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  1. #1
    I'm currently testing the first (Y) axis on my Warco WM16 mill conversion. I'm using standard M542 drives with THESE 4.2A, 3nm stepper motors and have noticed significant vibration at very low speeds. Is this a problem caused by lack of cable screening or is it a setup issue? At certain speeds the whole machine and stand will vibrate. At higher speeds, there are no issues. I've tried running the motor unmounted but it still vibrates at very low speeds. The motor is bolted to a solid mounting. Should I use some sort of rubber mounting to reduce the vibration or is it something I will have to live with?
    Last edited by birchy; 18-11-2013 at 02:26 AM.

  2. #2
    What's the switches set to ? and also Mach3 settings

  3. #3
    Answer Eddy's question first, but what your describing is resonance. When the machine is excited at particular frequencies, the vibrations will build up (like a tuning fork), so ideally you want to avoid these speeds or damp out the vibrations. One way to avoid them is to increase the micro-stepping resolution - this increases the frequency and can reduce the range of speeds at which resonance is a problem. One bonus of driving the ballscrews with timings belts is they have a noticeable damping effect.

    If the motors aren't actually stalling you might be fine. A video may help...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #4
    Yes, I was thinking they might be cogging badly at low speed due to low micro-stepping resolution, or starved of current.

  5. #5
    I'm using LinuxCNC set as per the picture below. Dip switches on drive are set to 800 steps (all switches 'off' except for 5, 7 and 8). I've also tried running at 1600 steps (and changed "Driver Microstepping" to 8) which did improve the resonance slightly. At 3200 steps, I had some error message related to the RTAI (realtime kernel). I didn't look up the specifics of the error as I just assumed it was related to the step rate being too high.

    Click image for larger version. 

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    Last edited by birchy; 18-11-2013 at 07:20 PM.

  6. #6
    Sorry for assuming you used Mach3, from my limited knowledge the settings appear to be okay, you've probably been at this longer than me anyway. I would be into trying a different motor and swapping the M542 just to eliminate those from the equation. If you think it's maybe a screening problem why not run a temporary cable between the motor and M542 that is well away from everything else. There was another thread a few weeks ago about rubber mountings and I suggested using heatproof silicone sheet like this SILICONE RUBBER SHEET 200MMSQ, 1,1.5,2,3,4,5,6,8,AND 10MMTHK | eBay, but the opinion was to bolt the motors straight onto metal.

  7. #7
    Quote Originally Posted by EddyCurrent View Post
    you've probably been at this longer than me anyway.
    Linux - probably...CNC - almost definitely not...

    I'm beginning to think that the resonance is a feature of the cheap setup rather than a fault? I'd be interested to see what Jonathon and John S have to say about this, as I know they use these drives and motors on a regular basis. The motor is bolted to 200Kg+ of metal so I'm surprised there's any noise. I'm thinking I might need to isolate the motor bracket from the main machine using some rubber sheet. Having said that, the issue is with the motor setup rather than something mechanical. Pics for reference:

    Click image for larger version. 

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  8. #8
    Is my BOB too close to the mains, I wonder? Having said that, I ONLY get resonating within a fairly tight range of low end speeds. What problems are usually caused by not screening cables? My panel is just straight tri-rated panel wires. I've tried to keep the mains and signal cables apart as much as is practicable. Cables connect to the motors via metal cored industrial 20mm Adaptaflex.

  9. #9
    As a matter of interest are you using ball screws or the original screws? Big credit to the neatness of the panel. ..Clive

  10. The Following User Says Thank You to Clive S For This Useful Post:


  11. #10
    Quote Originally Posted by birchy View Post
    Is my BOB too close to the mains, I wonder? Having said that, I ONLY get resonating within a fairly tight range of low end speeds. What problems are usually caused by not screening cables? My panel is just straight tri-rated panel wires. I've tried to keep the mains and signal cables apart as much as is practicable. Cables connect to the motors via metal cored industrial 20mm Adaptaflex.
    I don't think your BOB is too close to the mains, I used CAT5 4core (2 x twisted pair) networking cable for the connections between the BOB and Stepper Drivers as this eliminates a lot of interference.
    The problem you describe does not sound like a wiring problem and is likely to be resonance. I noticed the gap between the motor bracket and the machine was very small in places and I wondered if they were vibrating against each other like a tuning fork ?
    Last edited by EddyCurrent; 18-11-2013 at 11:34 PM.

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