I have four RCMC ESCs. Each ESC has a built in BEC. Out of the the ESC there are three wires going into a 3 hole servo connector. I have two questions:
Can I connect all 4 ESCs servo connectors to the Pixhawk without cutting any of the wires?
If I do need to cut ESC wires, should I leave all three wires in tact on one of the ESCs and only leave the survo wire on the other three ESCs? The reason I ask is that I see it both ways in setup information. The Pixhawk infographic has 3 ESCs with only the survo wires attached the the Pixhawk and the fourth with all three wires attached. However, the Quickstart Guide show only Survo wires attached to the Pixhawk.
I have seen it suggested you cut 3 out of the 4 red wires from your 4 esc’s [ assuming it’s a quad of course ] thus powering the servo rail with only one esc. But this never made any sense to me. They all supply 5 volts. So it would seem to me having all four connected would simply mean they share the load. The voltage would stay the same they are in parrellel. But perhaps there is more to it than I realize. I’m kind of curious what an ‘official’ answer is myself.
This is not an ‘official’ answer but hopefully can help.
There are a couple of reasons to not tie the outputs of multiple voltage regulators (which is what the BECs really are) together. First, even though they are all 5V, the actual output could vary, maybe one is 4.94 and the other is 5.04, for example. Depending on the design, the higher voltage one could feed voltage to the lower voltage one, at a minimum wasting energy. Another reason is that the voltage regulator is effectively a control system which adjusts its gain to ensure the output tracks the reference voltage (5V in this case). Tying multiple of the outputs together could lead to oscillations while the controllers are fighting each other, again because their reference voltage would be slightly different.
Note in both cases there are caveats, ‘depending on the design’, and ‘could lead to…’. In reality, it often works just fine. In fact, it is not unheard of to use regulators in parallel to increase capacity, for example see dimensionengineering.com/Pa … lators.htm
In this case, the design of the regulator is such that it works fine to put many in parallel. The problem with most generic BECs coming out of ESCs is that you just don’t know, and working on the ground is no guarantee there will not be problems while on the air, and so the wise recommendation is to not risk it and avoid tying the outputs together.