please help me diagnose this problem [ SOLVED ]

I've attached a picture of the sphere I tried to print. I'm using a Makerfarm Prusa i3 8". Printing w/ 0.35mm nozzle at layer height 0.25mm, 10% fill.

2 questions:

1. What would cause this random shift in X and Y? I know the belts are tight. I've slowed it down to:
- perimeters at 20 mm/s
- infill at 35 mm/s
- travel 135 mm/s

Are the stepper motors overheating, or the RAMPS board? Something is causing it to jump.


2. The tiny blobs you can see on the left hemisphere. I've tried adjusting the retraction, currently at 1.5mm @ 40 mm/s. Z-lift is set to 0. Any chance I can make it disappear?


I'd appreciate any thoughts.

Edited 1 time(s). Last edit at 08/05/2013 04:58AM by startingtoprint.

going to adjust my potentiometers on x,y, and z. I've read many people mention adjusting to a minimum where you can't stop the pulley with your fingers. going to reprint at these lower current settings.

It looks like a stepper driver is overheating and going into protection mode. Let us know how it works when you print with the new current setting. Otherwise, try putting a fan on your electronics. As for the retraction issue, it's just something you have to experiment with. Retraction speed is sometimes more important than retraction distance (faster is usually better). If you want to increase the speed though, you'll have to check your firmware to make sure its configuration will permit a faster speed (and make sure the machine is physically capable of producing that speed). In my experience, PLA has more issues with blobs and stringies than ABS, but they can be managed in any case.

just wanted to update. I used the steps outlined here: [www.nextdayreprap.co.uk] (Click on "11.4 Pololu Stepper Driver Calibration")

My stepper motors have a model number: 42BHH48-050-24A which apparently means they run at 0.5A.

Now the math on that site I linked says I need to take my 0.5A, multiply it by 0.7, then 0.4 to get the Vref. I did it and got 0.14V, tried another print, still gave the same jump problem. I then tried turning a fan on pointed at the RAMPS board, did another print, still had the issue.

I just now turned down the Vref to 0.07-0.08V on each stepper driver, tested all the motors to make sure they still turned, and am printing again.

Am I on the right track? Anything else that could cause this random jumping?

Edited 3 time(s). Last edit at 08/04/2013 07:07PM by startingtoprint.

belt slipping i would say happening to me, also if motors skip steps

---

Check my rubbish blog for my prusa i3

up and running
[3dimetech.blogspot.co.uk]

Try decreasing the acceleration value in marlin.

That has worked for me, though i haven't completely eliminate the loss of steps.

Also you should try to find out what is the fastest speed you can print without loosing steps.

The are my current values for federate and acceleration.

I had to drastically lower since marlin came with numbers like 9000, and i hace to lower the to 25 in order to get the machine working properly.

#define DEFAULT_MAX_FEEDRATE {150, 150, 3, 150}
#define DEFAULT_MAX_ACCELERATION {25,25,2,100}

#define DEFAULT_ACCELERATION 25
#define DEFAULT_RETRACT_ACCELERATION 50

Regarding the retraction speed, mine was so high that i wasnt get any retraction at all.

Hope this helps.

Let me know if you can fix it

Thank you santino for pointing me in another possible route.

To update this journey to fix the missing steps, I've tried the following:

1. Lowered stepper current by setting Vref to 0.13-0.14V --didn't work
2. Turn on fan pointed at RAMPS --didn't work
3. Set Vref to 0.07-0.08V --didn't work
4. Now I've turned up the Vref to 0.09-0.10V, set the default & max acceleration to 10% of the default value. Settings currently look like this:

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,945}
#define DEFAULT_MAX_FEEDRATE {500, 500, 2, 45}
#define DEFAULT_MAX_ACCELERATION {900,900,10,1000}
#define DEFAULT_ACCELERATION 300
#define DEFAULT_RETRACT_ACCELERATION 300

Printing again now. I have so many failed chunks of plastic, didn't imagine this sphere would be a torture test for my machine.

Edited 1 time(s). Last edit at 08/04/2013 08:31PM by startingtoprint.

ugh, this is getting aggravating. newest acceleration settings caused a skip to happen sooner. cut the acceleration in half.

#define DEFAULT_MAX_ACCELERATION {450,450,10,500}
#define DEFAULT_ACCELERATION 150
#define DEFAULT_RETRACT_ACCELERATION 150

Trying a print again. This is starting to become an obsession.

Damn it, it skipped again. I'm so frustrated, about to break something. Are these motors that damn sensitive? I will continue to cut the acceleration until I get a completed print, I will post updates. If anyone has other tricks in mind to stop the steppers from skipping, please let me know.

The belts are tight, motors aren't overheating, pololu drivers have Vref set to reasonable level. Only variable now I see is the acceleration values.

Great news, just woke up to a completed print. I switched the stepper driver for the X-axis with the one for the Extruder on the RAMPS board. I set the acceleration to 2% of the default. Used these settings:

#define DEFAULT_MAX_FEEDRATE {500, 500, 2, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {180,180,10,200}
#define DEFAULT_ACCELERATION 60
#define DEFAULT_RETRACT_ACCELERATION 60

Before:

After:

Finally I can end this obsession. Thanks for all who contributed avenues to pursue. Now my printer is quiet, motors are cool to the touch, and it moves with grace.

Calling this thread SOLVED!

Edited 1 time(s). Last edit at 08/05/2013 05:06AM by startingtoprint.

Ye its normal you had these problems kinda,
I also had this with my prusa i3 from makerfarm,
When talking with Colin for a couple of days we came to the conclusion those settings for accerlation are way to high,
I halved em and uploaded that, Colin also did that with his firmware and updated it to the website,

Please look at the website now and then for the ramps software since he does change it now and then to improve.
Like he just adjusted the extruder axis setting so its more accerate.


startingtoprint Wrote:
-------------------------------------------------------
> Great news, just woke up to a completed print. I
> switched the stepper driver for the X-axis with
> the one for the Extruder on the RAMPS board. I set
> the acceleration to 2% of the default. Used these
> settings:
>
> #define DEFAULT_MAX_FEEDRATE {500, 500,
> 2, 45} // (mm/sec)
> #define DEFAULT_MAX_ACCELERATION
> {180,180,10,200}
> #define DEFAULT_ACCELERATION 60
> #define DEFAULT_RETRACT_ACCELERATION 60
>
> Before:
>

What pot setting did you find to be best in the end?
And did you end up changing #define DEFAULT_AXIS_STEPS_PER_UNIT {} from the original?
I've updated these setting in my firmware as per your post

#define DEFAULT_MAX_FEEDRATE {500, 500, 2, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {180,180,10,200}
#define DEFAULT_ACCELERATION 60
#define DEFAULT_RETRACT_ACCELERATION 60

Troubleshooting my problem [forums.reprap.org]

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,841} // default steps per unit for ultimaker {78.7402,78.7402,200*8/3,760*1.1}920
#define DEFAULT_MAX_FEEDRATE {250, 250, 1, 22} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {1000,1000,5,1000} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for r retracts


Thats what i use ^ and what Colin/makerfarm website uses.

Hi nibake, sorry to get back to you so late. Got busy with school and didn't have time to play with the printer much. In the end I believe I used Vref to 0.09-0.10V on each stepper motor. I also switched the drivers for the X and the Extruder as I described. But the skipping didn't stop till I DRASTICALLY reduced the acceleration. Colin as recent as August has uploaded new firmware, but for my machine, those defaults are still way too high. I'd start low and work up till you can print with no skips and keep the motor nice and cool. I used to have motors that ran so hot it would be scalding hot to the touch. Hope this helps, if you need anything else, let me know and hopefully I can help.

You got your math backwards on the Vref setting.

The driver *shares* current between the two channels. If it's set to one amp, it shares out 0.7 of that to each channel. A one amp Vref setting puts 0.7A on the motor winding. The first step should be to multiply your desired current by 1.43 ( that is 1/ 0.7). For a 0.5A motor that gets you about 0.71A. That's what you want to calculate the Vref for.

Polou says that current limit = Vref x 2.5. That would mean Vref = Ilimit / 2.5. For a 0.5A stepper Vref comes out at about 0.29V. You could also put all the factors together and simply say that Vref = current limit / 1.75

Motors are not solid state devices. They can run quite hot and live a long and happy life. I have run into a *lot* of pro's who routinely run motors 20% over their ratings and they run for years and years. Worry more about air on your dirver board and it's heatsinks than about the temperature of the motors (within reason).

I got the math from this Polou Calibration guide [Click on 11.4 Pololu Stepper Driver Calibration] [www.nextdayreprap.co.uk]

Take a look and see if they did it wrong, if so I'd like to know for reference. So you're saying I could possibly run the motor hotter with no problems?

Initially this post was about skipping steps, and it's often attributed to either:
1. The motor running too hot
2. The acceleration being too high

If I can find a way to run the motors at a reasonable temp and go fast, I'd love it. I just came to the possibly wrong conclusion that these 0.5A motors can't accurately go that fast and be hot.

So right now I have my motors running super cool, but that means I have to use a really low acceleration. Maybe I should take a look at it again, but it was such a pain to get it to this sweet spot, that I'm reluctant. Tell me your thoughts uncle_bob

The example they give at the UK site is for their motors. They are using the 0.7 as a derating rather than as the current share adjustment. They very much did not do the math correctly for the general case. They have very high current motors for this application and they need to cut back on the drive to keep the stepper dirvers from melting. The net result is that they are running their motors at 1/2 to 1/4 the rated current (and likely still have the drivers right at the edge of cutting out without a fan). Bottom line - their motors are not as well suited for this purpose as the ones MakerFarm has.

The data and math I gave you is correct according to the chip manufacturer's data sheet:

[www.pololu.com]

The data and math is correct according to the dirver board manufacturer's web site:

[www.pololu.com]

It also coresponds to the settings on a factory new driver board from MakerFarm. Those settings (0.36V or 20% over the 0.3V) have been confirmed as correct for these motors by Colin at MakerFarm.

The only reason for the motors to skip is the *driver boards* overheating. That's not at all the same thing as the motors getting hot. The dirvers on your Ramps board are solid state based. They cut out to self protect when they get hot. The solution to that issue is to run a cheap fan on your Ramps board. Motors are mainly limited by the insulation in the field and / or armature windings, not the physics of diffused silicon crystals. You can easily design a motor that's quite happy at 150C. Doing the same thing with a a silicon based semiconductor (at heatsink temperature) - not so much. If you made a silicon carbide IC that would be different, but we have silicon based parts in this case.

If you are bothered by the motor's temperature, put a fan on them. They are $2, so it's not a big investment. I'd put a fan on the Ramps board first though.

Great information! I tried putting a fan on the RAMPS before, but I can try again. I'll update if I get more stable prints at higher Vref. Thanks again uncle_bob

There's a file on Thingverse (where else) for a push on fan mount for the MakerFarm. It works fine with the $2 fans and it's plenty study enough. If you mount the fan on the side of the mount away from the Ramps everything is out of the way when you want to fiddle with the Ramps wiring. It's more a "better safe than sorry" kind of thing. You may never need it, but for $2 it's not a bad thing to have.

Just to update uncle_bob,

I turned all 4 stepper drivers to a Vref of 0.34-0.36V as you've suggested. I reset my RAMPS firmware to have Colin's current default configuration with its default accelerations. All my stepper drivers have heatsinks and I had a desktop fan blowing on the board (hoping this would be blowing harder than any cheap fan I can mount on the ramps board.) By all accounts this would be the ideal situation. Printing should be fine.

Tried to print, after 2.5 hrs, it skipped in the x-axis. Now this is the same problem I had when I started this thread months ago. My solution has been to decrease the Vref to around 0.09-0.10V and to cut the acceleration to:

#define DEFAULT_MAX_ACCELERATION {180,180,5,200}
#define DEFAULT_ACCELERATION 60
#define DEFAULT_RETRACT_ACCELERATION 60

So now my question for you guys is, other than slowness, is there any other downside in turning down the Vref to the minimum that will send the minimum current to make the motors run? Using these defaults are louder but faster, but I just can't get it to print without skipping hours into it.

Should I keep trying to make this "default" setup stable, or say screw that and just stick to the cool and slow setup that's proven itself to work?

I don't think it's the drivers. I think your power supply is cutting out. The higher voltage settings do just fine for > 10 hours running here.

I really don't think it's the power supply. If the power supply stops, it doesn't immediately start back up, my power supply used to cut out before I realized that it needed a load across it's 5v rails to stay on. I simply use an old cdrom, and it has worked great.

I don't think the power supply is dying completely. I think it's dropping down to something between 6 and 8 volts. That will keep the Mega going fine, but it will really mess up the steppers big time. It would only need to drop out for a very brief period.

I decreased the Vref to 0.11-0.12V and decreased the accelerations, and it ran a 5 hour print with no skipped steps. I really think the Vref was too high for my specific stepper drivers, or that I would need more than just fan cooling and heatsinks to run at higher Vref.

Is there any problem with running safely at a lower Vref? What are the cons?

The gotcha with running low current is that the motors don't have very much torque (so no speed / acceleration / control). Past a certain point they don't have enough energy to properly step and they skip.

What if the motors were designed to produce their max torque at that lower current?

Quote
uncle_bob
The gotcha with running low current is that the motors don't have very much torque (so no speed / acceleration / control). Past a certain point they don't have enough energy to properly step and they skip.

On a stepper motor, torque and current are pretty much directly related. More current means more torque. It's not like a gasoline engine where you have a torque vs rpm curve with a peak somewhere in the middle.

Edited 1 time(s). Last edit at 11/03/2013 06:48PM by uncle_bob.

Quote
startingtoprint
Great news, just woke up to a completed print. I switched the stepper driver for the X-axis with the one for the Extruder on the RAMPS board. I set the acceleration to 2% of the default. Used these settings:

#define DEFAULT_MAX_FEEDRATE {500, 500, 2, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {180,180,10,200}
#define DEFAULT_ACCELERATION 60
#define DEFAULT_RETRACT_ACCELERATION 60

Before:

qef1.jpg

After:

mlou.jpg

Finally I can end this obsession. Thanks for all who contributed avenues to pursue. Now my printer is quiet, motors are cool to the touch, and it moves with grace.

Calling this thread SOLVED!

@ startingtoprint

Thank you very much for sharing your findings. I had the same problem with the X axle. Like you, I didn't know what the cause was so I went on a wild goose chase. Tighten belt, play with the ref... to no avail.
Then I found your post, re-upload the firmware. Now it works great, I even like the new accelerate sound, it sounds like a well tuned sport car.

Glad the post helped. Reading this post again made me realize how frustrating it was to chase down the issue. Happy printing.