Solved esc with bec or external bec?

Wildthing

Legendary member
This is an educational thread! I’m still green at figuring out electronic layouts beyond the basic 4 channel setup but it seems like bottom line, If I want to make a plane like the bushwhacker or ft legacy or sea duck or anything with more than 4 servos I should be putting in at least a 5 amp BEC. Is that true? I’m asking for guidance and clarification because there are cyber Monday deals to be had and planes to build😄
With 4 servos and a 3A bec you should be safe, 6 servos would be pushing it. Just look close at the servos when buying them to see what their bec amp rating is. I usually only wire in my ext 5A bec when I am using 6 or more servos.
 

Merv

Site Moderator
Staff member
This is an educational thread! I’m still green at figuring out electronic layouts beyond the basic 4 channel setup but it seems like bottom line, If I want to make a plane like the bushwhacker or ft legacy or sea duck or anything with more than 4 servos I should be putting in at least a 5 amp BEC. Is that true? I’m asking for guidance and clarification because there are cyber Monday deals to be had and planes to build😄
I have seen several people test the amp draw form 9g servos. The conclusion seams to be that they draw a maximum of about 3/4 of an amp. So 4 9g servos can safely be used on a 3 amp BEC. If you run a 5th and all of them max out at the same time you could have trouble.

My self, I generally look for 50 amp ESC's with a 5 amp BEC. They will take anything I want to throw it's way.
 

BATTLEAXE

Legendary member
I will definitely be looking into the BEC amp rating on my next ESC purchase, all are good points. One thing I would like to add as well. Once powered up, servos even at a static centered position still pull amps to hold that position, very little compared to full deflection, but do require power nonetheless. I think with my Bushwhacker I am pushing the limits, mind you the Flaps servos are 5g and no 9g might help a bit. The label has been removed from the ESC but I still have the manual for it so I should read up on it.

Some good servo/BEC education here, thank you.
 

The Hangar

Fly harder!
Mentor
So I set up two esc’s on my bushwacker - one for the motor, and one for the servos. I hooked them up with a y connector and powered it off one battery. The esc is plugged into the throttle port and the “bec” is plugged into the bind port. Be sure to remove the middle, or power wire from your esc that is powering the motor.
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Wildthing

Legendary member
So I set up two esc’s on my bushwacker - one for the motor, and one for the servos. I hooked them up with a y connector and powered it off one battery. The esc is plugged into the throttle port and the “bec” is plugged into the bind port. Be sure to remove the middle, or power wire from your esc that is powering the motor.
The motor maybe running off of the one esc but all the controls for the motor , rx and servos are all off of one bec your extra esc. To me you gained nothing but extra weight. The bec even though it is built in it still runs separate from the esc. Unless I am missing something here. :unsure::unsure::unsure:
 

Sero

Elite member
So I set up two esc’s on my bushwacker - one for the motor, and one for the servos. I hooked them up with a y connector and powered it off one battery. The esc is plugged into the throttle port and the “bec” is plugged into the bind port. Be sure to remove the middle, or power wire from your esc that is powering the motor. View attachment 149697 View attachment 149698
If those ESC's have linear BEC's you can keep both red wires connected and double your BEC amp rating, just don't do it with switching BEC's. I'd probably disconnect the signal wire from the ESC thats not running the motor, less prone to signal interference
 

The Hangar

Fly harder!
Mentor
If those ESC's have linear BEC's you can keep both red wires connected and double your BEC amp rating, just don't do it with switching BEC's. I'd probably disconnect the signal wire from the ESC thats not running the motor, less prone to signal interference
I’m not sure which one it is. So you would leave the esc as is and remove the “bec” red wire?
 

BATTLEAXE

Legendary member
If those ESC's have linear BEC's you can keep both red wires connected and double your BEC amp rating, just don't do it with switching BEC's. I'd probably disconnect the signal wire from the ESC thats not running the motor, less prone to signal interference
That is what would make more sense. The secondary ESC you are using as an aux BEC will have no power and just act like an open bind plug, hense just adding more weight, theoretically. Now if you have already tried all the controls and it all works then there is something we are missing lol.
 

The Hangar

Fly harder!
Mentor
The motor maybe running off of the one esc but all the controls for the motor , rx and servos are all off of one bec your extra esc. To me you gained nothing but extra weight. The bec even though it is built in it still runs separate from the esc. Unless I am missing something here. :unsure::unsure::unsure:
Doesn’t the motor draw from the bec? You might be on to something though😉
 

Wildthing

Legendary member
But why go through all that if you just need a higher amp rated bec, just get an external one and wire it in and it doesn't weigh as much . You have the extra weight of the esc and the Y battery connector and those external bec's are only $5.00 or so. Plus some of them have dual voltage out 5 or 6 volt setting if you want to speed up your servos or make them stronger,
 

The Hangar

Fly harder!
Mentor
But why go through all that if you just need a higher amp rated bec, just get an external one and wire it in and it doesn't weigh as much . You have the extra weight of the esc and the Y battery connector and those external bec's are only $5.00 or so. Plus some of them have dual voltage out 5 or 6 volt setting if you want to speed up your servos or make them stronger,
Yeah, you’re right. I’m not sure it seemed to be working better, but as I said, I have the turnigy esc in order and it has a 5 volt esc on it so that should cut it. The bushwacker should be maidened in about a week then.
 

Wildthing

Legendary member
Yeah, you’re right. I’m not sure it seemed to be working better, but as I said, I have the turnigy esc in order and it has a 5 volt esc on it so that should cut it. The bushwacker should be maidened in about a week then.
99% of the time 5 volts is all you need. My F14 which has larger/strong servos for the wing retract mecanism on 5V it was sluggish, switched it to 6V and wings worked great then.
 

Sero

Elite member
I’m not sure which one it is. So you would leave the esc as is and remove the “bec” red wire?
The way I'm interpreting what you're doing is that one ESC is for motor control, and the other is acting as a BEC. If they are both the same and both have linear built in BEC's you don't need to remove either red wire, therefore doubling your BEC amp rating. If its a switching BEC then you need to remove the red wire from the ESC that has the motor hooked up to it.

Doesn’t the motor draw from the bec? You might be on to something though😉
No the motor doesn't draw from the BEC. Say you have a 40 amp ESC that has a 3 amp BEC, you should be able to pull 40 amps from the motor while drawing 3 amps from the servos/receiver. They are 2 separate circuits.
 

BATTLEAXE

Legendary member
I think he just wants to maiden his Bushwhacker, and really the extra weight won't matter. It is a light airframe and will take the extra weight. Once he gets an external BEC it will just be a bonus on saved weight
 

Sero

Elite member
The motor maybe running off of the one esc but all the controls for the motor , rx and servos are all off of one bec your extra esc. To me you gained nothing but extra weight. The bec even though it is built in it still runs separate from the esc. Unless I am missing something here. :unsure::unsure::unsure:
I agree, its adding weight if its a switch BEC and you disconnect the red wire.