dc motor - spindle / shaft drive

[Jonathan]

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.

[JAZZCNC]

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.

Yep correct Boy wonder.!! Didn't really give it much thought and concentrated on the Nm and need for compact design but missed the 300rpm required.!!
Agree that with 300rpm needed that 3:1 and larger motor would be better suited. To keep the compact electrics then the UIM24004 miniture drives go upto 4A so will be ok for a 3Nm motor.!

That said would have thought 6Nm when attached to dedicated grinder should easily crush a Coffe bean.? . . . But hey I drink tea so what would I know.!!