Justgofly 450T2 and 550XT (12-magnet, and 6-magnet) - RC Groups
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Jan 09, 2009, 11:39 AM
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Dr Kiwi's Avatar

Justgofly 450T2 and 550XT (12-magnet, and 6-magnet)

Vinnie Finn at www.justgofly.com recently sent me a couple of new motors to evaluate - a 450T2 (~1450Kv) and a 550XT (~825Kv). So far, I've only done some no-loads and a single prop test on the 550XT (12-magnet bell), just to get Kv, Io and Rm. With the 450T2 I've run no-loads and several series with props, ranging from Zagi Carbon up to 8x4 APC E - this last takes the amp draw toward the limit of my Zurich Power Supply, and an 8x6 APC E or larger will certainly exceed its capability. To try some larger props, and investigate the suggested 25A-30A/250W max, I need to charge up some 3s packs.

This 450T2 is typical "450 outrunner" size (viz. Don's Wicked KA450H, ELE 460FX and the like) - 27.62mm OD x 25.25mm long, and weighing in at 63g with 2.5mm MP Jet Gold connectors. It is configured in "pusher" mode, and has a relatively long 3mm shaft (15mm exposed). The blue rear mount plate has 3M threaded holes at 16mm/19mm, and the one-piece bell is chromed. The motor has a 9-armed stator and 12-magnets.

The first prop I tried (for reasons which will become obvious) was a Zagi Carbon, and it produced 10.46oz @ 67mph from a very modest 7A/76W. I had bought some new props from Azarr (www.ecubedrc.com) amongst them what I thought would be two Zagi 130mmx125mm Carbons - Azarr provided me with the whole history of these props (with which I need not bore you), but the upshot is that he now stocks a very similar looking, slightly more flexible, "5x5 Maxx Carbon" (as I'll call it). So a comparison with the "original Zagi" [itself a copy of something else!] was on the cards. As expected, the performance of the two props was very close - the Maxx drew a bit more current, spun at slightly lower rpm, and generated an insignificantly larger thrust - thus its g/W "efficiency" was slightly lower. Pitch speed comparison is moot - I use 5.1x4.9 for the Zagi because that's how 130x125 translates (though 5x5 is also stamped on its blades!) - this new Maxx prop is labeled only with 5x5... so I have to use 5" pitch in my calculations.

After this I ran a newly acquired 6.5 x 6.5 APC Sport, then several 7" props - 7x5 APC E, 7x6 APC E and 7x7 APC Sport. Once again the 7x7 APC Sport seems to be a remarkable prop for a fast plane - 22.5oz @ 80mph at 3.32g/W... better than the 6.5x6.5 APC Sport which gets you only 16oz @ 80mph, and less "efficiently" (only 2.92g/W).

Finally I ran an 8x4 APC E - after my typical series with this 8x4 APC E (total usage 278mAh) I kept the motor at WOT until I'd used 1000mAh ... the motor ran perfectly smoothly and evenly for this whole extended run, which used up perhaps 750mAh @ ~20A (~2.25 minutes). At the end of the initial series the Eagle Tree temperature sensor had recorded a maximum of 44C... but by the end of the extended WOT section the "running" temperature had decreased to 41C (but, naturally, then rose [to a peak of 65C] as heat from the windings was transferred to the case). Direct measurement from the windings (using my IR gun) at the 1000mAh mark was a momentary peak of 73C. These temperature figures, obtained under "worst case scenario" static conditions, suggest that this motor will fare well at these power levels with even moderate in-flight cooling.

I have appended a photo showing my set-up for determining no-load rpm (though the two black Sharpie patches on the shiny bell do not show up well in it!). I can confirm the rpm readings with the Eagle Tree, but it is hard to get a single figure from the Power Panel during running (rpm figures shown on it fluctuate a little, typically by only <100 rpm - insignificant in the grand scheme of things - whereas the Hobbico Tach, rightly or wrongly, gives me a steady number to write down!) Two data tables are also attached.

More to come, later.

Cheers, Phil
Last edited by Dr Kiwi; Jan 17, 2009 at 01:54 PM.
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Jan 09, 2009, 03:04 PM
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Dr Kiwi's Avatar
I've added a Drive Calc screen shot for the 8x4 APC E - shows 71% efficiency at 10.6v. Hmm? Rm (0.11 v. 0.13) and Kv (1445 v. 1450) match well enough with what Motocalc computed. And calculated rpm/amps/thrust with this prop are very close to my measured figures.
Last edited by Dr Kiwi; Jan 09, 2009 at 03:18 PM.
Jan 11, 2009, 03:02 AM
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tungym's Avatar
looks like a very efficient motor
Jan 11, 2009, 09:03 AM
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Dr Kiwi's Avatar
Originally Posted by tungym
looks like a very efficient motor

I need to do some more comparisons, but yes, I think it does pretty well. Drive Calc seems to produce realistic efficiency figures, and this motor is neither hugely better, nor hugely worse than most "good quality" motors I've tested.

Of course, if you expect to get the 98% efficiency claimed by some Chinese makers... good luck!
Jan 13, 2009, 10:05 PM
Rochester, NY
JustGoFly's Avatar
I thought you might like a video of this motor in action in a balsa sport plane on 8x6 prop. I run both 3S 1500 25C, and 2100 20C LiPos in this setup.

Messing around with a R/C Airplane - JustGoFly Power (6 min 15 sec)

and 550XT
Slow Stick JustGoFly 550XT Crash.mpg (2 min 47 sec)

Last edited by JustGoFly; Jan 17, 2009 at 11:42 AM.
Jan 16, 2009, 10:57 PM
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Dr Kiwi's Avatar
I had a rough day at the office so I thought I'd take some relaxation time and test run a few more props on the 550XT 12-magnet 825Kv motor.

With such a low Kv this motor is going to need a monster prop on it to draw 20A or more - I ran everything from 10x6 GWS HD through 13x6.5 APC E on 3s and I still didn't get to 20A. The next step might be 4s!

The motor generates impressive thrust and g/W figures... that's good for 3D, if you don't need a lot of pitch speed.

The motor ran well with all the props I tried, but the 12"-13" props caused problems on start-up - they were simply too big for this motor to get them up and running without a helping hand flicking the prop. 30-40oz is a decent amount of thrust, and indeed the motor temperatures were not excessive until I got to the 12x6 and 13x6.5. As expected the 13x4 generates monster thrust (~41oz) from only 15.7A/169W (and the didn't really get very warm), but of course pitch speed is low (24mph). The 13x6.5 got me >42oz @ 35mph, but sustained running obviously put a big load on the motor and, under these static conditions, it got way too hot! You can see how loaded down it is by looking at actually prop RPM in relation to Kv x V... in this case only 65% [I usually figure that anything less than about 75% means you are loading the motor excessively]. It is a tough, well-made motor though, and in-flight with only short bursts to WOT it may well survive unharmed!

Here are the tables and a picture!

Cheers, Phil
Last edited by Dr Kiwi; Jan 17, 2009 at 08:22 AM.
Jan 17, 2009, 09:21 AM
Trying to defy gravity...
jimsky's Avatar
I picked up a 450T2 from Vinny at the 2007 NEAT Fair and used it in an original Superfly that I also got at the NEAT Fair. Very nice motor, great balance of speed and thrust, this would be an excellent choice for a GWS or Alfa sized warbird. Below is the link for the sale of Superfly I mentioned, it had some prop/watt numbers for reference:


Jan 17, 2009, 02:00 PM
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Dr Kiwi's Avatar
Just to complete the story, I have fitted the 6-magnet 'Speed Bell' to the 550XT. Since I had it apart I thought I might as well take some photos to show how well the copper has been packed into this motor - I guess we can also deduce how thick the stator laminations are (45 laminations in 15mm... so ~0.33mm). The motor loses 11g (down to 79g) when fitted with the 6-magnet bell (33g including shaft) as opposed to the 12-magnet bell (44g including shaft).

No-load and prop tests coming in due course.
Last edited by Dr Kiwi; Jan 17, 2009 at 02:08 PM.
Jan 17, 2009, 05:54 PM
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Dr Kiwi's Avatar
I ran the motor at no-load and then with 8x4 GWS HD, 8x4 APC E and 8x6 APC E props.

Kv comes out at ~1445Kv (about 1.75 x the Kv of the 12-magnet version), and Rm... (surprise, surprise) is the same 0.17 ohms I got for the 12-magnet version.

Maybe it is the Phoenix 45 but this version is also a bit hard to get started... then it runs smoothly, but I think we are pushing the limits at 20A or so. With the 8x4 APC E it got a bit warm at 17.20A/184W max, and with the 8x6 APC E (I held this at WOT at 22.10A/236W for a bit longer than necessary) it got very hot after less than a minute. Obviously in the air things can only get better, but perhaps 8x6 APC E is as much as is prudent.


Cheers, Phil
Mar 31, 2009, 07:43 AM
Survival is Attitude!
Skonkworkstexas's Avatar

What A Motor!

Just got my 450T2 and tested it for a sailplane I am building. I was a little astounded on the bench. Here is the lineup:
450T2 with 8&4 APC electric
Turnigy 40A Plush ESC
25C 3s1p 2200 LiPo
GWS test reciever
Tower optical tach
Bantam Estation


11.44Volts, 22Amps, 252 Watts.
12360 RPM
38 OUNCES THRUST! Better than hoped!
Maiden in a day or two with a Multiplex Easyglider pylon mounted at about 43 ounces weight with 3S2P 2200 25C LiPo giving 4400Mah. Should be up there awhile!
Mar 31, 2009, 12:11 PM
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Dr Kiwi's Avatar
That's fairly close to my measurement - 5oz more thrust from 40W more - that's 15.3% more thrust from 18.3% more power-in... sounds about right. You get 4.28g/W... at slightly lower power input I was getting 4.39g/W.
Mar 31, 2009, 08:32 PM
Survival is Attitude!
Skonkworkstexas's Avatar
OK, glad you clarified that. Cause you are always spot on, and I was higher, but used a 25 C battery, and at just over 20 amps it just doesnt load it much.
Using a 40 Amp controller probably doesnt hurt either. A heavier power fet will have a lower internal resistance at a given amp, I figure,
Motocalc predicts more, but the plane will have TWO batteries, which is a very light load for them. Plane is designed for endurance and altitude, and I think the T2 was the right choice for power AND efficiency.

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