Z Axis Home Calibration - Strange rumor

Hi to all,

i'm trying to configure my Z axis on Prusa I3X and i've the following Structure:

M8 threaded bar
Nema 17 -> 200 per revolution, setup at 1/16 of step

So, using prusaprinters.org/calculator with the following data, it get me a value of 2560 and i change it on Marlin and upload.

Now, from Repetitierhost i try to move Z axis UP and DOWN to check that all works fine -> and it it, Z axis move without problems.

When i try to "Find Home" on that Axis, the motors do a very strange rumor (like if they are blocked), but they move UP and DOWN perfectly.

If i try to change that value (2560) with the original value (that is 200.0*8/3 = 533.333) making Home on Z axix works fine (motor go very very slow), but works..

Someone have had a similar problem ?

Hi,

It's probably acceleration and/or feedrate too high.

++JM

for that parameters i have the default:

#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,10000} // X, Y, Z, E maximum start speed for accelerated moves.

But... how i should calculate them ?

Try 3mm/s instead of 5 for speed and 20mm/s² instead of100 for acceleration.

Ok thanks, so:

#define DEFAULT_MAX_FEEDRATE {500, 500, 3, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,20,10000} // X, Y, Z, E maximum start speed for accelerated moves.

And with that, i will change the value back to 2560 (as calculator say).

I will try this when i back home and if will works, i will post feedback here for other users that could have the same problem

Yep, that should do the trick! The default max velocity for x, y and accelation for x, y and e are too high too. You may want to start with
#define DEFAULT_MAX_FEEDRATE {100, 100, 3, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {1500,1500,20,2000} // X, Y, Z, E maximum start speed for accelerated moves.

You can bump it up once everything works properly.

Like the name says, thos values have effect only in acceleration... right ?

So, once i have setup correctly DEFAULT_AXIS_STEPS_PER_UNIT, the value for DEFAULT_MAX_FEEDRATE and DEFAULT_MAX_ACCELERATION will change the acceleration (and i dont know what is the effect in a print, i havent printed nothing yet ^_^)

Let's assume the value you have gived to me will works, why i should increase it? What will be the benefit of it?

sorry for all that questions....

Edited 1 time(s). Last edit at 09/30/2015 08:36AM by mistre83.

Velocity is the maximum speed at which the axes move. Acceleration is how fast the axes increase and decrease in speed.

Velocity is one of the most important factors how long a print takes. Acceleration to a much less degree, but has more effect on the mechanics. A velocity too high can cause a steppermotor to loose steps, when going faster still will stall, ie shake, back and forth. Acceleration too high, the mass that needs to be set in motion can't go from 0mm/s to 30mm/s instantly. If you set acceleration too high the steppermotor will loose steps. For an axis to reach a certain speed it needs the distance/time to reach it. Set acceleration too low it will not reach the wanted speed and slows down the printing process.

A high acceleration will put stress on the mechanics. If there's any play or springiness it will be seen in the print quality. What you want to achieve is a good balance between speed and quality attainable by your printer. That's why you may want to bump up these settings once you're sure it's working well.

I hope this makes some sense

Thanks a lot to your explain!

Yesterday i have had my first print (cube 25 x 25) with a very very bed result

First, i've noticed that extruder was totally uncalibrated. I was having the default value (760 * 1.1 = 836) and i think with my printer will extrude a lot (and i say a lot) of plastic.

With some modify now i've changed it till 80 and when i say to repetitierhost to extrude 1 CM, it extrude 1 cm

Now, this phrases is very intresting:

A velocity too high can cause a steppermotor to loose steps, when going faster still will stall, ie shake, back and forth

This is exactly what i have!!!! When the motors move to print lines, the bed (and i dont know if X Axis too) shake with a lot of vibration

My actual configuration is:

#define DEFAULT_MAX_FEEDRATE {100, 100, 3, 25} // This is Velocity right ?
#define DEFAULT_MAX_ACCELERATION {1500,1500,20,2000} // And this is the acceleration

So, in my poor experience i would like to make this test, to lower this value:

1 - Hot extruder and bed like i will do a print
2 - Remove the ABS from the extruder (i dont want to print anything, i just want to calibrate)
3 - Start the print

In this way, i could see if something will change, for example lowering those value from 1500 to 1000.

Another thing is the cube is "crooked", but is crooked from half of it, like if the printer have "loose steps".

So, another thing i can do is to change acceleration too. for example modify the previous values like this:

#define DEFAULT_MAX_FEEDRATE {70, 70, 3, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {1000,1000,20,2000} // X, Y, Z, E maximum start speed for accelerated moves.

Yes, feedrate and velocity mean the same thing. Your extruders steps per mm is way too low. You need to place the jumpers under the stepsticks, it will be able to run slow enough with better consistency. Same goes for the other axes, except maybe for the z axis, as the threaded rod already gears it down.

Yep, you can try those low values but also see if the motor current is set correctly.

See Triffid hunters calibration guide:
Triffid Hunters calibration guide

The value i've told you is 80 (a very low value) because i havent (big_gear_teeth / small_gear_teeth) but only one gear.

With repetitierhost i've tried to extrude 1 CM (making a sign on ABS filament) and it was so perfect

Motor current should be ok, however i will check again and i will try a test loweing the acceleration / velocity-

thanks a lot for you explain!