Hydraulic System for Walking Machine?

I'm looking for some direction on a project I'm working on; it's essentally a 6 legged walking machine (this is half of it)
http://personalpages.tds.net/~ksteuer/machine/IMG_1202.JPG
I'd like to design a *simple* hydraulic system that would, for right now, turn a geared shaft forward & reverse, with a high-torque servo running a fwd-neutral-rev valve; all in very low/high torque fashion.
I've got a B&S 6 horse motor, I'm asking for some input as to what components I'd need. I'm thinking I'd use the B&S to drive a pump, which in turn would drive a hydraulic motor, (spool valve for control), then off to the shaft, with gear reduction to my final drive of the legs.
Would "wood splitter" type components be suitable, considering I'm driving ahydraulic motor vs. a cylinder?
Thanks fo rany input- Paul
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I think I saw two such items on cable. One is done by the military. Another, I think, was done for the handicapped/injured. Discovery, History, one of them. -- Mr. P.V.'d (formerly Droll Troll), Yonkers, NY Stop Corruption in Congress & Send the Ultimate Message: Absolutely Vote, for *Anyone BUT* a Democrat or a Republican Ending Corruption in Congress is the Single Best Way to Materially Improve Your Life entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie, all d'numbuhs

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Well, yeah... but if you choose your pump and motor correctly, you may even be able to do away with the gearing.
Pumps and motors come in a number of different displacements. Couple a X displacement pump with an X displacement motor and you get (almost) 1:1 speed from prime mover to motor shaft.
But couple a 1X displacement pump to a 90X displacment motor, and you get a 90:1 reduction in speed at the motor.
And vice/versa.
LLoyd
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This is the type of thing I'm looking for, thanks!
At the final drive, I'm looking for verrrrry slow rotation, like 40/50 RPM so the legs do a slow down/back/up/forward rotation.
So "Disp. 0.067 cu.-in./Rev" is what I need topay attention to, correct?
Thanks a lot Paul

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Yep. Well... that's a bit much for a single-step hydraulic speed reduction. The motor would have to be too large, and the pump too small to be practical.
But keep in mind that in addition to the motor's small displacement, you can also use flow restrictors. Hydraulic flow restrictors will maintain an essentially constant flow at a particular setting, regardless of pressure or load. So you can, in essense, fully power a very slow drive via a pump large enough to provide the maximum necessary pressure for the desired torque, and a restrictor to limit the flow to the speed you want.
LLoyd
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Paul wrote:

Surely it would be more "simple to dispense with the hydrailic motor and use double acting rams to actuaste your legs?
Dan
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If I understand what you're describing correctly, I don't think so...the three legs per side will be linked mechanically via sprockets & chain, so one side of the driven shaft will drive 3 legs, the other side, the OTHER 3 legs (properly synchronized in a "double tripod" arrangement, like a hexapod insect)...so three legs have ONE main drive.
Your arranagement would be excellent under computer control, right now I'm trying to do it simple-
Thanks Paul

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Paul wrote:

about 3 feet in length, a couple feet in height, and maybe a few hundred pounds total weight. And when walking, it might move a couple miles an hour.
For this, 6 HP is way way overkill. In a prototype you'll be wasting a lot of energy in the mechanism, yeah, but still 6HP is way overkill.
I speak from a little bit of experience with robotic forklifts. In every plant/warehouse they were installed in, the owners were able to point at the holes that they had knocked in the cinderblock walls :-).
Pneumatics may be more appropriate and will allow at least some natural springiness that hydraulics will completely lack. Hydraulics are great when you want the output cylinder to move to the exact right place. For walking, exact right place is not necessarily known in advance, and just having it supporting the correct fraction of the total weight may be more appropriate. Think about how you walk, you don't command your leg to a given extension, you command it down until you know it's supporting most of your weight.
Most robotics experimenters use motors at pretty much every joint.
Tim.
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Hi TIm-
Thanks for the input. You're right about the general proportions, it's about 3.5 feet hight, but no matter. My idea behind hydraulics was to allow later hydo "attachments" as I saw fit, and I'll admit I do like the noisy industrial vibe of a gasoline engine roaring away (I initially wanted to use a motorcycle engine, talk about overkill...)
But you raise intersting ideas...perhaps an onboard compressor? With pneumatics, I'd have to redesign to use linear air actuators instead of rotation, correct?
Thanks a lot Paul

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R U Rich !! I can do it with cheaper electrics ...
Hyd needs variable pumps/motors like airplanes use .
Elect' linear motors are unpopular , but easy to build . They are very fast , but you must design in "latches' to hold , cause amps to hold is not practical .... If linear motors are too far out , use cranks and connecting rod , 1/2" drill motors from HF ..
Paul wrote:

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====================Thanks for the "roach" clip. :-)
While this may be possible to do mechanically using belts, pulleys, gears, etc. it appears this would be *MUCH* easier using all hydraulic power with computer control as the various ratios can be altered with a few keystrokes without replacing gears, altering crank arms, etc.
Without an in depth analysis, it appears that double acting hydraulic cylinders at the articulate joints would be your quickest and quite likely the cheapest route, given your size constraints and likely power/force requirements.
Most likely your B&S engine will provide enough power, but you may want to consider using a hydraulic accumulator to allow for surge demands, with reserve pressure throttle control.
This looks like a fun project. Please keep us updated.
Some URLs that you may find helpful
http://www.peninsularcylinders.com/sp_cylpos.htm http://surpluscenter.com/sort.asp?UID 06110201044202&catname=&byKeyword=yes&search=hydraulic
Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.
John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).
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Hi George-
Given that the legs would requre an up/forward/down/back motion, I would need several cylinders per leg for that control, then times the six legs, correct?
Roachlike hexapod locomotion is real simple, which is why I chose 6 legs. Always three legs supporting the body; one leg on one side, two on the other. Then they alternate. So it's not really a "crawling" motion (like an octopod), just two sets of three, alternating. As long as the three are in sync, it *should* work.
I agreee computer control would make all this much easier, but my initial idea was to make a simple (hah!!) mechanical prototype, then develop it from there.
I'm surprised at the comments about cost; I've done bike projects, car projects, big pulse jets, turbines, etc. and something like this is a lot cheaper then some of those other projects. Hydraulic pumps & motors, valves, all under $100 per component. Sprockets & shafts, dirt cheap. Plus whatever you can beg/borrow/steal...
Thanks Paul

http://surpluscenter.com/sort.asp?UID 06110201044202&catname=&byKeyword=yes&search=hydraulic

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Motive , using many cylinders at each leg , is not real world , its text book , .....college stuff .
Its the OPPOSITE of engineering .
Im an engineer , i do real stuff . Hydraulics only works where the space contained is small and the power needed are very high .
If your "vehicle" was carrying 10 tons , use hydraulic , if it carrys 1000 lbs , use electric . You will notice others always use electric at these sizes . You cant have so much "freedom" at each leg , it costs too much . Be practical and choose a method of "walking" that takes advantage of the mechanism available at lower cost .
I have a hobby , Off road stuff . Wheels still rule , but 4WD is too heavy for the "return" . Mine uses 6 wheel , shift wt to rear 4 wheels , so front can be much lighter , steer with "cutting" brakes . This is the lightest , fastest of all . Yet they can't see this for they have no imagination , only $$ Todays engineering is crap , even my 2000 Toy 4WD bent the flimse rack/pinnion steering and would not turn under 4WD as it had no "clutch" on the front drive shaft !! It would cost $20 to add a 200 HP clutch !
If speed and terrain are worse , there is only one vehicle .... Motorcycle . A bike can can climb straight up for as much as 7 feet vertical ( using a small rock to get the momentum in the right direction )
What kills many projects is friction , then weight .
Again , Hyd' is only used where there is limited space to put very high power to move ...
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    --Speaking of 6-legged walkers have you seen Mechadon yet? Here's a link to a short video of it in action: http://homepage.mac.com/roninsfx/Team_Sinister/iMovieTheater16.html
--
"Steamboat Ed" Haas : There's never a tachikoma
Hacking the Trailing Edge! : around when I need one!
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Cool project. I know a machinist who built a lifelike walking robot (2-legged) with the knees driven by cams and a swiveling waist for balance. The "Walking Man" pulls a chariot at almost 20 mph (the machinist/driver stands in the chariot).
I don't know about your budget, but I once worked on a Jacobsen Tri-King professional ride on lawn mower for athletic field work. It had a 3 cyl. Kubota Diesel which powered a hydraulic pump which ran 3 hydraulic motors for the drive wheels (it's tricycle, 2 in front and one in back. The back swivels to steer) as well as 3 smaller hydraulic motors for the mowing reels. It would have made a great source for hydraulic pumps, motors, and valves, etc. The pump was even connected to the engine by a weird differential thing that would have been easy to disconnect and connect to an electric motor, Jacobsen still sells replacement parts, and if you found one used you could probably pull the parts out of it fairly easily. Since it is tricycle, the parts often come in threes, a good match for a 6 legged robot.
Also, Northern Tool has lots of hydraulic and PTO stuff. I've never ordered from them, but I like to browse their catalog. I don't know if this is way off the mark, but I hope it helps. WW88
Paul wrote:

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Woodworker:
Any clips or pics of the Walking Man? The Hexadon clip above is very cool, but that thing screams big budget and a crew of 40 people!
Yes, I've looked at a lot of hydrostatic transmissions and whatnot...I think for all the trouble of sourcing an appropriate machine and adapting it to my purposes, I can put together a hyd. system to turn the leg shafts easier & cheaper. Lloyd S. laid a few simple concepts out for me, and The Big Lightbulb came on. I also like the ease of repurposing/moving/changing hyd. pumps as discrete components.
Gasoline engined is an absolute requirement here; face it, the machine is useless, purely an aesthetic exercise and I want it to be loud and greasy (I'd LOVE to find a small diesel motor, then it would have the right smell too!!). Many robots I see tend to be low, enclosed and electric, and that just doesn't excite me like exposed hoses and sprockets & chain looking bite errant body parts...
Thanks Paul

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Got to agree. Your description of the engine reminds me of a one-cylinder diesel welder we have in the shop, sounds like a beast, but when we pulled it out of storage after 5 years, it fired on the first pull, without even a boost. I'll try to get some pics or videos of the walking man. I think i've got a couple around here somewhere. ww88
Paul wrote:

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