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Old Aug 09, 2012, 05:21 PM
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DT750 and 7 propellers - Efficiency test

HexTronik DT750 750KV 18A 3S motor,
7 propellers: APC 9x4.7, 10x3.8, 10x4.7, 11x4.7 and 12x3.8, Graupner 10x5 and 11x5.

Test made with:
Right angle test bench, 200mm both sides,
Turnigy Nano-Tech 3S 4000mAh 35-70C,
Hobbywing Pentium 30A - Timing mode: Middle,
Turnigy Servo Tester and Micro Tacho, GWS Servo Tester MT-1,
Junsi PowerLog 6S Wattmeter - LogView software - Soehnle scale.

Two levels:
1 - Mid throttle, 50%, usually used to hover
2 - WOT, 100%, maximum values, thrust and current
Turnigy Servo Tester has a position giving mid throttle (1.49ms pulse).

Results:
APC 11x4.7 is the best performing prop with this motor.
APC 12x3.8 requests too much power WOT, exceeding the 18A allowed.
Graupner props don't seem to like low KV, they would probably work better with more RPM.

Hoping this test will be helpful to find the right motor and the right prop according to AUW.
My previous test of HexTronik motor: DT700 and 24 propellers: http://www.rcgroups.com/forums/showthread.php?t=1594904

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Last edited by Mortimer; Aug 09, 2012 at 05:46 PM.
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Old Aug 10, 2012, 07:43 PM
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did not realize many people were still using the DT750, good motor from what I have read. I never tried them myself but was tempted.
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Old Nov 06, 2012, 07:00 AM
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great info bruv think i will stick with my dt700's then
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Old Nov 12, 2012, 11:37 PM
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Can you actually get the APC props suitable for a Quad? CCW/CW

I have a few at home for my (broken) Tri, wouldn't mind putting them on my newly scratch built quad
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Old Mar 18, 2013, 09:19 PM
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sorry to bring this back, but i've been flying 10x4.7.. looks like 10x3.8 is really the 10 inch prop to use though. Who would have thought.
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Old Mar 26, 2013, 11:57 AM
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Thanks a lot Mortimer. Just what I was looking for. APC 1147 for my tricopter it is then.
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Old Aug 16, 2013, 12:11 AM
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I have 36 of those , but all of the bearings went bad .I like it. That's all I need the good bearing ( 4mm x 8mm x 3mm ) it has a lot of power , I used 12x 4.7 prop.
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Old Sep 25, 2013, 11:12 AM
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How did you mount the APC 11x4.7 props to the DT750? The smallest locating ring that came with those props is still too large for the M4 motor shaft on the DT750. So how do I keep the prop centered and balanced?
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Old Sep 25, 2013, 12:48 PM
Jack
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Originally Posted by Budge View Post
How did you mount the APC 11x4.7 props to the DT750? The smallest locating ring that came with those props is still too large for the M4 motor shaft on the DT750. So how do I keep the prop centered and balanced?
You can put a couple of layers of heat shrink tubing about the shaft and it will take up the play. Add as many layers as is needed and then trim to a little less than the hub height.

I have used prop savers a lot on the DAT-750 and DT750 motors, you can see them on the motors in the image. I use them with the highly elastic Thera-Band prop saver bands and have never lost one in flight. And my rewound DAT/DT750 motors can get up around 250-300W at full toot (and run dead cool at that level too).

Details on the Thera-Band prop saver bands is here:

Prop Savers - Fitting, Using, Testing, & Making Thera-Band Bands - www.rcgroups.com/forums/showthread.php?t=1419378

I have had one report that prop savers did not work well on a tri copter, that the flyer felt that they were the cause of some oscillating. But I think that cutting the bands slightly thicker or maybe using two or even three bands to get a firmer hold down will prevent that. That prop saver seen there is the ACC366 from Maxx Products some of the more generic tapered cone style prop savers will not have a cone that is large enough at the base for some prop to seat on the taper. The Maxx ACC366 will work fine though.

Jack
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Old Sep 25, 2013, 01:36 PM
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Originally Posted by Budge View Post
So how do I keep the prop centered and balanced?
With great difficulty 😜
I used standard 4mm nuts n washers. Nut, washer, nut,prop,washer, nut. Tighten as much as possible without damage.
Never liked it, but simplest answer I've found and it works.
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Old Sep 25, 2013, 06:38 PM
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Best way to mount apc slow fly is to use an old dt750 bearing. Use some epoxy or CA to seize up the bearing so it no longer moves freely then press it into the bottom of the prop. Fits near perfectly and fits the shaft perfectly.
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Old Sep 25, 2013, 07:04 PM
Jack
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The problem of keeing the prop turning with the shaft is basically what drove me to using prop savers on the DAT-750. There was just too much torque and not enough clamping force between the nuts and washers.

The prop saver is locked to the shaft with the two 3mm screws bearing against small flats I grind on the shaft. Doing that only take a few seconds with a Dremel tool. And you can even just cut the stock threaded shaft off (leaving a few threads on the end) leaving it long enough to locate and center the prop hub. This post over on the DT750 thread in the motor construction and rewinding subforum shows how to do that:

http://www.rcgroups.com/forums/showp...postcount=1080

And anyone that thinks a prop saver cannot handle larger props and higher power levels needs to try it with Thera-Bands. Send me a mailiing address and I'll send you some free Thera-Band prop saver bands to try.

Here is a link to a video of an APC 13x8 Thin Electric being run up on a DAT-750 with a pair of Thera-Bands as a demonstration of how well it can work:

APC 13x8 on prop saver.mp4 (1 min 33 sec)


I have intentionally mounted a big prop with a single aged and weakened band just to see what happens with the band breaks. I did it in a static test with the prop shaft vertical and the prop simply went away from the motor a few feet, lost speed, and fell to the ground. With two or more bands I had never lost a prop in flight.

Jack
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Old Sep 26, 2013, 11:52 AM
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That looks like a clean solution Jack.
Has anyone ever done a definitive test on weather the rumor that prop savers on multirotors causes some instability is true or not?
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Old Sep 26, 2013, 12:03 PM
Jack
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Originally Posted by TheNiceGuy View Post
That looks like a clean solution Jack.
Has anyone ever done a definitive test on weather the rumor that prop savers on multirotors causes some instability is true or not?
Not that I know of but if you want to be the guy that does it, send me a mailing address and I'll send you some Thera-Band to use.

I really thing that if the props were held down firmly that the problem would not be there. The guy that reported it as a problem to me said that the blades were tilting slightly from the inputs from the controller and that the problem was that the controller was sort of "chasing" that but not catching up with it.

I have since seen two or three other mentions of props savers being used successfully on other multis. If they worked OK I would use them there just for convenience if nothing else. There no faster or easier way to mount a prop or change props as far as I am concerned. And it also does away with all considerations as far as CW or CCW rotations and self loosening prop nuts and all that.

Jack
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Old Sep 26, 2013, 12:43 PM
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Quote:
Originally Posted by Budge View Post
How did you mount the APC 11x4.7 props to the DT750? The smallest locating ring that came with those props is still too large for the M4 motor shaft on the DT750. So how do I keep the prop centered and balanced?
For APC props on my DT7xx motors, I use the adapter rings from a set of Gemfan props. They fit firmly in the APC props with no slop on the shaft...
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