Ammo 24-33-4040 or Ammo 24-33-3500 direct drive? - RC Groups
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Apr 06, 2007, 04:11 PM
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cjbucher's Avatar

Ammo 24-33-4040 or Ammo 24-33-3500 direct drive?

Anyone have any experience with this motor in a direct drive setup?

I was thinking of using a 5x3 APC prop with a 3S lipo and putting this into a Stryker.

I haven't had much luck with motor calculators correctly estimating amps/thrust/speed with direct drive high kv in runners...
Last edited by cjbucher; Apr 13, 2007 at 01:13 PM.
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Apr 06, 2007, 04:23 PM
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cjbucher's Avatar
Another option is going with the Rimfire 28-30-1450 outrunner with a 7x5 prop.

The motor calc that I was using seems to estimate about 28 oz thrust with around 80 mph speed drawing up to 21 amps at full throttle. But again - this is coming from a motor calculator so I'm not sure how accurate it is...

Whereas the 24-33-4040 was estimating around 34 oz of thrust with a speed of 116 (I'm guessing it's not accounting for the air resistance of the plane) with an amp draw of 33.6 (which is above the max for this motor). But this is where I'm thinking this motor calc is probably over estimating the amp draw and performance. I say that because I have another motor that is a similar KV motor and it puts out 25 oz of thrust at 27 amps on that same 5x3 prop.
Apr 06, 2007, 05:54 PM
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Dr Kiwi's Avatar
The 24-33-4040 is an 18A/200W max motor - with such a high Kv I cannot imagine how small a prop one could use to keep the amp draw down enough - a 3x2?

I can't get anything sensible out of Motocalc for this motor! Put a tiny prop on and it draws far fewer amps than it should - put on a slightly bigger prop and the rpms are ridiculously low and the efficiency is at 30%?????

Someone needs to run a small prop on it and let us know what it actually does.

Look at this!

Motor: GPMG5165- AMMO 24-33-4040KV; 4040rpm/V; 1.1A no-load; 0.573 Ohms.
Battery: Thunder Power TP1320 (ProLite) (13C); 3 cells; 1320mAh @ 3.7V; 0.033 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Direct Drive Propellers; 5x3 (Pconst=1.07; Tconst=1) direct drive.
Motor Amps = 8.6
Motor Volts = 10.2
Input (W) = 87.3
Loss (W) = 58.3
MGbOut (W) = 29.0
MotGb Ef(%) = 33.3
Shaft Ef(%) = 30.6
Prop RPM = 15720
Thrust (oz) = 6.2
PSpd (mph) = 44.7

Kv x v = ~41000 - you can't tell me that putting on a 5x3 prop will drop the rpm to <40% of that and yet only draw 8.6A. If rpm are that low the motor is basically stalled and amps will be huge!
Last edited by Dr Kiwi; Apr 06, 2007 at 07:44 PM.
Apr 06, 2007, 09:48 PM
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cjbucher's Avatar
Thanks for the info, Dr. Kiwi.

The motor calc web page I was using was this one:

And it gave very high amp usage but also really high thrust and speed ratings as well.

The one motor that I have tested is the Park 400 4200 using a direct drive 5x3 APC prop. This combo works well with an an 8 cell NiMH pack (Great Planes Slinger battery) which seems to put this motor at 18 amps at full throttle. I borrowed a scale and measured 19 oz of thrust. The plane is pretty fast too. Don't have a radar gun so no telling how fast - just seems to cover a lot of ground in a hurry!

Unfortunately, I can't go lipo in that plane - I tried a static test with a 3S lipo and it pushed the motor up to 27 amps at full throttle! Maybe with throttle management it might be ok. The calculator above said it would only draw 22 amps. I tweaked the motor numbers and found that if I set the resistance to .14 instead of .24 (manufacturer's spec) then it did show 28 amps in the motor calc, and ~25 oz of thrust. I didn't have the scale anymore but the motor did rev up quite a bit higher and seemed to be generating quite a bit more thrust (for the few seconds that I ran it - didn't want any magic smoke to get out).

This made me think that the rm rating on the Park 400 is either not accurate or the motor calc is just wrong.

Now this Electrifly motor has lower resistance numbers which causes the motor calc that I was using to really jump up in amps - just not sure what the reality is though.

Without an actual test there's no way to know what this motor will really draw - it might really draw 33 amps or maybe 27-28 like the Park 400.

I'm thinking the Outrunner is probably a much better choice. Only 19 amps draw and lots of thrust ~ 28 oz. Not as fast as the inrunner, but should make for a much more interesting Stryker.
Last edited by cjbucher; Apr 06, 2007 at 09:53 PM.
Apr 07, 2007, 05:57 PM
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Anyone have any experience with the Ammo 24-33-4040? I'm still curious about this motor...
Apr 07, 2007, 09:43 PM
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Bruce Abbott's Avatar
Originally Posted by Dr Kiwi
I can't get anything sensible out of Motocalc for this motor!
Motor: GPMG5165- AMMO 24-33-4040KV; 4040rpm/V; 1.1A no-load; 0.573 Ohms.
Rm is an order of magnitude too large. It should be 0.0573 Ohms.
Apr 07, 2007, 11:43 PM
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Dr Kiwi's Avatar
I took that exactly off the website, because the figure in my Motocalc was a lot lower than that - but obviously they mislaid a decimal point and I didn't think to check it.
Apr 08, 2007, 04:14 AM
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Bruce Abbott's Avatar
I checked the latest Motocalc database and the numbers are correct, but someone called 'Jake M.' has contributed a bunch of AMMO motors with inflated Rm numbers. I don't ever trust User Contributed Data!

Anyway, it looks like the 24-33-4040 would work fine on 2S with an APC 5x3 prop. If you can't stand the notion of using a 7.4V battery, you could try a GWS EP4025 on 3S (but will it survive 35,000 rpm?).
Apr 08, 2007, 11:07 AM
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cjbucher's Avatar
How about the 24-33-3500 on a 5x3 prop with a 3S?
Apr 13, 2007, 01:27 PM
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cjbucher's Avatar
After fiddling with different motor calcs, I went ahead and ordered the Ammo 24-33-3500.

Since there is very little about these motors in RCGroups, I thought I'd share my experiences on it in case anyone finds it useful... Here goes:


Got the motor yesterday and did a few tests. With an Ultrafly Apollo 25amp speed controller and an Electrifly 1500 3S lipo (20C), 5x3 prop, it was drawing about 22 amps full throttle.

This motor is rated for 16 amps continous and 25 amps burst. While it did warm up quickly at full throttle but not that bad. Looks like it can take the amps pretty well (I don't normally run at full throttle anyway - mostly half). The thrust was pretty impressive. More than my Slinger setup (Park 400 4200, 5x3 prop, 20amp speed controller, and 8 cell NiMH which gave about 19oz thrust using 18 amps).

I'm still working on installing it into my Stryker. I'll post more after I get a test flight in.
Last edited by cjbucher; Apr 13, 2007 at 01:40 PM.
Apr 13, 2007, 02:08 PM
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Dr Kiwi's Avatar
Is that a 1/2A Free Flight 5x3 you are using? What is the max safe rpm with that?
Apr 13, 2007, 02:53 PM
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cjbucher's Avatar
Yes it is (from APC). Not sure but I've never had a problem with them and I've run on more than a 100 flights on my Slinger at similar RPMs. The blades and hub are thicker than the APC E props are. Very rigid prop.
Apr 13, 2007, 03:16 PM
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I went to the APC site and found the limits:

For Glow engine and Thin electric props it is 190,000 / prop diameter in inches.

So for the 5x3 prop it's 38,000. The motor calc I'm using says this motor with this prop runs just under 30,000 rpm. I have 8,000 rpm to spare...
Apr 14, 2007, 10:43 PM
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Well I got some good news and bad news ...

First the bad news. Turns out I have a defective motor. I noticed when I first tested it, it wouldn't start. After switching wires around from the motor to the speed controller it started working. Wasn't sure why but at the time I thought it was good. Today, the motor wouldn't start again. This time after testing with another speed controller it looks like it's the motor. If I wiggle one of the motor leads, starts working - there must be a weak or broken connection somewhere.

Now the good news. I completed installing all the electronics into the Stryker and did a couple tests (after wiggling a wire to get the motor to start ). It has more than 1 to 1 thrust! It was trying to pull out of my hand when I pointed it upward. Of course I couldn't fly it with a flaky motor. So I'll have to wait for the replacement to come... (Tower Hobbies is replacing it under warranty).

The nice thing about this upgrade is the motor weighs 2.4 oz (1.1 oz lighter than the Speed 480 motor) and the battery weighs 4.3 oz. (1.5 oz lighter than stock 8 cell) This shaved about 2.6 oz off the stock Stryker. This gives me about a 19 oz AUW Stryker...
Apr 21, 2007, 10:30 PM
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cjbucher's Avatar
Finally got to maiden today!

Lots of power! Infinite vertical at 3/4 throttle. Definitely moves but it's hard to tell how fast. Not quite as fast as I was hoping but a LOT faster than the stock brushed motor. Also using hitec servos and transmitter made me feel much more in control.

Since it's lighter it's definitely more floaty than before. You can really slow it down.

Interestingly it's not that loud. It does have a high pitch whine to it when you give it full throttle but it's actually quieter now that it was stock.

After a 10 minute flight, the motor was only warm and so was the battery. Keep in mind since this was a stock Stryker A that I upgraded - there really isn't any ventilation for the battery. Interestingly when I went home to charge up I found that I probably had another 3-4 minutes left on the battery.

Overall I'm quite pleased with this upgrade.
Last edited by cjbucher; Apr 21, 2007 at 11:53 PM. Reason: spelling

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