Proportional Electrohydraulic Systems??

[jgrreed]

What is the price and models of the valves you are using? I just did some searching on servo valves. and I was constantly seeing them priced at over $1000 each.

I haven't found any specific valves yet, but you're right, that could be the kicker right there......

I saw some solenoid type on Surplus Sales website for around 100$, I guess I assumed that the proportional ones wouldn't be all that much more. I'll keep looking and see what I can find.

Did find some on eBay for anywhere from 300 to 1200$, and I have no idea what model i should be looking for. None of the ones I've found so far specify open or closed center, so I'm guessing that means that they're closed center. I'm starting to feel like a grade 5 student with a rocket made from old paper towel rolls who's calling the Jet Propulsion Lab looking for parts!! Maybe I should just go buy a shovel and a wheelbarrow!!!....

What is the difference between a 'servo' valve and a 'proportional' valve. Eaton lists them as different on their website.

How 'jerky' would the controls be if I just used on/off solenoid valves?? Could I simply reduce the flow to the ports to make it a more precise adjustments. I foresee wanting my TnT controls to be fairly precise, but not needing to be super fast moving, whereas the grapple control could be quicker moving, but less precise...?? Could even add flow control valves to the system to make each circuit more versatile - ie high flow for speed, low flow for precision. What are the thoughts on that??? Seems it would save a lot of cash, and likely frustration.

-Jer.

 

[Wayne County Hose]

Jer,

I understand what ccsial is talking about, he is definately the man. If anything that Eaton makes will be of use to you, I can probably obtain them for a major discount. I am a Weatherhead distributor and they are owned by Eaton. You are doing something I am awfully interested in, keep us informed.

As far as switching directions goes, forklifts do it but with a computer involved. The pot or encoder would have to be calibrated to neutral and travel extremes then the computer would recognize whatever signal was at neutral then whichever way the handle was stroked would be the direction that the fluid would be ported. Pretty complex, but really, very elementary. Again, a computer was involved.

Good luck, Andy

 

[ccsial]

What is the price and models of the valves you are using? I just did some searching on servo valves. and I was constantly seeing them priced at over $1000 each.

We don't supply any hydraulics. Our customer does that. The valves are Rexroth I think. They make a maniford for them. These are fair sized since they go on big trucks used by cities and counties. I'm sure they are not cheap.

 

[ccsial]

Jgrreed:

The Scorpian Digital (EM-DC-D) looks pretty good. It says it will control two bi-directional valves. That would be an X and Y axis on the joystick.

Don't be afraid to call them and ask for tech support. Most of these vendors have engineers that are willing to help with applications.

KennyD says, "I think one problem you may run into that will be a showstopper is that most of these advanced systems are designed for closed-center hydraulic systems with variable displacement pumps. Your tractor has a open-center system with a fixed displacement pump".

He may be right about that. I am not a hydraulic expert. We design our circuits to the customers spec. They do the hydraulics design.

 

[jgrreed]

Jer,

I understand what ccsial is talking about, he is definately the man. If anything that Eaton makes will be of use to you, I can probably obtain them for a major discount. I am a Weatherhead distributor and they are owned by Eaton. You are doing something I am awfully interested in, keep us informed.
Good luck, Andy

I will for sure. I've put out some emails to Otto and Scorpion already. If it does become a reality I'd definitely be interested in getting my valves, fittings, etc, through you. Would mind contacting Eaton and see if they make 12V proportionally controlled valves that are open center, without an LVDT feedback loop??? My JD runs ~ 11GPM through the system.

Jgrreed:

Don't be afraid to call them and ask for tech support. Most of these vendors have engineers that are willing to help with applications.

Yes, both Otto and Scorpion welcoming websites. I'll be calling them.

It seems that Scorpion will likely customize the control module for me.

It's a fun project, and I'm learning a lot. Even if it isn't a go (either due to price or lack of available parts) I'll post a summary of all the info I've gathered and learned so far.

I'm prepared to pay up to around 3000$ to get this up and running. The stupid JD diverter kit was going to 2000$ before install time was added, and would be a lot less functional than what I'm trying to accomplish, and would be a lot less fun to get set up and use!!! Does JD offer a joystick that can put my neighbors Kubota into a missile lock??..... I DON'T THINK SO!!!......

-Jer.

 

[jgrreed]

Does anyone have any thoughts on these Q's???

What is the difference between a 'servo' valve and a 'proportional' valve. Eaton lists them as different on their website.

How 'jerky' would the controls be if I just used on/off solenoid valves?? Could I simply reduce the flow to the ports to make it a more precise adjustments. I foresee wanting my TnT controls to be fairly precise, but not needing to be super fast moving, whereas the grapple control could be quicker moving, but less precise...?? Could even add flow control valves to the system to make each circuit more versatile - ie high flow for speed, low flow for precision. What are the thoughts on that??? Seems it would save a lot of cash, and likely frustration.

Thanks!!

-Jer.

 

[ccsial]

The hydraulic servo and proportion solenoid valves are similar in many ways.

There is not a lot of difference between an expensive proportional and a cheap servo.

Two differences would be that the servo valve responds faster to electrical signals and would have less hysterysis and stiction.

A valve with stiction means that as you increase current in the valve nothing happens until the stiction is overcome and then flow starts. How much of this there is depends on the quality of the valve. This is generally very low in servo valves.

 

[Redneck in training]

I work on steam turbines where Electro/Hydraulic positioning system are videly used to operate inlet valves etc. The nice thing about them is that you can adjsut the response just by changing few parameters in the electronic positioner. The bad thing is that they require high degree of knowledge and test equipment to set them up (calibrate them) and/or troubleshoot them. Most of them are also very sensitive to cleanlines of hydraulic fluid. Are they expensive? You bet. 20000 to 60000/unit.

There are two basic types of proportional systems. With feedback (closed control loop) and without (open control loop). Feedback systems are more complex and require position sensor. Open loop systems are simpler and work similar way as regular hydraulic valve but instead of mechanical conection from the joystick to the spool there an electrical connection. In example some new cars have "fly by wire" gas pedal. Fuel injected Harley Davison motorcycles are also fly by wire. Closed loop systems can have additional functions such as automatic leveling or prevention of tiping over due to high center of gravity etc.
The electro/hydraulic system actually has two spools. The coil operates very small spool that in turn operates the spool that supply fluid to the servocylinder. You can call it hydraulic volume or flow amplifier.

 

[denmansoft]

Find a short list of valves that might work for your application (open/closed center, size flow etc.)
Then you have some specs to go back and look at the controller boards. Either of the 2 already shown could work depending on the valve.
Most of the electro hydraulic systems I've worked on were Variable displacement pumps NOT like the fixed displacement ones we have on our tractors.
I work a lot with robotics and the joystick to PWM control is actually simple and cheap unless you want to operate High voltage coils (>24Vdc) or high current (>10A).
If you valve needs + and - voltages to operate the different directions then you will need a full H bridge type of control.
A physical lockout may be necessary if your valve does not have a deadband area in its input. This would be say where an input voltage of -0.5V to +0.25V does nothing. the valve actually moves with 0.5V - 12V on the input ( or negative as appropriate).

It must be cold in Hinton right now. I think Seattle being nearby is wishful thinking.
Scorpion stuff looks good. what are their prices like?

Another thought: what is the breakdown of the costs of the $2000 JD kit ? (valves, Hoses, fittings, mountings)
Most of these you will still be needing to get one way or another.

 

[skidsteer.ca]

How 'jerky' would the controls be if I just used on/off solenoid valves?? Could I simply reduce the flow to the ports to make it a more precise adjustments. I foresee wanting my TnT controls to be fairly precise, but not needing to be super fast moving, whereas the grapple control could be quicker moving, but less precise...?? Could even add flow control valves to the system to make each circuit more versatile - ie high flow for speed, low flow for precision.

-Jer.[/QUOTE]

Though I will be watching this thread for a outcome I think think above train of though it much more practical for your application.
Our 200 serco wood loader has 4 pumps, one a 40 gpm vane pumps that runs a hydraulic slasher , 1/3 of this flow is split off though 3 solenoid valves to control the saw arm, bunt board and the length slide cylinders. The rest goes to the 60" saw motor. They are on or off and though they move a bit quick once the oil is warm, they are manageable. Not what I'd call jerky, just fast.
Flow control valves would provide an adjustable speed control if you feel its needed. Also the solenoid valves seem pretty reliable, power on it moves power off it stops.

Also depending on your pump size versus the cylinders you control it may not be too fast. If you tractor has a foot throttle thats even better.

Most of the skidsteer attachments have a 1/8" orifice to control speed if its needed in their application. A flow control would be much handier, of course some machines are proportional but they still don't work all that great and tend to be quick in my experience. (Bobcat 773 g and 853c)
I have put flow controls on the swing of my backhoes attachment, on my tilt attach and on my old meyers snow blade I converted to skidsteer, just to slow things down and was very happy.
Its not a perfect system because it forces the extra oil that can't get through the flow control fast enough, "over relief" which draws some unnecessary engine power. On a skidsteer we are talking about 16 to 20 gpm though, your pump is likely much smaller and the cylinders your controlling similar in size to a skidsteer. say 2 to 3"

If you figure this out I may be interested for my 773 g aux hydraulics, as the proportional bobcat valves sticks on, I have spent $300 on new needles to no avail, we figure its a internal leak in the 3 spool valve body, I have not bother to ask Bobcat what a new main valve would be worth. As you can tell I'm a fan of k.i.s.s
jmho

Ken