Configuring battery monitor with FPV ESC

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Hi we have configured and calibrated our Voxl FPV ESC 4 in 1 to run our T Motor MN5006 450KV motors but have not been able to get battery monitor working. I've tried all options in /etc/modalai/voxl-px4.config

Running voxl-inspect-battery results in NA values in all the fields. There is also no Mavlink message for battery monitor.

Edit: this is on a VOXL2 mainboard.

Moderator

@restore The FPV ESC power monitor should work just like the Mini 4-in-1 ESC power monitor https://docs.modalai.com/voxl2-mini-offboard-sensors/#power-monitoring

Alex Kushleyev

@restore , please make sure the voxl_esc px4 driver is running and VOXL_ESC_PUB_BST px4 parameter is set to 1 . here is a link to the param definition : https://github.com/modalai/px4-firmware/blob/voxl-dev/src/drivers/actuators/voxl_esc/voxl_esc_params.c#L234

What version of PX4 are you running? I just want to make sure that has the functionality for battery reporting from the mini and FPV ESCs.

Alex Kushleyev

Additionally, since you are using a relatively low kV motor, please review the following document that helps to make sure you adjust ESC parameters to avoid desync (and test to confirm) : https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc/-/blob/master/voxl-esc-tools/doc/low_kv_motor_tuning.md

Dan Jennings

@Alex-Kushleyev
Thank you for the instructions, I will look into those tomorrow.

We have the ESC plugged into Voxl2 J18 as indicated in the VOXL2 ESC configs

Low KV guidance is very welcome. We were having trouble getting the motors to work and looked into the param files to try and figure out what was wrong. Changing the KV made motor response much better. We have good motor behavior now but I'll go through those instructions to be sure the motors are properly tuned.

Alex Kushleyev

@Dan-Jennings, you are welcome. Just one note about the low kv tuning, instructions say set this param to 1 (demag_timing: 1 ), but leave it off (at zero). I will correct the doc - this was an experimental feature, you should not need. Also instructions say to use m0134-6 esc, but the FPV esc is just fine for this purpose. You can keep your existing tuning file and check the parameters that are suggested in the guide.

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PX4 version 1.14.0-2.0.68
VOXL_ESC_PUB_BST is enabled
Voxl-esc is running, can spin and calibrate motors.

Still no battery monitor

Low KV tuning worked, motors responding well.

Alex Kushleyev

@restore , This should be the correct PX4 version (it has support for this feature)

When you start PX4, are the blue LEDs on the ESC blinking? if not, then PX4 is not communicating with the ESC, you may need to double check the baud rate setting (baud rate in ESC params needs to match the VOXL_ESC_BAUD.

Related question, is the actuator test in PX4 working?

Alex

Dan Jennings

@Alex-Kushleyev
Yes, ESC is working, we're able to calibrate ESCs using esc tools, spin up motors in QGC, and have flown several times. Just having to be very conservative without battery status.

Alex Kushleyev

@Dan-Jennings,

We will figure it out quick question - what baud rate are you using for the ESC and also esc firmware version / hash? I will test with exact version of esc firmware and px4.

If your baud rate is 250k, please change it to a higher value, we typically use 2M. If baud rate is too low, may not be fast enough to send the extra packet with total current.

Alex Kushleyev

Another question - when you use voxl-esc tools and spin id 2, do you get a total current measurement printed in terminal along with regular esc feedback?

Alex Kushleyev

@Dan-Jennings , did you figure out this one?

the way the battery publishing works on M0138 (FPV) ESC and M0129 (Mini) ESC is as follows:

one of the MCUs on the ESC is hooked up to the total current sensor. On M0138 it is ID2, on M0129 it is ID3
when flight controller requests feedback from the ESC (by setting appropriate bit in the commanded RPM or Power control packet), the ESC ID with the current measurement will send out its regular feedback packet and right after the special battery status packet
this battery status packet is received and parsed by PX4 and if the VOXL_ESC_PUB_BST px4 param is set to 1, the battery status is published, code here
this only happens if voxl_esc px4 driver is running and and it is communicating with the ESC (e.g. UART baud rate is correct). You will see the ESC flash all 4 blue leds, which means the commands (disarmed rpms = 0 if not in flight) are received from the PX4 flight controller
you can view the battery status message in VOXL2 terminal using the following command:

px4-listener battery_status

I hope this helps!

Alex

Dan Jennings

@Alex-Kushleyev still pending on this. Have had other issues to solve. Will be starting another thread shortly.

restore

@Alex-Kushleyev

We're finally rebuilt and recalibrated, but still no battery status. All 4 blue LEDs are flashing on the ESC, so the voxl_esc px4 driver should be running but we get:

voxl2:/$ px4-listener battery_status
never published

Where would that PX4 param be located?

Alex Kushleyev

@restore , can you please check which version of voxl-px4 you are using? You can use “voxl-version” tool.

restore

@Alex-Kushleyev
We are using px4 version 1.14.0-2.0.68
I connected to px4 with QGC and was able to confirm that VOXL_ESC_PUB_BST is enabled. It'd still be handy to know where those params are stored so we can edit them while connected through adb.

Thanks

tom

@restore The px4 parameters are stored in a binary file at /data/px4/param/parameters so you can't modify that file directly.

However you can use the following to set a param:

px4-param set PARAM_NAME PARAM_VALUE

or view parameters with

px4-param show

Alex Kushleyev

@restore, also can you please check which version of ESC firmware you are running on the FPV ESC? you can do this using voxl-esc tools (while px4 is not running). voxl-esc scan

I suggest to update to the latest ESC firmware in voxl-esc repository (dev branch).

restore

@Alex-Kushleyev
ESCs are firmware version 39, hash 17d64675
I checked /usr/share/modalai/voxl-esc-tools/firmware and the M0138 firmware matches the one here.

modalai_esc_firmware_m0138_1_v0_39_RC11_17d64675.bin

Alex Kushleyev

@restore, thank you for checking.

Let's do another test:

for safety, remove propellers from motors
with px4 disabled, go to /usr/share/modalai/voxl-esc-tools on voxl2
run: ./voxl-esc-spin.py --id 2 --power 0 -- this will send a zero power command to ESC ID 2 (which measures the total current and sends back the battery status message). Motors will not spin. This will also request the battery status and you should see output (if possible you can use the latest voxl-esc tools from dev branch from (https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc/-/tree/dev) since I am not sure which voxl-esc version is installed on your board).

./voxl-esc-spin.py --id 2 --power 0
...
Found voxl-esc tools bin version: 1.6
VOXL Platform: M0054
Detected RB5 Flight, VOXL2 M0054 or M0104!
...
...
	Board      : version 42: ModalAi 4-in-1 ESC (M0138-1)
...
...
[0.017] (2) RPM: 0, PWR: 0, VOLTAGE: 15.612V, TEMPERATURE: 35.87C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.612V, BOARD_CURRENT: -0.232A
[0.034] (2) RPM: 0, PWR: 0, VOLTAGE: 15.609V, TEMPERATURE: 35.88C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.609V, BOARD_CURRENT: -0.200A
[0.060] (2) RPM: 0, PWR: 0, VOLTAGE: 15.610V, TEMPERATURE: 35.86C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.610V, BOARD_CURRENT: -0.248A
[0.080] (2) RPM: 0, PWR: 0, VOLTAGE: 15.618V, TEMPERATURE: 35.85C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.618V, BOARD_CURRENT: -0.224A
[0.095] (2) RPM: 0, PWR: 0, VOLTAGE: 15.612V, TEMPERATURE: 35.87C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.612V, BOARD_CURRENT: -0.272A
[0.120] (2) RPM: 0, PWR: 0, VOLTAGE: 15.608V, TEMPERATURE: 35.90C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.608V, BOARD_CURRENT: -0.240A
[0.134] (2) RPM: 0, PWR: 0, VOLTAGE: 15.612V, TEMPERATURE: 35.92C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.612V, BOARD_CURRENT: -0.264A
[0.160] (2) RPM: 0, PWR: 0, VOLTAGE: 15.613V, TEMPERATURE: 35.90C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.613V, BOARD_CURRENT: -0.248A
[0.174] (2) RPM: 0, PWR: 0, VOLTAGE: 15.608V, TEMPERATURE: 35.92C, CURRENT: 0.000A, BOARD_VOLTAGE: 15.608V, BOARD_CURRENT: -0.168A

note that there are BOARD_VOLTAGE and BOARD_CURRENT printed, which are parsed from the battery status message coming from the ESC ID2. Please note that the current around 0 is not very accurate due to a very large measurement range (showing -0.2A, but the discharge current should really be positive based on our convention).

Alex