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Not enough Power?

#1
Hey all!
Ive buillt 2 electric aircraft so far, a bonsai and a 3d plane. On my 3D, i built the reccommended setup, but my plane wont vertical! Im not sure why. im thinking maybe the prop is too much load for the esc or something. im using an 8x4 airscrew and a 1900kv motor, and a turnigy 10 amp esc, busrt 12 amp. Im running nano tech 3s. Im not sure whats wrong. do i need a higher amp esc and higher output batteries? Thanks!
 
#3
not sure. but i do know that when i put a 5x5 on my bonsai, the motor wouldnt get up to full rpm, and it would slowly die down. because the prop was too much for the high kv. how do i test amp draw?
thanks!
 

tramsgar

Senior Member
#4
What motor is it exactly? Is the prop on the right way?

You attach an amp meter (or some kind of power meter) between the battery and the esc. A multimeter works fine, just connect it in series.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#5
Longboarder,

overdrawing your ESC isn't like overdrawing on a battery. If you draw to fast on a battery the voltage drops and you have less power. If you overdraw on the ESC it delivers full power, then suddenly none at all. Ever again.

As Tramsgar said, having a watt meter to plug in-line between your battery and ESC on the bench can help you work that out and prevent burning out your ESC or motor.

Now, too weak of a C-rating on your battery or going with a lower cell count can lead to lower power. If it seems weak overall, it may be the cell count, but that's not what you're seeing, right? If it seems like the mid range has good power, but as you near the top the power levels off, this could be a low C-rating or a cheap prop (flattening out when you ask too much of it). What's the size & C-rating of your battery? What's the max spec'ed current on your motor?


hmmm . . . 10amp ESC, you say? You're looking at a max of 120-150 watts on 3s before the ESC burns out. Gut feeling is this is on the low side for the FT3D, but haven't built one myself. What's your AUW(All Up Weight)? (specificaly trying to find out what the watts/lb your ESC can provide your airframe)
 
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#6
the plane isnt a FT3D, not sure if thats bigger or smaller than what i got, mines got an 800mm wingspan. ill have to measure it when i get my scale out. im using 25-40c 3s 460mah lipos. they hold about 550mah though. Im using an airscrew prop, have heard great things about them. almost perfect balance out of the box. i have balanced my prop too. max motor specd current is 7.3A. the recommended esc is 10 amps, and its a turnigy plush. i have found another esc, think 12 amps will do any better? or should i go like 20? Thanks!
 

Craftydan

Hostage Taker of Quads
Moderator
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#7
Naw. For that motor, you're ESC is fine. As long as you haven't over-proped it, that's a good size, and even then the ESC isn't gonna rob you of top end power. A good watt meter would tell you if it's over-proped, but if your motor isn't getting burning hot, it's probably still ok -- might want to get one and test it, just to be safe.

Sorry about the FT3d -- saw the 3D mention and just assumed -- my bad.

Assuming you've treated them nicely, your batteries are close in the C-rating to the motor's max, but still plenty of room -- the battery is spec'ed to draw up to 11.5A continuously until near dead.

If you want more power, a couple of options:

- if you've gone *cheap* on your prop, might want to get a stronger one. If it flexes to flat at top speed, you'll loose thrust. You should hear a change in sound from whirr to buzz if this is the case.
- if your motor *isn't* drawing 7.3A, you could step the prop size up.
- if it is drawing that much, think about a bigger motor (with a larger ESC to handle the draw).
 
#8
I was planning in the future to upgrade ESC anyway, but not quite yet. The 8x4 I'm using is a good prop as I have heard. I'll check for buzzing on my next day out. I doubt it flattens out, but ill check. I am buying some batteries that are actually the right size for this plane. The ones I'm getting are 90c nano techs so that'll eliminate the possibility of battery fatigue or problems of that nature. My ESC heats up rather quickly, but it never shuts down due to heat failure. The motor becomes only warm to the touch. Lipos are slightly warn after each flight. Again, no heat failures. I'll double check my setup next outing. Any more ideas? This plane is supposed to vertical on 2s, and I'm running 3s and get no vertical. Thanks!
 

Craftydan

Hostage Taker of Quads
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Mentor
#9
If the ESC "shuts down" for that, there's a good chance it'll never power the motor again. The ESC should get pretty warm and be OK. The flat side is a heat sink designed to cool the power transistors so if they're working hard, expect it to be warm (also, always mount the flat side outward).

90C is overkill for this motor, but if you're willing to take the cost and weight penalties, It won't give you any trouble. If you want to better size the C-rating of a pack, take the lower C-rating and multiply it by the capacity, then divide by 1000. This will give continuous current in amps. In your case, the 25*460mah/1000 = 11.5A. Just make sure this is bigger than your motor's draw, and it won't be able to over-tax a healthy battery at full throttle.

hmm . . . seem to hit all the major points. If there are reports of success with this power system and the battery size either you've got some extra weight or inefficiency, OR the reports may be exaggerated (it will go vertical, following a dive, for a 5 ft climb).

I agree, I'd expect higher voltage pack to give you more thrust, but are you using the same capacity as the 2S or the same weight as the 2S? In general, 3S will be roughly 50% heavier than a 2S of the same capacity. These batteries are kinda small, but a 1/4oz on a small foamy can mean a huge difference in performance.

Back to tramsgar's post, are you sure the prop isn't on backwards? You'll lose quite a bit of efficiency that way. prop writing should always point to fresh air an away from thrust.

Also, did you run through calibrating the ESC's throw?

BTW, what model is this?
 
#10
If the throttle range is calibrated, the prop on the right way (numbers forward) then let's hear that AUW - it's not a big power system, after all.
 
#12
Prop numbers are in front. This is a hobbyking 3D Reaktor. and actually, i bought 3 2s nano techs, and soldered them together. the weight is not much more. and i noticed yesterday, did a quick bench test, and i tested with 2 lipos, in parallel. to see if the load would be less. my test was where i held the plane, full throttle, and watched for like 15 sec. the speed the motor spins goes slightly down almost the whole time while spinning. is this voltage sag? Or...? Thanks! ill get that AUW soon!

edit: AUW is about 10.5 oz, or 297 grams. This is a rough estimate. my scale is a mail-weighing scale. so it might not be perfect. but its a good estimate. Thanks!

ANOTHER edit: on the product page, it says flying weight is between 250 and 290 grams.... why is mine so much? i didnt add anything crazy. but i did use 9g servos instead of recommended 5g servos. but still thats only 16 grams. Ideas? Thanks! ALSO, weighed plane without batteries to see the weight. then its only 240 grams. my battery is 56grams! the recommended TWO CELL lipo is 49 grams! only 7 less. my 3s lipo should be able to make up for that... why wont it?
 
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xuzme720

Dedicated foam bender
Mentor
#13
If you are holding the plane for testing, then the weight isn't what is causing the RPM drop. There is something in the electronics that is doing that. Best option is to get a wattmeter on it and see if it's drawing more than it should be. Could be something hanging up, rubbing, bent that is creating more of a strain on the system. Estimates on a calc program or formula will get you in the ballpark, but real live numbers will always be better for double checking and like this case, for troubleshooting.
 
#15
A multimeter can measure voltage, current and resistance. Use it to measure the current flowing from the battery to the ESC. Almost all RC suppliers carry RC specific ampmeters/wattmeters, but any will do as long as you can connect it.
 

xuzme720

Dedicated foam bender
Mentor
#16
HK has these. Heads up has these which seem to be a little cheaper compared to HK's similar versions and shipping is only $2. HK does have more selection, though.
 
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#17
Hmm. I'll have to look into those! In the meantime, I'll probably fly today, and watch my results. I'll check for parts maybe resisting the motors movement. Anything else to check while I don't have a watt meter? Thanks!
 

xuzme720

Dedicated foam bender
Mentor
#18
Not really anything else to check. Seems like you've gotten all the suggestions that pretty much cover everything.

Let us know how it goes!
 
#20
i flew it today for a short flight and had to emergency land on my street... with no landing gear XD but it flew the same. i took apart the motor today, and no bent shaft, cleaned it out. but it does make an odd kind of flapping noise.... at low throttle settings... like the sound it would make if there was a leaf in it, but there wasnt.... it only made the noise spinning one way. ill double check it tonight. Im gonna buy some more lipos and experiment with 2s and 3s, and different capacities. But how would anyone be able to get the AUW down to like 250??? the parts would all have to weigh nothing! how? my plane is already 240 with no battery! Thanks for the help!

Edit: just flew it again. not unlimited vertical, but i did move the battery a bit back and it worked better. more vertical, but not unlimited. i was satisfied though! I will still buy more batts, each one lasts like 5 mins haha
 
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