Guys,

Thinking about motor selection, it seems that if choosing between motors with the same K value/resistance the one with the larger diameter should have more torque. Are there some brands that have larger bell diameter then others for the same weight and K value?

Best,            DennisT

no,

torque = constant * current / KV

dimensions are already "included" in KV, larger motor has lower KV (if the rest is the same)

larger motor or stronger magnets result in lower resistance and higher no load current (if the rest is the same)

In other words, the KV and motor resistance pretty much determine the torque.

It may be easier to build a light weight low-speed, high-torque motor by going to a higher diameter, but once it's built it's built.

Nope ...
Kv and current. Torque is proportional to current and inversely proprtional to Kv in RPM per volt.
Dean P.

Show me a constant current battery and I'll agree with you.

Until then, if you present a motor with a set voltage it'll have a torque vs. speed curve that depends on Kv and the combined resistance of the motor, battery, and speed control.  Yes, for a given Kv and current the torque is very much constant (ignoring 2nd-order effects like windage) -- but that's not the environment in which a modeller's electric motor runs.  Most RC speed controls that I know of either supply a fixed proportion of the battery voltage as a function of the input command, they switch between a low impedance connection to the battery and high impedance (in which case the voltage/current relationship of the controller is complicated), or they actively servo the motor speed.  Constant current drive can be done, but would add to the cost of the controller and who'd want it?

Motor Kv and power rating.

Kv is about how fast a motor will try to go for a given applied voltage, but it says little about how much power the motor can handle.  A quick look at the Horizon Hobby website shows the Eflight "Power 25" with a Kv of 1250, the "Power 10" with a Kv of 1100, and the "Park 300" with a Kv of 1320.  The Kv values are fairly similar, but the "Power 25" is rated for 50 amps, the "Power 10" is rated for 32 and the "Park 300" for a mere 7 -- if you manage to shove 50A through the "Power 10" then it'll be dissipating about 2-1/2 times as much power in the motor as it's designed to.  It probably won't go up in smoke immediately, but you'll almost certainly damage it.  Be absurd and shove 50A through the Park 300 and it will go up in smoke*!

But to reiterate: assuming that everyone is telling the truth then a motor from manufacturer A that has a given Kv and power rating will work pretty much the same as a motor from manufacturer B with the same Kv and power rating.  There's a host of secondary factors -- winding resistance is among them, as it impacts both efficiency and power rating -- but if you just want a motor to fly a plane then match the Kv and the motor's power rating, hope the manufacturer is truthful and the bearings are decent, and go fly.

Better yet, if you don't want to be a trail blazer find someone who has a plane similar to yours and use whatever motor they use.  Or find five people with such planes, and use the motor that most of them use, and hope that they're all right*.

*  And take over 16V of battery voltage, because of the winding resistance.

** As an engineer who often thinks outside the box, I've found that there are exactly two reasons that your design is different from everyone else's:  either they're all idiots for not seeing a brilliant new way to do things, or you're an idiot for not seeing the pitfalls in your brilliant new way of doing things.  When I was young I was a conceited little ass*** it took me a while to learn the second rule, but that's not a reason not to try new things -- just a reason not to try a whole bunch of new things all at once, and not without a plan on backing up and doing things over 'the old way'.

*** Now I'm a model of demure and modest behavior -- really!