Connecting ESC power wire to Navio 2 servo rail

#1

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From the emlid Navio2 docs/Hardware setup:

Redundancy

In case of power module failure Navio2 will switch to power from the servo rail.

Powering servo rail

Power module does not power servos. To provide power to the servo rail plug your drone’s BEC into any free channel on the servo rail. Use BECs that provide voltage in a range of 4.8-5.3V. If you’d like to use high voltage servos use a power separation board.

RC output

ESCs

ESCs are connected to RC outputs labeled from 1 to 14 on a 2.54mm header.

Only one ESC power wire (central) should be connected to Navio2 servo rail, otherwise BECs built in ESCs will heat each other.

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In the ‘Wiring the ESC PWM Lines to Flight Controller’ lesson of the ‘How to Build a Raspberry PI Drone’ there is no mention of having only one ESC power wire connected to the Navio2 servo rail. So, I am confused as to whether or not I should cut the ESC power wire from three of the ESCs connected to the servo rail, leaving only one ESC with a power wire per the Navio2 docs.

#2

This is a great catch on your part and I will need to update the videos.

On 3 of the 4 ESCs, you can do something like I’ve done here:

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Using a needle or pin of some sort, press on the metal electrode flap that is in the black molex connector (for the middle red line). While pushing down, pull out the red cable. After the red line is free I simply tied it down with electrical tape.

#3

I disconnected the red wire on 3 of the ESC’s and found the one with the wire still connected was hot. This was dis-armed and using the battery only.

I disconnected the red wire on the 4th and it is no longer getting hot as it was. All motors seem to power up ok. Is it ok to disconnect the red power wire on the 4th ESC? I’m not sure why it would be required as the ESC is connected to the battery via the power distribution. ??

#4

Hi there, @Mikejsharp

I think it actually should be ok to unplug all the UBEC power from the ESCs. I have always kept one plugged in, for the times where I need a hot servo rail to drive some part I have attached (like a servo or something).

But if your motors are spinning alright with the 4th out, then you should be good to go!

It should be noted just a week ago, one of the drone dojo members experienced a weird issue where the motors with the red UBEC line unplugged from the servo rail would not run. And only the ones that had the red UBEC line in would spin.

Be interested to see what you report!

#5

Thanks. I browsed the Emlid forum and confirmed these can be disconnected.

Possible downside is that the esc’s can provide redundant power to the servo rail so in some cases so this may be (exception cases)

My esc’s provided 5v on the red wire and apparently this was causing the heating when connected to the Servo rail.

I’ll report if I find anything contrary.

Thanks for the response.

#6

I am having similar issues powering the servo rail with the ESC as well. There was another post that was more relevant to my problem but it was closed so I will continue the discussion here. I am trying to power a raspberry pi from the pixhawk, but when I plug the wires from the pi into the telemetry port there is a voltage drop and only 4.7v are going to the pi. Telemetry port 2 does not work for the pi at all, and only in telemetry port 1 does the pi successfully power on, but with the low voltage. To get around this I decided to try to power the pi from the servo rails. Using the red wire from just one of the ESCs, I was able to power the servo rails. I saw I need to include a zener diode on the rail as well, so I did. The pi starts up and works, however, now the ESC with the connected red wire gets very hot. Not sure what other options I have. How can I prevent the ESC from overheating if I plug in the red wire?

#7

Hi there @pattent !

If the ESC is utilizing the UBEC to supply actual power to a device, heat will be generated and you will feel that on the heat sink. So a hot ESC shouldn’t be a big concern. If it is extra super duper ouch hot than that may be an issue, but I think you’re good.

#8

Thanks @caleberg! The esc was getting hotter than I was comfortable with so i kinda found another way around using the esc by adding a UBEC to the power distribution board to power the raspberry pi instead

#9

That’s a smart setup, @pattent!

closed #10