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Not getting the power I expect - Axi 5345/14

Old 01-12-2008, 01:13 AM
  #1  
sbritton
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Default Not getting the power I expect - Axi 5345/14

This is what I have:

AXI 5345/14 - 225kv
2 x 6s Flightpower 5000 - 25c batteries in series
Phoenix 110HV ESC
17x12 APC Electric Prop.
Eagletree Micro Data Logger

Without a prop, it will get just over 10,000 rpm.

With the prop, it maxes out at 60 Amps, 2200 Watts and 7500 RPM.

This is going into a H9 Sundowner and I was expecting a much higher amps/watts in this setup. I'm aiming for outright speed (130-150mph). Is there something I should be doing like a higher diameter or higher pitch? Will this even help with top speed?

Can someone calculate what kind of speed I can expect?
80" wingspan, 13lbs, very thin airfoil, 933 sq/in wing area.

Thanks...
Shawn
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Old 01-12-2008, 05:15 AM
  #2  
Dr Kiwi
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Two things I see: with your 17x12 at WOT you are down to close to 3v/cell so the pack is not keeping up with demand: 2200/60 = 36.7v... divide that by 12 and you get 3.06v/cell... not good.

At 7500rpm with a 17x12 you are only getting 85mph pitch speed - fairly clearly you need to be spinning a smaller, far higher pitched prop if you hope to get 130-150mph.
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Old 01-12-2008, 05:19 AM
  #3  
jooNorway
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You have a much too small propeller...
Since 20x13 is recommended for acro I would estimate your propellerload is appr 60% of what the motor is able to handle within the efficiency range...
But since you aim for a lot of speed I am not sure which propeller would suit. Maybe you should browse for Majzlic and Engel carbon-propellers and see if you find a high-pitch 3-blade.
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Old 01-12-2008, 05:49 AM
  #4  
sbritton
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Default Battery Voltage...

Dr. Kiwi...you may be on to something.

I noticed at full throttle, the volts on the packs were dropping very quickly. But came back up to normal when the load was off.

What does this mean?

Should I look at a different motor? If so, any suggestions?
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Old 01-12-2008, 06:36 AM
  #5  
Larry3215
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Dr Kiwi has the key elements covered.

The pack cant handle that load. It could be because you have a bad conection somewhere. Look for a loose conector or bad solder joint. other wise, you will need a larger pack.

Those packs should be able to handle that many amps easily, so I think something is wrong there.

If you went with a smaller diameter prop, the load would drop and rpms would come up.

Not sure if they will ever get to where you want though. If you had the same 12 pitch at say 8500 rpm you would still only be at 96 mph pitch speed.

That motor is a pretty low Kv for speed applications. Its intended for 3D or normal acro flying.

I think you need to go with a higher Kv motor and a smaller diameter prop if its speed you want.

Id look for a motor with a Kv about double what you have.

Good luck!

Larry
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Old 01-12-2008, 07:23 AM
  #6  
BuzzardBait
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few more questions.. were packs fully charged and balanced

I agree, either you have a bad pack, (the odds go up the more cells you put into the mix), or something in the wiring sytem is really draggin the juice.

Seems weird that a 5000mah pack, theoretically capable of 125amps would dump that quick.. But.. @ 60 amps draw... you should be seeing closer to 2600-2700 watts with expected voltage sag...

PS.. with your motor and batteries, and a generic assumption of the plane from the wing dimensions you gave, moto calc geeked out 100+mph airspeeds with a 16X16 prop.. but it also stated that the motor temp would be fairly high...
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Old 01-12-2008, 07:50 AM
  #7  
sbritton
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Default Packs are good.

Well...they are brand new packs and freshly charged. I will look at the balance, but I'm 99% sure they are in good shape.

There is a chance that there is something going on with the wiring from the ESC to the motor...there aren't many good connectors out there with 10 guage wires. So I used those crimp-style tubes that you crush to make a connection. I wonder if that is creating an issue.

What does it mean if the voltage drops that quick? I guess in the morning I will do another run with the e-logger and post the results.

Thanks...
Shawn
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Old 01-12-2008, 08:35 AM
  #8  
Larry3215
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Thats a good idea.

If the e-logger shows the pack voltage is hi, then its probably those motor conectors.

You could always solder them directly and eliminate that potential problem.

By the way, Steve Neu sells some good large bullets. Castle Creations also just came out with some that look vey nice for hi amp applications.

Larry
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Old 01-12-2008, 04:52 PM
  #9  
sbritton
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Default Data Logs...

Ok this morning it is looking a bit better. It is WAY cold out...so might affect the battery performance.

RPM is up to 9740. (Could only get 10,100 with no prop)
Watts only 2150
Amps max of 56
Volts went down to 38.6 from 48.1

What do you think...are these numbers looking better?

I guess in this case as long as the AMPS are low, volts don't drop any lower the power system is running fine. For speed, I need RPM, and I don't think I'm going to get more RPMs out of this motor. I might be able to go to a 16x13 instead of a 17x12.

Thoughts?
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Old 01-12-2008, 05:21 PM
  #10  
Matt Kirsch
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Cold will definitely hurt the performance.

60 Amps is 12C. With good cooling those batteries should be able to handle that load continuously. A quickly-dropping voltage indicates overloaded battery packs, usually, but in this case it was probably cold batteries.

38.6V is still only 3.21V per cell. How long was your test run? If it's still cool outside, you might still be running into cold battery issues. Try doing a run indoors, CAREFULLY!!! We ran the 5345/16 on my G202 in my basement. There were no more cobwebs left down there
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Old 01-12-2008, 10:43 PM
  #11  
Larry3215
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Or warm the packs up and do a quick run outdoors before thay have a chance to cool down.

Thats still too much voltage drop at that amp level I think - unless the packs are really really cold. In that case, you should see the power drop off fast then level off and INCREASE as the packs warm up under load.

Even at 9700 rpm that prop is only going to give you a pitch speed a little over 100 mph. Actual air speed will be a good bit less.

You need a higher Kv motor

Larry
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Old 01-12-2008, 10:47 PM
  #12  
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Wait a sec - max voltage was 48.1?

Thats only 4.0 volts per cell. Your pack isnt fully charged.

That, combined with the low temps will lower your numbers.

You still need more Kv if your shooting for 150 mph

Larry
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Old 03-28-2008, 09:09 PM
  #13  
feathermerchant
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As a point of comparison, I have a Sundowner with a Hacker A60-16M which has a 215kV.
With an APCE 17X12 it's ~3kW initially dropping to about 2850W. That's about 65A on 12S Polyquest 4350's.

It is certainly fast enough. It also has unlimited vertical. It lands like a slippery pig though.
Here's a video:
[media]http://www.youtube.com/watch?v=GPX_oySp3SM[/media]

Sorry for all that ugly noise in the background.
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