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Old May 30, 2012, 09:46 AM
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when i had the torque/boss combo on a rhino 2350 4s pack using apc 12x6, it wasn't anywhere near 700w. It only pulled a little over 600W static. Could have been the elevation (~5280 ft)
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Old May 30, 2012, 09:54 AM
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Quote:
Originally Posted by DenverJayhawk View Post
when i had the torque/boss combo on a rhino 2350 4s pack using apc 12x6, it wasn't anywhere near 700w. It only pulled a little over 600W static. Could have been the elevation (~5280 ft)
I saw the same low numbers at my field and I'm about 2900ft MSL.
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Old May 30, 2012, 01:20 PM
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Quote:
Originally Posted by DenverJayhawk View Post
when i had the torque/boss combo on a rhino 2350 4s pack using apc 12x6, it wasn't anywhere near 700w. It only pulled a little over 600W static. Could have been the elevation (~5280 ft)
Here's why.... I fly at 23 ft ASL and the last time I checked, which was a while ago, I got 10,200 RPMs out of the Torque and airboss combo on 4S, and measured 43A and 640W. That's 14.88v at an 83.7% Kv efficiency. A 12x6 APC turning 10,200 is 547 Watts-out so there were about 100W consumed in one way or another. That battery was definitely a Turnigy blue, which means that at the same Kv efficiency, I should expect 10,600 RPMs at 15.44v on one of my better batteries.

That's about 615 Watts-out, so I would expect to see about 720W on the meter, which is very similar to what Roger is reporting, but his voltage is better than what I would expect from my tired 4S Sky's. Haven't bought a new one in a while and expect about 3.9v per cell at WOT.

So the bottom line is that we will see different reading on the same motor with the same prop if our voltage is different, and it always will be from person to person and from minute to minute. This is one of the reasons why RPM readings is so important to power comparisons.
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Old May 30, 2012, 01:37 PM
Grumpy old git.. Who me?
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Originally Posted by bigroger View Post
Tried out Apc 12x6, APC 13x6.5, vox 13x5 and Vox 13x6.5 with Turnigy 40C4s2200 cells.

Numbers were very interesting and not what I expected.

APC 12x6, 10650rpm, 46A, 761W
Vox 13x5, 10110rpm, 42A, 646W
Vox 13x6.5, 9300rpm, 51A, 796W
APC 13x6.5, 9390rpm, 60A, 950W.
Roger,
I think there may be something amiss with some of that data. What seems odd is that the amps and the RPM dont correlate as would be expected. Lower RPM must mean more load, and more load must mean more amps. But those figures dont tie up that way, for instance the 13" APC pulls way more amps than any other prop yet its not the lowest RPM. Also the 12" APC has the highest RPM yet not the lowest amps?

Also the battery voltages are all over the place. The 12x6 APC figures calculate to a battery voltage of 16.54v, which is way too high for a loaded 4s battery. The Vox props calculate to about 15.4v which is much more realistic but 13" APC calcs to 15.8v when you would expect that to be lowest of the lot due to highest amps
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Old May 30, 2012, 04:28 PM
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The APC 12x6 spinning 10,650 at 16.54v is a KvE of 78.5% and 622 Watts-out using 37.6A. He measured 761W and 46A so that’s 139W consumed and about 8.4A.

When he put a bigger APC (13x6.5), he measured 9390 RPMs, 60A, and 950W. That’s a KvE of 72.4% and a Watts-out of 627 on 39.6A, so a difference of 323W and 20.4A and consumed.

The Vox 13x5 with spin 10,110 RPMs on 15.38v at a KvE of 80.16% and generate 608 Watts-out which needs only 39.5A, so 38W is consumed needing 2.5A.

The bigger Vox 13x6.5 spinning 9,300 RPMs at a KvE of 72.67% is generating 609 Watts-out on 39.0A so 187W are being consumed on 12A.

Vox 13x5 @ 10110 RPMs = 38W consumed and 2.5A (80.16% KvE)
APC 12x6 @ 10650 RPMs = 139W consumed and 8.4A (78.5%)
Vox 13x6.5 @ 9300 RPMs = 187W consumed and 12.0A (72.7%)
APC 13x6.5 @ 9390 RPMs = 323W consumed and 20.4A (72.4%)

I don’t really see anything wrong with this.

APC 12x6, 10650rpm, 46A, 761W = 16.54v = 4.136v/cell
APC 13x6.5, 9390rpm, 60A, 950W = 15.83v = 3.958v/cell
Vox 13x5, 10110rpm, 42A, 646W = 15.38v = 3.845v/cell
Vox 13x6.5, 9300rpm, 51A, 796W = 15.61v = 3.902v/cell
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Old May 30, 2012, 04:50 PM
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Jim,
It's really quite simple, no need to estimate efficiency or prop power out.
  • A motor will pull more amps if you put more load on it.
  • A motor will turn slower if you put more load on it.
If you accept the above two statements then there is something wrong with the recorded numbers.

Also i've never seen a battery that would hold 4.14v per cell under a 46A load but only 3.8v per cell under a 42A load.. There is something amiss IMHO (in fact i've never seen a battery hold 4.14v per cell under load period)

Steve

PS.. 608W out and 646W in for the Vox 13x5 would make the motor 94% efficient, not 80.16%
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Old May 30, 2012, 04:58 PM
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Guy,
It was only some down and dirty testing before a flight yesterday.

I will retest today and this time I will use a fresh lipo for each test.

The plane did fly much better on 4s compared to the 3s previous. Also the 12x6 really does fly like it's in mud.
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Old May 30, 2012, 05:09 PM
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Using the same lipo for all the tests without re-charging would explain most of the 'oddness' .. Only the unusually high voltage remains hard to explain.

It will be interesting to see how numbers from a more controlled test compares.
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Old May 30, 2012, 05:28 PM
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12x6 at that rpm was fun for me before I moved to motroflys and the bigger props. I had to work more on hovers as it just didn't have thrust that I now have.

Top speed was what I liked about it as I usually have the throttle wide open a lot.
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Old May 30, 2012, 06:50 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post

PS.. 608W out and 646W in for the Vox 13x5 would make the motor 94% efficient, not 80.16%
No, if you are spinning a prop at a specific RPM and on a specific number of volts, then the KvE is determined by the difference in RPM, not Watts. All the numbers there for KvE are calculated by volts, Kv, and RPMs and not Watts, and seem to be correct.

Also, if you think the 12x6 spinning 10,650 RPMs should use less current than the 13x5 Vox spinning 540 RPM less, then you may have a good argument, but if these numbers were read correctly, I don't really see any reason for there being a problem with them.

It may be the APC weighs more than the Vox and the added pitch and RPMs is causing the additional Amps, and not the additional diameter. It could happen. There is definitely more work as far as RPM and the static thrust calculator backs this up by saying that it would take 14 more Watts to turn an APC 12x6 the additional 540 RPM than an APC 13x5 540 RPMs less if there was such a prop. So the evidence is at least leaning in the direction that the bigger diameter with the lower pitch rotating slower draws less current. If the Vox was less weight, it should close the door on this, IMO.
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Old May 30, 2012, 06:57 PM
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Has anyone flown the 48" EXP's with a Xoar or Vox 13 x 5? APC-E 13x4?

I'm on the Torque 2814-820 w/ AB 45 using the APC-E 12x6 and thinking of moving to a larger disk.

Thanks,

JC
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Old May 30, 2012, 07:02 PM
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Originally Posted by JC Spohr View Post
Has anyone flown the 48" EXP's with a Xoar or Vox 13 x 5? APC-E 13x4?

I'm on the Torque 2814-820 w/ AB 45 using the APC-E 12x6 and thinking of moving to a larger disk.

Thanks,

JC
Good question. I bought a Xoar 13x5 to try on the Torque combo on the Extra but Tom swapped out the APC for the 12x6 Xoar and gave it the thumbs-up. So that's as far as we went for now. It's the only Torque we still have and he may not be flying it for a while again as it's taken a back seat to the bigger stuff.
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Old May 30, 2012, 07:49 PM
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I used an APC 13x6.5 with a Torque 2814-820 for a couple sessions before I decided I liked it better than the 12x6. Based on the prop preference I went to an appropriate motor.

John
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Old May 30, 2012, 08:03 PM
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I'll throw the Apc 13x4 into this retest today.

I've never had much use for 13x4 in the past.

Always found it as just a noisy no traction type of prop.
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Old May 30, 2012, 08:42 PM
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Numbers from yesterday, all on the same lipo and not recharged between.
APC 12x6, 10650rpm, 46A, 761W
Vox 13x5, 10110rpm, 42A, 646W
Vox 13x6.5, 9300rpm, 51A, 796W
APC 13x6.5, 9390rpm, 60A, 950W

Today, fresh lipo each time but not same lipo (maybe in IR issue leading to strange numbers).

APC 12x6, 10200rpm, 44A, 686W
APC 13x4, 9930rpm, 53A, 841W
Vox 13x5, 9930rpm, 41A, 615W
Vox 13x6.5, 9300rpm, 55A, 883W
APC 13x6.5, 8850rpm, 56A, 895W

Numbers still feel a bit screwy to me, but you can clearly see that the vox spins at higher rpm than the same size apc prop where you would expect. One would assume this means more thrust on the vox over the apc, but I have no way of measuring thrust apart from flying.
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