rhodenga500
I installed two Emax RS 2306_2700KV Drone motors in my homemade F-15. Using 4S 5000 btry and 80 amp ESC,s. Flying weight 87 ounces and thrust is 120 ounces (60 oz. X 2). Both motor burned up on the second or third flight. I normally fly half throttle and were using 5 inch 3 bladed props.

My motors are rear mounted and my ESC's are located at the front of the nacelle intake (underneath the mainframe) with long extensions connected to the motors. 

Need help figuring this out?   

 
Quote 0 0
Wildthing
rhodenga500 wrote:
I installed two Emax RS 2306_2700KV Drone motors in my homemade F-15. Using 4S 5000 btry and 80 amp ESC,s. Flying weight 87 ounces and thrust is 120 ounces (60 oz. X 2). Both motor burned up on the second or third flight. I normally fly half throttle and were using 5 inch 3 bladed props.

My motors are rear mounted and my ESC's are located at the front of the nacelle intake (underneath the mainframe) with long extensions connected to the motors. 

Need help figuring this out?   

 

Have you used that combo of prop and motor before on 4S ? 
Quote 0 0
rhodenga500
Yes, The specs are good. 
https://www.amainhobbies.com/emax-rs2306-2750kv-brushless-motor-cw-thread-white-emx-rs2306-2750-w/p613295
Quote 0 0
rhodenga500
Here are the specs from hobbyking.com
https://hobbyking.com/en_us/emax-rs2306a-2750kv-black-version-motor.html

Here is the unofficial testing from youtube.com
Quote 0 0
solentlife
The 2750 is not listed on eCalc ... but the 2400kv version is. Its common that the lower KV version will allow a larger prop or battery power ... eCalc shows the 2400 way over temperature with 4S and 5" props. I assumed 5x5 props ... 

The 2306 equates to a 2817 sized motor and that is a bit on the small size for 4S and 5" in my honest opinion. Even the 2826 2200KV motor is running warm on 4S and 5 - 6" props ... 
I would suspect the 2306 is designed around 5" for 3S rather than 4S

A good way to check if it will survive ... ground test the motor and touch test after short run for temperature ... if the temperature is significantly different to surroundings after a short ground test - then its likely you are overloading the motor. Example - if you run for 1 minute at 75% .. to full throttle and that motor case is hot - then its a no-deal combo.
I'll fly anything if I can launch it ! Youtube : solentlifeuk
Quote 2 0
Wildthing
To add on to Nigel's post which could be part of it is when using as pushers and hidden behind the thrusters and engine mounts they are not getting anywhere near the same airflow past them as you would mounted on a quad. 
Quote 0 0
rhodenga500
Thanks Wildthing,

My nacelles are completely open for air flow from the front to the rear of the aircraft.  Air flows around the motors/motor mounts.
I believe that the specs are wrong from the manufacture. Using a 3S battery will not get me airborne on a grassy field with retracts.

Solentlife maybe right, 4S is too much.  The spec said that a 4S battery can be used with a 5X4X3 prop and will produce 60+ ounces of thrust with this Emax drone motor.
Quote 0 0
solentlife
Just looking at that second photo ... those props look as though they have some serious pitch to them ... 

I've also been thinking about the data you gave ... 87oz ... that's 2.5kg. I have to be honest and say that the motors chosen are IMHO too small for such weight and size of model. I would suggest something like the common Turnigy 2826 2200kv ... or the 2312 2450kv Racerstar motors would be more suitable ... and capable of 5x4x3 on 4S. In fact I would do away with 3 bladers and go for more efficient two bladers - ie 6x4

Lastly .... it may be an idea to stand the model on ground, turn props till a blade is pointing down ... then tilt the model nose up - to see what angle prop blade hits the deck .... Its a problem my Vulcan had ... 
I'll fly anything if I can launch it ! Youtube : solentlifeuk
Quote 0 0
lysle42
as one extends the leads from ESC's to motors, any bad connection will drop voltage and increase current, and that will burn up motor as the ESC is a power device.
Homer
<'(((><
Quote 1 0
solentlife
lysle42 wrote:
as one extends the leads from ESC's to motors, any bad connection will drop voltage and increase current, and that will burn up motor as the ESC is a power device.


Never heard that one before ... extending leads from ESC to motor is the accepted way to extend .... just use good quality extension wire as the voltage loss is the main consideration.
A bad connection - is a bad connection ... causing increased or fluctuating resistance ... 
To cause current to increase to levels of damaging motor is hard to imagine .. I would expect ESC to burn out first ... BUT !! he's using 80A ESC's ... 

Here is Emax themselves showing results for their motor ... WOW ... now I understand why they burnt out ... look at the WOT results of 4S and 5" prop !! 

I honestly cannot see how such a small motor can survive such setup ... that's truly big watts total ... ~60A @4S = 1000W

Back to extending leads :  Extending battery leads to ESC will cause problems if too long and is to be avoided.
I'll fly anything if I can launch it ! Youtube : solentlifeuk
Quote 0 0
Wildthing
Try the GepRC CR2306 2750kv quad motors, they spin the 6X3 TGS prop no problem on 4S and great thrust.  Scott has specs on it when he tested them .
Quote 0 0
rhodenga500
Thanks for the info.
The motors shown in the second photos are not the Emax motors. I have tested the Turnigy D2826/6_2200 kv and the A2212 5T_2700kv and both motor types were too weak.  If it wont take-off in grass, I can not use them. The large jets I build are fully loaded (flaps, retracts, 4X4 setup, thrust vectoring, removable wings with carbon fiber sleeve/tubes, removable fuselage, front retract doors, and added reinforcement thin plywood on the inside of the fuselage walls and for the front retract plate.). The reason for the reinforcement plywood inside the fuselage walls to prevent adding weight to the fuselage to maintain the correct CG. However, this reinforcement also helps me so I can lift the aircraft by the fuselage if needed without collapsing.
The jet flies like it is on rails and carries the weight effortless in the air.

To prevent the props from touching the ground on take-off is to pitch up slightly on take-off to clear the runway and then switch the DR from low to high rate for serious TV. On take-off the props are always in the slightly upward position.

The Emax RS2306_2750KV (dual motors) would lift the jet in the air on a grass runway with 3/4 throttle. That is why I thought they would work.

Thanks,,,,
Quote 1 0
solentlife
I'm surprised you say the 2826 is weak compared to the smaller '2306' ..... also that the 2826 will run 4S on 5" without burning out.

Emax motors - I have to say have never been strong motors when I've used them. I have several and all of them have shown I need to stay well under their max spec ratings. It would appear that may not have changed. They are also not cheap compared to other brands.

Given the weight vs size - I would suggest looking for a better motor in a slightly larger size ... have a look through RC Timer ..... Banggood ..... for example. RC Timer are a very good site to scroll through ad the data they give on their motors is in my experience fair and honest.
I'll fly anything if I can launch it ! Youtube : solentlifeuk
Quote 0 0
solentlife
Here's a much better motor ... 

https://www.banggood.com/Racerstar-2507-BR2507S-Fire-Edition-1800KV-2400KV-2700KV-3-6S-Brushless-Motor-For-RC-Drone-Frame-Kit-p-1281548.html?rmmds=category&ID=47980&cur_warehouse=CN

And nearly half the price of the Emax ... 
I'll fly anything if I can launch it ! Youtube : solentlifeuk
Quote 0 0
rhodenga500
Solentlife,

I tested the Turnigy D2826/6, 2200kv with a 4S battery as follows:
5x5 prop, 31 amps, 32 oz of thrust
TGS 6x4 prop, 37 amps, 49 oz of thrust (got very hot after 15 seconds)
APC 6X4 prop, 38 amps, 38 oz of thrust


If you read the motor performance data (at the bottom of the banggood website), the Racestar 2507_1800 KV on 6S only produce 1480 grams (53 ounces ) of thrust which is not enough. The 6S battery is too big/heavy and will add additional weight to the aircraft/fuselage. My 4S-5000mah lipo is already a tight fit in the fuselage. To acheive a good 5 minute flight, I would need a 6S-4000mah lipo, 40c rating. My flight testing indicate that I need at-least 60 ounces or more of thrust per motor using a 4S 5000 battery for this F-15 to fly at a nice speed at 1/2 to 3/4 throttle.
Quote 0 0