I’ve recently used some DC brushed motors from Phidgets and found them to be pretty nice:
phidgets.com/products.php?category=24
It’s hard to do a rigorous apples-to-apples comparisons of torque/speed/mass specs without doing testing, but they were the optimal choice out of this class of (relatively) low-cost motors for the project I used them on. The bigger selling point to me though is the build quality, which is the best I’ve seen short of going to expensive motors (Maxon, Faulhaber). Admittedly, these are more expensive for the same specs as say, your 37mm gearmotors.
The other thing to mention is the encoders on these motors. Not sure if the supplier or Phidgets integrates them, but they are available with a US Digital E4P optical encoder.
usdigital.com/products/encoders/ … ry/kit/E4P
These are the cheapest and smallest optical encoder kits I’ve found, and they’re available in a variety of options. I’ve always found the exposed magnet Hall effect encoders to be a little kludgey (plus I’ve had some get break in transit, not from Pololu though), plus they’re relatively low resolution. The more expensive motor vendors only use that style of encoder (but nicely housed) in very small motors where I presume there are problems with doing optical discs that small.
Lynxmotion and RobotShop sell a specific model of the E4P for $26, but otherwise they’re a little difficult to get in small quantities. Phidgets adds $30 to each motor for a version with an encoder.
Anyway, the point of this post was to make y’all aware of these motors and encoders if you were not already. They pair nicely with Orangutan controllers, which is how I used them. If Pololu carried them, I’d buy them here rather than at Phidgets, next time I needed any.