After using Cube Oranges in the past, now I have setup my first build with Pixhawk 6X in order to have more available serial UARTs.
FC is flashed to ArduCopter 4.5.4 but it does not boot, when a serial device is connected to TELEM1 (SERIAL1, UART7) port.
First, I tried to attach an ELRS receiver to TELEM1: FC does not boot. After connecting it to SERIAL6 (User UART4) (which required attaching another cable with 7-pin JST GH plug and configuring this to PROTOCOL 23 (RCIN)), FC is booting.
Second, I tried to attach an ESP32 (acting as serial bridge) with itâs serial port to TELEM1: FC is not booting!
Plugging it into TELEM2 (SERIAL2 UART5), FC is booting.
I also tried to set BRD_SER1_RTSCTS to 0 (RTS/CTS disabled) - FC still does not boot, when something is connected to TELEM1. Then I tried to disable DMA in the SERIAL1_OPTIONS (RX_NoDMA and TX_NoDMA checked in the Bitmask Popup). FC still is not booting. Then I tried activating âRX_PullDownâ: FC still no booting when something attached to TELEM1. So, none of these options helped.
As FC is booting and the tested devices are working, when connected to other serial ports, I am sure, that it is no issue with these devices or their cables.
Unfortunately, I currently have only one Pixhawk Cube 6X, so I cannot compare with another sample if it is only an individual problem with that particular item.
My hope is that also others (or @Holybro ?) are able to reproduce this.
Some additional information:
The output voltage on the +5V line of TELEM1 is only about 1 V, when the FlightController is powered over the PM02D power module. The other serial ports provide 5V. When the flightcontroller is powered over the USB-C port, also TELEM1 provides 5V but as long as a device that needs 5V power is attached, the board does not boot at all, so there definitely seems to be something wrong with that board.
Another strange thing: I have a rangefinder (Benewake TF03) attached to the GPS2 (SERIAL4 / UART8) port. This rangefinder works as expected, when the flightcontroller is powered from USB. But when the flightcontroller is powered from battery via PM02D, it provides no data.
All this together leads me to the assumption, that my board has a hardware defect.
Update:
The problem seems to be the TF03 LiDAR (Benewake), which may draw too much current from the 5V line, when also other components (GPS, HereFlow, ELRS receiver, ESP32 serial bridge) are connected. In total this seems to overwhelm the 5V supply.
When TF03 it is not connected, the Pixhawk 6x also boots, when something (consuming 5V) is connected.
Yes, nothing new here.
Additional auxiliary devices should be powered separately as many FC have only limited current supply to the various ports. If you push it to much it can actually cause a system crash mid-flight which would be most likely the end of your drone.
Yes, not really new. But here it was just a single beam lidar which Benewake specifies to consume 180 mA / 0.9W. I didânt expect that this (+ GPS + ELRS receiver) already brings the Pixhawk 5V supply to itâs limit.
Holybro specifies it like this:
Current Ratings:
Telem1 output current limiter: 1.5A
All other port combined output current limiter: 1.5A
There is a thing called ârush-in currentâ which is mostly found in devices with an electric motor but can also be happening with electronic devices having a large capacitor. In those within the first second or two large currents (up to 10 times the usual current) can easily occur. So any power supply has to be able to push that much current out in a short time. - This fact is often overlooked when planning for a power supply arrangement. (I.e. Including people using generators to run fridges/freezers during a power outage and then getting a nasty surprise when generator dies).
The other thing to consider is the fact that no technical device is perfect and lasts forever. So if you have multiple devices drawing power from a FC and one of those suddenly has a short circuit, then most likely that short circuit current (once again usually multiple times that of regular current) will damage or destroy the FC almost instantly.
âŚAfter all thatâs the reason we use fuses in regular wiring.
As far as I know, the Pixhawk 6X carrier board provides separated power supply for the FC and the connectors for periphal components. And as I wrote already, in the Pixhawk 6X the TELEM1 output has a seperate supply and 1.5A current limiter on itâs own. So the assumption, it should be possible to connect a lidar specified for 180 mA constant current to that port should not be too inappropriate.
But anyway: After providing +5V for the TF03 lidar from a seperate BEC, the weird effects are gone now. Thanks for your advice. Perhaps this discussion may help others planning to use the TF03.