|Mar 30, 2010, 03:46 PM|
Ammo 24-45-2900 or Ammo 24-45-3790 ?
Anyone either of these motors?
I was thinking using either of these on a Funjet. Maybe a 5.5x4.5 on the 2900 kv or a 4.1x4.1 or 4.5x4.1 on the 3790 kv...
The specs looked promising.
Rm: .0382 Ohm
Lo: 1.1 at 10v
Weight: 3.6 oz (a little heavy)
Rated at 296 watts continuous up to 590 surge.
Rm: .0221 Ohm
Rated at 277.5 watts continues up to 555 surge.
The motor calc looks promising. Just wondered if anyone had any real world experience.
Obviously the 2900 with bigger prop is going to do well thrust wise but the 3790 would do great for speed. The motor calc I'm using showed 26.6 oz thrust from a 4.1x4.1 and 32.6 oz thrust from a 4.5x4.1. The low resistance and high kv seem to give the 3790 some impressive abilities. Even on the 4.5x4.1 prop it's drawing 42.6 amps at 83% efficiency (according to the calc).
Anyone with some real world experience?
|Apr 01, 2010, 05:58 PM|
My concern is the amps/watts rating for these motors (less of a concern for inrunners than for the outrageously optimistically rated Rimfire outrunners)... but I just can't see a 3790Kv motor spinning even a 4" prop without frying.
105g... maybe 300W is okay... but not 500W+
|Apr 03, 2010, 11:20 PM|
Well... it should handle more than what I've currently got...
Right now I have an Ammo 24-33-3500 (only 2.4 oz) and I have been pushing it up to 27-28 amps which is pretty close to 300 watts (static amp test on the bench). Probably in the air it's less and I'm not running full throttle all the time, just 30 seconds at a time for some fast passes and vertical climbs.
The motor gets warm but not hot. It does have some good air flow over it though - so that probably helps.
|Apr 04, 2010, 11:51 AM|
santa barbara, CA
Joined May 2009
i always calc prop speed to see if i am even able to achieve the desired flying speed. the variables are huge but if you dont reach desired prop speed static you probably wont get there flying.
the point here is using 3 cells and 70 % of no load speed, i get 113 mph with the 3790 and 95 mph with the 2900. as im sure know small props rarely make their pitch speed in the air do to lack of thrust .
for the fun jet 95 makes maybe ~70 tops in flight , i would go for more static pitch speed . either more pitch or more kv and like you said the low impedance in the 3790 should handle the current better.
as always the watt meter tells all, but for high speed i like more kv and less pitch.
fwiw i have 3900 kv 20mm 2 oz inrunner and 200 watts is about it, so i think your estimate of 300 is realistic and 590 is jive. and on the hi kv one 400 burst with cooling possible.
good luck, chuck
|May 06, 2010, 01:50 PM|
After doing a number of Motor calc scenarios, I decided to get the 24-45-2900.
This one has a resistance of .038 with 2900 kv, while the other was .0221 at 3750 kv.
The 3750 kv version would pretty much only allow me to run a 4.1x4.1 prop - maybe up to 4.5x4.1 and it would be close to 40 amps on 3s!
The 2900 one lets me run larger props. So far in tests using a 4.75x4 pylon prop, it only draws 23 amps but yet the motor revs higher (not dramatically) than my old 24-33-3500kv motor with the same prop on 3s. Even better, it's drawing 4 amps less!
So with the same prop, this 2900 kv motor is outperforming my 3500 kv motor because of the lower resistance (the 3500 kv motor is .079 ohms).
I also tested a 4.75x4.75 APC prop. It drew 27 amps, and 4.75x5.5 drew 30 amps (on 3s).
But since this motor has a higher amp capacity (up to 40 on 4s), I'll be getting some 4s batteries soon. That's when the fun really begins. The motor calc estimates 35 amps on the 4.75x4 pylon prop. It also estimates 35 oz of thrust and 130 mph pitch speed!
That should get my Funjet over 100...
I know I could have saved some money going with the Turnigy motors but I just didn't like their resistance numbers. Yeah lots of people are pushing crazy amounts of amps through them but I don't think they are all that efficient. Less efficient means shorter flights or bigger batteries and bigger batteries means more weight and less fun...
|May 07, 2010, 10:32 AM|
First round of tests on 3s in my Funjet
One set of test flights with the APC E 4.75x4.75 resulted in a top speed of 92 mph. Static amp test came to 28 amps on freshly charged batteries. Measured static thrust was 22 oz.
This morning I ran the APC 4.75 x 4.0 Pylon prop. It resulted in the same 92 mph BUT... it only drew 24 amps static and the static thrust measured 28 oz!!
Those pylon props are amazing! I could definitely tell the difference in the prop noise. The 4.75x4.75 had more of an air rushing churning sound, the 4.75x4 pylon prop was more of a clean sound. Basically the pylon prop was "on-step" while the 4.75x4.75 was cavitating a little. I think the funjet is probably not slippery enough to get it completely onstep...
So for those of you who were getting awesome speed from your 4.75x4.75 prop - try the 4.75x4 pylon prop - you might be surprised how much better it is with less amps!
Next step... Get some 4s batteries... (gotta place my order...)
|Jun 17, 2010, 01:18 PM|
All tests with a Funjet and Ammo 24-45-2900:
Ok, more feedback on this motor. I did try to go 4s on this motor unsuccessfully. I was using my 4.75x4 pylon prop but the Turnigy Plush 40 ESC kept pulsing at full throttle. I tried messing with settings but still couldn't get it working right. I don't think it was LVC because the battery was a 1880 mah 40C pack and the amps were around 38. Unfortunately on one test the motor shaft bent under the load and basically destroyed to motor.
Not sure of the cause. The prop was balanced. Too much for the 3mm shaft? This prop is heavier than an E prop. Maybe that was it?
I did get a replacement motor under warranty. I explained what happened and they asked me to ship it in and I got a new motor 2 weeks later.
The new motor seemed to have a slightly higher kv. It revs higher and draws more amps too. After the previous disaster, I decided to stay with 3s batteries...
So far I've done tests with the following props:
4.75x4 APC Pylon prop: 27 amps static, 94 mph average speed, did get 100 mph in a dive. Very good climb.
5.5x4.5 APC E prop: 37 amps static, 98 average, but I did get a 100 mph level pass as well. Climb was ballistic.
6x4 APC Sport prop: 40 amps static, 100+ mph however didn't quite like the flight characteristics. Climb was also ballistic. Lots of thrust but seemed a little less nimble. Also drew down the batteries a little faster.
So far I like the 5.5x4.5 for overall thrust and speed. But the 4.75x4 gives me close to the same speed and much lower amps. However flight times were not dramatically different between these two props... I think the 5.5x4.5 unloads well in the air, also the 4.75x4 required more throttle to go the same speed so in the end it was only about a minute or so difference in flight time.
One other thing, this motor has a flat spot on the shaft. While it is possible to use a collet style prop adapter, it makes it difficult to get the prop to balance out. It is best to use a set-screw style prop adapter with this motor.
If you want to go 4s on this motor, I'd recommend a smaller prop - 4.5x4.1 or 4.1x4.1. I did not go this route because the Funjet needs a bigger prop because prop is partially blocked by jet nozzle on the back.
|Sep 21, 2010, 09:28 PM|
Ended up going back to the 6x4 sport. (I got a couple more) I found one that was better balanced than what I tried earlier.
This did get me to 107 mph! And did it more consistently than the 5.5x4.5 prop. After getting things adjusted out correctly, this prop really does seem the best for my setup. The thrust is crazy! When I come in straight and level at full throttle and then pull up, it climbs so quickly and doesn't really show any signs of slowing as it climbs. It's like I strapped an Estes rocket to my Funjet!
The better balanced prop ended up drawing similar power to the 5.5x4.5 prop as well.
So chaulk that up as a successful power system for Funjet:
Ammo 24-45-2900 with APC 6x4 Sport (not the E prop)
Turnigy Plush 40 amp ESC
1800 40C Turnigy 3s packs.
Still keeps the plane at around 21 oz AUW so launches and landings are still pretty easy.
|Oct 12, 2010, 12:02 PM|
United States, FL, Orlando
Joined Aug 2007
So what's the difference between the "sport" and "e" props??? I am using the 6x4E in my Stryker and all is well, but if I can squeeze something better I would like to try.
Mega 16/15/3 on a 2200 4Cell
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