# Motor calibration

Here is a little manual describing how to find the correct motor calibration value for your setup – the mathematical and most precise way. This can now also be found in the documentation:

The miniEngine 2 offers the possibility to calibrate the motors you are using. This calibration takes the motor and its specifications itself as well as the rig it is driving into account. This chapter is aiming at helping you finding the correct calibration value for your motor(s). The calibration values needed, should be given with the following units:

• steps per centimeter for linear movements
• steps per degree for radial movements

As stepper motors come in a variety of form factors and specifications we need to add the most important of these specs to our calibrations. This is the degrees been moved by one full motor step. The most common one is 1.8°. This means that such a motor needs 200 full steps to do one full revelation:

$\frac{360^{\circ}}{1.8^{\circ}} = 200$

Because we are using multi-stepping to achieve a finer resolution, we need to multiply this full-step-value with the amount of sub-steps done. In this example we are using 1/16th stepping (which is the default for the recommended Big Easydriver):

$200{\times}16 = 3200$

..or if you prefer the full version

$\frac{200}{(\frac{1}{16})} = 3200$

Ok – so we need 3200 steps to do a full revelation with the stepper motor in micro- stepping-mode. Now let‘s add the rig that this motor is driving to the calculation. For now we are assuming we are driving a toothed belt with the stepper. The gearwheel has a circumference of 3.5cm. This means that 1 stepper revelation moves the belt 3.5cm. Here is how we get how much steps are needed for 1cm – which is also our final calibration value:

$\frac{1cm}{3.5cm}\times{3200}=914.29$

Now we can enter 914.29 steps / cm as the calibration value into the system.

If we had a motor that would do a radial move, the calibration-calculation would just differ in the last step. Assuming you are not using the motor to rotate your axis 1:1 but with a reduction of 1:4 (four revelations of the motor rotate the axis one time) , the final calculation-step would look like this:

$4\times\frac{3200}{360}=35.56$

The final calibration value for the radial setup is 35.56 steps / degree.

I hope someone finds this useful.

Have fun!
Airic