I can't power the drilling machine no matter what I do. It just keeps saying overstressed. I added a custom recipe for ice mining with a 128 stress value, which is lower than all default recipes. I'm using C&A Electric Motor and at any RPM it says overstressed. Only the Creative Motor works.

Everytime I set the Electric Motor speed to match the required stress value of the drilling machine, the stress value on the drilling machine doubles. I have to use a Rotation Speed Controller to double the RPM to match the required value. Am I misunderstanding Create mechanics or is this a problem with the mod?

If you increase the speed, the stress value also goes up, that's default Create behaviour, you probably have to place multiple motors or use gears or Rotation Speed Controller to lower the rotation speed while increasing the stress capacity. Craft a stressometer to see the stress required.