This will be a long note, but to get the punch line in at the top - if you are ever trying to source motors for a new design, I strongly recommend contacting George [url]sales3@china-bgmotor.com[/url] of Ningbo BG Motor Factory. Now for the long explanation.
For the tilt function of my project chair I had bought a small, 42 mm diameter, planetary gear motor meeting my torque and speed needs. It turned out, however, to be extraordinarily noisy - far too noisy to use in public. At first, thinking that this was typical of cheap planetary motors, I posted an RFQ at Alibaba for a similar size, similar output, low noise motor. I got quite a few replies, most of which did not respond to my specs, but George wrote to me offering to send a test video of a nearly silent motor BG Motor had built for a U.S. customer. It was impressively quiet, nearly silent. However, it was brushless and I needed a brushed motor. George said he could make a brushed version, but that it would not be as quiet - 55 dB with plastic gear, 60 dB with metal. Given that it is a basic design and not engineered for low noise - spur gears, plain bushings for planets and radial ball bearing on output I was skeptical. This was about mid-way through a long series of e-mails back and forth, with George making various suggestions and making sure that he understood what I needed. Obviously not just a run-of-the-mill salesman, but someone with an engineering background actually involved in building motors. The only alternative I was offered, from a different mfr, was a motor designed for low noise - helical gears, which also means needle and roller bearings and heavy cages to handle the axial loads produced by the helical gears - but it was 10mm larger diameter and 30mm longer so would have required a lot of re-design of the lift & tilt. Despite my skepticism, George's price was reasonable (US$ 24.28 for the motor, + US$33.30 for shipping) so I decided to chance it. After discovering how expensive it is to ship to Italy, he even spent more than an hour hunting up an express company that wouldn't add a $30-40 "remote area" charge for delivery to my address (on a national highway all of 25 km from the regional distribution centers of almost all the express companies!).
Paid on Nov. 26, they built one with plastic input gear but it was torque marginal so he asked if he could make mine with metal gear, sent me a test video on Dec. 9 - despite the metal gear it came out at 55 dB - and the motor arrived here on Dec. 14. It is not silent, but the noise level is certainly acceptable. Visually it differs from the awful one in two ways that might have lowered the sound level: the motor itself is 8mm longer and lower RPM and the commutator is fully enclosed rather than ventilated. In the meantime, however, I became suspicious that the awful one was not noisy by design, but defective, so I did a tear down. Quiet at no load, horrid just touching the output shaft, and no grease in the 1st stage! I didn't see any obvious damage, but adding grease didn't help so the gears were probably AFU.
Sourcing stuff has been my biggest obstacle as a hobbyist wanting just 1 or 2 of an item. George was remarkably patient and thorough for a small-ticket sale with no prospect for it becoming an industrial-sized order. Ningbo BG
http://www.china-bgmotor.com/ produces a very wide array of motors so if you are every searching for something special, they, and especially George, might be the place to look.