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Hydraulics,ICE Motors
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maddox



Joined: 21 Dec 2006
Posts: 786
Location: Belgium


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Hydraulic drive is heavy and expensive.
Especially the proportional valves needed to control speed.

And the main thing against an hydraulic drive, inefficient . It loses up to 60% of the input power to friction and therefor heat. You'll need a fair sized oil reservoir of a good heatsink.

Post Sun Dec 24, 2006 8:21 pm 
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Jason Team Grimlock



Joined: 06 Jan 2007
Posts: 95
Location: Sydney-nsw-bondi


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On the subject of hydraulics, you just cant go past a decent tailgate lifter.
Youd need to source one second hand-but you should be able to get the motor/tank assembly and 2 double action rams at a wreckers. the motor and pump assemblies I have seen are quite compact(about the size of a
normal home vacuum cleaner)-take a look next time your near one, they
run on 12volts. Also, power steering pumps are fine, ive sourced ones
that put out an easy 1500psi for large cars!!-but you still gotta get a motor
to turn it, truck tailgate lifter units are pump and motor in one!!! good luck!

Post Mon Jan 08, 2007 12:38 pm 
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maddox



Joined: 21 Dec 2006
Posts: 786
Location: Belgium


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I'm a certified d'Hollandia mechanic. Specialised in tailgates and lorry loading hatches. (not that I do that for a living ATM)

A tailgate hydraulic group is very compact, but has several disadvantages.

-It uses an alternative valve setup, were you need 3 commands to lift the tailgate and 2 to lower it. You would have to strip the valve setup completely and buy new valves.
-Uses a series wound motor, that gets fed by a big heavy lorry battery, the fuses there are in the range of 300 amps. Anyone batteries to deliver 300-400 amps. Also, series wound motors are rather inefficient. At best 60% will go in mechanical energy, the rest in heat.
- Are set in the pressure range of about 2000 psi. This means the motor pump combination is ment for this pressure. Increase the PRV setting, and your setup will draw even more amps.
- Are not ment to be light, they are a part of a lorry or a truck, who cares about 20 kg extra on the hydraulics when the loading hatch supports are into 100's of kilo's.
- No upside down running ,with the original tank.

But those units are cheap second hand, and they come with all included.
But with a bit of bad luck you have a knackered one, burnt motor, pump dead because run without oil. Very sparky worn solenoids/relais . Handlever valves.

Have fun.

Post Mon Jan 08, 2007 7:39 pm 
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Jason Team Grimlock



Joined: 06 Jan 2007
Posts: 95
Location: Sydney-nsw-bondi


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Thanks for the info Maddox! Very Happy Ive done design work on a heavy-super heavy
bot-with a hydraulic weapon for down the track, being a SFX technician Ive had some work with hydraulics, not much though! - Ill bear those words in mind-handnt considered the inverted tank problem-may be safer(and cheaper in the long run!) to design my own-fortunately I have friends at work who are
experienced in this area, a case of beer should get me some help!!!
Cheer

Post Mon Jan 08, 2007 8:26 pm 
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maddox



Joined: 21 Dec 2006
Posts: 786
Location: Belgium


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One solution for the oiltank is to use the bladder of an accumulator. This is the easy and compact solution.

Other solution is to use a tank that is so large the oil will not be in the middle in what position whatsoever. The vent is then a tube in the middle and the oiltube is then the same as the fueltube in a RC aircraft, so it always will be in the oil.

Post Wed Jan 10, 2007 4:12 pm 
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Glen
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect


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question, how much pressure could a clutch activation cylinder take? they work both ways in a car despite only having one port so could you just hack a pump and accumulator in and run the valve in reverse to retract the ram say.
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Post Fri Mar 09, 2007 5:55 pm 
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Rotwang
Experienced Roboteer


Joined: 15 Jun 2004
Posts: 1589
Location: Vic


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Bad idea, you would be asking the air pressure to push the piston back.

The seals only seal one way.

It would suck air and go spongy.

In a car a spring pushes them back.

Either the actual spring in the clutch or that and an extra one on the linkage.
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Post Fri Mar 09, 2007 6:32 pm 
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