[BK1]

Hi

Any feedback on helping me diagnose this problem is greatly appreciated!

I have a twin otter with 2 eflite 25s on it. I am running 4s 3200 30C batteries with a 60 amp esc.

The problem- when I hook everything up it all works well until I try to take off. When I increase the throttle both motors spin up however when I get towards the top of the throttel curve they seem to "cough". If I increase the throttle rapidly form idle to wide open, both motors bind to a stop at the top of the throttle curve (wide open throttle).

There is nothing the motors can rub against and the prop adaptor is not slipping..

Any thoughts? ESC or Motors?

Thanks!

[Cougar429]

You cannot run two brushless from one ESC. Each requires its own dedicated unit. Please confirm it this is the case.

The reason is each ESC reads information back through the 3 motor leads that helps it set the phase, timing, etc. Two motors would likely throw the ESC into confusion.

If you are running two ESC's then perhaps your battery is not supplying enough current for full throttle ops.

[BK1]

Originally Posted by Cougar429

You cannot run two brushless from one ESC. Each requires its own dedicated unit. Please confirm it this is the case.

The reason is each ESC reads information back through the 3 motor leads that helps it set the phase, timing, etc. Two motors would likely throw the ESC into confusion.

If you are running two ESC's then perhaps your battery is not supplying enough current for full throttle ops.

Thanks for the response- I have an esc for each motor, one on each motor...

The batteries are good- I use them on other planes, one of which has an eflite 25 on it.

I have also tried running the motors independantly (while the other is unplugged) and it does the same thing.

I am thinking that I may put a differenct esc on the motors to see if it changes anything. Jsut suprising ot me that that both motors would be dead at the same time..

[davidmc36]

Is there a problem with a timing/frequency setting of the ESC that the motors are not compatible with? Is there any type of current limit feature of your ESC's that may be kicking in too early?

Do you somehow have a throttle curve set in your radio for that particular model that actually goes back to zero when your stick is near the top?

[williame3590]

Overproped??

Bill

[davidmc36]

Originally Posted by williame3590

Overproped??

Bill

Yeah, good question. Overpropped and hitting a current max cut-off or voltage dropping so much it is hitting an LVC?

[Cougar429]

Due to the behavior with rapid throttle response I too think it may be a timing issue. If you have the instructions check to see if it is or can be reset to MID to test. This may be the DEFAULT setting.

As william3590 asked, are you running within the "recommended prop range of 11x8 to 14x7?

Some more info as to your ESC make and parameter settings may help us determine if you are mismatched.

Another one that seems to cause trouble is too long a battery/ESC lead length. You can run extremely long leads to the motor(s), but unless you account for it by adding capacitors, must stay close to the original length on the power feed side.

An easy way to tell if you are pushing any of the components to check heating at the end of a run. If your battery, ESC or motor in each circuit are too hot to touch, (or puffing in the case of the battery) then you have to deal with that or will suffer short component life. And, since we do not know if your ESC's have adequate cooling airflow then that too can account for performance problems.

On a twin either or both lead length and adequate cooling air can be difficult. If you mount the ESC's in or near the motors with the batteries in the fuse you come into the lead length factor. If you avoid that by mounting the ESC's inside the fuse and then feed the motors you can have the ESC's sitting in stagnant air with no cooling. They will quickly overheat and likely shut down or fail altogether. Most every ESC I worked with rates max output specs ONLY if supplied with a minimum 5 MPH airflow.

p.s. One other factor is how you feed your receiver and servos. If each ESC has a resident BEC then you need to disable one of the units by popping the RED wire from the receiver plug, insulating it and tie it out of the way.

[BK1]

Hi Guys,

Truly appreciate the feedback- thank you.

Full disclosure the Twin otter is that I bought here in RC in the fall and have tweaked a few things over the winter with regards the the airframe (did not touch the electronics). The persn I bought from was a good guy and indicated that it flew very well. I assume he was running a 3s however i thought i would go with one more cell and run 4s as it has a 60A esc x 2- internal BEC.(4s too much? It is within the specs)

The plane is prop'd as recommended and has the recommended eflite 25 motors (1250kv).

The ESC are HK 60A & vented well. the wires form the battery to the esc are 4 inches long and the leads to the receiver are about 10 inches ( one is 5 inches and the other is 10 inches as it has an extension on it- could this casue issues? It does not happen when one is running alone with the other not attached). The motors are Y'd to the receiver as oultined in the manual from Hanger 9.

The plane was started this am- stone cold- and the stalling started right away on take off. I gave it half stick to get her going straight then opened it up and it binded..it floated down nicely.

We all thought the prop adapters were spinning on the shaft however they are not..II tested this.

I am starting to think esc...I will try an Castle esc mid week (away with work)..as you guys know .......motors or esc's are 190 bucks either way.

The other thing is that the motors have the bad electronic smell- lile when you fly an indoor heli and one of the servos goes..

[BK1]

Originally Posted by davidmc36

Is there a problem with a timing/frequency setting of the ESC that the motors are not compatible with? Is there any type of current limit feature of your ESC's that may be kicking in too early?

Do you somehow have a throttle curve set in your radio for that particular model that actually goes back to zero when your stick is near the top?

Thanks- no....throttle curve is good, esc's are HK and I dont have link like I do for my castle esc's..

[Cougar429]

Have you disconnected the red wire from one of the ESC's? And is each ESC supplied with it's own battery?

If this is the case and you only have the problem with both ESC's connected I can only recommend trying the second ESC mixed to a spare channel if you have one available.

Have you tried testing it with 3S packs?