float axis_steps_per_unit[X,Y,Z,E]
These values tell the chip the number of steps the stepper motor needs to make
to move the respective axis or extruder by 1mm. There are four values and they
which correlate to to “the x axis”, “the Y axis”, “the Z Axis” and the “Extruder”
you will notice that there are preset values here for different types of printer.
To calculate these values we need to take a few hardware variables into account.
Calculate X & Y values
1. Motor Step Angle/Size
2. Motor Driver Microstepping
3. Belt Pitch
4.
Tooth Count
We can then apply the above values into the following equation to give us the steps per mm value
for the X and Y Axis
Steps per mm = ((360°/Motor step size°) * (1/Driver microstepping))/(Belt pitch * Tooth count)
We use Stepper Motors with a 1.8° Step Angle and 1/16 Microstepping on the A4988 Polulo
Stepper Drivers, our belts are T5 Pitched and we use 12 tooth Pulleys so our value calculates as
follows :
Steps per mm = ((360°/1.8°) * (1(1/16)))/(5 * 12)
= 53.333333 Steps per MM
As this results in a recurring number we round it to the nearest non recurring number hence our
value of 53.2mm
This is the value we use for X and Y axis
Calculate Z Axis value
To Calculate the the Z axis value we use a fraction (steps for a
360°
rotation of stepper/Threaded
Rod Pitch), as our our Motors have a 1.8° step angle and the Pololu A4988 Stepper Drivers use
1/16 stepping this results in 3200 (360/1.8)= 200 then multiply by 16 results in 3200. The pitch of
our Z Axis Rod is 1.25, so the value for our Z axis is “3200/1.25”
Calculate the E Axis value
This is the value for the Extruder and this is the one variable you might like to play around with as it
is affected by the type of filament used. The default value used is “1487” in order to test weather
this is accurate for your printer we need to perform a test. We need to extrude a set distance of
filament and then measure how much has actually extruded and any variance between the
requested distance and the actual distance then needs to be factored into the default value.
The default extrude distance set to 5mm for the manual extrude button within pronterface, so we
then need to mark the filament and measure how much the filament actually moves. The bigger
distance you measure the more accurate your results will be so we’ll start with 50mm.
10.0 Computer Setup - Reprap Prusa Mendel Build Manual
©2012 NextDayReprap
Prusa Mendel Kit Build Manual V1.01 - 07/2012