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Thread: A New CNC Build

  1. #136
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    Hi Rod Thanks for your comments.

    Received my KRESS spindle from Germany today. Looks like a very well made bit of gear. Got the extra 1/8" and 1/4" collets and a spare set of brushes too.

    Now all I have to do is arrange a mounting for the spindle, finish the electronics, make up an MDF bed for it and hopefully make it do something worthwhile. Nothing else to spend money on other than some milling and router bits to suit.

    I'm starting to smile!

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  3. #137
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    Hi Geoff,

    Nearly ready to make noises now
    Cheers,
    Bob

    http://www.woodworkforums.ubeaut.com...og.php?u=14230 CNC Router Wood Suppliers

  4. #138
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    Hi Bob

    Won't be long now, although I have a concern that someone may be able to help with.

    I've put my power supply together, but instead of the 49.5V I expected out of it, I've got 51.4V.

    Bearing in mind I'm going to be using G251 drivers which are rated at 50V, am I in trouble?

    The transformer I used is a toroidal with a supposedly 35 secondary connected through a bridge rectifier to two 8000uF filter capacitors in parallel (16000uF).

    If 51.4V is likely to damage my G251s, how can I reduce the voltage by a couple of volts? Do I need to or will the 51.4V be OK?

    Cheers
    Geoff
    Last edited by Geoff Sims; 9th June 2009 at 02:26 PM. Reason: Omitted something

  5. #139
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    Geoff

    That is probably with no load. With a load it will most likely be a bit lower.

    Hook it up to your drivers with motors attached and measure the voltage then.

    There will be a small loss across the bridge rectifier. It should end up about 48v.

    Greg

  6. #140
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    Geoff,

    The latest thread on the yahoo geckodrive group raises this same issue.
    The answer from Mariss is that the drive is tested at 60v and (in his words) "comes apart at 68v".

    51.4 volts won't be a problem but as Greg says, it will likely drop under load.

  7. #141
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    Hi Greg and Geoff

    Thanks for your re-assurance. I'll carry on and connect it up.

    As a matter of interest, I did put a load on it using a 240V light bulb, thinking that would be enough to try it out. The 51.4V was with the light bulb attached, although a 240V light bulb might not have been the best load to use.

    Anyway, I'll press on....thanks

    Cheers
    Geoff

  8. #142
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    Haven’t posted for quite a while, mostly because I haven’t done much until the last couple of days.

    I’ve finally finished off my power supply/control box and all seems well. Not the tidiest bit of work I’ve done, but the power supply works and the BOB communicates with the PC OK.

    Since my power supply transformer had a 15V winding on it, I made up a little voltage regulator (about $2.50 worth of parts) to drop the voltage down to 12V to run the two cooling fans.

    I also installed another small power transformer and another small voltage regulator to supply regulated 5V power to the BOB since the main transformer didn’t have a suitable winding. (Less than $10 including the transformer). I preferred this setup rather than dragging 5V from the computer via a separate USB cable.

    The cooling fans draw cool air in through the top and bottom of the heatsink and exhaust it out the back of the case. The case has vents through the top and bottom covers at the front which gives a good airflow through the case and everything stays nice and cool.

    I’ve kept everything fairly simple, so far only wiring up an E-Stop button on the front, but as I learn more, I’ll incorporate a touchplate and what ever else I think will be handy. Best to start out basic.

  9. #143
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    I’ve finally made up a stand to sit the machine on. It’s just welded up with a bit of scrap patio tube. I’ve yet to put a couple of braces on it, and a shelf near the bottom which should make it fairly solid. I’m also going to put a swarf tray directly under the machine.

    The only construction then to be done is to fit a bed on the machine, and I’ll be doing the same as Rodm did with Morphy, using his push-pull method with grub screws to get the height just right.

    In the meantime, I’m trying to study up on Mach 3 so I can hook it all up, set it up properly and make it do something. I hope it’s going to work OK.

    Cheers

  10. #144
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    It is good to see the machine grow and of course it will work.
    I like the stand.
    Not much to do now.
    Cheers,
    Rod

  11. #145
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    Great to see the progress Geoff.

    You are going to get a lot of use and fun out of this machine.

    It is a bit hard to get perspective from pics but it looks to me like you have signal wires running more or less together with power wires.

    See if you can get a bit of physical separation between the LPT ribbon cable and the power wires.

    Is there room to relocate the panel mount BB25 to the other side of the heatsink? Or maybe underneath the heatsink?

    No big deal. You can always just see if you have problems first.

    Greg

  12. #146
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    Hi Rod. Getting close. All I have to do is find the time.

    Hi Greg. I'm already getting a lot of fun out of it, even though it hasn't moved yet. I see your point about the close proximity of the signal and power wires. I didn't really give the layout as much thought as I should have. I just wanted to get the thing together and get the machine going.

    It actually never occurred to me to run the ribbon cable under the heatsink, but I think what I might do is just turn the BOB around, and put the 25 pin plug in the front panel.

    Once I get the machine running, I'll hopefully be able to machine new front and back panels for the box as I've already changed things a couple of times and have some holes where they shouldn't be.

    I appreciate your advice. I need all the help I can get.

    Cheers
    Geoff

  13. #147
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    After modifying the cable layout in my control box to keep some separation between the signal wires and the power wires, I finally hooked everything up for a test.

    I actually got movement in the X & Y axis which pleased me no end, but I have problems with the Z axis.

    The Z axis stepper made some horrible noises when I tried jogging it. It moved, but it was very loud, and violent, each step causing the whole machine to shake.

    The stepper also ran very hot, and I mean VERY hot. Too hot to touch. The X and Y steppers were just very slightly warm.

    I powered it down and let it cool and I thought it may have been an issue with the Z axis wiring so I checked it all over until I was sure it was correct. Mechanically, everything was ok and moving freely.

    To try to isolate the fault to either the driver, or the stepper motor, I connect the X axis to the Z axis driver, and the Z axis to the X axis driver and fired it up again. This time the Z axis worked fine and the X axis displayed the same fault as the Z axis did before. The stepper motor got VERY hot and made the same horrible noises.

    I noticed also that as well as the stepper running hot, the G251 Z axis driver was also running very hot. The main capacitor on the driver board was hot to the touch and yet the capacitors on the other two drivers were quite cool. I powered it down again and let it cool.

    Next, I restored the X & Y axis and just left the Z axis stepper disconnected. This time, without a stepper connected, the Z axis driver stayed nice and cool.

    So, I have to conclude that the Z axis driver doesn’t like to have a stepper motor connected and assume it must be faulty, although I can’t imagine why. The G251s were all installed at the same time, are all wired identically and were all powered up at the same time from the same power supply. So why are two OK and one faulty? Don’t know.

    So, I’m stumped.

    Does anyone have any suggestions please?

  14. #148
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    Hi Geoff,
    As you say the problem is from the point where you have disconnected the motors to swap them over back to the computer but more likely the Z axis driver board.

    Concentrate your efforts on the Z axis driver back to your power supply and your Bob. Check you have right polarity from power source to that drive. Check you have the signal wire grounded from the Bob to the G251 - important to have pin 12 grounded to the Bob.
    Also check the 4 motor leads going out from the drive if you are going to a plug.
    If you have disconnected the motors from a plug then this could still be suspect. Get a magnifying glass and make sure a strand of wire is not bridging the terminals.

    Swap the signal wire (parallel port signal wire) from say X over to Z and see how it goes. Recently I tracked a faulty setup for a fellow down to a crappy computer that was sending garbage out of the parallel port - first time I came across it but it does happen.


    If it is all OK then email Marus as he gives very good support.
    Last edited by rodm; 8th July 2009 at 01:29 AM. Reason: Geoff I have added a couple of things so re-read this post
    Cheers,
    Rod

  15. #149
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    Hi Geoff, I don't know too much about Gecko's but I will have a guess.

    Don't they use a resistor to set the current? If so I would be checking that it has the correct resistance, a multimeter should give you an idea of its condition. Lots of heat sounds like too much motor current, that would be my guess anyway, hope it helps.

    Cheers.

    Russell.

  16. #150
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    Hi Russell,
    The resistor sets the idle current. It is a feature to reduce the idle current to reduce heat and a power saving mode. It could explain the overheating but not the cause of it not running correctly - I think the heat is a result of the fault and not the idle current but I am only guessing.
    Cheers,
    Rod

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