Need help with Prusa I3 calibration

Hi,

I hope someone can help us with the following:

My brother and I, both 3d printer newbees, bought a prusa I3 at reprapworld.com.
A kit consisting of a single plate I3 and megatronics 2.0 board with marlin firmware.

We put it together and everything seemed to work at the end, every axis moved in the right direction and end-stops where functioning,
so we started the calibration process.
We took the firmware form reprapworld and changed the settings quite a bit.

The settings currently are:
// #define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402*2,78.7402*2,200*8/3*2,760*1.1*2} // default steps per unit for ultimaker
#define DEFAULT_AXIS_STEPS_PER_UNIT {53.37,78.7402,1500.38,746.43} // default steps per unit for prusa i3
#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.

#define DEFAULT_ACCELERATION 3000 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 3000 // X, Y, Z and E max acceleration in mm/s^2 for r retracts

The Y-axis is spot on; when we tell pronterface to move it 100mm it moves 100mm.
However, in most forum posts the X and Y values are roughly the same, while we have to set the X value much lower, for the X-axis to move 100mm when told to do so.
Is this ok?

With current setting for Z, the Z-axis moves just about 50mm when 100mm was expected, but when we set it to 4000 (or anything higher than 2000), like the prusa calculator says,
the Z motors move a little and then stall.. they only vibrate.
Adjusting the voltage doesn't help.
What are we doing wrong here?

Thanks a lot.

Theo

Edited 1 time(s). Last edit at 01/02/2014 06:06AM by ice73.

sound like they are trying to go too fast. Try and reduce the feed rate from 5mm/sec to say 0.5mm/sec. if that works, keep increasing until it stops again.

If Y & X are mechanically the same, the steps should be very close. If you have different size pulleys, then the steps would be different. I would start by slowing down your speeds. Instead of 500 mm/sec, use something like 25 mm/sec. This will insure your steppers are not locking up. Then start turning the speed up once calibrated.

Thanks very much.
Lowering the max feed rate fixed things for the Z-axis.
We don't know what happened before with X, because now we use the same values for X and Y and things look pretty good.

The 20mm calibration cube is printing now.. not entirely correct, but I'm sure we'll get there.

Thanks again.

I'm building a Prusa I3 as well.
I had the same problem with z axis.
#define DEFAULT_MAX_FEEDRATE {200, 200, 5, 25} // (mm/sec)

I've found that if i give a G1 Z(something) F180 it's marginaly OK. If I send more than F185 stalls. F180 = 180 mm/min. Converting to mm/sec it's 3.
I change default feedrate to 3, and everything is fine now.
#define DEFAULT_MAX_FEEDRATE {200, 200, 3, 25} // (mm/sec)

My problem now is that:
I have a little stall in Y axis, during printing.
It looks like the system loose steps (I can hear something sometimes) and printing layers are moving a bit in Y direction.
The question is, if I change Default Max feedrate for Y to, say, 180 mm/sec (until find optimum), do I have to change X axis too, or what?