Azzir325

I have a small (22 inch long by 21 inch wing) foam fighter jet (loosely speaking) which I bought a brushless setup for. It's a feigo (1208 series) motor with esc bought as a set. It's setup in a pusher config, direct drive and the prop size is limited to 4 inches. The plane is elevon with 2 mini servos. I have tried 3 cell lipo, 1300 mah, and also a 7 cell nimh. With either setup, the motor run is erratic and brief. It will scream like it should but almost immediately start to slow down. It also heats up like crazy-actually melted the foam some one time. The esc gets warm but not crazy hot like the motor. There is a instruction sheet with the esc in Chinglish, if you know what I mean, which indicates the esc is BEC and also has a brake. There are instructions to enable/disable the brake, and it says "You can force to select 2 lipo by push the selector switch jumper, or pull out jumper select 3 lipo". Any of this make sense to you? Any suggestions? It's a shame because when this little plane is running it is really a nice flyer. Thank you.

salnsp

I can address a few things here.

First of all it sounds like you have a fairly high drain on the battery with that prop and motor configuration. I think you need to go to a better li-poly battary that can give you more output. My suggestion would be a 2070 TP battery that can pout out as much as 50 amps continuous.

The instructions mean that with the jumper in the ESC its cutoff is setup for 2 cells. You remove the jumper for 3 cell. This is my best guess. at 3 cells you are overheating the motor so I would go to 2 cells and try this with a better battery. If this does not work for you you could always replace the motor system with something better.

Azzir325

Thanks for the reply, Sal. I'm a little lost with all the talk of amps and output, etc. Isn't 50 amps output kind of incredibly high? I just checked a dealer website and the highest output level I could find was about 20, and those batteries were very pricey. All this electric stuff, which on the surface, I like, is just way to complicated for me. The motor/esc I bought and described in my question set me back 50 dollars already. I could have bought an LA 40 for only a few dollars more, and I know I can get that to run good. LOL! Thanks again
Rick

salnsp

Sure, it can get pricey, but if it doesn't work its even worse! The 2070 mah ThunderPower batteries have a 25C output. That works out to over 50 amps continuous.

As I have said in this forum before. Try to buy the best equipment that you can afford and make sure what you buy will match the airplane/sailplane/heli you are trying to power.

From the price that you paid for the motor and esc I would guess that you bought a Chinese motor system. Do you have the specs on the motor? If you did I could run the numbers and see what amp draw you are getting.

The problem is that since you have a system that is heating up with 3 cells you are definetely overloading the system so you do need to make some changes. Was the motor and esc that you bought receommended for the airplane that you have?

Azzir325

Thanks Sal. The motor and esc was recomended to me for the job by a flying friend in my club. The motor is a feigo 1208 series. I don't have the whole number, and the dealer was xushobbies.com. There wasn't any info regarding the motor, and the esc just had that chinglish instruction sheet (BTW, thanks for explaining that cutoff voltage thing). The few seconds when the motor was running good and the plane flying, it flew well, but powered down rapidly. Thanks again for your helpful info.
Rick

salnsp

try and e-mail message to vendor that supplied the motor to you. Ask him for the specs. You want the Kv, idle amps and internal resistance. with this we can figure out the rest.

Azzir325

Thanks. I will do that, but I don't have much hope, since I already sent him an email asking for advice on the problem several days back and have not heard from him. If I get any response, or can track the info elsewhere (I think balsa products stocks this line), I'll post.
Rick

Azzir325

Sal, I got this info from the balsa products website:

Designation: 1208425L
Turns: 25
Max Amps: 5.5
Resistence: 0.3160
RPM/V: 5866
IO(A): 0.6
Shaft Size: 1.5mm Diameter / 6mm Length
Weight: 17 grams / 0.60 oz.
Dimensions: 12 mm Diameter x 31mm Long

I hope this is helpful because it sure doesn't help me any!
Rick

salnsp

OK...Here is your problem.

The motor has way to high a Kv (RPM per volt) for a 3 cell operation.
here are the specs based on a 3 cell 1500 mah Li-Poly battery of 20 C

Motor Chinese
Kv 5866
prop 4 x 2
amps 35
prop speed 97 mph
thrust: 32 oz

Even assuming a very low pitch 4 x 2 prop, this is way over the 5 amps max limit of the motor and is outside the operating current of the battery you own.

On two cells this does better but is still outside the operating limits of the motor

amps: 19
prop speed: 74mph
thrust: 16 oz

I think this is the wrong motor for the job.
The motor you have at that high Kc is really designed to be used with a geardrive
If you are going to use a 12mm motor direct drive I would hope that the total flying weight of the model is under 5 ounces.

Azzir325

OK Sal. Thanks anyway. Rick

salnsp

Sorry I could not be of more help. Still another motor for your airplane wouldn't cost too much. You could still use the esc and battery.

Azzir325

Can you offer a few suggestions because I still don't have a clue what would work. I don't imagine this plane is more then 10 or 15 ounces fully RTF. Thanks

salnsp

Sure! Can you direct me to a website so I can have a look at the model? This would help me make a recommendation.

Azzir325

Hi Sal. This plane is a homemede job, and I doubt there's a website for it anywhere. I have given you the dimensions earlier, and tho I don't have a weight, it can't be too much. From where I sit, I'm thinking the fact of it's being a pusher, which because of the way it's built (twin vertical stabs and fuse members underneath) means that the cut out for the prop is restricted. What if I was to modify the nose to take a flat plywood mount and put the motor on the nose. Would I be able to use that Feigo motor with a lower voltage battery and a bigger (please recomend) prop? With the motor up front of course I would move the battery rearward to balance. What do you think? Rick

salnsp

Due to the prop restrictions, I would go to a motor with a Kv of 3600-4200. I would stay with 3-cells but make sure you have a battery that can do at least 15C.

Azzir325

How about if I move the motor to the nose. That would remove any prop size restrictions.

salnsp

Of course that would be fine and would open your choices, but your current motor will not work.

Azzir325

Thanks.

salnsp

You are most welcome