Quote Originally Posted by JAZZCNC View Post
Just use a stepper with integrated driver like this SYINTSD233-4 (INTERGRATED STEPPER MOTOR)

Very neat and compact and if you Gear it 5:1 then it should do the job. (Or find larger Nm version and keep 3:1)
300rpm is needed, so at 5:1 the motor is spinning at 1500rpm. At that speed the output torque is about 0.46Nm, which with the 5:1 ratio means 0.46*5=2.3Nm. The torque at very low speeds, i.e. when starting is 1.24Nm, so 6.2Nm at the grinder shaft which is below the 9Nm you specified.

Just use this spreadsheet to compare the different motors at Zapp and you'll be able to determine which motor/driver, if any, is suitable. It's substantially cheaper to use a separate motor and driver. The PM752 from Zapp is quite compact and I'm sure there are others.