Uncommanded movement at power-up

[electro]

Hi, folks.

I have a PRT Alpha since 2004 and it has worked well except for some recent overheating problems which The good folks at Shopbot have provided a fix for even though the unit is out of warranty.

Late Thursday night, I powered the unit up and it started moving by itself in all three axes.

I quickly killed the power. I still can't believe it didn't break the bit.

In any case, I power back up, and the problem didn't recur, but there were new problems with the inputs from the e-stop switch and the zero plate that were not able to be solved.

What is really bizarre, is that I could change the operation of the e-stop to normally open via the VN command, and it would still function as e-stop, but would give no warning light on the control software. Input #1 stayed lit green no matter what I did.

So, I am purchasing replacements for both base-board and the processor board.

What I am wondering is if anyone else has ever had their bot move uncommanded, and if so, what was the problem and resolution?

Thanks,
David

[harryball]

Nothing to that extent, I have a PRT Alpha, the most I've every observed is a slight jitter at power up and that is not often.

Hope you get it solved, keep us posted.

Robert

[henrik_o]

We have had two such occurences.

1/ Due to the spindle fan being wired to the power supply in the control box. We are not sure exactly how it was wired incorrect, and neither was Scott and Jamie at Shopbot, but our best guess is that the cable caused interference issues: we never got to test that theory because by then we had already moved the fan wiring to an independent (outside of the ctrl box) power source.

2/ Once, when I jacked out a USB memory stick during cutting. I don't know what I was thinking. It caused a violent plunge into the table but nothing broke, not even the bit. It turned out the usb jack I evacuated was on the same internal root hub as the usb for the ctrl box: in any case, I would not mess with the usb jacks even if I moved the ctrl box connection to an independent card.

[electro]

I hear you one the USB port. In my case, the computer was just sitting there. Besides that, the contactors aren't supposed to close without a reset, at least that is my understanding.

Nothing at all had changed with the machine other than I had turned it off earlier.

David

[harryball]

That's interesting... come to think of it the only few jitters I've observed were after I changed out my spindle fan to one that gets power from the control box. Like I said, only happened a couple of times and if it wasn't for the sound I wouldn't have noticed it at all.

You learned an important lesson the same way I did... never eject or insert anything while the bot is running. If I eject the PCMCIA network card while it's running it stalls and lurches violently. I pulled a USB memory stick out once... the bot lost communication long enough to mess up my work.

Robert

[henrik_o]

Robert,

I don't want to pretend I understand what was going wrong for us -- I do not -- but IF you supply your spindle fan from the ctrl box, you may want to be sure you're using quality cabling and that you are not having any loops on that cable inside the ctrl box. I don't know, but that was probably our problem.

[Brady Watson]

David,
I've experienced the 'run away' personally & it was a result of loading new control software, but not installing the outboard driver software before moving the tool (install control box firmware ALWAYS before running a new version)

Also, some computers have really crappy USB interfaces/busses. I always recommend installing a PCI USB card in the computer and plug a USB 2.0 hub into that, then the Bot. It will clear up just about any communication or USB problem by putting the Bot on it's own USB channel/bridge, separate from the keyboard and mouse. Dell computers in particular have issues with their USB devices (KB & Mouse) and conflicts with the SB USB.

-B

[cnc_works]

I recently installed a spindle on my smaller CNC and if I powered it up before the steppers were activated, all three axis would move with the steppers growling like a grizzly with a seizure. Grounded the spindle properly and the problem went away. Probably not related to your situation, but the symptoms are similar.

Donn

[electro]

Thanks for the replies.

I hadn't installed anything, merely powered the unit up. I installed new software AFTER the incident in hopes that it would cure the problem. It didn't. The bot had been functional earlier. What it did do was get very hot (control box), so I shut if off.

Thanks for the advice Brady. I will make sure that I don't install control programs before firmware upgrade. What is the current version of the firmware? Last I looked it was 1.3 something.

David

[Brady Watson]

David,
The latest Windows version of the control software for PRT, Alpha and PRS tools is v3.5.3. You can download it here: http://www.shopbottools.com/files/Setup_sb3_5_3.exe

-B