dc motor - spindle / shaft drive

[dsc]

Hmm wouldn't mind using a drill motor, although they tend to get a bit noisy, plus are not easily available off the shelf (apart from replacement parts).

Steppers seem like an interesting idea that I keep coming back to, one can find some with rather high holding torques, which should mean rather high torques at low speeds as well (I'm guessing a loss of around 10-20% of torque at 200-300RPM). The problem with those is you need a controller and a power supply and I'm not so sure I can fit everything inside the box. I'm also tempted to go down this route as I'm planning to use a small stepper on the lead screw, so using steppers for both would solve all problems.

Oh yeah, forgot, this is indeed for grinding coffee, Jonathan is right, although it might sound like a joke.

Regards,
dsc.

[Jonathan]

Steppers seem like an interesting idea that I keep coming back to, one can find some with rather high holding torques, which should mean rather high torques at low speeds as well (I'm guessing a loss of around 10-20% of torque at 200-300RPM).

If operating below the 'corner speed', which at 200-300rpm almost certainly is the case, you'll get about 2/3rds the rated holding torque as rough guide. However with a 3:1 ratio it's going to be less - try the motor calculation spreadsheet irving posted a long time ago and you'll see what I mean.

It looks like you're after 9Nm at 300rpm? Power=torque*angular velocity, so P=9*300/60*2pi=283W
So if you definitely need 9Nm at 300rpm, your motors needs to output about 300W which is not really realistic for a stepper motor. That's realistic for a drill motor with planetry gearbox, but as 2e0poz has hinted, the brushed motors in those, although cheap, are not likely to last long. However if the duty cycle is low that may still translate to several years use.