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Old 09-07-2012, 11:48 PM
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akabull akabull is offline
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Default Hydraulic help/question

I have a friend who is looking to make a cart/crawler to twitch logs out of the woods with. He has two of these wheel motors he would like to use

My question is what size/displacement pump do i need to drive these things? He has a diesel motor from a refridgeration unit that he is going to use to drive it. IIRC he stated it was around 30 hp.

I know very little about hydraulics, but I know there are several resident experts here and I was hoping someone would be willing to help us out. i am sure I haven't listed enough info for you yet, just let me know what else is needed and i will post it as soon as i can.
Chris in Maine
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Old 09-08-2012, 03:59 AM
Arr Tee Arr Tee is offline
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We will need a little more info. The hydraulic motor is designed to operate a 2500 psi max. Is that going to be the system pressure? Does he plan to use a pressure compensated variable pump (piston) or fixed (vane, gear). I assume this will be open loop valve controlled. 30 hp at what rpm?
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Old 09-08-2012, 04:39 AM
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The hydraulic motor is designed to operate a 2500 psi max. Is that going to be the system pressure? Does he plan to use a pressure compensated variable pump (piston) or fixed (vane, gear). I assume this will be open loop valve controlled. 30 hp at what rpm?
Arr Tee, I think that's the info he needs help with.

It appears he has two wheel drive motors and an engine to drive a pump he does not have and would like help spec'ing in the pump, valves and the rest.
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Old 09-08-2012, 06:15 AM
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Matt Shade Matt Shade is offline
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I can't help with choosing a pump, but I was wondering if he plans to drive the wheels directly with those?
Judging only by the size and bolt pattern, those look like drives for a zero turn lawn mower to me. I'm just wondering if they will have enough power to drag a log? And can he get suitable wheels/tires to provide enough traction? I've run a lot of z-turn mowers and they don't have any balls when it comes to pulling.

I've tossed around the idea of building a small utility vehicle like a gator, or ranger and I always figured I would use truck axles and drive them from the pinion with a smaller higher rpm hydraulic motor. That way you get torque amplification and utilize the truck hubs for carrying the load.
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Old 09-08-2012, 08:24 AM
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Scrapper Greg Scrapper Greg is offline
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I think you might be right, Matt. But if this was my option to use those motors, I would mount the motors remotely and chain drive the final drive. That way you could get some extra torque by using a small sprocket on the moyor and a big one on the drive. plus that would allow a sturdier axle design. Here's onethat I looked over a while back. might yield some ideas.
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Old 09-08-2012, 09:00 AM
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Once you get your info together there is a worksheet in the Index Manager that will give you all the answers, just plug in the info.
It will give you the horsepower, and rpm and volume of the pump you need.

Basically, in hydraulics there are three things to remember.
First, pressure is equal to horsepower
Second, volume is equal to speed.
Third, volume to speed is a ratio, like in a gear box. A hydraulic jack has a small, tiny pump and a big piston, so it lifts the load slowly without effort.
If your pump volume is small, on a large hydraulic motor, it will turn slowly just like the jack.

But slow is something that has to be in the range of practical, if a beetle crawling can beat it, you need more volume.
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Old 09-08-2012, 10:03 AM
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There's a PDF catalog here with a lot of specs:
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Old 09-08-2012, 09:17 PM
1-800miner 1-800miner is offline
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Ironman pretty well said the important stuff.
For sizing a pump just think of gears or pulleys.
Big pump to little motor equals all speed no torque.
Little pump to big motor equals no speed all torque.
Your answer is somewhere in the middle of those two.

Call surpluscenter and talk to the tech guy.He does know his hydraulics.

Do some math. You know the horsepower know the weight you want to move and how fast you want to move it.
Do those numbers and you are in the ball park for the hardware you need.

Last edited by 1-800miner; 09-08-2012 at 09:25 PM. Reason: afterthoughts
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Old 09-08-2012, 11:01 PM
Arr Tee Arr Tee is offline
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Do you plan to put each wheel on a separate valve section or tie them together on one circuit?
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Old 09-09-2012, 02:44 AM
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camdigger camdigger is offline
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Here's my opinion, FWIW.

If you already have the motors, that's where you start. With a little ciphering, you can figure out if what you have will work.

From the spec sheet, the volume per rev is 28.3 cu-in. Max continous speed is 160 rpm.

160 x 28.3 = 4528 cuin/min

4528 / 231 =19.6 gpm per motor at max speed.

19.6 x 2 =39.2 gpm flow rate

As far as pump displacement,

pump disp = flow rate / speed

4528 / 2000 rpm = 2.26 cuin/rev

net HP = p x q/ 1714

P = HP x 1714/ Q = 30 x 1714 / 39.2 = 1311 psi

Exceeding 1311 psi will overload the engine because the net HP is exceeded.

Assuming torque output is directly related to pressure (a so-so guesstimate, but you gotta start somewhere)

The rated continuous torque is listed at 9700 inlbs and the max continuous Pressure 2500 psi

The torque ratio is 9700 / 2500 = 3.88 inlbs/psi

1311 * 3.88 = 5086 in lb per motor at 1311 psi.

With a 28" dia (14" radius) wheel estimated tractive effort per motor,

F = T / r = 5086 / 14 = 363 lbf per motor, or 726 lbf for both motors - should be enough to start and skid a couple thousand pound log, especially if an arch is used.
Design to 0.001", measure to 1/32", cut with an axe, grind to fit..

Last edited by camdigger; 09-09-2012 at 02:54 AM.
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