stepper motors glitching

[Robin Hewitt]

My stepper driver runs under DOS

Ancient history maybe, but I have the computer's undivided attention and all it takes is one setvect(0x1c,service); for the timer interrupt to become mine, real time, glitch free.

The only real escape for Windows is to add a slave processor on the end of a cable. The slave can then do all the timing while Windows makes it pretty.

[routercnc]

Thanks for all these suggestions and explanations. AVG is out of there! If this does not work then I had made my mind up last night that it was time for a fresh install. That machine actually has 2 hard drives (the other one is not used but contains the old system that got too clogged up) so I am going to reformat the other one, re-install windows, any vital drivers, then mach3.

Wife is asking when she can have things engraved again, so no pressure then!

By the way, if I were to create an 8KHz square wave (of about 3-5v) and inject it into the system3 parallel port pin 3 and earth, would the stepper rotate or does it need all the other pins to be present (board has a charge pump override)? I have access to lots of signal processing kit at work and could easily do this, or even borrow a signal generator to do it live.

Thanks
Barry

[irving2008]

yes it would, in fact thats exactly how I test my drivers. You may have to patch the enable lines and disable the charge pump but these should be jumpers you can move on the system 3 board, or make a 25way test adaptor from a 25pin male connector and some hookup wire.

[routercnc]

I re-formatted a spare harddisc, installed windows xp, and then added mach3. Same problem with glitches. I'm now open to try anything, so . . .

I downloaded ubuntu-8.04-desktop-emc2-aj13-i386.iso onto another machine, then burnt it onto a disc. However, when I put this disc into the cnc PC with the reformatted harddisc (setting it to boot to CD in BIOS) I get 'Boot from CD :' then 'disc boot failure, insert system disc and press enter'. It does not recognise this as a boot disc. Not being familiar with linux install I don't know how to proceed from here. Any offers?

[irving2008]

did you burn it as an ISO image using 'disc at once' or burn it as a file? If you open the CD on your PC do you see the ISO file, or do you see a collection of files? If the former then you need to find out how to correctly burn an ISO image...

[routercnc]

I borrowed a function generator from work yesterday and set it up for a square wave TTL output of 8KHz (=1500mm/min on my system). I connected this to pin3 and earth on the driver board and the stepper motor ran smoothly. I then tried different speeds and at low speeds <8KHz the motors glitched. This was the same result as when the PC is connected whereby it glitched at lower speeds. Although this doesn't rule out the PC glitching, it certainly means that the driver board, stepper motors, or power supply are causing part of the problem and need to be resolved before connecting it back to the computer.

The driver board is a brand new replacement since the previous board glitched (but on the X axis only). The power supply is a 33v 10A unit and is the one recommended by Roy at DIY CNC. This power supply provides 33v (I've checked this with a DVM), which goes through a switch and a current display 0-5A. I plan to directly connect the power to the board to elimate the switch and meter. Next is to double check the wiring to the steppers, but I was very careful with this when I wired them up. Might be getting somewhere !!

[routercnc]

This morning before work I connected the driver board directly to the power supply, thus eliminating the switch and the current display. Again driving directly from the function generator it still glitched <8KHz (i.e. <1500mm/min).

I then checked the connections to the motor and they are all tight. Checked the coil resistance and they both read about 2.8 ohms. I think I read somewhere that this is OK.

I did notice that if the earth connection from the function generator is not made to the parallel port connector, (i.e. only pin3 square wave input is connected) then the stepper motors will still run. This must be earthing through the mains since the power supply and the function generator both run from the mains.

Therefore since the board can run from 24v - 33v, I'm thinking about running it from 2 small 12v batteries in series, as a test. The function generator can also run from batteries. This might tell me if there is some kind of earth loop problem, although Roy tells me that there should not be. The board is not optically isolated.

Are the other users of the DIYCNC system3 all-in-one board out there? What is your set up like?

[irving2008]

Is the glitching at the same frequency? Is there one speed where its worse? I wonder if you're experiencing mid-band resonance where the mechanical and electrical parameters combine to absorb energy to the point where the motor cannot maintain enough torque and therefore loses steps. If you sweep the frequency can you determine a specific point where the glitching is worst? If so, try adding some damping to the motor shaft, e.g. a flywheel or some other angular weighting. Does it still glitch then and has the glitch point moved? If so this would indicate a resonance issue.

[routercnc]

Hi Irving2008,

The glitching is random, and occurs consistently at any speed lower than 8KHz. There is no bad point, they are all equally glitchy until about 8KHz where it starts to smooth out. Above 8KHz it never glitches.

Note that I'm not actually connected to a cnc machine at the moment to resolve this. There is just the 33v power supply, system3 board, one stepper motor, and the function generator. I've disconnected limits, estops etc. There is no load on the stepper and it is still glitching in the same way as when connected to the machine. By the way it sounds I don't think that this is a resonance issue, more like an electrical spike or interference type problem, but I'm open to try all ideas.

I've got 2off 3Nm motors (Arc Euro) which both glitch in the same way, and have different length wires, and one 1.8Nm motor (DIYCNC) which also glitches in the same way and has different length wires again.

I think the best thing for me to do is try and get a video posted so you can see the set up and hear the results of different speeds. Bare with me, never posted video before!

Thanks for your continued support. Determined to resolve this one . . .
Barry

[Swarfing]

Could i suggest you set it off running and then disconnect your screen plus its power supply. I have a similar issue with a dell and it has bad earthing issues from the screen power supply. The interference from these are notorious, could even be the machines power supply chucking spurious outputs all over the place. Worth a punt?