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Old Jun 15, 2013, 01:10 PM
SteenPedersen is offline
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Dr. Mad Thrust 50mm problems

Hi

I am new to this forum but hope I have posted this the correct place.

I just got Dr. Mad Thrust 50mm 4S version today
http://www.hobbyking.com/hobbyking/s...DF_3300kv.html

Unfortunately I didn't get the results I expected.

I use a Dynam Dectrum 30A ESC http://www.hobbypartz.com/60p-dye-1003-30a-esc.html

For the test I used my nanotech 850mAh 4S battery http://www.hobbyking.com/hobbyking/s...lipo_pack.html

I only draw 22A / 315 Watt and about 350 grams of thrust.

Any idea why?

BR
Steen
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Old Jun 15, 2013, 01:38 PM
Kevin Cox is offline
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I have these fans in my Banshee. I think your battery is too small.
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Old Jun 15, 2013, 02:53 PM
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Thanks.

I thought it would be enough. 0.85 x 45 = 38 amps?

I'll try order another (nano-tech 1300mah).

BR
Steen
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Old Jun 15, 2013, 06:27 PM
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might try adjusting the timing on the dynam esc but watch the heat and watts
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Old Jun 15, 2013, 07:44 PM
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An 850 mah Battery!? A wee bit tiny.
As for C ratings.. Brochure Babble..
Divide claimed ratings by half and then these would be only optimistic, rather than laughable.
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Old Jun 16, 2013, 11:02 AM
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Better battery and high timing should see numbers close to spec.
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Old Jun 16, 2013, 02:36 PM
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Agree with the above, such a small battery will sag under the load of that motor and the thrust will drop off dramatically. Suggest you test with the biggest pack you can muster (parallel them if you have to) and then draw comparisons.
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Old Jun 16, 2013, 04:17 PM
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Thanks for your help. I only have 3S batteries. The little 4S is for my funfighter :-) I will take the plane with me to the club tomorrow and put a bigger 4S on. I'll be back with the results.
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Old Jun 17, 2013, 08:55 AM
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Tried today with a bigger battery with the same result.

I guess I should read the "max" 650g thrust. In the real world it delivers 350 grams.

New motor on its way.

BR
Steen
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Old Jun 17, 2013, 09:02 AM
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Quote:
Originally Posted by SteenPedersen View Post
Tried today with a bigger battery with the same result.

I guess I should read the "max" 650g thrust. In the real world it delivers 350 grams.

New motor on its way.

BR
Steen
Hi Steen,

Have you set the ESC time mode in higher position and calibrate the throttle range with ESC.. Since some brand ESC is needed to do the calibration for getting the full throttle position either add 20% travel of throttle channel to test again... The related EDF 4S version to be able gained up to this thrust if the setting is correct.
Hope the above to be assisted you.

Thanks,
Tim
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Old Jun 17, 2013, 09:38 AM
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Quote:
Originally Posted by SteenPedersen View Post
Tried today with a bigger battery with the same result.

I guess I should read the "max" 650g thrust. In the real world it delivers 350 grams.

New motor on its way.

BR
Steen
True, 650gr is maximum for a few seconds when the battery is full but I have seen consistent 600gr after the initial peak. This is outside the airframe though on a test stand.

As above, make sure timing is set to high.

Are you measuring in the airframe?
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Old Jun 17, 2013, 12:45 PM
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Hi again.

Thanks for your help.

Yes I am measuring in the frame. I put the aircraft on the nose, reset the weight and gives full throttle.

I just changed the ESC time mode to fast/high (the 3.rd choise).
I fully charged the battery and made the test. Only 350 grams of thrust.

The aircraft weight is 475 grams with the battery and I was hopening for a vertical acceleration.

I have now ordered a 2815 4800kv for this fan. I read on the thread below the product on HK website that this should do the trick?

In the meantime I have put back my old hyperion y22s 6000kv with my wemotec fan - it's giving me 450 grams with a 3S battery :-)

BR
Steen
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Old Jun 17, 2013, 03:32 PM
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Quote:
Originally Posted by SteenPedersen View Post
Yes I am measuring in the frame.
This is the reason. The 650gr thrust is with fan out in the open air.
When the fan is installed, the intake restriction and backpressure from the exhaust result in much lower thrust levels for these 10blade fans.

When you fly though, the air ducts work quite well and the thrust decrease is not so noticeable.

I suggest that you sand the exhaust a bit to open it up 2mm at a time and/or cut cheater holes to help the fan pull more air in. This will definetely improve thrust.
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Old Jun 17, 2013, 08:48 PM
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I'm thinking this CS rotor is barking up the wrong tree.
Inserted a Haoye 50mm 7 blade rotor which incidentally Fits! the CS Alloy shroud Very well.. better than the 10 blader does OR the Haoye in it's own Haoye shroud.
Using a hk 2815 of 4000kv on 4s it measures ~38 a @530 watts and generates 750 gms thrust... In a Nacelle :-).
No shroud contact at 50K .. yet.
10 blade rotor is decidedly poor in comparison during my experimentation, although I'm liking the alloy shroud's concentricity and rigidity ...a lot .
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Old Jul 24, 2013, 01:49 PM
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I also have the 7 blade and 10 blade, and I concur that the 7B fits better in the aluminum housing than its own. I have been using the 2815 4800kv motor in the 10 blade fan for some time and with good flight results, and on a warm 1300 3S pack this setup provided 47A, 11.31V, 532 Watts, and the RPM gets pretty high but the impeller has held together thus far. This motor runs only warm as it is free to cool in the fan's airstream. Its enough power to move the 50mm F-16 at moderately high speeds, such that it goes from being barely within sight to almost out of sight again in under four seconds, and could move a 64mm class airframe, although not necessarily fast in that scenario. I am not sure what your plans are SteenPedersen, but this setup flies nice at half throttle, and normal mixed throttle flights with several WOT passes will last about 3 minutes, as nobody flied with the throttle at full for the entire duration. This setup does put the 50mm airframes near the limit in terms of ease of hand launch. I have had over 100 flights on this airframe, the same one since 2010 without any incident. As you get into larger packs, larger ESCs and in this case, a pretty hefty motor that would normally be seen on a 64mm fan, it begins to push the tip stall point during hand launches and you can feel it in high-bank turns as it overshoots (which looks really cool). It is important that you balance the impeller and ensure that the adapter is straight on the motor shaft. If you're only able to get low thrust on 4S even on the stock motor, there is something wrong. I do not place any great credence in C ratings, but they can guide you to lower IR packs, but nothing more and it has to be verified by yourself first. An internal resistance meter like those built into the FMA and iChargers is a great help here, and since you have measured your systems power, you should also take note of the voltage drop at your relatively low 22A current draw. If the voltage appears strong, then you can eliminate the battery as the problem for the time being and move to the next component in the chain. If you have a servo analyzer, you can verify if your throttle channel is receiving full throttle or not. I have spent a lot of time lending advice to others in the Power Systems forum and on occasion this type of low power issue is caused by the transmitter throttle endpoints. It could also be a wrongly wound motor but they typically vibrate when a coil has the incorrect number of turns compared to the others. A bad ESC with high impedance semiconductors or a high IR cell can induce your weak power symptoms, too. Those parts have to be verified firsthand. Below is a photo that I took depicting both fans just for comparative purposes:
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Last edited by Cody f86saber; Jul 25, 2013 at 10:23 AM.
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