Hydrostatic Drive Design

drankin

Did a little more work on the schematic. Added a flow divider and high-speed circuit.

Attached Files

BUGGY HYDRAULICS 20JAN10.pdf (33.5 KB, 90 views)

larkinja

Its looking really good! One question. I have a Symbols chart here, but some of the symbols don't match exactly. Do you have a chart for the exact symbols you are using? I am attempting to put together a parts list as you add things to the schematic, and this would help me.

Also, as far as the schematic goes, this design uses a variable disp pump. What would be the implications of using an actual hydrostatic pump? Are they basically the same thing only with some of the circuitry built in? I was kind of looking at this pump as a possible candidate.

https://www.surpluscenter.com/item.a...name=hydraulic

Looking at this as a possible motor. Seems to mathematically fit the bill .

https://www.surpluscenter.com/item.a...name=hydraulic

Let me know what you think.

Thanks

drankin

The gerotor motor looks like it will work. The RPM range is there. Working pressure is a tad lower than ideal but I'd say it's a go.

The pump in the schematic is the symbol for a hydrostat (simplified). The Sunstrand that you picked out looks like a perfect fit. Make sure the counter-clockwise input rotation will work with the engine output. See if you can find the cut-sheet and/or manual for the pump.

I'll spec out the valves for you. I plan on designing the manifolds for the valves. Most will be cartridge valves. They are inexpensive and easy to maintain. www.sunhydraulics.com

Because of the lower pressures we're working with, <3000 PSI, we can use aluminum body components. Brings the weight down.

Just let me know what symbols you have questions about.

I've come up with some ideas for dynamic hydraulic braking I'll include in the next schematic.

RonL

I have used the surpluscenter for a lot of things and have never been dissapointed.

I would also like to pass this link on to you guys, find out if they have a store near you and if not, you might contact one and order the design manuals that most apply to what you are working on.
The manuals give good rule of thumb examples for calculating use of hydraulic, air and electric power design needs.

http://www.womack-machine.com/education/textbooks.aspx

Ron

larkinja

Thanks for the referal on surpluscenter, definately good to know. Thanks for the education link. I had been looking at getting some books for general knowledge on the subject.

larkinja

Just to make sure, the motors will be ok? I am thinking about ordering 1 for now just to do some test fitting with. We are in the process of finalizing the a-arm design, and figuring out the best way to couple the motor shaft to the cv axle, so I would like to have one of the motors in hand to do that with.

Helping us with the valves would be a huge help. Thank you! We had an idea that we are not sure if would be possible/practicle. Thought I would run it by you. I might have mentioned it before, but we are contimplating using a hydraulic steering cylinder to steer the front wheels. Could a single joystick control be used to control both the motors and a steering cylinder? The control would have to be able to steer while the forward and reverse control were in any position. Similar to a computer gaming joystick. Is this possible, at least without costing a lot?

CW rotation shouldn't be a problem. We are going to gear down the engine before going to the pump, so we can reverse rotation if needed.

What exactly do you mean by designing the manifolds?

Lastly, for the valves for free wheel, and hi-speed, will those be dc solonoid type? I would assume that would necessary for timing when switching modes.

The last question of the night is about the resevoir. Am I assuming right that this is still a open circuit? So some sort of tank will be required? How small can this be? Obviously space and weight is an issue. Just trying to figure out where this may need to go. Also, is it possible to do a closed loop, or does that complicate things?

Again, thanks so much for everything you are doing for us. You have no idea how much I appreciate it. We'll have to figure out some way to repay you for your efforts.

drankin

The motor looks like it should work fine.

Yep, a hydraulic pilot operated joystick will work in for you. They use these on hydraulic excavators. Look into picking one up at a heavy equipment dealership (Deere, Case-Linkbelt, etc.) parts department. Might be a bit spendy new so see if you can find one used.

Because the circuit is going to require a lot of valving we're going to need a manifold to pack all the cartridge valves in. Otherwise you end up with a bunch of individual valves that you have to hook together with tees/fittings/hose/tubes. It gets really ugly really quick. A single manifold can house several hydraulic circuits into a small package. I'll send you an example later.

All solenoid valves would be DC. Preferably 24VDC but we can go 12VDC.

Never intended this to be an open circuit. I think this would work best as a closed circuit. An air/oil cooler and small reservoir would be req'd.

As far as repayment, you could start by being a contributing member of PF (top, second to left button, "Upgrade"). I think it's around $15/yr. Post some pics so the rest of us here can follow your project.

larkinja

Great, I will start looking for one of those. I would think it would have to fall in a particular gpm range correct? What values do you think I would be safe with? Seems the pump may be pushing close to 70gpm at times. Is there a particular kind that I would need that will work with both the motor circuits AND a steering cylinder?

Is there a disadvantage to using 12v vs 24v. The engine ignition and charging system, headlights, radios, etc. will all be 12v, so it would seem to make the most sense to use 12v, but if there is a big disadvantage, we can implement a 24v system as well, just complicates things a little, and adds another battery to the vehicle.

I am officially a contributing member now. :) I will get pics up soon. I intended to take some shots when I was out there Thursday (We work on these projects every Thursday), but I had not realized the battery in my camera had died, so I will get some soon, promise.

drankin

Because the pilot operated joystick is used for piloting (signalling larger components/valves), it is a low flow component. It will drive the pump swash plate with the forward and reverse operation and the steering valve (that in turn drives the steering cylinder) with the right to left operation. It is basically four variable pressure reducing valves, one at 12, 3, 6, & 9 oclock. All it does is regulate pressure, the flow capacity is very low in the area of .25-.5 GPM max in the 0-500 PSI range.

12VDC is fine. I usually work with 24VDC components when working on mobile hydraulics. It's typical with mobile hydraulic equipment. The solenoid coils are smaller, wiring is gauge can be smaller, etc.

Welcome to contributor status!

larkinja

So would this be the type of componant?

https://www.surpluscenter.com/item.a...name=hydraulic

or mor like this one?

https://www.surpluscenter.com/item.a...name=hydraulic

Then this would control 2 different valves? One for steering and one for the motors? I don't know if any of the valves on that site will work. The pump has a 12vdc solonoid on it. What does that do? Does that operate the swashplate, or something else?

drankin

The first one, https://www.surpluscenter.com/item.a...name=hydraulic, is the one you want. See the 4 buttons on top? That's the four reducing valves. GOOD PRICING.

I need more info on that pump, spec sheet. Don't know what the solenoid is for. I'm pretty sure we can hydraulically actuate that swashplate. A single joystick will control the pump and steering. The two buttons at 12 & 6 oclock control the pump and the 9 & 3 oclock control the steering. We need spec sheets for all these components so we can verify everything will work together.

drankin

Here is the spec sheet for that joystick. This shows the handle and buttons as well but I just need the hydraulic performance information. If you can find spec sheets like these for the other components it would help a lot.

Attached Files

re64555_05-03.pdf (362.7 KB, 49 views)

drankin

Found out what that solenoid is for. EDC stands for Electronic Displacement Control. So the hydraulic joystick won't work for it as is. Depending on how the pump uses EDC we may be able to disable it and go direct hydraulic. Need more info though. Because Sunstrand is no longer around you might have to try a pump repair shop for info on that pump. I couldn't find anything with Google.

larkinja

Ya, I'm having trouble finding info on the pump too. I'l keep digging to see what I can find.

larkinja

I called about a half dozen places today with no luck. The pump has been discontinued. One guy told me that parts were not available for it. Would this mean I should stay away from it? I'm worried that if we have to replace parts, we won't be able to get any. Do you know of any pumps that might work that aren't such a mystery that would be in the same price range?

RonL

That is one problem with buying from surplus dealers, too often they bid on product lines that for one reason or another have been discontinued and most of the time repairs or replacment parts can't be found.
For expirmenting or one off design work its not anything to worry with and the prices can save a bit of money.
If the plan is to build a business and sell product, you have to find and use parts and suppliers that will be around to keep your business going.

Ron

larkinja

I'm not after selling anything, I just want to make sure I don't spend $1100 and have to toss it in the scrap pile 3 months from now. I'm curious what the reference point is though? What would a similar pump cost that is current? If I can buy three of the $1100 ones for one of the current pums, then it is worth getting the old one. If it's a smaller difference or something, then I would go with a newer one.

Maybe I should go about it this way. What would a typical life of a pump like this be. Or how soon before it needs rebuilding? Because at that point it would be time for a new one since parts aren't available.