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Upgraded to metric rods

Discussion in 'Mods and Upgrades' started by Matthias, Dec 29, 2013.

  1. SteveC

    SteveC Well-Known Member

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    Does anyone know if stainless steel or steel rods work better or the same?
     
  2. Matthias

    Matthias Member

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    I tried both. I felt that it depends on the nut. You can use either one but make sure you don't use stainless nuts along with stainless rods. That combination has a tendency to lock up. I use stainless rods with brass nuts and it works ok for me.
     
  3. Deadwood

    Deadwood Active Member

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    I have changed the setting and tried to re flash but I keep getting an error message as per the picture , any ideas?

    Untitled.png
     
  4. Deadwood

    Deadwood Active Member

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    a larger pic
     

    Attached Files:

  5. SteveC

    SteveC Well-Known Member

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    You did not load the correct file into the Arduino environment. I can tell because only the configuration.h file tab shows. You need only open the marlin.ino file. That will automatically bring in all other files in the project. Then hit upload and you will be all set! Note that the folder that you unzipped all the files into will need to be named marlin, it needs to be the same name as the file that contains the setup() and loop() main code.
     
  6. SoLongSidekick

    SoLongSidekick Active Member

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    The easiest way to compile the firmware is to just drop the firmware folder into your /Arduino/ folder, normally in your /Documents/ directory. Then just open the Arduino IDE and select File > Sketchbook > Firmware.

    I spent an hour or so at R3D headquarters last night working with Jerry to debug my metric setup. Got to take a look at the new Y axis upgrades (which they are still waiting on a few parts for), and they are solid and beautiful. I can't wait to get mine.

    I've got a splitting headache right now, but as soon as I feel a bit better I will post what we found and how to avoid the issue.
     
  7. Mike Kelly

    Mike Kelly Volunteer

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    For those out there looking to upgrade to m8 threaded rods. I found Ace Hardware sells M8-1.25 coupling. It'll be handy to use couplings to do the auto leveling mod.
     
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  8. John Rygg

    John Rygg Active Member

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    Where is everyone sourcing these metric rods from?
    website ? part #

    thanks
    John
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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  10. John Rygg

    John Rygg Active Member

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    Thanks, I was looking for feedback if there were any new sources or if any rod was better then what was found
     
  11. 69charger

    69charger New Member

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    I had EXACTLY the same issue after going with the metric rods. Moved fine when I told it to move. Make it home and start a print and it locked up and buzzed.

    I changed to the settings in bold and the problem went away:

    #define HOMING_FEEDRATE {50*60, 50*60, 5*60, 0} // set the homing speeds (mm/min) //robo
    and
    #define DEFAULT_MAX_FEEDRATE {500, 500, 2, 25} // (mm/sec)

    Slower than normal homing and start of print but it works.
     
  12. Ziggy

    Ziggy Moderator
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    What is happening here is that the stepper torque required to move the metric rod is higher than the 5/16" rod. The reasons is the pitch of the metric rod is slightly less than the 5/16" and the overall stiction/friction between rod and nut is slightly higher.

    You have a few options.

    - adjust the stepper movement speed down so the stepper does not have to generate quite as much torque - which is what you have already done.

    - adjust the stepper torque to be a little higher by following the instructions here

    http://bootsindustries.com/portfolio-item/pots-adjustments/

    - or reduce the overall stiction/friction by using a nylon nut on the Z axis and dry PTFE lube on the threaded rod/nut. This gives a dramatic improvement and makes the Z axis movement a lot quieter.

    I would suggest you do both the second and third options. Just adjusting the max feedrate speed down may not be enough and could mean you have problems with lost steps during printing.
     
  13. Matthias

    Matthias Member

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    I had this issue as well. Just try to flash again with the same settings until it's back to normal
     
  14. 69charger

    69charger New Member

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    Wish I had my good camera but.... WOW! Can't see how I could possibly get any better quality out of this machine! So happy!! :)
     
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  15. polylac

    polylac New Member

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    Hi together

    I changed my rods from 5/16'' to 8mm. And hat the same problem with the speed as a lot other here.
    It is important to change the homing speed and the max speed (funny thing).

    I also did some testing, because there are different ideas why this happens, like:

    1) to fast movement, so the stepper motor can't catch up (as i understand this idea: the stepper motor is at 12V and 2 Amps not able to spin that fast)
    2) to much force/torque

    But this is not the case (or not entirely)
    1.) The Z-axis rotates less than 300rpm or 5mm/s (with or without load). So it should not be possible to move the X-axis (oder the Y) faster than 200mm/s. But (with or without load) it can be up to 500mm/s or 750rpm.

    2.) the torque requiered should not be higher. A Screw does the same as a wormgear does. If you have some torque, lets say 1Nm and a pitch of 1mm, the you generate 3.14 Nm per rotation (not torque but energy!), thi is translated into the linear motion, because the distance is smaller the force ist bigger, in this case 3140N. If you have a higher pitch you need more torque for the same amount of pressure. So the M8 needs actually less torque (also friction is less because the angle of attack is smaller).
    BUT the rotation speed needs to be higher (13 to 41% depends if you use 1.25 oder 1mm per revolution). So rpm * torque is about the same.

    So why does this happen then?
    One part of the answer is: because there are two motors on one driver. I took one away and now I can run it at 15mm/s or 900 rpm (without load, but remember it was only 5mm/s bevore also without load) and at least 10mm/s with load or 600rpm (all the load on one side).

    The other part is likely midband resonation. As I noticed I can move the X-axis with load as fast as 500mm/s ( (at 5000mm/s^2 so it gets to 500mm/s at 25mm) But without load at acceleration of 3000mm/s^2 i can't get over 300mm/s.
    So the funny thing is at higher torque I can run faster than at lower... That's why I guess there's midband resonation. This occurs ar a certain speed - torque range of a stepper motor. In that case the motor begins to spring back one step, and then forwards again (oscillation), so the net torque goes to zero, because the motor is simply not turnig any more.
    Another load, speed, current setting and so on can influence this more or less and change the behaviour (so it's not a simple thing).
    There ar actually dampers avaiable that are in fact little mass wheels (which seems confusing because to accelerate them you need more torque) but they can help coming over this midband and go beyond that (where everything is fine again).
    Pictures:
    mid band: http://www.geckodrive.com/support/step-motor-basics/mid-band-instability.html
    damper (the black thing on the shaft): http://jason-webb.info/wp-content/uploads/2013/05/Y-axis-pulley-misalignment.jpg

    Maybe someone knows more about this resonation, maybe I'm completly wrong with this idea...
     
    #95 polylac, Aug 22, 2014
    Last edited by a moderator: Aug 22, 2014
  16. Ziggy

    Ziggy Moderator
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    As I see it.

    Ignoring any energy loss due to friction, the energy required to lift the X carriage mass 1 mm is the same for 8mm or 5/16" rods.

    So the difference between 8mm and 5/16" comes down to the difference in friction (and stiction).

    I don't think your statement "(also friction is less because the angle of attack is smaller)" when referring to 8mm rods is correct.

    Coefficient of friction is probably the same if you are using steel nuts (about 0.8). But the surface area and angles are different. The speed of rotation is also different and higher for the 8mm rod (2560 steps to move up 1 mm versus 2267).

    Putting aside all the theory and given that the usual purpose of a nut on a rod is to hold something tight (ie to maximise friction) , then what would you rather have to make sure a nut stays tight - a fine thread or a very coarse thread? If the nuts are the same length, I'll take the fine thread every time.

    So IMO the 8mm rods (using steel nuts) have higher friction (and stiction) so need more torque from the stepper. This conclusion is also supported by the fact that the A4988 driver power needs to be increased to make the 8mm rods operate smoothly.

    Better solution is to use nylon nuts (or better still delrin nuts) on the 8mm rod. Steel rod, nylon nut and dry PTFE lube has coefficient of friction of less than 0.2. Far quieter as well.
     
    #96 Ziggy, Aug 22, 2014
    Last edited by a moderator: Aug 22, 2014
  17. polylac

    polylac New Member

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    @ Ziggy

    Yes the energy to lift 1mm is the same, but you need more turns for it => less torque (because torque * numbers of rotation => energy)

    The statement about the angle is correct, when you imagine a pitch of 25mm you get a 45° angle, the torque goes horizontal and the friction is in direction of the angle, to overcome friction you have do push, and on that angle you push also more on the surface => more force more friction (at 90° angle you push and nothing goes up, like pushing against a wall, the resulting upwards force depends on the angle).
    you also have a downhillforce, and this force depends on the angle...

    the coefficient is assumed the same, the angle not (view the above), the speed has no influence on the force of the friction (not if the difference is that small).

    That argument is not logical, because our nuts are loose. The contact area has maybe a little influence of sticktion, but the difference is small and friction is usually not depending on the surface area (only in extreme cases like on a needle or motorsport etc.) and the difference between 1.25 and 1.41 is not that big...

    I say that has nothing to do with more friction, but with the higher speeds, a stepper has it's speed limits (read about the testing I did) so this seems reasonable. From the physics I see no clue to higher friction but less.

    One point that can cause higher friction is that the M8 nuts sit much tighter than the 5/16'', on my machine one almost didn't went inside the hole. The original nuts were pretty loose. So maybe this reduced ability to move causes a pressing force between the nuts and the rods => higher friction than before.
     
  18. Ziggy

    Ziggy Moderator
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    #98 Ziggy, Aug 22, 2014
    Last edited by a moderator: Aug 22, 2014
  19. polylac

    polylac New Member

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    maybe bad choice of words, but you cant make a point when the situation is totally different.
     
  20. Ziggy

    Ziggy Moderator
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    The situation is not different. Please read the reference and think about it. "Loose" just means the linear force is lower. The mechanics etc are the same.
     

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