Template:UGC-RescaleFactor

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Setting the Rescale Factor

There are three pieces of information to consider when setting a rescale factor to change your units into degrees or rotations:

  • Your encoder's CPR (counts per rotation)
  • Your encoder interface's resolution
  • Your motor's gear ratio

First, check your encoder's datasheet for the CPR. It's usually 360 or 300. This is the number of quadrature cycles the encoder will send out for one full rotation.

Next, you need your encoder interface's resolution. The encoder port on the {{{1}}} has a x4 resolution, meaning it reads in 4 pulses per quadrature cycle (see the Encoder Primer for a more in-depth explanation).

Next, you need to find out the gear ratio in your motor's datasheet. Note: If you plan on having your motor run for many rotations in a row, try to find the exact gear ratio, expressed as a fraction. Using the rounded value will result in accumulating errors the more you rotate.

Once you have these numbers, you can calculate the rescale factor:

DCC1000-equations.jpg

For example, if you wanted to have your motor's position measured in degrees and your encoder had 300 CPR and your motor had a 50 801⁄895 : 1 gearbox, you would set your rescale factor to 360 / 300*4*(50+(801/895)), or 0.005894.