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Mini Arrow postmortem help

#1
Hi,

I'm new to the rc hobby and would like a little help. I've recently built a mini arrow but using parts sourced locally in Australia. I look it out for a maiden flight the other day any everything went well. It was a bit wobbly but climbed ok, but then with a stream of smoke all power was gone. The silver lining is the it controlled quite well and I was able to glide it nicely to the ground. Below is a picture of the damage i found. The motor wires had got hot and melted/burned the insulation off. I assume the motor drew more current that it could handle?

I am using a motor that is (i think) equivalent to the recommended A power pack. Would the larger F power pack motor fair better? Could this be caused by something else? ESC (Emax 20A), propeller, weight (~350g), my flying technique or maybe some calibration that I didn't complete?

Thanks

thumbnail_IMG_20191222_101218_1920x1080.jpg
 

The Hangar

Well-known member
#2
It looks like the motor wires touched and shorted. In that case, you will probably need a new esc and motor. It is very similar to the A pack. It shouldn’t matter whether you get an A or an F motor, but the F motor will be faster. Have fun!
 
#3
Hey thanks for replying. I suppose the motor wires touched after the insulation melted away, but do you have any ideas why the motor and insulation got that hot to begin with? I think the only way they could be touching before the incident would be a fault in the motor. Everything was insulated and covered in heat shrink.

I forgot to mention in my first post but I've fried two motors in the same way. So the esc seems to still be functional. Do you think I had two faulty motors or is it likely to be something else?
 

BATTLEAXE

Well-known member
#7
Hey thanks for replying. I suppose the motor wires touched after the insulation melted away, but do you have any ideas why the motor and insulation got that hot to begin with? I think the only way they could be touching before the incident would be a fault in the motor. Everything was insulated and covered in heat shrink.

I forgot to mention in my first post but I've fried two motors in the same way. So the esc seems to still be functional. Do you think I had two faulty motors or is it likely to be something else?
It sounds to me that the ESC is the common denominator here. The motors will only draw the amperage they require to perform a task. They won't be fed to much amperage, more then they need anyway, it's a draw not a push from the battery. This motor and your two others should work fine. Have you tried them on a different ESC?
 
#8
Hey. Thanks for all the replies, I appreciate all the ideas.

As a couple of people asked, the other components I'm using are:
  • MASTER AIRSCREW MASEP0603 Propeller, Electric, 6 x 3
  • Tattu 11.1V 850mAh 3S/3 Cell 75C Soft Case Lipo Battery
  • EMAX BLHeli Series 20A Brushless ESC
Also the motor specs are:
Item name: D1806 2280KV Brushless Motor
KV: 2280
Max Trust: 460g
No. of cell: 2-3S
Framework: 12N14P
Propeller: 5" ~ 6"
Length: 26.7mm
Shaft: 2mm
Diameter: 23mm
Weight: 16g
Usage: for QAV250, QAV280, FPV 250 Racing Frame

Tested with 11.1V voltage and 6040 propellers:
Load current: 11.5A
Pull: 468g
Power: 128W
Efficiency: 3.7g/W



The mounting screws are clear of the windings. I know this because the first firewall i made was too thin and I had to make a thicker one before i tired to fly.

Too many watts into the motor makes sense to me. The heavy prop will require more power (watts) from the motor. Where
power[watts] = torque[N.m/ft.lb /relative to weight and shape of the prop] * angular velocity[RPM] right? This could cause the motor to draw more power (current x volts) than the 128W its rated for and burn the wires. A faulty ESC also seems like a reasonable possibility.

As I need to get some new motors anyway, I will try a lighter prop and a different ESC. I think a watt meter might be useful in this case so I can measure real values rather than guessing. Anyway it will take a while for everything to arrive, but ill try to report back with how it goes.
 

Keno

Well-known member
#9
Hey. Thanks for all the replies, I appreciate all the ideas.

As a couple of people asked, the other components I'm using are:
  • MASTER AIRSCREW MASEP0603 Propeller, Electric, 6 x 3
  • Tattu 11.1V 850mAh 3S/3 Cell 75C Soft Case Lipo Battery
  • EMAX BLHeli Series 20A Brushless ESC
Also the motor specs are:
Item name: D1806 2280KV Brushless Motor
KV: 2280
Max Trust: 460g
No. of cell: 2-3S
Framework: 12N14P
Propeller: 5" ~ 6"
Length: 26.7mm
Shaft: 2mm
Diameter: 23mm
Weight: 16g
Usage: for QAV250, QAV280, FPV 250 Racing Frame

Tested with 11.1V voltage and 6040 propellers:
Load current: 11.5A
Pull: 468g
Power: 128W
Efficiency: 3.7g/W



The mounting screws are clear of the windings. I know this because the first firewall i made was too thin and I had to make a thicker one before i tired to fly.

Too many watts into the motor makes sense to me. The heavy prop will require more power (watts) from the motor. Where
power[watts] = torque[N.m/ft.lb /relative to weight and shape of the prop] * angular velocity[RPM] right? This could cause the motor to draw more power (current x volts) than the 128W its rated for and burn the wires. A faulty ESC also seems like a reasonable possibility.

As I need to get some new motors anyway, I will try a lighter prop and a different ESC. I think a watt meter might be useful in this case so I can measure real values rather than guessing. Anyway it will take a while for everything to arrive, but ill try to report back with how it goes.
You are on the right track. It can fly without trailing smoke. No fuse, something going to burn. Happy Flying..
 

CarolineTyler

Well-known member
#10
Hey. Thanks for all the replies, I appreciate all the ideas.

As a couple of people asked, the other components I'm using are:
  • MASTER AIRSCREW MASEP0603 Propeller, Electric, 6 x 3
  • Tattu 11.1V 850mAh 3S/3 Cell 75C Soft Case Lipo Battery
  • EMAX BLHeli Series 20A Brushless ESC
Also the motor specs are:
Item name: D1806 2280KV Brushless Motor
KV: 2280
Max Trust: 460g
No. of cell: 2-3S
Framework: 12N14P
Propeller: 5" ~ 6"
Length: 26.7mm
Shaft: 2mm
Diameter: 23mm
Weight: 16g
Usage: for QAV250, QAV280, FPV 250 Racing Frame

Tested with 11.1V voltage and 6040 propellers:
Load current: 11.5A
Pull: 468g
Power: 128W
Efficiency: 3.7g/W



The mounting screws are clear of the windings. I know this because the first firewall i made was too thin and I had to make a thicker one before i tired to fly.

Too many watts into the motor makes sense to me. The heavy prop will require more power (watts) from the motor. Where
power[watts] = torque[N.m/ft.lb /relative to weight and shape of the prop] * angular velocity[RPM] right? This could cause the motor to draw more power (current x volts) than the 128W its rated for and burn the wires. A faulty ESC also seems like a reasonable possibility.

As I need to get some new motors anyway, I will try a lighter prop and a different ESC. I think a watt meter might be useful in this case so I can measure real values rather than guessing. Anyway it will take a while for everything to arrive, but ill try to report back with how it goes.
A watt meter is such a useful tool, all my plane power electronics setups go on it so I know I'm running within the specs.
Initial look at the equipment you were using I would be surprised if you were pushing it too much. I'll run it through motocalc and check later.
 

Hai-Lee

Old and Bold RC PILOT
#11
Hey. Thanks for all the replies, I appreciate all the ideas.

As a couple of people asked, the other components I'm using are:
  • MASTER AIRSCREW MASEP0603 Propeller, Electric, 6 x 3
  • Tattu 11.1V 850mAh 3S/3 Cell 75C Soft Case Lipo Battery
  • EMAX BLHeli Series 20A Brushless ESC
Also the motor specs are:
Item name: D1806 2280KV Brushless Motor
KV: 2280
Max Trust: 460g
No. of cell: 2-3S
Framework: 12N14P
Propeller: 5" ~ 6"
Length: 26.7mm
Shaft: 2mm
Diameter: 23mm
Weight: 16g
Usage: for QAV250, QAV280, FPV 250 Racing Frame

Tested with 11.1V voltage and 6040 propellers:
Load current: 11.5A
Pull: 468g
Power: 128W
Efficiency: 3.7g/W



The mounting screws are clear of the windings. I know this because the first firewall i made was too thin and I had to make a thicker one before i tired to fly.

Too many watts into the motor makes sense to me. The heavy prop will require more power (watts) from the motor. Where
power[watts] = torque[N.m/ft.lb /relative to weight and shape of the prop] * angular velocity[RPM] right? This could cause the motor to draw more power (current x volts) than the 128W its rated for and burn the wires. A faulty ESC also seems like a reasonable possibility.

As I need to get some new motors anyway, I will try a lighter prop and a different ESC. I think a watt meter might be useful in this case so I can measure real values rather than guessing. Anyway it will take a while for everything to arrive, but ill try to report back with how it goes.
Whilst the damage looks noteworthy the only possible cause I can see from the supplied photograph is that you did NOT run the wires through a hole in the firewall/Bulkhead but rather looped them over the top and hence they were crushed together. At full stick the wires do get warm normally BUT when jammed tightly together there is enough heat to soften the insulation and allow the wires to short out. Hence the shorted wires and any other damage due to the wires shorting/touching.

The wires should be kept clear of all crush and pinch sources as well as clear of any moving parts when installed in a plane for flying purposes.

Regardless of what you do during the rebuild and what you need to replace you must pass the wires for the motor through the bulkhead and NEVER allow the wires to be crushed or pinched.

Have fun!
 

CarolineTyler

Well-known member
#12
Well, I put it through and you are right on the top end of the wattage but I would not expect the motor to burn.
motor_calc.png
So it's more likely the ESC or the wiring shorting against each other.
 

Captain Video

Well-known member
#14
I'm with cranialrectosis
first thing that caught my eye was what I believe is the prop is on backwards. If that is the case the motor works harder as you are pushing it harder. And it probably screamed like a banshee!
 

PsyBorg

Wake up! Time to fly!
#17
Im thinking even though the specs work out and the numbers looked good specially since it was stated wattage was on the high side that the heavy prop on that quad motor that was designed to spin lighter smaller props was the issue. If you were up and down on that throttle like we are on quads to turn and such you were stressing that motor hard on a heavy 6 inch prop.

I wouldnt use any thing larger then a 5x4x3 quad prop on that for a wing with that size motor. IF you want to stick with bi blade heavy props since you are replacing the motor go with a kv rating probably in the 1000kv range
 

PsyBorg

Wake up! Time to fly!
#19
Probably doesnt help but many people fly no problems with same or similar setups. The only variation is a super heavy prop that I can tell. The only other thing is ESC timings that would do things like that. The OP did not state he made any changes from default values.