"external rotor" stepper

[stirlingnut]

Does anybody make "external rotor" stepper motors? I ask because brushless motors,and stepper motors are similar in design. I have been flying electric planes for a few years now,and the use of brushless motors have really improved performance. At first most all brushless motors were "in-runner",the magnets rotated inside the can of the motor with the windings fitted to the can.Nowadays most are "outrunner",the magnets rotate around the windings.
This has provided a huge boost in performance. Mostly the tourque increase being the main improvement. But there are other things too.Cooler running,simpler to make,no need for a gearbox,etc. I realize that a cover for the motor would be in order,but wondered if any manufacturer had tried this route yet. Having used both types of brushless motors,and built many different types/sizes of "outrunner' motors,I seems this might be the next logical move of the technology.Any input?

[mcpltd]

IMS make an IOS motor.
http://www.imshome.com/ios_motors.htm
But you dont get any increase in performance.
Has other benifits though.

Does anybody make "external rotor" stepper motors? I ask because brushless motors,and stepper motors are similar in design. I have been flying electric planes for a few years now,and the use of brushless motors have really improved performance. At first most all brushless motors were "in-runner",the magnets rotated inside the can of the motor with the windings fitted to the can.Nowadays most are "outrunner",the magnets rotate around the windings.
This has provided a huge boost in performance. Mostly the tourque increase being the main improvement. But there are other things too.Cooler running,simpler to make,no need for a gearbox,etc. I realize that a cover for the motor would be in order,but wondered if any manufacturer had tried this route yet. Having used both types of brushless motors,and built many different types/sizes of "outrunner' motors,I seems this might be the next logical move of the technology.Any input?

[Jason Ross]

I'm surprised that brushless outrunner motors run cooler. It would make sense for a brushed motor because now the cooper would be on the outside. Magnets typically make a poor thermal path, maybe it feels cooler to the touch but I would guess that its Km would be lower.

[stirlingnut]

[QUOTE=Jason Ross]I'm surprised that brushless outrunner motors run cooler. It would make sense for a brushed motor because now the cooper would be on the outside. Magnets typically make a poor thermal path, maybe it feels cooler to the touch but I would guess that its Km would be lower.[/QUOTE
Since the stator is attached to the bearing holder,and it is part of the mount,some heat-sink effect takes place.Also "outrunners" are open to the elements(not good for cnc),they get better airflow.What do you mean by "Km"? Do you refer the to Kv(motor speed)?Out runners are also typically more efficient,but it does make the motor larger in diameter.100-200 watt motors are common place on r/c model weighing only a pound or so. Here is a pic of one.

[H500]

The max power is largely limited by how much heat the motor coil could dissipate. From the photo, it looks like increased cooling was accomplished by putting large air spaces between the coils. In RC apps, the propeller would also create a lot of air flow.