Insane Hydraulics
Bold and audacious blog about fluid power
(Note - there's a prequel to this post)
Now, where was I?
Oh yes, I ordered a top tier JS1-H joystick from Danfoss and it "went out on strike" as soon as I finished installing it on a Terex handler (or, as my "backup theory" would suggest, I may have accidentally installed the joystick "to its death"). After double-checking the connections, the cable (all the 25 wires plus the SUB-D connector) and then disconnecting everything but the three power wires (+12 V) and the ground wire - the joystick still would not work. What a fun place to be at!
I said to myself - the system passed all the tests without a hitch but a couple of hours ago, so what's different now? The only thing I could point out was the fact that last time when I ran it - the joystick was sitting in my lap and not resting on a support. I knew for a fact that the metallic support was well grounded, I had verified this, but I checked it again - and yes - perfect grounding and zero potential between the board ground and the cabin.
Surely - a well designed joystick from one of the best manufactures in the world can not possibly have grounding issues now, can it? Well - I guess it wouldn't hurt to try anyway - so I removed the joystick form the mount and - what do you know? - it began working again!
It was then that I discovered that, for some reason, it had a 3 V potential on the metallic screws and the aluminum collar that makes the mounting base, and shorting it to the ground would cause the joystick to stop working.
An instant solution was to isolate the joystick with a gasket and plastic shims and sleeves around the bolts. The system worked absolutely fine after the "modification", but I didn't like it. Not a tiny bit. Metallic enclosures on mobile should be grounded or, maybe, isolated. 3 V on the collar?! That'a big "No-No", Mr. Danfoss!
Under the circumstances I couldn't possibly make the client wait for another 4 to 6 weeks for another joystick. Leaving the handler stranded was out of the question - it had to work no matter what - so I applied the quickest solution I had in my disposal. But it was one of those solutions that rob you of your sleep and keep you on a permanent watch for "that call" (at least during the warranty period).
A couple of days after the installation my phone rang:
"Hey, it's me, it's about the handler joystick..." - I feel the ground move under my feet " - "How do you activate the winch again?..." - I sigh in relief - "Just push the middle button and move the joystick left and right while keeping the button pressed." - "Got it, cheers!"
A day later:
"Hi, mate, it's me again, about the Terex..." - I feel like someone punched me to the gut - " Do you know what oil I should use in the hydraulic system" - I sigh in relief - "Use the 68, the one that you put in the excavator" - "Thanks!"
Three days later I got another call:
"Hi man, what's up, you good? About the joystick..." - my breath goes away - "the turret won't rotate..." - so I ask - "Is the rotation lock pin engaged? There's a proximity switch above it that enables the rotation only when the pin is up" - "Oh, yeah, you're right. It's moving again now, thanks, buddy!" - I can breathe again.
Well, that's my life now - whenever I get a phone call now - I imagine a joystick. Seriously. I can't even watch TV anymore - "We interrupt this program to bring you this important message - a telescopic handler operator and several other construction workers were severely injured an hour ago when a defective electronic device, presumably a joystick controller, exploded in the operator's hand."
I finally got a word from Danfoss, by the way. I was told that it "probably" wasn't normal, and that I could apply for warranty. Unfortunately the machine is far away and the client can't stop it, so I guess I am going to have to wait and see how this one plays out.
I also tested a standard program joystick I got last week - the 162F1107 - and the aluminum collar and the bolts are isolated from everything, so, I guess I did get a "lemon" from Danfoss.
From now on, whenever I work on a new mobile control system - I will never skip checking shielding and grounding for "funny voltages", before taking the parts to the filed, just in case...