Hi Jeremy,
Thanks for your knowledge here, lots of useful info there, however I think I should have been clearer.
I'm a relative newbie at motor design and reading these charts, so please correct me if anything that follows is incorrect.
What I'm really interested in is how
low an RPM different designs produce their peak torque and the torque characteristics or speed-torque curves up until that point, basically what I meant by low rpm torque characteristics is the starting torque characteristics rather than the working range torque you might be thinking about. I read an excellent article about smooth, quiet and high torque PMDC motor design that for the life of me I can't find now, which is what I'm interested in learning about as well as gathering information for my single-stage drivetrain design, power and Kv requirements. I may end up building my own motors and dyno to learn what I want to.
I certainly agree that the working range can be roughly considered "a constant torque per unit current machine", at least until you reach the limits of the permanent magnets before needing to look into electromagnets for higher flux. However most data/charts leave out the starting speed-torque data that I want, and I'm trying to extrapolate this from what data there is, and I'm not sure the constant torque per unit current machine applies here.
To give an example of low rpm peak torque from the data I've found, the new Crystalyte HT24 (high torque, 24mm stator) hub motor produces it's max torque of 47.74 Nm @ 46.1 RPM using 35 V according to
their figures, while the HS24 (high speed) produces about the same 47 Nm @ 21.9 RPM because of the fewer turns and lower resistance, however this is at the expense of efficiency which approximately halves resulting in a nice frying pan to cook on at the summit of any long and steep hills with a view.
The Cyclone chart illustrates the ramp up to the low rpm peak torque I'm talking about, where the blue dot torque curve shows peak torque at 600 RPM of 100 somethings (Nm or lb/ft - too lazy to work that out)... that tapers off over the working range because of the losses that occur that you mentioned. On compact, low power, low Kv motors this ramp appears very important to get up and over as it can be a large percentage of the motors operating range.
So what I'm looking for is
actual data for non-hub motors that include the speed-torque curve data up until peak torque RPM in different designs including; inrunner, outrunner, radial, axial, skewed/straight laminations, # poles, teeth, windings, etc.
The following is a nice illustration of speed-torque curves for very small motors of different motor types in
one company's range that only tells part of the story. Ultimately I'm looking for speed-torque curve data over these motor types as well as reluctance motors.
Thanks for pointing out about the GM motor at 145A to get the higher torque, my brain was stuck on the peak of the efficiency curve!
Thanks for your input.