Tribunus 80/120 – Servo Induction Voltage, Issue / Fix

The Issue –

Since we put the Tribunus 80A and 120A on the market we have seen some people are having issues with the BEC of the ESC’s going into protection mode and shutting down. When we started hearing about this issue, we started looking for the cause of it, and we finally found the cause, and the fix for it.

The Cause –

We have found that some brand/ type of servos have a very high induction voltage. What this means is that the servos actually create voltage and it back feeds into the BEC. In some cases we found that the induction voltage from some of these servos can end up being up to 30% higher then the actual output voltage from the BEC. So if you are using the BEC on 7.1 voltage and the servo generate 30% extra voltage, it brings the voltage to 9.25 volts which can actually damage the BEC and some RX/ FBL units.
Since the BEC is then sensing voltage which is higher then what it is outputting, the BEC goes into “protection” mode in order to save itself from this high induction voltage.\

We have also found that some brand/ type of servos simply just have a VERY high amp draw when starting and stopping the movement of the servo. These high Amp peaks can also trick the ESC into thinking there is a short circuit in the system, thus causing it to go into protection as well.

Some servos have 1 of these 2, or even both, of these issues. So if you are experiencing this issue with your BEC shutting down when moving the servos rapidly, it is likely caused by your particular servo brand/ model creating voltage and inducting it back into the BEC, or your servo having a very high amp draw when starting and stopping, thus causing the BEC to have to protect itself by shutting down.

The Fix –

The solution to this servo generated induction voltage and/ or high Amp draw,  is to add a capacitor to your RX or FBL unit. This capacitor will absorb the excess voltage first before reaching the BEC and causing a issue. Additionally the Capacitor will help provide voltage during the high Amps draw peaks of the servos.


We recommend using a 1000uF – 4700uF , 10-25v Capacitor and soldering a servo lead onto it and then plugging it into your RX or FBL unit. For the servo lead, for best results we recommend using large wire (20 gauge) and having it be no longer then about 2 inches (5-6cm).
The capacitors cost only a few dollars, so it is a cheap and easy fix to implement. In addition to the capacitor, if your issue remains then we recommend also lowering the RX voltage to 5 Volts as this will lower the Amp draw of the servos as well.

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