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Jan 23, 2014, 01:32 AM
WAA-08 THANK FRANK!
JimNM's Avatar
1860kv is a hot motor for 5-6 inch props on 3s. You cannot put enough air over it to run an 11" prop.

Diameter increases the load on a motor by the fourth power. Pitch increases load by nearly linear factor. You run the risk of damage to the ESC and certainly the battery by pushing your motor on a huge prop. When the heat gets high enough it will melt the insulation on the wires a d you have the magic smoke moment that immediately preceded a crashed plane.

950-1100 kV for 10-11 inch props in such small motors. Generally use the 3watt per gram figure for motor sizing.
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Jan 23, 2014, 07:48 AM
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Grapp68's Avatar

Hello!


Greetings to you, I follow with great interest the discussion having just ordered the Dragonfly from the website Hobbyking Holland.Even if the model seems relatively unknown,I really like.I live in Italy, in Verona.Excuse me for my broken English.I wanted a forum to report on the French model;
http://www.modelisme.com/forum/aero-...y-hk-1m80.html
I can not wait to arrive to mount it and fly!!
Jan 24, 2014, 03:45 AM
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Andy1248's Avatar
I have just ordered my 'Dragonfly' from the UK Warehouse.
Looks like we may have a Dragonfly owners thread here.
Jan 24, 2014, 04:32 AM
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Matty12's Avatar
Thread OP
Hehe, how do you plan to power it Andy? I think I'll be sticking with the 6x4 prop for the moment.
Jan 24, 2014, 08:59 AM
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Andy1248's Avatar
I have ordered an NTM 2836 1000kv from HK at the same time, not expensive, just in case the stock motor is crap.

https://www.hobbyking.com/hobbyking/s...ess_Motor.html

Not sure what prop size I will use, I tend to use a Wattmeter to check on current and watts per prop. I will post how I get on.

NTM 2836 1000kv prop data:

11x7E - 11.1V / 220W / 20A / 976g thrust
11x7E - 14.8V / 412W / 27.7A / 1.485kg thrust
12x6E - 11.1V / 215W / 20A / 1.08kg thrust
12x6E - 14.8V / 430W / 29A / 1.42kg thrust
13x4E - 11.1V / 223W / 20A / 1.06kg thrust
13x4E - 14.8V / 400W / 27A / 1.48kg thrust

Not sure that I will go with that big a prop, maybe 10x6 max.
Last edited by Andy1248; Jan 24, 2014 at 09:44 AM.
Jan 24, 2014, 04:53 PM
Registered User
Grapp68's Avatar
With regard to this motor 28-36 1000KV i found this on the net;
Parabolic glider Robbe first video (4 min 27 sec)

mount a different propeller (Prop.9/7" Aero-naut)
Wingspan: 1510mm
Overall Length: 1000mm
Flying Weight: 760g
Andy,you say is a good enough x acrobatic flight
Before purchasing a new engine I want to try the stock,Hoping that will not burn immediately
Jan 24, 2014, 09:40 PM
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Matty12's Avatar
Thread OP
Quote:
Originally Posted by Grapp68
With regard to this motor 28-36 1000KV i found this on the net;
Wingspan: 1510mm
Overall Length: 1000mm
Flying Weight: 760g
Andy,you say is a good enough x acrobatic flight
Before purchasing a new engine I want to try the stock,Hoping that will not burn immediately
Sorry Grapp, if you use the stock motor with the included prop then you WILL kill it
The Dragonfly is 1800mm wide and over 1kg, so it won't have the same performance as the plane in the vid with that motor. The motor does look like a good option Andy but you'll have trouble getting 1:1 thrust ratio out of the motor which is ok, just be aware that it's going to be tricky making your Dragonfly into a hotliner

I've got a 6x4 on the front of mine now, it looks pretty silly but i've my fingers crossed that she will fly well!
Jan 26, 2014, 05:14 AM
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Matty12's Avatar
Thread OP
I had a fly today, she was gliding nicely but I just didn't have the power to climb to a good altitude. I'm going to pull the motor and ESC out this week for swapping and inspection.

It's such a shame because it's really a beautiful bird!

Now the motor is staying somewhat cooler but whenever I run it up to >60% revs the motor cuts out and I have to throttle back before it starts again. Other guys at the field thought it was odd too
Jan 26, 2014, 10:31 AM
Flys Like A Brick
Bob_B's Avatar
The motor cutting out sounds like a possible timing issue. For that Kv I would think low would be Ok, but you could try medium timing to see if that solves the problem. Also while you are at it also recalibrate the throttle on the ESC. These things could be done before you go to the trouble of pulling everything apart.

Bob

Got a watt meter? If not see if your friends have one you can borrow. Always good to know what is going on with a new setup. Good to add to the top of the list of "things I need to buy"
Last edited by Bob_B; Jan 26, 2014 at 10:37 AM. Reason: To add a little bit more.
Jan 26, 2014, 11:00 AM
WAA-08 THANK FRANK!
JimNM's Avatar
Timing issues will cause rough running and or squeelings. Motor cutting g off is due to over draw on the motor resulting in low voltage cut off. Repeatedly doing this will damage your battery.

No mystery here. The prop is too big.
Jan 26, 2014, 02:23 PM
Flys Like A Brick
Bob_B's Avatar
Matty12

Back a couple of posts you said you had a 6x4 prop on it? Is that what you had when it was cutting out on the last flights? According to HK the NTM 2836 1800kv motor should be more than able to handle the 6x4 prop on 3 or 4 cell batts. I know that sometimes the info on HK may not be too accurate, but still a 6x4 on 3 cell batt should be easy. That is the motor you are using?

If you where still running the original prop I would have to agree with JimNM that for that KV it is too much prop, but if it is cutting out with a 6x4 then something else is causing you problems. The best I can tell you is to check everything! Motor turn freely? Shaft rubbing firewall when running. Different battery, different ESC, throttle calibration on ESC. Bullet connectors for motor? All the solder joints look good? Battery connectors sized to handle load?

To find out what is the bad part you may have to take everything apart. I love it when there is a charred and smoking part that you can point at and say "yep, that's the problem". But most of the time it is something else that causes the "Magic Smoke" to get out. Now you have to find it.

Bob
Jan 26, 2014, 09:23 PM
Registered User
Matty12's Avatar
Thread OP
Yep, 6x4 prop here. I checked ESC calibration a few times, my first thought was that it was going to VLC so I tried a few batteries. Must be a bad connection or faulty gear I guess? Pretty sure the motor isn't rubbing but it's still getting quite hot
Jan 28, 2014, 03:43 PM
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Andy1248's Avatar
Quote:
Originally Posted by peterlngh
Hi, Matty. I have a general hint for you. Sometimes the ply formers look like they are well glued but they really aren't. A very easy precaution one can take is to add an epoxy fillet to any joints you can reach. I'm looking forward to the flight review.

Cheers!
Good point about the ply glue. I got mine and made a start on the build. Although I have got a different motor, I thought I would try the stock motor installed and on a 8x6 prop. Moto ran OK but at about 12 Amps the front bulkhead just ripped out of the fus. Scary! So new bulkhead is on the agenda and a check of all the other glue joints.
Jan 28, 2014, 04:44 PM
Registered User
I got very lucky with my Specter, Andy1248. The first time I started to run the motor up it started shaking and the mount was completely loose, but had not ripped out, by the time I shut her down. I was able to just scrape out the old glue and use the original mount and it's extremely strong now. It even survived two props breaking at full throttle with no damage at all!
Jan 29, 2014, 08:14 AM
Registered User
Matty12's Avatar
Thread OP
Quote:
Originally Posted by Andy1248
Good point about the ply glue. I got mine and made a start on the build. Although I have got a different motor, I thought I would try the stock motor installed and on a 8x6 prop. Moto ran OK but at about 12 Amps the front bulkhead just ripped out of the fus. Scary! So new bulkhead is on the agenda and a check of all the other glue joints.
Wow, all that power eh? :roll eyes: I hope you're having luck with your repairs Andy. You can be sure that I threw a big wad of epoxy on my firewall tonight, just for you!

I've isolated my issue, I was sure it would be the ESC but I plugged in the stock dragonfly motor into my power train as is and it worked beautifully. Plenty of power or at least as much as I'd expect off that kv/prop combo.

I had a good look at the suspect motor and saw a loose wind inside, pulled it and the wire was broken! I guess the motor was running less one pole? In retrospect it did seem to run a bit rough at low revs...

Oh well, I'm very excited about making the FOURTH flight on this bird a proper one!
Last edited by Matty12; Jan 29, 2014 at 08:14 AM. Reason: Learning to count!


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