# Hydraulics questions (a bit long)

vaguely proposed a theory ......and in reply I say!:
I will try the smaller hose size. The danger of hoses bursting is not
unknown this machine anyway, so new lines too smalle are probably the least of my worries<G>
This is actually an industrial setup, but old.

Spike....Spike? Hello?
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Hi all,
Thanks for all the help/suggestions. It's very much appreciated.
I'll take the liberty to ask another question while we are here:
There has been a lot of talk about having things sized properly such that the system is controllable. Is proper sizing just a question of making some assumptions and doing the math? For example, lets say that I wanted the loader to go from the ground to the full-up position in 3 seconds (is this too fast? too slow?). Assuming:
Two hydraulic cylinders with a bore of 2", and a stroke of 14" to go from down to full up. 3 seconds to extend ram 14"
To compute flow: Speed (in/min) = flow (in3/min) / area (in2) flow = speed (in/min) * area(in2) = 14"/0.05min * 3.141in2 = 880in3/min * 1g/260in3 = 3.4gpm and since we have two cylinders, we need 6.8gpm?
This estimate seems to be reasonable based on what I have seen for other loaders regarding pump size. Is this (basically) all there is to it? And from there should I pick the lowest pressure which will (a) operate all the parts and (b) give me the force which I need to do what I want? So if I want to have the loader capacity be 1000#, I would have two cylinders which could produce (minimally, since I guess there is geometry to consider and the loss of usable lifting force - haven't gotten there yet ;) ) 500# each at a given PSI (seems like 1500 is the lowest common on, and this will produce a force >> 500#)?
Easy...so what am I missing?
As always, thanks a lot for your help.
don

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Probably most useful to work backwards from what you want to accomplish and are willing to spend. Look at the tractor, figure out how much weight can be cantilevered how far in front of the front wheels, and what size pump (pressure x volume) the engine can drive. Then work out the geometry of the linkages and cylinders to figure out what straight force is required at each cylinder or pair of cylinders to accomplish the lift (force, not speed). Then compute the cylinder bore to provide that force. This will tell you the lifting speed.
If you want a different lift speed, resize the pump (and maybe the engine) or lower the lifting load capacity.
It's probably best to go with a 2500 psi design pressure, going lower is a waste of \$ as the common pumps, valves, hoses are intended for that working pressure.
I've never designed and actually built anything hydraulic, just lots of pencil exercise. So this is pretty rough. A basic valve will give you some fine control. I think you're better off to get finer control by throttling down the engine than by going with a fancier design.
As for your geometry and mechanical design, that's more on topic I suppose, but it's hard to quantify. A well-engineered piece of professional equipment will be much lighter for the same strength than a quick-and-dirty homebrew. You can use handbook references to size the main members, pins, bolts and such but figuring out all the stresses in 3-D is much more of a challenge. Stresses will concentrate at joints, that calls for gussets, and you'll want to consider side forces and twisting forces from off-center loads or digging with the corner of a bucket. Common sense and intuition goes a long way. I've been impressed with some homebrew loader designs but they tend to be overbuilt and work better with a large, heavy tractor. If I was going this route with a small tractor I would literally prototype it, cut and patch and try different geometry until it felt right and then finish, clean and paint it.
Bob
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On Fri, 30 Jan 2004 11:16:56 -0500, "don schad"
OK. You think even the theory's simple. I am a RAG (Rough as GUTS) dirt breaker "engineer" who uses old "big boys toys" to try to make my property behave itself, but hydraulics fascinates me, and I needed to look at a few things, because I wanted to make up strong things to fit on buckets etc.
I am reasonably bright, even though I often hide it well. But I am not qualified and I am ony fiddling around the fringes.
So even at my level I am constantly coming up against inertia, pressure, area, physics, geometry, just in design. Then when I started welding the steels used in these machines, along came chemistry, metalurgy.....and in some cases quite a bit of bloody inertia, when trying to move the bits about.<G>
Then there is bearing mechanics, lubrication, wear steels etc etc.
You don't _need_ to be qualified. But remember that many years' worth of though has gone into machines that continually evolve as new mistakes are made.

Yes. Provided you make the right assumptions. From what you say you are not even looking at tractors with loaders on them.
Assumption #1. You do NOT knwo what you are doing Assumption #2. Others do things for a reason.

WooHoooo! Too fast. Just sit there and imagine you are in your tractor (or sit in the tractor if it's available) and imagine a tonne or so of stuff raising to right above your head from the ground in 3 seconds! Most tractor-based loaders lift very high towards over your head to get the height for trucks etc.
Speaking of which, you would not want to go _too_ far. The rams should not be too long or too short.
Also, imagine the force on the back of the tractor. You would probably bite the dirt right under the bucket.
8-15 seconds is more common, with lowering a lot faster. For a farm tractor, head toward the 15 seconds IMO.
You should need to keep the revs up to get a fast lift, so that you have a slow lift when needed. To give you an idea of how important this is, a commercial loader often has a brake pedal that also disengages the auto transmission, so you don't need to be in neutral when raising the bucket.

Nope. To go from full down to full up will take more like 2 x 36" cylinders, maybe 2.5" working diam. A lot of this is neeed not for lift but for strength.

shudder....wrong attitude.
In answer to your question....what you are missing is that geometry that you "have not got to yet".
This is off the top of my head. I may get a few details wrong. but I think I am close. For 10 to one maybe say 8:1 etc. But the errors will cut both ways, I am sure. Prove me working and you are on the way to designing <G>
Your 14" cylinders above will have to move the end of the bucket maybe 12' full down to full up. So to lift 1000lbs _at the best angle_, firstly we need 144"/14" = 10,000 lb. Then the cylinders are often at an angle (to the _direction of effort required_) of maybe 45 deg. Divide by the sin of 45 deg. 14500 lbs. If the angle changes to 30 deg than divide by the sin of 30 deg. I admit that I did quick diagram that showed 14" rams at 90 deg. So we could arrange that to go. But as soon as the arms begin to lift, the angle changes. best check at many locations.
Remember the weight of the loader arms and bucket. Probably a good 100lbs in themselves, spread in quite a complex manner. So let's say the arms are weight spread evenly. You immediately add another 1000lb with COG at 4' from the fulcrum. In other words you have to multiply all your forces by 1.5.....say 21,000 lbs. The beam strength at the rams attachment point would need to be impressive with such short rams, as they need to be attached right near the fulcrum. The fulcrum pins would be impressive as well.
etc
It can be quite complex, and is very dynamic as the loader cycles through its actions.
There is no way that two 500lb pushes will lift a 1000lb bucket in a loader. Not even near the mark. What will probably happen is that with the pump you are using in your calcs, you will need 3 times the ram area - volume and get the 10 seconds' lift I want you to get above <G>.
For instance I have a loader that I did some calcs for. The crowd cylinders are able to do 21 tonne. The bucket tip actually comes to about 7 tonne....at the best angle. This constantly changes as the bucket moves. The Lift rams are 32 tonne. The lift theoretically is about 6.25 tonne, again at the max situation, which continually changes....and yes I _can_ lift the back of the bloody loader off the ground!
Immediately the system changes from that best angle, it all goes haywire, in both directions. You don't want to get the load halfway up, and then find that you simply cannot lift any further.
You will also be surprised at eh length of ram needed to do a job, even with all the mech disadvantage that hydraulics allows.
In all of this, remember that most tractors are not designed for really heavy loads at the front. When you hang the bucket out there, allow for the moment of arm of the weight, especially when driving around and going over bumps. loaders wreck tractor front ends.
Are you going to make the bucket self levelling? That's law here, because a few guys have dropped things on their heads as they raise the load.
etc.
See if there are any plans on the net, or buy secondhand. Believe me, making one from scratch, the excitement could be only _starting_ when you have finished the loader.
While you may well be able to work out all the answers, the hardest part is knowing all the questions.
And I am not even very good with hydraulic circuits in practice, although the _theory_ is not that difficult. **************************************************** sorry remove ns from my header address to reply via email
Spike....Spike? Hello?
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vaguely proposed a theory ......and in reply I say!:
I actually have a bucket and arms from an old bobcat lying around. When I mentioned in machinery circles that I was thinking of fitting them to my tractor, some guy said "Well, I hope you've got the geometry right" Naturally I said yes. Then I started to think about it all......
It's a fascinating idea, but quite a project, and with expensive/dangerous consequences if done wrongly. I shudder to think waht would happen if a loader arm let go while I was sitting in the tractor, because a pin bent or broke.
Your mention of steering rings a bell, Ken. My little Zetor has no power steering. It would have been useless with a loader anyway.
It must have been something to have the fron drop with a full load. I have losta wheel, with just a plough on the back and that was alarming enough.

Spike....Spike? Hello?
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Old Nick wrote:

Well to be honest about losing the front end , it was all over by the time it occured to me to get scared . Heart sure got going though . One spindle broke and when it that side hit the ground the weight transfer took out the other one . Called up a dealer who said new spindles would be \$800.00 a side and break again since it was a weakness of this model . This tractor is a 25 HP Satoh a make I would not recomend to anyone . So made up my own for about a days labour and \$200.00 . Still holding up the tractor so guess the fix took , ;-) . On the other hand this tractor is such junk it runs so few hours . Loaders are great but for most people it is easier to live with " too small " then " too big " not to mention safer . Me I am looking forward to bouncing a few grandkids on my knee so tend to think a hell of alot more then I did when younger . Ken Cutt
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A bobcat is a lot different from a same-size farm tractor with a front-end loader. I don't know much about farm tractors but I think the whole setup is much different - how far out front the load is held, ratio of load capacity to machine weight, and protection of the operator from the load and/or equipment failure. Yes grafting a bobcat loader onto tractor would require some thought.
A bobcat holds the load close in and when fully raised the load is literally right on top of the operator. Mine is 34 years old and even then it came stock with a roll cage with steel plate on top, a 1/4" welded-wire cage on the sides and a seat belt. Even with the top, raising a full bucket without tilting it forward dumps it on your knees from 11' up. Without the roll cage any number of mechanical failures would make sausage of the operator.
The bobcat can lift about 2000 lbs close-in in the bucket and about 1000 out on forks, limited by balance not power. The machine weighs about 4000 lbs and is counterweighted on the rear to the point of being unsafe to operate with the front attachment removed. I routinely operate it right at the tipping limit, where the back wheels aren't doing much of anything, and all the weight is on the front spindles, 3000 lbs dead load plus considerable shock load. The spindles are approx. 2" solid steel.
Aside, it's a great shop tool.
Bob
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vaguely proposed a theory ......and in reply I say!:

I agree. The tractor was actually physically quite a bit larger than the bobcat. But because the bobcat has its anchor points right at the back, and up on arms, for lift height, the arms fitted really well around the tractor, as if for a normal tractor loader.
I take all you points about dumping the load in your lap. My silliest actio on a backhoe was to put some pipe across the arms behind the bucket to simply carry it from a to b. When I lifted the arms I was glad the pipe was only light! A lucky lesson. **************************************************** sorry remove ns from my header address to reply via email
Spike....Spike? Hello?
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vaguely proposed a theory ......and in reply I say!:

Ah! Like falling off a motorcycle! <G>
One

hmmm....right good PR! <G?

Taken into consideration.

But so tempting to get that extra bit of dirt!

Yeah. I stopped riding motorcycles.

Spike....Spike? Hello?
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Old Nick wrote:

Well really I use a 70 HP with a loader to work with . But it will not go inside the barns :-( . No matter how big the loader you always want/wish for more . Gave away my old racing bikes summer before last , :-( . Nothing quite like a bike but when on one I for some reason still seem to think I am 20 . Oh well always the memories . Ken Cutt
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Hi all,
Thanks for all the help/suggestions. It's very much appreciated.
I'll take the liberty to ask another question while we are here:
There has been a lot of talk about having things sized properly such that the system is controllable. Is proper sizing just a question of making some assumptions and doing the math? For example, lets say that I wanted the loader to go from the ground to the full-up position in 3 seconds (is this too fast? too slow?). Assuming:
Two hydraulic cylinders with a bore of 2", and a stroke of 14" to go from down to full up. 3 seconds to extend ram 14"
To compute flow: Speed (in/min) = flow (in3/min) / area (in2) flow = speed (in/min) * area(in2) = 14"/0.05min * 3.141in2 = 880in3/min * 1g/260in3 = 3.4gpm and since we have two cylinders, we need 6.8gpm?
This estimate seems to be reasonable based on what I have seen for other loaders regarding pump size. Is this (basically) all there is to it? And from there should I pick the lowest pressure which will (a) operate all the parts and (b) give me the force which I need to do what I want? So if I want to have the loader capacity be 1000#, I would have two cylinders which could produce (minimally, since I guess there is geometry to consider and the loss of usable lifting force - haven't gotten there yet ;) ) 500# each at a given PSI (seems like 1500 is the lowest common on, and this will produce a force >> 500#)?
Easy...so what am I missing?
As always, thanks a lot for your help.
don

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On Fri, 30 Jan 2004 11:21:05 -0500, "don schad"

I'm not an engineer and don't play one on TV or the net, but...
That's just a f'rinstance. Calculations will tell you a bit more closely whether the load@velocity will overstressthe beams and/or unbalance the tractor.
Grab a rigging book from the library. I just returned Rossnagel's "Handbook of rigging, for construction and industrial operations" to the library as I didn't have time to go through the thing, but it looked interesting. Any book on hydraulic design might be of help, too.
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On Fri, 30 Jan 2004 22:45:05 GMT, Larry Jaques

??????
Sez exactly what I envisaged an of course said in more words. <G> **************************************************** sorry remove ns from my header address to reply via email
Spike....Spike? Hello?
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brought forth from the murky depths:

Wull, if he just lifted bunny rabbits that fast...

Just a few more words. Well done, Nick.
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On Sun, 01 Feb 2004 03:05:00 GMT, Larry Jaques

Hmmmm...happens in Oz from time to time. :-<
Question: How far can _your_ loader throw a bucket of rabbits? <G>

Been down that path. I really wanted to pound the message home. Guess I felt strongly about it. Hydraulics make things look simple and easy because they have so much bloody _power_, and that power coould do a lot if it lets go. **************************************************** sorry remove ns from my header address to reply via email
Spike....Spike? Hello?
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brought forth from the murky depths:

Ayup. Bloody messy, that.
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Just an FYI - here are some interesting specs for commercial add-on compact tractor loaders:
http://www.greatbendmfg.com/compact_specs.html
The raise times on these loaders are on the order of 3-6 seconds, with time increasing as the loader capacity increases. I would assume that these times do not result in catapulting the operator into the next county, but the points about moving a big load so fast are well taken.
Thanks for everyones input throught the thread. There were a lot of good comments and points made. I'll take them into consideration.
Thanks and the best to all,
don

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On 28 Jan 2004 06:45:19 -0800, snipped-for-privacy@frontiernet.net (don schad) vaguely proposed a theory ......and in reply I say!:
So I am not a complet naysayer:
http://www.okdpm.com/catalog/product_16142_ARC_WELDED_PROJECTS_Volume_III.html
ARC WELDED PROJECTS Volume III This book gives you the plans, material lists, and instructions for 67 Welding projects!
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I have Vol II and the plans vary in depth and quality, bt there are a lot of useful ideas in these books for the \$\$.

Spike....Spike? Hello?
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