Thanks for the reply Jonathan. I'm actually quite happy with less speed on the output, which is why I'm currently running the motor at 240RPM and the shaft (output) at 90RPM. At 240RPM there's plenty of torque, around 5.5Nm at 68VDC, this over 2.66:1 ration gives around 15Nm on the output (at 90RPM). This is on the verge of stalling, sometimes it runs fine, sometimes stalls. Max voltage both the HBS86 or the AM882 can handle is 80VDC, would that give enough bump to the torque? Here's the power / torque vs. speed data from Excel:

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With a Nema 34 12Nm, which is only 25mm longer than the HBS 8Nm I'm using now (it's got an encoder fitted which I don't need at all), I'm planning to run that at the same speed of 240RPM. This gives around 7.5Nm, which over 2.66:1 ration gives 20Nm on the output (at 90RPM). Hopefully that's enough to get past stalling. Similar data to the 8Nm motor:


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I've thought about geared motors, fitted with a planetaty gearbox, but those seem to be rather expensive and overall the cost was similar. I know size is different, but length is comparable and that's the only thing that limits me at this point anyway. With a planetary gearbox I could run with the same pulley size as the gearbox handles the ration, but even for a 10:1 planetary, I'd need a motor which can deliver 2Nm at 900RPM (to stick with the 90RPM on the output and 20Nm torque). This means typical smaller sized motors are out of the question, steppers probably as well, and it leaves me in the AC motor territory, which tends to go huge, bulky and loud. Unless of course I've missed something which is quite possible.

Regards,
T.