LUA - read named float mavlink msg failed

Blue Robotics Software ArduSub
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1

Hello everyone,

I’m facing two challenges related to Named Float values in my ArduPilot setup:

1. Issue with Mission Planner:

  • I successfully set a Named Float value using pymavlink.
  • I can observe the Named Float variable (e.g., “my_named_value”) in the Mission Planner’s Quick View Tab.
  • However, the value associated with the variable always remains 0.
  • Using Mavlink Inspector, I’ve confirmed that Mission Planner is indeed sending the Named Float message to the Autopilot.
  • I’m puzzled as to why the value isn’t correctly displayed in the Quick tab.
  1. Reading Named Float Values in Lua:

I’m encountering an issue while trying to read Named Float values in my ArduPilot Lua script.

  • I’ve written a Lua script to listen for Named Float messages.
  • The script appears to be running without errors, but it doesn’t seem to be receiving any Named Float messages from Mission Planner.
  • I’ve verified this by using gcs:send_text(0, " **** ") that the if msg then block in my script is not being executed.
  • I used gcs:send_text(0, " **** ") to confirm that the script isn’t receiving messages.
  • Additionally, I verified that the NAMED_VALUE_FLOAT_msgid is correctly defined as 251 within my script.

Can you help please.

Lua script:

function mavlink_receiver()
   local mavlink_msgs = require("mavlink_msgs")
   local NAMED_VALUE_FLOAT_msgid = mavlink_msgs.get_msgid("NAMED_VALUE_FLOAT")
   local msg_map = {}
   msg_map[NAMED_VALUE_FLOAT_msgid] = "NAMED_VALUE_FLOAT"
   -- initialise mavlink rx with number of messages, and buffer depth
   mavlink.init(1, 10)

   -- register message id to receive
   mavlink.register_rx_msgid(NAMED_VALUE_FLOAT_msgid)
   local msg,_,timestamp_ms = mavlink.receive_chan()
   
   if msg then
      local parsed_msg = mavlink_msgs.decode(msg, msg_map)
      if (parsed_msg ~= nil) and (parsed_msg.msgid == NAMED_VALUE_FLOAT_msgid) then
         -- convert remote timestamp to local timestamp with jitter correction
         --local time_boot_ms = jitter_correction.correct_offboard_timestamp_msec(parsed_msg.time_boot_ms, timestamp_ms:toint())
         local value = parsed_msg.value
         local name = bytes_to_string(parsed_msg.name)
         gcs:send_text(0, "Got mode change ....  " .. value)
      end
   end

   return mavlink_receiver, 1000
end

return mavlink_receiver()

The python code:

from pymavlink import mavutil
import time

mavlink_connection_string = "udpout:127.0.0.2:14550" #"tcp:192.168.43.1:5760" #
mav = mavutil.mavlink_connection(mavlink_connection_string)

def send_named_value_float(mav_, name, value):
    # Get the time_boot_ms as the time difference since the first heartbeat received
    time_boot_ms = int((time.time() - mav_.start_time) * 1000)
    # Ensure the name is exactly 10 bytes long
    encoded_name = name.encode('ascii').ljust(10, b'\0')
    mav_.mav.named_value_float_send(time_boot_ms, encoded_name, value)
    
def main():
    try:
        while (1):
            # Send the NAMED_VALUE_FLOAT message 
            send_named_value_float(mav, 'ty1 980', 5)
            time.sleep(0.1)
            send_named_value_float(mav, 'Battery1 voltage', 4)
            time.sleep(0.1)
            send_named_value_float(mav, 'lol voltage', 6)
            print("send   ")
            time.sleep(0.2)  # Wait for 0.5 seconds before sending the next message

    except KeyboardInterrupt:
        # Handle any cleanup or resource releasing if necessary
        print("Interrupted by user, stopping message sending.")
main()

The Mavlink inspector:

sade
sade1038×392 17.1 KB

Quick view tab - Mission planner:

image
image506×580 21.1 KB

2

Hi @Amer,

I expect you likely want to be asking about this in the more general ArduPilot forums - the Blue Robotics forum is specifically for discussing marine robotics, and we don’t use Mission Planner so can’t provide support for it. They also will have more experience with Lua scripting, and likely with Pymavlink as well.

Note that this can pad a name out to be 10 bytes long, but it will not reduce the length of values that are over 10 bytes, and 'Battery1 voltage' is 16 characters long.

If it’s relevant, I have an example from several years ago for sending a NAMED_VALUE_FLOAT message with Pymavlink, which I managed to receive correctly in a custom build of QGroundControl. Nowadays that would be substantially easier using Cockpit and it’s Very Generic Indicator widget, but if you’re not running BlueOS on an onboard computer on your vehicle then Cockpit is quite challenging to set up at the moment.

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3

Hello @EliotBR

Thank you for your time, I will follow this question on Ardupilot forums.

also thank you for your links. I appreciate that.

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