I've posted about this before, but I feel I must reinforce this:
You MUST use a completely independent power supply for your APM or Pixhawk than you use for the Servos. DO NOT use one BEC to supply both the Servos, and the APM/Pixhawk.
On most of my helis, I use a 2S battery direct to HV servos, with a separate regulator going to the Flight Controller. On the rare case that I use a BEC for the servos drawing from the motor battery, I use a completely separate BEC to power the Pixhawk.
This is vitally important.
One user suffered a bad crash on Saturday because of this. If you use a single power supply, the servos will eventually cause a brownout, and you will have a crash. It's just a matter of time.
Replies
Robert,
Tell me if this works.
I am running the APM power module to power my Pixhawk then after the power module I have my BEC to power my servos. Is this right?
https://store.3drobotics.com/products/apm-power-module-with-xt60-co...
I assume you men the BEC is on the down stream side but wired to the fat cables not the thin cables that power the APM? If so that is fine, and you servo/bec current will be measured by the power module.
I just wonder, i m going to put retravtable skid in my hexa my Apm and reciver get power from the apm power module, if i put another bec or retract controler with diferent power is it possible to damage the apm from the channel six which will be connect to the retract bec or controler and then to reciver????
ok, i should read this, before i crashed my T1000 ...
https://www.youtube.com/watch?v=1re5kn3h2nY
I'm wondering whether a larger capacitor may still keep the voltage within range? After all the voltage input of Pixhawk has quite an acceptable range, APM is somewhat sensitive to voltage though.
They definitely help, no question. It's just that they may not be enough by themselves. A Zener with a capacitor will help even more. The capacitor helps both with the positive spikes, and the negative spikes.
But really, separating the two power supplies, kills the problem absolutely, is easy, and doesn't cost a whole lot so why would you not do it?
Hello,
I'd like to add a few remarks on what has already been said:
-Assuming you follow Robert's advice to use a separate battery (and eventual BEC on it) to power directly the servos, do not forget to connect the ground wire of this battery to the ground of the main battery (otherwise your servo control wire signal level might be off or parasited with noise)
-Servo spikes higher than 5.7V on Pixhawk's output rail can be avoided by adding a 5.6V zener diode on Pixhawk's output rail, as described in the wiki.
Hugues,
This is a good point to bring up. I'd have to have a think about whether or not this is true in the case of a normal ESC, which would already provide a ground connection, but maybe not a good enough one.
However, in the case where the system is using a *true* Opto-isolated ESC, you should absolutely not connect the grounds. This is the whole point of Opto ESC's, to isolate the rest of the avionics from the nastiness going on with the powerful motor currents. True Opto ESC's have no connection between the signal ground, and the motor ground, and you should not make one.
Opto ESC's are a very good idea in 600 size helis and larger. Some ESC's marketed at "Opto" actually are not, they have simply omitted the internal BEC. You can check this by testing for continuity between the signal ground wire and the battery ground wire. If there is continuity, it is NOT a true Opto-isolated ESC.
About opto ESC, unless pixhawk board is using also a true opto isolation between the power port and the output rail, you have connection between grounds...
Hello,
regarding the zener diode: here Reverse current of the servos it seems they are not so convinced.
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