Burnt Out Motor

Hi guys, I am after a bit of advice please

As you maybe aware from a previous thread my brand new Axi motor decided to cook itself at the weekend, about 5 minutes into the flight the motor made a strange noise and was way down on power. Jon landed the plane and the motor and esc were so hot you could hardly touch them. In the previous thread Chris mentioned that the motor was only intended for a 6S 2550mah battery, the battery i am using is a 6S 5000mah pack, does this matter?? Can the battery be too big (mah wise)

On a side note I have called the distributor this morning and they have agreed to replace the motor but somehow i doubt they will be so helpful if a fry another one

I'm sure your understanding of electrics is just fine, Chris. The capacity of the battery makes little difference. A 6S 2550 (not that this size exists - does it?) will provide nearly the same voltage as a 6S 5000 and they will both, therefore, draw the same current. The only difference would be if the motor was slowly getting warmer and warmer through the flight until the extra capacity meant it was running for too long and getting too hot.

When you get your replacement, make sure you measure the current - I have a clamp meter that is usually at the field when I'm there. Others use Watt-meters, but these require that you have the same connectors as their Watt meter. If the current is within the specification of the motor and controller you should be fine. The only other factor that can cook a motor and ESC is if the timing and/or PMW frequency are completely wrong.

Finally, does the motor still spin? If it's just burnt out it should still spin.

It does still spin, but not freely like it use to

Mike, when the new motor arrives if i bring the instructions and the instructions for the ESC could you please have a quick look through and make sure i haven't missed something??

I think the motor is rated for 50amps, so i am thinking the first place to start is checking how many amps it is actually pulling, I assume less pitch on the prop equals less amps being pulled??

Hi Chris

Check the motor mounting screws are not too long and touching the windings. This could cause shorted turns which would definitely cause overheating of motor and ESC.

For prop size this is an excellent resource, it will attempt to get you to pay for it but there is everything you need available free.

www.ecalc.ch/motorcalc.php

first select battery size
then esc size
then you need to dig through the motors, find a motor that is the closest match to yours in terms of power rating and KV.
throw on the prop you are using.

this will tell you the 3 important things that you need to know.

Current draw (amps)
thrust in Grams
thrust speed.

Current draw needs to be what the batteries are capable of putting out as well as esc rating and motor rating.
thrust in grams should always be more than what the model weighs
thrust speed is a little tricker its model dependant. this motor is in a yak I think? so somewhere around 50 mph is a good place to start.

by adjusting the diameter and pitch of the prop you can change all 3 of those, generally go up in pitch to get the pitch speed then go up in diameter to get the amps up to a sensible figure.

This calculator also works well. Chris and I used it to confirm that the Turnigy SK3 motor was going to work in his Wot4 (and then my Blue Angel)

brantuas.com/ezcalc/dma1.asp

It has not been updated for ages, but on the motor tab, find 'custom' right at the bottom of the drop down list and enter the values.
Pick the NeuEnergy 4900 battery and a Castle Creations Phoenix 125 ESC.
I just got figures of 54A and 60mph pitch speed.

The model motors website states that the motor can withstand 52A for 60 seconds and also recommends a 15x8 on 6s.

www.modelmotors.cz/index.php?page=61&pro...0&serie=20&line=GOLD

In short, you've got the right motor and it should be fine. Why it stopped working might always be a mystery.

Chris, I am assuming that you pre-programmed the ESC before actually using it to fly. It may work without making settings changes on the bench but in flight that is a different matter. There are at least 6 settings to check. General order is: Brake on/off, cell type, number of cells/auto check, power down voltages, start up, etc. etc.

This has been mentioned in this thread before but - overheating motor? timing not suitable for motor or to high (in other words like gas engines, too far advanced. High timing can give increase in power but at a cost, eg heat. Usually default settings on most ESC is "middle" but that could be 12 deg or 15 deg depending on maker. Do you have a programming card which is the easiest to use but programming can be done by the TX throttle stick. I am sure somewhere I read some time ago that AXI motors don't like high timing settings. I do know that the AXI 4120/18 like low timing. Check the ESC settings before connecting to motor with out prop on!

I have cards to program Turnigy, Hobbywing, YEP, Black Mantis ESCs. Probably one of them is compatible with what you have.

My preference is use an ESC with 25% minimum capacity over and above what I am likely to ever demand.

I think the safest option is to wait for the new motor to arrive and then ask one you kind people to check it for me before I fly again

Chris73 wrote: I think the safest option is to wait for the new motor to arrive and then ask one you kind people to check it for me before I fly again

Good bet!

I was not condemning AXI motors, they are supposed to be good, but for the size motor you are using - £90+. Would have to be a serious model for me to drop that in Their outrunners are made under contract in China but apparently the Inrunners are still made in Czech.