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Air Power 400DH

The 400DH is a 4400kv brushless motor and a relatively new entrant in the brushless motor market. It is at the very light weight end of the spectrum for a T-Rex motor with a weight of 42g. This makes it the lightest motor tested to date.
Fitting the motor proved to be very straightforward as the motor is tiny in comparison to some of the much bigger motors I'm used to testing. I fitted a 9T pinion which came supplied with the motor. Having set the Phoenix 35 appropriately (fixed throttle, the 400DH does not like governor mode, current limiting disabled.....some explanation of this in the flight testing). I did a test spool up to measure headspeed. The figures returned a willingness to head up beyond 2600 RPM, so I had to use the curves to keep the wood blades within specification of 2400-2500RPM. One of the things I noted during installation was the very thin wires that supply the 400DH with power.

Specifications Max Current: 15 Amps. KV: 4200 - 4400 Weight: 42.1 grams Shaft Diameter: 2.3mm Mount holes: standard 16 & 19
During my test spool up to set the curves the motor suddenly cut out. The problem was that the wires on the motor had got so hot they had melted the solder and electrical tape holding the bullet connector in place. This is a problem in my view and the wires need to be thicker to stop this over heating. On the main test the same thing started to happen and the electrical tape was melted around the solder point, fortunately this time it didn't come apart. Update 06/05/2005 : Following some more investigation this problem has been mostly solved. The fact that only one wire was getting hot didn't seem right as I would expect all wires to get hot if there was excessive amps for their size. Some further investigation revealed a faulty bullet connector. Having replaced it the wires are getting warm but not to the extent that I am concerned. The T-Rex is still pushing the 400DH beyond its specification of 15A but having resolved this issue the motor doesn't appear to be suffering from operating outside of specification. The 400DH is very attractively priced with respect to it's competition, a strong perfromance would be quite significant given this price differential. I'm going to run one test for the 400DH, using stock wood blades. The test will follow the format in the table below. I have decided not to run the carbon blade test as I fear the extra amp draw will have further melting effect on the bullet connectors and electrical tape. The test was conducted in an ambient 20 degrees centigrade, 68 degrees Fahrenheit. The pitch range on the T-Rex being from +/- 10 degrees. The power source was a Kokam 3S 2000mah pack. So the results will need normalisation against the previous motor tests using the less capable Tanic pack. Also new for this test are charts created by the CSV data from the Hyperion Emeter which shows Volts/Amps and RPM on one chart and Watts on a separate chart. Hopefully these will provide a better consolidated view of the data.
Time period Activity 90 seconds Spool up and hovering throttle/pitch (mid stick) 30 seconds Full power / full pitch 30 seconds Hovering throttle/pitch (mid stick) 30 seconds Pitch pumping from full negative to full positive pitch 60 seconds Hovering throttle/pitch (mid stick), spool down
The 400DH recorded the following maximum values : 24.62 amps 12.5 volts 252 watts The recorded minimum voltage was 9.97 volts during the 30 second full throttle/pitch. The motor temp at the end of the test was 43 degrees centigrade, 107 degrees Fahrenheit. The lithium pack reached a max temperature of 39 degrees centigrade, 102 degrees Fahrenheit. All of this is well within specification and nothing of concern. However, the motor wires did melt the electrical tape holding and insulating the bullet connectors. During the 30 second climbout the headspeed dropped from 2475RPM to 2220RPM, a 255 RPM drop in overall headspeed over a full 30 seconds of full pitch. This is a very very respectable performance and is comparable to that of the AON when using the Tanic pack, however the AON did produce a more powerful result on the Kokam pack. Given this motors size and weight it is very powerful indeed. Flight tests will show if this performance translates into power in the air, especially as the 400DH is 56g lighter than the Medusa and AON motors. Amp draw was relatively high on this motor, with 24.62 Amps maximum over the course of the test. This level of draw will of course affect flight times. Given it's light weight it should be possible to increase head speed but reduce maximum pitch throws to produce a more efficient running combination. Next is flight testing, which should prove most interesting given the light weight motor but strong power delivery. Flight Testing Well the 400DH has proven to be one of the most interesting motors I have had to review so far. It has this rather unique characteristic that it will (if allowed) rev up when you give it full throttle instead of bogging down immediately. This charcteristic is contollable through the proper application of throttle and pitch curves, ideally the rotor RPM should stay constant rather than rev up. The 400DH also has a rather annoying habit of causing the ESC to cut out on spool up. This can be fixed by setting the ESC to current limiting disabled, which I prefer not to do as insensitive current limiting is normally sufficient and will protect the ESC from large power spikes. This may only be limited to the Phoenix range of ESCs, I've seen reports that the Align ESCs don't have this cutout problem with the 400DH. I've yet to get the 400DH governed properly, the recommendation is to run it in fixed mode which requires some very careful setup of the throttle and pitch cuvres to stop the motor just running away as pitch is introduced. The 400DH is extremely light at just 42g and when coupled to a light weight pack (like the Thunder Power 3S 2000mah pro-lite) the total weight saving over an AON 3500 and Kokam 3S 2000mah configuration is close to 100g. This is a very significant amount of weight and the T-Rex feels quite lively and light on it's feet in this configuration. The light all up weight lends itself to longer flight times as well as a better vertical perfromance. I very much like the 400DH motor, it is compact and powerful and as such when matched with a Thunder Power pro-lite pack gives a sparkling performance. The 400DH is also priced extremely competitively. On the negative side it appears to be unhappy in governor mode and will cause ESC cutouts if ESC currentlimiing disabled is not used. In flight the 400DH provides good climbout performance and the whole machine seems lighter and more responsive. Even though the 400DH might not have the overall 'grunt' of the AON 3500 or Medusa 28-40-3400 it's lack of weight gives it a distinct performance advantage, particularly when matched to a Thunder Power 3S 2000mah pro-lite pack. Update : 9/05/2005 The governor mode of the CC25 or CC35 will now work OK with the 400DH as of software release 1.13. The settings are governor high mode, current limiting disabled and standard advance. The key to getting it working is in the setting of the high and low end points for the throttle channel. The high end point being the most sensitive and the one that once set correctly will stop the motor from hunting/surging.

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