaller diameter prop (shallow water)

This is where you lose the most of the energy. I mean the small prop you need. Why not to forget the prop and make a water jet of a pump. It's not better with the effiency but it's surely better for shallow water..

[alan white]

Originally Posted by Rick Willoughby

Alan
I have not looked at any human power scale hydrailics. My figure was based on larger power hydrailic systems. I know you can get small units though so I am sure if you Google hydraulic drives you will find small units.

Rick

I will try. The reason I would be interested would hinge on the 70% efficiency you mentioned. Obviously, a slave unit could be located more easily than an entire engine. The motor could be conveniently located anywhere in the boat, driven by a small engine.
This is similar to an electric drive but far simpler and practically maintainence-free.

[alan white]

Originally Posted by TeddyDiver

This is not totally true. It's true for gases, but liquids only theoretically becouse they don't considerably compress through pressure. The heat still is the way how hydraulic transmissions lose energy, but it comes from the fluid friction (eddies) and pressure reliefed throw pressure valves.
Some hydraulic systems can be up to 90% efficient when it normally stays in 70% in closed circuit and less in open circuit systems. Best effiency can be gained in such "man powered" system where fluid velocity is moderate (large diameter piping) and pipes are short and straight..

I am assuming all system losses are due to compression. Like with an electrical circuit, where pressure is called voltage, tube diameter resistance, and volume displaced amperage.
Friction occurs exactly because of pressure, unless I'm mistaken. Decrease the pressure to zero, and no heat is generated. Increase the pressure and heat is generated. Eddies increase due to greater pressure, etc..
The most efficient system would, I think, use large pipes, low speeds, and smooth polished surfaces. Then what? What would a human-powered set-up look like? What currently available units would you recommend?
Would it make sense to use a system designed for more power in order to decrease the system resistance?

[Guest625101138]

Alan
Standard hydraulic systems are designed for compact, robust power transmission. They generally work at relatively high pressure. Under these conditions there is a little loss in the compressibility of the fluid.

The losses are a combination of leakage through clearances from high pressure to low pressure at high velocity, flow resistance through pipes, compression/expansion of the fluid often increased due to entrained air, compression/expansion of the plumbing if it is non-elastic and seal friction on shafts and sliding seals.

Going to large components will add weight and if under water will add drag. So as in all things like this there will be an optimum for given conditions. Do not underestimate the contribution of seal friction in low power applications.

I am sure there are some hydraulic experts out there who can give plenty of references. My experience is mostly with Rexroth equipment but there are heaps of brand names.

Rick W.

[TeddyDiver]

Originally Posted by alan white

I am assuming all system losses are due to compression. Like with an electrical circuit, where pressure is called voltage, tube diameter resistance, and volume displaced amperage.
Friction occurs exactly because of pressure, unless I'm mistaken.

Just the opposite. The pressure can be what ever, but if there's no flow there's no resistance and no loses due it. Pneumatics has the issue of incresed resistance under pressure. It's so obvious phenomen it affects to breathing during deeper dives.

[tinhorn]

Apparently we are not alone in this quest:

http://forums.hydraulicspneumatics.c...1/m/7081003972

http://www.plctalk.net/qanda/showthread.php?t=38343

[alan white]

Originally Posted by TeddyDiver

Just the opposite. The pressure can be what ever, but if there's no flow there's no resistance and no loses due it. Pneumatics has the issue of incresed resistance under pressure. It's so obvious phenomen it affects to breathing during deeper dives.

Thanks, TD.