Help! Motor cuts off at 75% throttle

[LittleWrecks]

Hello,

I just finished my first build, however I am now having electrical issues. When throttling up, the motor cuts off at around 75%. I went ahead and did some testing of the voltage, and measured 7,77 V at 0% throttle. When it cuts off, it is at 7,65 V. This leads me to believe that the low voltage cut-off on the ESC is not to blame.

The current draw of this motor/prop combo is supposed to be 10 A at most. Thus, I wouldn't think that the 20 A of the ESC is surpassed. I have not yet measured this though.

Any help would be great.

Specs:
LiPo: Turnigy 1300mAh, 2S, 20-30C
ESC: T-Motor AT 20A ESC - 2S-3S
Motor: 2225 1350kv Brushless Outrunner
Prop: Gemfan 9050
Receiver: FS-IA6B
Transmitter: FlySky FS-I6X

 

[quorneng]

LittleWrecks
"When it cuts off, it is at 7,65 V " I presume this is voltage measured after it has cut.
The important bit is what is the voltage just before it cuts out.

If this is your motor then with a 9x5 it is over propped and will be drawing rather more amps than it should. This will drop the battery voltage to below the ESC voltage cut off.
If this is what is happening not only is it not doing the battery any good but sooner or later the ESC may give up as well.
A Wattmeter is the tool you need (it goes between the battery and the ESC) so it measures both the volts and amps in real time and most show the peak readings as well.

 

[LittleWrecks]

LittleWrecks
"When it cuts off, it is at 7,65 V " I presume this is voltage measured after it has cut.
The important bit is what is the voltage just before it cuts out.

That is the voltage before it cuts out. Don't think the voltage cut off is the issue... Do ESCs cut off when a power limit is reached?

If this is your motor then with a 9x5 it is over propped and will be drawing rather more amps than it should. This will drop the battery voltage to below the ESC voltage cut off.
If this is what is happening not only is it not doing the battery any good but sooner or later the ESC may give up as well.
A Wattmeter is the tool you need (it goes between the battery and the ESC) so it measures both the volts and amps in real time and most show the peak readings as well.

Interesting. I bought the Motor on this (german) site, where it is clearly states that a 9x5 prop is to be used with a 2S LiPo for a maximum power draw of 10A. This appears to be incorrect.

Would you recommend exchanging the ESC for a 30 W version or using a smaller prop?

Thanks for your help!

 

[Taildragger]

That is the voltage before it cuts out. Don't think the voltage cut off is the issue... Do ESCs cut off when a power limit is reached?



Interesting. I bought the Motor on this (german) site, where it is clearly states that a 9x5 prop is to be used with a 2S LiPo for a maximum power draw of 10A. This appears to be incorrect.

Would you recommend exchanging the ESC for a 30 W version or using a smaller prop?

Thanks for your help!

I would say that based off the comparison to a penny in the pic i'm guessing its way overpropped, should have like a 6in prop

 

[FlyingMonkey]

You may need to set the end points in the ESC.

 

[quorneng]

There is another possibility that has occurred quite recently and concerns the mounting bolts.
Depending on the thickness of the plate or bulkhead they go through it is possible for them to actually touch the windings. Many motors have a long and short bolt sets to account for this.
If they do touch the windings the drag it causes slows the motor which greatly increases the amps drawn without an increase in the motor performance. If the motor is run like this for long it may permanently damage the windings, create a part short circuit and the motor is scrap.
The way to be sure is to see if the motor spins by hand more freely with the bolts backed out. If it does use shorter bolts or add a suitably thick washer to make sure the bolt does not go so far into the body of the motor.
I you are satisfied there is no mechanical issue effecting the motor's free running a smaller prop say 7x6 would significantly reduce the amps. If this then allow you to use full throttle you know that for some reason the motor is effecting the ESC. A 30A ESC should be quite adequate but it is possible the ESC itself is faulty.

 

[Bricks]

OOOops Qourneg and I must have been posting at the same time. same thing he said only short version LOL.

Just curios as they do not show an X mount did you mount the motor with screws from the back side of the firewall......Possibly the screws are a tsd long and hitting the windings in the motor?

 

[cbf123]

A 9x5 prop with a 1350Kv motor on a 2s battery should draw under 12A and consume around 80W, so theoretically the setup described in the first post should work just fine.

 

[Merv]

.... When it cuts off, it is at 7,65 V......

You might try fully charging your battery and see what happens. Using a half charged battery may be thrown off the ESC. A fully charged 2S battery should be 8.4v.

Also when it cuts off, is the motor completely dead or does it run jittery. If it runs jittery, it may be a timing issue.