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Alternate ESC/BEC Wiring Solution Help

#1
Hi there all, I am new here and just getting back into the hobby. I am planning on building the FT Sparrow Twin for my first FT build and I am trying to cram differential thrust into a 4 channel Rx (Radiomaster R84). I know that typically the solution for 6ch Rx's would be to have the ESC's just on a separate channel and also use the ESC's built-in BEC. The ESC I selected has no BEC AND I want differential thrust for the sweet sweet flat spins and shenanigans on a 4ch Rx. I have drawn up a solution and need the rubber duck test since I am no electronics wiz.

I just want to "tap" the negative from the BEC to a negative from one of the servos.

Thank you in advance and I look forward to learning and maybe even flying with some of y'all! :cool:

See the upper right-hand corner and the negative lead from the BEC for what I am proposing. If that will just not work, then I will get a 6ch Rx, but the 4ch is what I have.


(Parts list for ref)
https://www.racedayquads.com/products/spedix-20a-esc-lite-dshot-600-blheli_s?variant=36300447431
https://www.racedayquads.com/produc...tal-gear-digital-servo?variant=39447772725361
https://www.racedayquads.com/produc...pwm-2-4ghz-rc-receiver?variant=32194640773233



Dual Motor on 4ch Rx.jpg
 

JasonK

Master member
#3
it would probably be better to just use a servo splitter cable, then your not 'tapping' wires and it should give you the same result (use the splitter between the receiver and one of the devices and plug the BEC and the device in to the splitter).
 
#4
it would probably be better to just use a servo splitter cable, then your not 'tapping' wires and it should give you the same result (use the splitter between the receiver and one of the devices and plug the BEC and the device in to the splitter).
OK, but using a servo splitter, the 5v that the Rx needs is missing, right? Since the BEC is on the splitter, the servo will get 5v but not the Rx? I need to draw it out so I can see it, ya know?
 
#8
Normally you're getting all your grounds from the receiver. You plug in a device or Servo or bec into the receiver. The receiver has all the negatives connected together. Sometimes you can make your own connections, connecting black wires together giving the receiver more points of contact from the bec, Ubec or receiver battery to the receiver. The same can be done for all the red wires from the receiver can be connected to the output of Bec. Often the esc's 3 wire red leads are disconnected when using a bec. Some esc's will not even turn on when it sees voltage on the three wire red lead that goes to the throttle port on receiver when a separate bec or RX battery is in use. There are exceptions though. If ESC internal Ubec and external dec's are used together, it is importance to use a isolating diode to prevent 2 conditions. One is to prevent one bec from pulling down the other. The other issue is the bec's and ESC Ubec are not perfect, voltage can go in reverse from the input of the bec to the output of the bec driving ESC even turning the motor when there's no flight pack battery but receiver battery in conjunction with bec or Ubec which also requires a diode isolation. CONFUSING I KNOW.
You may put a isolating diode on the input of the bec to prevent this.
Caution.
If your bec is already at 5v out and you put a diode on the output of bec, you may lower the voltage too low so it is best not to do this on the output of the bec. Input okay. Output not okay unless bec is at a higher voltage to overcome the voltage drop across the diode. Receiver voltage drops too low, you will Brown out and crash.
Thoroughly check everything on the ground before flight. another good added test is to add a dummy load resistor to the receiver and move all the control surfaces rapidly and measure voltage drop. Some telemetry receivers show receiver minimum and maximum voltage. I have used 2 receivers and two transmitters to do this test monitoring the aircrafts receiver voltage if the aircraft itself that did not have it.
 
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