HSM8378 220 - 240 V DC treadmill motor
A quick look at a motor salvaged from a broken treadmill. This motor appears to come in two variants (the other being advertised as 180 VDC) and can be found on auction websites as "suitable for lathes" and other machine tools. It is a high RPM motor (about 3000 RPM) so would need a countershaft and the 220 - 240 VDC motor range is inconvenient unless you have a suitable power supply. In my personal opinion, better options exist.
DO NOT SIMPLY RECTIFY MAINS (240 VAC RMS) as the peak output voltage will be around 339 V and therefore considerably higher than the recommended supply.
Feel free to suggest a good motor speed controller for this motor if you know of one but the ones I have seen so far on eBay have no documentation or datasheet and may not meet safety standards.