stepper motors glitching

[irving2008]

Definitely sounds like there might be a heat issue.

A useful trick from my 'making the design work on the manufacturing line' days... Pop to maplins, get a can of freeze spray (or B&Q pipe repair freezer) - its a bit pricy (£14 B&Q) but you only use tiny amounts. direct the spray onto hot parts one at a time, small bursts, till you find which component reacts. A temperature probe (Maplins £19.99) is also useful. Obviously adding a fan would help but sometimes replacing a part with a better rated part is a more effective answer, or adding localised heatsinks. Classic examples of poor design are the lack of heatsinks on voltage regulators so they flip in and out of thermal limiting - doesnt stop the circuit working but causes odd side effects as the regulator current limits and the 5v supply rail drops out of spec for a millisecond or so.

[routercnc]

Hi Irving2008,

I was beginning to think that this was a heat issue, but went back in the garage after work today and the reading direct from the parallel port was full of glitches again. I'm getting very confused by what seems to be perhaps multiple contributing factors.

Started disabling every other port and piece of hardware I could, and disabling AVG at startup, removed printer driver, and still got glitches on the port.

Only encouraging thing from this is that I've managed to ''hold" scope readings on the screen to work out the pulse spacing. Sorry I'm struggling to get these as a good photo (there is no output on the scope either), but I think the following will give you the numbers you need. These are the Mach3 settings, and theoretical pulse spacing:
INPUT
320 steps / min (calibration: stepper per rev, 1/8 microsteps, 5mm pitch)
1500 mm / minute traverse rate (my jog speed)

THEORETICAL OUTPUT
= 480,000 steps / min
= 8000 steps / second
= 8000 Hz
= 125 microseconds between pulses

Comparing this to a typical scope reading shows several pulses spaced at 125 microseconds, then a spacing of about 187 microseconds, followed by more at 125 microseconds. This 187 microseconds is probably:
125 + (125/2) which is 187.5

This means there are several normal pulses, followed by a gap of 1.5 times the correct pulse rate. This is odd, I was expecting missing pulses rather than a mis-timed output. It is more of a jump than a missing pulse. Does this give anyone any more ideas?

Thanks for your continued support and ideas . . .
Barry

Re-read your post, and thought I'd add a bit about the system 3 board and the heat. There are transistors with metal plates which I think are the regulators (see photo in post above). These do get quite hot to the touch within perhaps a minute or two, hotter than the allegro chips. I had considered heat sinks on these, but with the glitches on the parallel port that area of investigation will have to wait. Good suggestions about the cooling spray etc, thanks.

[Robin Hewitt]

Comparing this to a typical scope reading shows several pulses spaced at 125 microseconds, then a spacing of about 187 microseconds, followed by more at 125 microseconds.

A quick explain might be called for, if you already know all this someone else might find it useful.

Windows time slices the processor, that's how it can run several programs at the same time. A Windows programme is actually a whole mess of unconnected programmes all working to a common purpose.

For example: You ask Windows to put a button on the screen, a resource. You the ask Windows to allocate the button to you, and come to you should someone press it. Your button might require part of the screen to redraw but your button can only invalidate that part of the screen. Nothing happens until Windows asks you redrawing program to refresh that part of the screen.

Without time slicing the machine nothing works.

MACH has to assume that other programs do not create appreciable delays. If they do you get glitches. That is why you you want to crock everything possible apart from MACH.

AVG 9 has a bad habit of creeping across your disk checking files. I know this because I had a corrupt sector on my disk, if I tried to read it Windows crashed. It took about half an hour for AVG to find it running it's background scan and then POW, dead machine.

Go through your Start up and crock anything you can get away with.