The tracks are powered from the same hydraulic bank but are connected mechanically by foot pedals. There is an additional electrically connected button which increases the track speed which may be what you see on the diagrams.


Gerry

 

Here's a proof-of -concept schematic (NOT a full working drawing!), assuming
1) the joystick itself has all connections (3 pot terminals plus 2 x 2 direction switch terminals) presently uncommitted,
2) the valve itself has no inbuilt smarts,
3) the valve has 2 solenoids with 2 terminals per solenoid,
4) the joystick pots and valve solenoids can handle 12V,
5) the solenoids are not polarity-sensitive.

U1a,U1b form an astable oscillator providing a triangle wave output which is summed with an offset voltage. Adjustment of the offset enables the width of the dead zone at the centre of the pot movement (i.e. the neutral point) to be set. The sum is buffered by a unity-gain opamp. For each of four channels the output JS from its joystick is summed with the opamp output and applied to a gate U1c etc to generate a PWM output (relying on the inherent switching threshold of the gate). The PWM signal drives either of two FETs, depending on which of the two direction switches is closed (e.g. a closed switch A pulls down the gate of the FET for solenoid B thus holding it off).
One opamp and one CD4049 suffice for four channels.
Simulation shows the circuit logic and timing are not affected noticeably by voltage (9V -15V) or temperature (-20C to 50C).
Disconnection of a joystick drops the PWM duty cycle to 0, for safety.
Other safety features may need to be added.

 

Thanks Alec t,
That's quite a detailed solution. I'm afraid I'm a novice to this area and I would not know where to begin. Is there a simple "off the shelf" solution which could be tweaked to suit? or I would willingly pay someone to construct an interface to suit.
As a result of someone stealing the part from my machine I am left with a digger of only scrap value.

Thanks again
Gerry

 

As I mentioned earlier, I believe this is not a trivial project.
If I was involved in this I would want access to the machine.
If it were not for the fact the J.S.'s were zero referenced to 2.5v, a small analogue to PWM servo drive or the El-cheapo simple 555 ones on ebay may work to operate the valves in a simple fashion, a small mod to them may work also, but a little extra would be needed to incorporate the cycl enable N.O. switches.
Keep in mind the original had a central processor so there was more than a little degree of sophistication.
Interesting project, non-the-less.
ebay (400586595552)
Max.

 

I'm afraid I'm a novice to this area and I would not know where to begin.

Then for safety's sake it would be unwise to tackle construction of a DIY controller, especially without full knowledge of the joystick and valve ratings/properties.

 

"the cycl enable N.O. switches."

I take it these are the additional controls for safety features which I do not require. These are a modern phenomena and many older machines are still operating without this aid.
I'm still in favour of the simple solution. The device you suggest, I assume controls the valves, (although I think I need a 10v version). Where does the joystick input feature?

Gerry

 

The N.O. switches are to indicate or enable a particular valve coil/side that that function has been selected, in the OFF position, I see the switch open and disable the amplifier for that particular side.
If you have a amplifier of some kind with 0-10vdc output, I do not see the current requirement being more than an amp or so for pilot operated valves.
The voltage of 5v supply I assume is no more, as this was supplied by the swiped control, so in that case they can be configured in various means such as a 12v supply.
The problem or thing that has to be addressed is at present the centre off represents the 50% point of the supply across them.
Max.

 

I do not see the current requirement being more than an amp or so for pilot operated valves.

In the article I linked to the typical current is quoted as 0-2.1A.

The problem or thing that has to be addressed is at present the centre off represents the 50% point of the supply across them.

In the circuit I posted that is averted by connecting the two ends of the pot together. The resistance then varies non-linearly with wiper rotation, albeit symmetrically about the centre (off) point; but the non-linearity can be an advantage in that resistance changes more slowly near the off point, giving a 'soft start' effect to the ram movement.

Edit: PWM variation with joystick output volts

 

I do not see the current requirement being more than an amp or so for pilot operated valves.
Max.

In the article I linked to the typical current is quoted as 0-2.1A.

An amp or so!
I don't think I would design for that tight a spec anyway.
Max.

 

An amp or so!

Right . Further research (on Bosch Rexroth valves) indicates the solenoid resistance is ~2 Ohms cold, 3 Ohms hot (up to 150C!) and that max allowable current is 2.5A, so current-limiting (straightforward to do) would need to be added to my bare-bones circuit.

Edit: Oh, and the typical system is 24V, so the electronics would need a Vreg to drop the volts to e.g. 10V-12V. Plus transient suppression, fusing, ....

Presumably the stolen control box had proprietary electrical connectors. Are these available as spares at a sensible price? Or would you rip off the joystick/valve connectors and replace with common types?

 

I was planning on replacing the connectors with Deutsch type ones.
I have also been in contact with a company in Australia who have a replacement/bypass for the part I'm missing (apparently they commonly go faulty). I may have to go this route albeit at a hefty price of over AUS $1,000
I also checked the joysticks which are the same as those used in a bigger machine and operate with 12v

Many thanks
Gerry

 

Won't your insurer cough up for the stolen kit?

 

no insurance I'm afraid

 

If building custom circuits isn't your thing, maybe programming the desired operation in a graphical format would be easier for you. Check out the Danfoss Plus+1 system; designed specifically for what you are trying do (control proportional hydraulics on moving heavy machinery). I don't know if it will be cheaper than whatever the aussies are trying to sell you, but it's an option to consider.