I was sent some small AEO EDF units (27mm, 30mm, 35mm, all three complete with motor/housing/impeller; and a 40mm housing + impeller).
In discussions with AEO I had expressed concern that these tiny fans all have push-on impellers... given that, with their extraordinarily high Kv motors, one could expect RPM to be in the 50-70,000rpm range... I suggested that impeller adapters would be almost imperative for safe operation.
My opinion on that has not changed since, on the first test run I tried with the 35mm unit (not anywhere near WOT), the impeller detached itself and whistled across the room. Add to that, the fact that the motor bearing tube itself is a push-fit into the housing. With the current design of the motor, there is no means of securing it within the housing, and with the torque effect of spinning an impeller at high RPM, the motor's bearing tube tends to rotate within the housing. There is, in fact, a flat machined on this bearing tube, but no way to make use of it, perhaps via a set screw through the fan housing. In the case of both impeller and motor, extended runs would surely warm the motor shaft and bearing housing to the point where the plastic of both impeller and housing would soften and exacerbate the problem. I wonder whether AEO might consider adding a disc (11.5mm OD, with threaded screw holes to suit 10mm mounting hole spacing... the housing already has the holes!) to the front end of the bearing tube... THEN the motor could be secured safely into the housing. THEN supply a shaft adapter for 1.5mm shaft, and the impeller could be secured, too! [Here is a link to a guy who has resolved the impeller issue... maybe AEO could offer him a subcontract to provide the necessary parts for their products! http://www.rcgroups.com/forums/showt...php?t=1391683]
To obtain the no-load data, I had to resort to gluing the bearing tube into the fan housing. For the one series of runs, at 6v through 8.4v, I also had to glue the impeller to the motor shaft. It is interesting to note that this motor has a 9-arm stator, and 12 magnets, but those magnets are arranged in like-pole pairs, so it actually a 6-pole motor.
I made up a mount so that I could fit the EDF unit to my standard test-stand... the outer housing was glued with medium CA to a shaped balsa cradle attached to one of my standard motor mount plates.[see photos]
No-load amp draws seemed amazingly high... for most motors I've tested, voltage does not make a dramatic difference to no-load amp draw, but in this case amp draw more than doubled in going from 6v to 8v....at 8v it required 5.55A/44.4W! Most motors I've tested manage no-load RPM which is 98%-99% of the "calculated Kv x V"... this one only managed 85% (79920/94400).
With the motor secured within the housing, and the impeller glued with CA to the motor shaft, I set the unit up on my test stand with the usual array of measuring devices (Eagle Tree v3, Medusa Power Analyzer Plus, Ohaus Digital Scale, Hobbico Digital Tach, IR Temperature gun... and my Zurich Power Supply to provide set voltage). I ran the unit at 6v, 7v, 7.4v and 8v, measuring all the usual parameters. The motor ran smoothly and well, and since I gave it only very brief bursts to WOT, for just long enough to record the numbers, it didn't get unacceptably hot. At 8v, peak amp draw of 16.50A/138W produced 55600rpm and 152g of thrust... at a fairly dismal 1.10g/W. "RPM as a % of Kv x V" is a telling statistic, and most EDFs I've tested seem to manage somewhere in the mid-80's to mid-90's%... this little AEO motor clearly struggled and could only spin the 35mm impeller at ~56% of Kv x V.
From the no-load values and the few data points from impeller runs, [I'm sure, not nearly enough for truly accurate calculation] DriveCalc and MotoCalc indicated ~11800Kv with an Rm of about 0.25 ohms (this later parameter varied a lot, depending on which figures I fed in).
Further, DriveCalc computed a maximum efficiency of only 47.5% at 12A, and if one takes the AEO suggestion of 22.8A max. current at face value then, at that level, efficiency drops to a dismal 38%!
Here are some photos of the set up, and the data table for performance (such as it is).