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Ox CNC motor issues

Discussion in 'CNC Mills/Routers' started by Cbrown330, Mar 6, 2016.

  1. Cbrown330

    Cbrown330 New
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    I just finished my OX CNC build, but having issues with motor current.

    I am using the CNC xPro controller from openbuilds
    Nema 23 motor from openbuilds.
    bosch colt router

    My build is 1000mm by 1000mm using the OX plates, gives me a 818mm by 700mm cutting area.

    My issue is that i am not getting any cutting force to speak of. I have created a job in Sketchup to plane my spoiler board to level the board to my spindle. If i set my feed rate to around 800 then i can cut a depth around 1-2mm, but it i try to cut 3mm deep then my motors will skip and stop turning. I have tuned the current following the xPro instructions. I am at a point if i turn the current POT another 8th turn then the motors wont run(assuming to much current), but i still get bad motor steps.

    What i think is going on is the controller is not powerful enough to run the nema 23 motors, or that the motors dont have enough torque. Motors are rating at 2.8 Amps and the controller is rated at 2.5 amp peak, but run around 1.75. Has anyone built a maching this big using the xPro controller? If so can you share how you got good cutting force.

    I am thinking of buying new motors, i am looking at these.
    http://www.automationtechnologiesin...14”-dual-shaft-stepper-motor-kl23h2100-35-4bm

    But if i get these then i need to upgrade the controller, which i am looking at.
    Gradus M1 PRO GRBL CNC Controller With the bigfoot drivers(if they are avaiable yet). It will give me a 4 Amp driver and should run the 3.5 Amp motors.

    I am alos looking at a new spindle. If anyone has a spindle in mind pls let me know.

    My over all goal for my CNC is aluminum milling. I just want to pass this by a forum before i replace my motors and controller. So any feed back is greaty welcomed.
     
  2. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Hello C,

    I'm almost done with those DRV8825; they are good for NEMA17 and small (short) NEMA23 motors, but they just become a pain in the behind when cables are becoming too long, plus not shielded, and motors are getting too big. Anything over 1.25A @ 24vDC continuously gives problems most of the time. Sure you can put a fan on it (you need to!) but I don't see that as a good solution.

    For my next personal build I'll use a 16MHz Arduino Uno and TB6600 drivers (don't touch the 6560! Most are bad copies). I would go that way over that 75USD shield with Arduino 328p soldered on it.

    -Ronald
     
  3. Chillimonster

    Chillimonster Journeyman
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    What psu are you running?
     
  4. Cbrown330

    Cbrown330 New
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    So the motors are not big enough to run what i need, plus the controller is undersized.

    Chill i am using a 24VDC 8 Amp supply, not using the ATX.

    I was wondering about the DRV8825, i have the same drivers running my 3d printer with Nema 17s and i get ALOT more drive force with my printer. I guess i will just upgrade the motors and the controller, and repurpose my motors. I may build a small Cbeam with the controller

    Has anyone seen these big foot drivers? Just wondering how they are. I like the Pancutt devices controllers. I am using one for my small 3d printer and just bought the Azteeg Pro for my big 3d printer. I guess i need to try to post some pics of my builds

    Thank you guys for your responses.
     
  5. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Motors are fine.

    Same here, I like the Pancutt stuff, still I would forget about getting something as small as possible and thus would leave those big foot drivers aside and look for something that can handle 5A (peak). The thing is, when you use separated drivers you can also power them with more than one PSU, using for example one PSU to power two motors and another PSU for the other two motors. This is the reason why OpenBuilds now stocks a 350W 24vDC MeanWell PSU, small boards will crap out before that PSU does, and when you need more power you just use one PSU more on separated drivers. Those TB6600 are able to deliver for NEMA34 motors and they are cheap (17-18USD or so).

    What is the brand or model of the PSU you are using? It doesn't drop much in voltage when you start to run the CNC machine?

    -Ronald
     
  6. Chillimonster

    Chillimonster Journeyman
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    I'm running the standard 2.8a Nema 23's with a 24v 15a psu and the cncxpro controller.

    Quite happily cutting away at 5000mm / min and above. 3mm bit at 4mm passes (did a 9 MM pass by accident and didn't stall the motors.

    Took a while to get it dialled in. One of the issues was the psu pushing out 29v. Turned it down and it behaved better.
     
  7. Cbrown330

    Cbrown330 New
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    well i guess i lied to you both. I am using the 24V supply from openbuilds, its a 14.6Amp. I havent checked the output power though (duh) should have done that already. I have checked all the mechincal build though and everything slides nice with no force required, so i wouldnt think i have mechincal bind. However the cables are about 5 foot long, and i am using a Banner 4 prin field wirable connector for fast disconnect of the motors. I use the banner connectors alot for work and never seen a considerable voltage drop accross them.
     
  8. Cbrown330

    Cbrown330 New
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    O and by the way i am using a 1/4 inch end mill, brand new and cutting MDF. So the material is soft and the blade is sharp.
     
  9. Cbrown330

    Cbrown330 New
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    Ok i am at 24.02 measured voltage. So i am good there. Tried it again with no luck at all.
    I lifted the X axis at tried to run at 1500, 2000, and 5000 feedrate with no load and the machine stalls at every feed rate. I adjusted the current POT a 8th of a turn each adjustment say it go from bad to better to terriable. Even when i was half way through the POT i could very easily just apply a small bit of restance to the Y axis and it would stall. I am running at 30 microsecond step pulse in Grbl, and the steps/mm are dead accurate, measured with calipers. So i dont know what other Gbrl settings coule help.

    So i dont know. I do know i had this same issue with my Nema 17 on my 3d printer, but i was able to measure the current to the motor with a meter. Is there a spot to measuer so i can set the current with a meter?

    Chill is there anyway you could share your settings with me, maybe its something in there as well that could help me.
     
  10. Ronald van Arkel

    Staff Member Resident Builder Builder

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    What about the stepper divider settings? 1/8? 1/4? The smaller the step, the less power you get from the motors.

    So, you have the MeanWell PSU? Does the voltage drop much when you run the machine?

    Wires should be okay, what AWG or mm2 are we talking about?
     
  11. Chillimonster

    Chillimonster Journeyman
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    I will sort my settings later if i venture into the workshop.

    I'm running 1/16 stepping (More for accuracy), and my voltage is at 24.9 (To allow for a little voltage drop)

    I am also running dual belts, properly pensioned, as are the wheels. When i first set it up they were too tight resulting in stalling at any feedrate and current setting so may be worth checking.
     
  12. Cbrown330

    Cbrown330 New
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    I am running at 8th step, i measured the output voltage while running as was not getting any drop from the PSU. The wire is 16AWG.

    Now i am really going to sound like a Green Noob here. I found a post from you Ronald about a year and a half ago, talking about heat sinks. I have sinks but dont have them on the drivers yet. I knew i needed them but didnt think they would cause a huge issue like i seen in your post. So today after work i will be installing them and a 24V fan to draw the heat out of my controller box.

    I am certain that i am getting thermal overload, the controller is open to the air but in Texas that dont mean to much. One question though would the heat cause the motors to lose tourqe? I noticed when i power up the machine the motors lock really well and takes a good amount of force to skip them(which is a good sign), but when they start to move i lose it all. This could mean that the drivers are heating up within a few minutes causeing me this issues.

    So after i apply the sinks and the fan ill try it again tonight and let you guys know.
     
  13. Chillimonster

    Chillimonster Journeyman
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    Thermal overload can cause the drivers to completely shut off until a 'safe' temperature is reached. This could be a fraction of a second or a few seconds, giving the symptoms of lack of torque, so naturally you increase the current and end up in an endless loop :-(

    Fit the heatsinks and the fan especially if the ambient temp is high (Which it is from the sound of it), and start from scratch with the tuning of the motor currents.

    let us know how you get on.
     
  14. Cbrown330

    Cbrown330 New
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    Ok my sinks are a little big, But after i put them on i did see a small inprovement. So i think i am going to print me a new box with 3 fans and get some smaller sinks. Still didnt get a real rock solid feel on the force of the motors, but i guess it could be becuase the sinks are not sitting correctly. Ill keep tinkering away and keep you guys posted thank you
     

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