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Sizing hydrualic motor


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#31 fordmustang1984 OFFLINE  

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Posted August 09, 2010 - 08:44 PM

Alright, i went back through your calculations, to get a target speed of 10 mph. i realized i would need this speed since i have a 4 speed now with extra low first gear. i came up with an input rpm of about 442rpm.

#32 hydriv OFFLINE  

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Posted August 10, 2010 - 09:41 AM

If the target speed is now 10 mph and there's 5280 feet in a mile, then (5280 x 10) the tractor must be capable of travelling 52,280 feet in one hour or (52,280 divided by 60) 871.333 feet each minute.

Since the tire rotates 98.38 inches per revolution, it will take (871.333 x 12 = 10,456 inches divided by 98.38) 106.28 revolutions of the tire each minute to cover that distance of 704 feet. We now know what the target wheel speed is. 106.28 RPM

The rear end has a ratio of 4:10 to 1 so in order to get 106.28 RPM at the wheel, the input shaft of the rear end must spin at (106.28 x 4.1) 436 RPM. If you put a standard automobile 3 speed transmission or the 4 speed truck tranny you now have in front of the rear end, top gear is still going to be 1 to 1 so that means the hydraulic motor must still spin at 436 RPM.

The link you provided yielded some interesting information to me. The model number of your pump indicates that you have two model 116YC pumps mounted in tandem with separate inlet and outlets. According to the charts, these pumps are NOT designed to spin faster than 3000 rpm. This is important. If you bought this as an "engine with pumps" setup and it came out of a piece of manufactured equipment, then the manufacturer should have spec'd the engine to be GOVERNED at 3000 RPM MAX. You need to verify that. Go to the website of the manufacturer after you locate the engine model and spec numbers. Make sure that this engine does not rev higher than 3 grand.

Governed engine speed affects pump output. The chart says that each of these pumps will THEORETICALLY produce 14.7 gallons of oil per minute at 3000 RPM and at 2000 PSI. We now have a lower flow rate than in our previous calculations.

We want 436 RPM at the motor shaft but if the pump/motor/system gives us a 10 percent loss, then realistically, we only have 13 GPM to play with. To arrive at 436 RPM, we need a motor of a certain internal displacement. 13 GPM is also 3003 cubic inches of oil (231 x 13) and we need to pass that through the motor every minute. In order to do that, we need a motor displacement of (3003 divided by 436) 6.89 cubic inches. But can we find a gerotor motor that will come close to our needs?

Grainger offers one that is smaller (5.9 cu in) and a couple that are larger (7.3 cu in). If you were to go with the smaller motor, it is capable of spinning UP TO 585 RPM but your theoretical 13 GPM will only spin it to 509 RPM which is well under the max and that's a good margin. So, let's say you choose this motor. What will the performance be?

Motor, Hydraulic, 5.9 cu in/rev, 4 Bolt - General Purpose Hydraulic Motors - Hydraulic Motors - Pneumatics & Hydraulics : Grainger Industrial Supply

If the motor does spin at 509 RPM, then the wheels will now spin at (509 divided by 4:10) 124. 15 RPM and if they cover 98.38 inches per revolution, then the axle will travel (98.38 X 124.15) 12,213.877 inches per minute or if you divide that by 12 it becomes 1017.823 feet per minute and if you multiply that by the 60 minutes in one hour, then you arrive at 61,069.38 feet per hour divided by 5280 to end up at 11.566 miles per hour. While this is higher than your target travel speed, it isn't stupid-fast.

Personally, I don't agree with your choice of transmission but there's no harm in trying it. The reason I don't agree is simple. You essentially end up with a trans-axle that has 4 ranges instead of the customary two. If this 4-gear is out of a typical 1 ton truck and it has a "bull-low", I think that you will find that range completely useless. You will be able to put it in that gear, step off the tractor and take a ten minute nap, wake up and find that the tractor has moved only a few feet away.

If you had all the spec's for the transmission ratios, the wide-open throttle travel speed in first gear could be easily calculated. My choice would have been the most compact 3 speed tranny I could find that was preferably all-synchro to make shifting on the fly easy.

There are other on line hydraulic sites such as Burden's Surplus Center that might have a better deal on a motor for this application. The above was nothing more than me trying to teach you how to choose a motor by showing you the math used. It is important that you use hydraulic hoses no smaller than 1/2" ID with a working pressure rating of at least 3000 PSI or a bit above. There's no justification to choose higher rated hoses unless you like tossing money away. Under-sized hoses cause internal friction which causes heat and heat is not desirable as it ruins hoses and degrades oil quality.

You will need a "motor control" type of valve to allow you to slowly meter the oil out to the motor in both directions. A low cost valve could be bought off of e-Bay from a parted out Case tractor. I've seen those sell for as little as ten bucks and if you get the travel/lift valve, then that would give you a spool to look after your 3 point hitch. Each spool in those valves has it's own relief which is exactly what you will need. The lift spool uses 1/4" hoses and the travel spool uses 1/2". The IN and OUT ports are 1/2" and the valve is more than capable of handling 13 gpm. You will need a pressure gauge to set the reliefs. They cost less than $20.00 at Northern Tool. I suggest a 5000 psi glycerin-filled model. The relief for the travel valve should be dialed back from the normal 2100 PSI setting used in a Case tractor to the 1800 PSI spec'd by Char Lynn. The implement lift relief could be dialed up from the normal 575 PSI Case setting to 1000 PSI as long as the cylinder you select will handle that much pressure safely.

When you think about how one normally operates a tractor, having the three point on the same circuit as the travel motor is no big deal. It won't interfere with your ground speed because you won't be using it while trying to move at ten mph. I think that I'd use the other pump to run the loader and power steering. You have way more pump volume than you need but that's ok. I'd use an adjustable priority valve to constantly steal 4 GPM from the 15 gpm pump flow and send it to the power steering unit. That would leave 11 gpm for the loader, which is still very high but it should be managable.

We may have to install flow controls on the loader lift and bucket cylinder circuits if they prove to be twitchy. But that's something that can be worked out later. You have the engine and you have the pumps. It's all about working around that combo and tailoring everything to it. Once again, I caution you.. I am not a hydraulics engineer. I don't know everything there is to know about hydraulics. What I have given you is my theory as to a choice of motor. Most of the hydraulics houses have people who are more educated on this issue than I am. I urge you to send them an e-mail and tell them what you are trying accomplish.....leaving out no details. Tell them what you have come up with and how you came up with it and ask them to review this information to see if something has been overlooked. The time to ask questions is when someone is hoping to sell you something, not afterward when those questions come in the form of a complaint about poor performance of their product.

#33 fordmustang1984 OFFLINE  

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Posted August 10, 2010 - 08:41 PM

Ok, that all sounds very good. If i can ever get to a hydraulics place, i will have them review this to see if there is anything else. My reasoning behind the 4 spd is that a compact 3 spd is not easily found here, never mind a cheap one. The 4 spd i already had, and connected to the axle without the need to any adapters. It also had a short enough tailshaft to fit my tractor frame. I dont mind having the extra low gear. I'm sure i will find a use for it at some point.

Oh, and i think its 52800 feet per hour, not 52280. Just watching the math.

#34 fordmustang1984 OFFLINE  

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Posted August 10, 2010 - 09:07 PM

Is this the valve i should be looking for?
Case Garden Tractor Control Valve 220 222 224 444 446 - eBay (item 250677795664 end time Aug-11-10 17:33:53 PDT)

#35 ducky OFFLINE  

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Posted August 10, 2010 - 09:07 PM

If you ever have a snowblower on it W/4Feet of snow in front of you that Grannie gear may come in handy.
You would still have the top 3 gears for normal tractor work the same as if you had a 3 spd.
Granted the ratios may vary a bit between the different trannys.
My MF 12 had 4 speed with a (granny) gear (#1) just for blowing heavy snow.

#36 fordmustang1984 OFFLINE  

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Posted August 10, 2010 - 09:42 PM

Yup, theres some good ideas. Especially since we do get huge snow falls around here on occasion.

#37 ducky OFFLINE  

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Posted August 10, 2010 - 09:49 PM

Yup, theres some good ideas. Especially since we do get huge snow falls around here on occasion.


I remember picking up roll paper in Bangor and having to stay a day 2 before we could get out.

#38 hydriv OFFLINE  

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Posted August 11, 2010 - 07:15 AM

Yep.... me bad. It should have been 52,800 but even with that figure, it just moves the wheel speed from 106.28 to 107.339 RPM. That changes the motor target speed from 436 to 440 rpm.

IF......you find a motor with about 5.9 cu inch displacement, it's going to run a bit faster than the original target speed anyway but I'm sure that you've already concluded all of this. At least now, with the math in front of you, it should be a simple matter for you to figure out what will happen if you run across a motor slightly larger or smaller than the one in the link.

No worries on the tranny choice. Use what you've got. If it turns out that bull low is a pointless gear, then just don't use it unless you're trying to pull stumps.

#39 hydriv OFFLINE  

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Posted August 11, 2010 - 07:21 AM

Is this the valve i should be looking for?
Case Garden Tractor Control Valve 220 222 224 444 446 - eBay (item 250677795664 end time Aug-11-10 17:33:53 PDT)


Yep. That is exactly what I was talking about except there are too many people chasing that one. However, now that you know what valve to look for, just keep monitoring e-bay and watching until you find one going cheap.

You see those two acorn nuts on the left side of the valve? Those nuts cover the relief adjusters.

You will also see travel/lift valves that have the holding feature. You don't want this valve. And that's a good thing since it often sells for $200.00 on average.

#40 fordmustang1984 OFFLINE  

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Posted August 11, 2010 - 04:25 PM

Ok, that helps alot! I know of a guy on another forum that will likely know whether all this will work like you say, which even with my limited hydraulic experience looks makes sense enough to work. Thanks for all the help, and I'll report back with his opinion, and what i finally go and find.

#41 TUDOR OFFLINE  

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Posted August 13, 2010 - 05:22 AM

The engine/double pump combination suggests to me that two individual circuits were in use and that you could do the same.

The not so good news is that your relief valves will have to be set no higher than 1000 psi. or you run the risk of stalling the engine.

The bad news is that you will need both pumps feeding a larger motor in order to get the most use of the traction available. You will have to manifold the two pump outputs together and you will need big hoses to flow 29 gpm. I don't think the Case motor valve will work for you at that volume.

The worse news is that by using 1 or 2 gear pumps to power 1 gear motor, you will compound the efficiency losses. Over 1/3 of engine horsepower will be lost, and possibly as much as 44%. At best you will be able to deliver all of 14 horsepower to the ground. That's very respectable, but it leaves nothing for the loader or power steering.

On the positive side, with a 3 speed gear box and the weight you are talking about, 1st gear will pull like no tomorrow. You will rarely require max power while using the loader, and almost never will you need your power steering when putting that much power to the ground. A 6-8 gpm. pump for the loader and a GM power steering pump will be coasting most of the time and are unlikely to be drawing more than enough power from the engine to spin them when you need to put the most into your transmission.

Will you be able to add 2 more pumps to the engine? If you can only add 1, you will need a priority valve on an 8 gpm. loader pump in order to supply the steering.

In all honesty, it's a nice exercise, but not viable. Gear pump/motor efficiencies are unacceptable. You're burning 22 hp. worth of fuel to get 14 hp. of work. Low pressure and high volume increases component costs (relief valve, motor, hoses and fittings get expensive faster as they get larger). Adding at least one more pump for the loader/power steering circuit is a must no matter what.

Replacing the existing double pump with a single pump with the same flow as one of the pumps will double the pressure capabilty, and halve the flow which brings that Case motor control back into the equation, and allow a smaller motor, relief valve and lines at less expense. The low efficiency will still be there, and you still need a pump for the loader/steering. Blocking off one pump is not a plan.

A vane or piston pump of comparable size would have a marked increase in efficiency, but at a severe price unless you really luck into a deal.

Using the 25 hp. engine will only hide the defficiencies of the existing system, not correct them.

Sorry to rain on your parade. You may be farther ahead to make a 6:1 reduction unit on the engine and go straight from there to the transmission, and forget the hydraulic drive this time. Hydraulics are expensive.

Maybe someone else can put a more positive spin on this build.

If you decide to go ahead with this build, I'll help, where I can, in a positive way. I figured that I better get the negatives out front so that you can see and understand them.

Bob

OCH, do the smilie codes from the other site work over here? I miss my pipe.

Edited by TUDOR, August 13, 2010 - 05:36 AM.


#42 TUDOR OFFLINE  

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Posted August 13, 2010 - 12:42 PM

Fordmustang1984, I'm sorry if the above comments sound rather sharp. When working up a design for myself, I tend to look at the worst case scenario that I can think of, for the design criteria. Even then, reality usually proves to me that I underdesigned somewhere, so I try to be cautious on a build such as this.

It will work, just maybe not at a level that you are expecting. It will put 10 to 25% more horses on the ground than a MF1655 is capable of, with the weight and traction that you expect. To be honest, I think your weight estimate is high if this is going to be a GT sized machine. That is a lot of very heavy metal.

Experience has shown me that max power requirements are rarely needed, but you do want that capability when required. The rest of the time you don't need much over half of that max. Remember that that max is only available at full throttle and full flow on the pump. It is not available to start a load moving with a partially opened motor control valve. That's where your choice of transmissions will come into play.

Let us know your thoughts and questions after reading these comments. I'm sure that there will be several.

Bob

#43 fordmustang1984 OFFLINE  

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Posted August 15, 2010 - 02:18 PM

Its alright about the comments. I often do the same when im helping someone with something i am familiar with and they arent. I thought my weight was somewhat high too. i'll work on that as the project progresses.

Oh, and welcome to the forum! :welcome:




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