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How to Set Current Pots on Black Box

Discussion in 'Controller Boards' started by Vic Phillips, May 25, 2020.

  1. Vic Phillips

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    Does anyone know how to set the current pots on the blackbox controller i just finished hooking it up and dont want to do any damage. I have not used it until i figure this out....Please Help.
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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  3. sportsracer

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    That documentation is lacking a little. How exactly do you do this?

    "Adjust the current until you can no longer stall the motor under normal operating conditions."

    Run the axis and adjust until the motor stops and then turn the pot up a little? Adjust it until the red led comes on? Seems there should be a little more precise way to do this?

    -----------------------

    OpenBuilds BlackBox has four onboard Stepper Drivers. As part of bringing your machine online, you are required to adjust the stepper driver current for each axis.

    [​IMG]

    • Adjust each axis in turn
    • Adjust the current until you can no longer stall the motor under normal operating conditions.
    • Adjusting the current too high can lead to the stepper driver overheating. The axis will shutdown until the board is power cycled, and light up the Red Exclamation Mark LED on the front.
    • Adjusting the current too low, will lead to lack of torque, and subsequently skipped steps.
    Note: Pay attention to the Red Exclamation Mark LED below each axis's Current Adjustment Potentiometer: if the driver experiences any fault it will shut down and turn on the LED.
    Faults that trigger the LED:

    • Overcurrent (Adjust current down a little)
    • Overtemperature (Adjust current down a little, check fan)
    • Short circuit (Check wiring, Check motor)
    • Low Input voltage (Check Power Supply)
     
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  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Its that easy. Run the machine through its paces as you'd normally do

    If it stalls, feels weak. Dial in a 1/8-1/4 turn
    If it overheats the driver (red led) or motors burn your skin, dial back 1/8-1/4 turn etc

    Don't over think it default works for almost everyone

    There is actually plenty big dose of human interface engineering behind it. It is an offset scale potentiometer (far left is not 0 as you'd find on lesser solutions, but rather 1.2A. Far right is 3.2A RMS* ). Also, the factory default potentiometer position is setup so it works out of the gate for all our machine bundles (NEMA23) anyway. Only the Acros needs a bit of turning it down for the nema17s

    That's why there is no need to work in 1 degree turns for example, as the spread scale means the potentiometer is not overly sensitive like the little 3D printer drivers are.

    The thermal indicator LED removes guesswork on that front.

    Just hook it up, motor on the desk and play with it. You'll see its really apparent where the sweet spot is (and its wide target - you are aiming at a field, not a gate). Too high and the motor will feel violent and dangerous and too warm. Too little (but like all the way down) and you might still hurt your fingers trying to stall the shaft, but it will be weaker than where it was before. Play, learn.

    *note: Say your motors are spec'ed 2.8a, don't go dialing in 2.8a from a linear scale of the potentiometer either now, thats a Maximum rating (exceeding that damages the windings for sure) - not a rating of "you should be running this"
     
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  5. Federico77

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    Hello Peter,

    as I was tuning a little my motors recently I spotted this post and while I agree with most of what you report, I am fairly surprised by this specific part:

    Too high and the motor will feel violent and dangerous and too warm.
    Too little (but like all the way down) and you might still hurt your fingers trying to stall the shaft

    I have to say that my Workbee setup with NEMA23 motors never felt this way at any potentiometer level. To be honest it always felt more on the weak side even at default or higher levels. To clarify: when the motors are just energized I can hardly move them by hand, when in movement I can quite easily stop them and let them loose steps without opposing much force and definitely not hurting my hands.

    Also (hence my concerns), I always noticed that X axis felt a bit weaker than the others and it is usually the one that makes my jobs fail every now and then: curiously enough it usualy does that in conjunction with Y axis movements and almost never on straight lines.

    So, what you suggest checking other than potentiometers levels that may affect motor torque/performance?

    Thanks a lot for the wonderful support,
    Federico
     
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    All OpenBuilds parts or any 3rd party components at play?
     
  7. Federico77

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    I sourced my Workbee 1510 from Openbuildsitalia and to be honest I was fairly unexperienced at the time so I don't know for sure.
    If you can provide me a list of NEMA23 motors you guys usually ship I can check against this list as soon as I am back to my garage.

    Thanks a lot,
    Federico
     
  8. Federico77

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    Just to clarify: my motors are definitely not marked as "Openbuilds" as per this sheet: NEMA 23 Stepper Motor
    Best I can do with my models is take a picture and search for specs online.
     
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  9. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Possibly the reason for difference in performance. Our motors are just well rounded in all its specs (inductance, resistance, torque curve, quality) and we spent a lot of R&D to match then well with the rest of our ecosystem.
     
  10. Federico77

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  11. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Our datasheets are on the store. Of course that particular suppliers motors are well known (negatively) around here. Whether the spec sheet even match the product is up for debate.
     
  12. Federico77

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    I see your point although I am honestly not that skilled to even just debate the specs sheet: at first noob sight they don’t seem that different but I can relate to the product not matching the sheet... that’s how it felt at least.

    Now my thing is: should I go ahead and swap at least the X axis and see how it goes? Do you forsee problems from mixing the motors? Z axis seems easy to deal with keeping what I have and Y axis have two motors that should get the job done although a bit weak overall.

    Also, I don't want to pollute this ticket as it is slightly changing topic: should I open a different thread?

    Thanks a lot, I am honestly impressed by support.
    Federico
     
    #12 Federico77, May 31, 2021
    Last edited: May 31, 2021
  13. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Re the specs. They used to have motors with higher voltage requirements and higher inductance than us. I guess the more we had to help guys here who fell for their fakes, the more refunds they may have had, and about a month ago their docs got that new "datasheet" with our very similar specs. Thus my doubt. The underperformance of the motors speak for themselves. I immediately questioned whether you have 3rd party parts, based on the symptoms.

    Replacing motors and power supply (if you are still using their "LED power supply") with ours will make your machine feel different yes. Mixing is Ok except on axes with dual motors.

    Just before you do. You didnt maybe overturn your X axis potentiometer and broke it at some point (unlikely, you sound like a careful guy and it takes quite some force to break it, but he have seen it once or twice) which breaks the current adjustment of that axis.
     
    #13 Peter Van Der Walt, May 31, 2021
    Last edited: May 31, 2021
  14. Federico77

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    Ok, so regarding the motors I will definitely order 1 of the originals for the X axis in the next few hours: I have to confess that I am a bit disappointed at having received something different with my kit although the italian distributor was very kind in many aspects. I never asked for anything different and the pricing was in line with original components. I should have known better.

    Anyway, regarding the potentiometers: I know they are just one rotation in total and I never forced them but, as I stated in another post, the screwdriver easily chipped and broke the plastic screwdriver inset (sorry, I lack a better english term) so I had to order a bunch of fresh ones that I will change most likely today. I did not expect those to fail so easily under such a small screwdriver force. It seems like the x shaped inset lost 2-3 teeth as soon as I touched it... maybe an unlucky batch.

    Let's hope the motor will be in my mailbox soon enough to update you!
     
  15. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    If the potentiometer is damaged, that axis is running with the minimum of 1.2A.
     
  16. Federico77

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    That is a useful information but I confirm you that the potentiometer itself is not broken and I can still rotate and adjust it properly with some effort and care with the remaining teeth.
    As you may understand this is sub-optimal and being a tiny bit of a perfectionist I like it to be pristine again so a bit of solder and new potentiometers will surely do. :)

    Thanks,
    Federico
     
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  17. Federico77

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    So, after a few days I finally have my Workbee operative again. This time with a fresh original NEMA23 for the X axis and 2 swapped potentiometers for the sake of perfectionism.
    I ran a test with the same gcode and boom... same problem at the same positon. At this point I had an insight and changed a few params on Fusion360: I swapped all the linear movements with the more "compressed" arcs and the stuttering is gone!

    By the way, I'm not celebrating just yet as the X axis seems to still be losing steps easily during a cut (not anymore during tests with no load on the bit involved). :(

    I tried to re-tune the X pot and stopped just before the led goes red; re-checked belt tensioning and wheels grip. They all seem fine to me.
    At this point I checked feed rate and spindle speed by running several times the same job varying those two params on the fly from Control (I have Interface but I like Control better if I have the laptop with me): so far none of my tests changed the fact that the ususal critical curve easily causes my X axis to lose a few steps with the bit getting stuck in the piece. Oh, on these regards I am using a 6.35mm upcut bit on plywood to cut in 1.8mm Z increments.

    Help, what am I missing??
     
  18. Federico77

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    Hello once again,

    I know I am getting quite annoying but by writing this down I also hope someone with similar issues may find it useful.
    After several attempts I still could not solve this puzzle and it is getting a bit frustrating. So let me start again from the basics:

    1. I checked the wheels, and I registered them. Current status: they all have grip although I stayed to a level where I could still rotate them by hand with a bit of force.
    2. I checked the belts (all of them despite having issues only on X axis) and tightened them slightly. They seem pretty rigid with no elastic behavior if I push them down and let them go back in position.
    3. I checked the X axis pulley and tightened the grains as I noticed that it got slightly loose over time. This was spotted by osserving a visible micro movement (less than 1mm) on the axis when moved back and forth. I believe it happened because of all the tests carried these days. It is now as firm as it can possibly be.
    4. I checked the motor cabling an made sure that each wire was well connected.
    5. I checked the X potentiometer again and raised the level until the motor did not loose any step while applying some reasonable force by hand. Here I thought I found the solution to my issues but this level causes the motor to stop (red led on blackbox) after a few minutes. I tuned down the pot. a little but now the axis feels a bit weak again when applying the same force.
    6. I switched the Blackbox with a fresh one (v2.8 i think) borrowed from a friend that is building a new CNC and repeated point 5 with exactly the same results.

    Now, most of the "force" tests have been carried without working on the actual wood but just applying some moderate force to the moving/static axis.
    Whenever I tested with some material I used: birch plywood, 6.35 upcut cutter, 2mm depth per layer. This is pretty much my common setup. Tested with various feed rates and spindle speeds. In the end I applied a conservative settings from G-Wizard. Few months ago, similar settings were perfectly fine for plywood.

    Last but not least I have a couple of questions if some can provide feedback:
    a. PSU is reporting 24.3v, I believe it is ok but is that something I should investigate and tune?
    b. birch plywood is basically based on hardwood. Should I use a high-torque motor instead? As it is my usual wood, would my Workbee gain some edge by going high torque? If I do, should I consider to change some settings for the change?

    Thank you very much for reading and hopefully answering,
    Federico
     
  19. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    The biggest recommendation I would offer, is to ditch belts and go for a Leadscrew setup if at all possible. Better torque transfer and mechanical advantage, more precise, more reliable.

    And next up, replacing 3rd party motors with Openbuilds motors.

    In itself, thats OK. The question is how badly does it ripple (multimeters show an average. You need an oscilloscope), any dangerous surges, fast reactive overcurrent protection, etc. Does it droop under load (need a programmable load to test). We lab other PSUs often - the Meanwell just knocks them all out of the park everytime.
     
  20. Federico77

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    Thanks for the quick reply Peter. Let me reply to you:

    1. my future plan is to switch to screw driven at least still for the X axis. Not sure if 1500mm is good for screw driven Y axis.
    2. I understand your point, sadly I don't have an oscilloscope to verify that.
    3. third party v. open builds motors... I am not sure to be honest: I was expecting that swapping them for the X axis would have solved my problem but, at least for my use case, the one I changed is behaving exactly like the others.

    What I don't get is: my build is pretty standard and with current settings I should not require high-torque motors, lead screws or other upgrades.
    I see many people succeed with this setup and I don't see why this is not the case for me. Also, for the forseeable future I will be cutting mostly birch plywood or soft woods and I don't even need blazing speeds as it is just a hobby for me.

    Please understand that I know the problem is just "mine". I love my Workbee and I don't mean that Openbuilds is to blame for that, but I need to have my platform working smoothly as supposed with this setup before considering to spend more money into it for the basic stuff that I am doing.

    Last but not least: should I add 1 more volt to my PSU to make it a bit more stable? PSU is by the way the original one (Meanwell LR350-24), no silly named chinese clones.

    Thanks,
    Federico
     
  21. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Wasn't back in the day, but we use the tensioning system on the LEAD1515 without issue: See OpenBuilds LEAD CNC Machine 1515 (60" x 60") - just fit the tensioning system to yours.


    OK, but
    Didn't know that yet, so one less worry :) - they are good. No adjustments needed, not the source of your problems.

    Which is why I put the leadscrew upgrade above it. The torque advantage is significant

    Has me baffled too, but run a search for B****man and "knockoff" in the search box above. Lack of power comes up ALL THE TIME and usually relates to their motor choice: Search Results for Query: knockoff motors | OpenBuilds

    Just baising that on the history. "standard" vs "yeah, looks like standard, but lots of sub-par parts that makes you think you have a standard"
    One other thought, what teethcount is their pulley (vs what our now discontinued belt drive workbees were) - more teeth = higher speed but less torque.
     
  22. bencouture

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    What is the actual default setting? I've tweaked them all, and now I don't know where they were rotated to originally. Are they just set at halfway or something out of the box?
     
  23. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Halfway / 50% is factory default. That gives you approx 2.3A - good setting for our motors that won't overheat
     
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  24. krazeekirk

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    Peter I have the high torque motors from Openbuilds and when I started to adjust the current it makes the stepper motor make lots of noise when stationary. Depending what direction I turn the dial the motors make a louder or softer "wining" noise. Is this normal?
     
  25. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Yes, totally normal.
     
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