Integrating a fuel flow meter to the APM autopilot


We are putting together an UAV prototype were we initially intend to use the APM autopilot. We are intending to use the 3W-55Xi CS two stroke engine. In order to be able to make some engine/flight performance measurements we will need to install an fuel flow meter to measure consumption at various speeds and RPM´s. I have found a small light weight and accurate flow meter that I think will suite our purposes, please find the link to the flow meters data sheet below: … eet_V2.pdf

As I can understand according to the data sheet it should be possible to bypas the RS485 communication and directly communicate with the sensor using I2C protocol. This would be great as I understand that the APM autopilot also uses I2C to interface extenal sensors. If possible I would like to have some assistance from the APM community to integrate this flow sensor to the APM autopilot. First as basic things as hooking it up on the I2C bus. The UAV prototype will be equipped with an external magnetometer also connected to the I2C bus, so I guess I will need some I2C hub to connect both external sensors to the single I2C connector of the APM board. Secondly I would like to have the possibility to onboard the APM logg the fuel flow meter data, and most ultimately also telemetry down the information to the Mission Planner software on the ground control station laptop.

Is there anyone in the APM community that could assist me with some of these topics ??

Best Regards

Unmanned Anders

Hi Anders,
I’d be interested in adding fuel flow sensor support to APM. The datasheet says that “Information on bypassing the RS485 cable and communicating directly with the sensor via I2C is available on request” which sounds hopeful.
I’d be happy to write an APM I2C driver for the sensor if you send me one. I have an I2C bus analyser, so even if they don’t provide good I2C info I suspect I could work it out. The driver itself is likely to be very simple, although we’ll need some new mavlink messages for fuel rate and remaining fuel (unless we just overload the battery current/mAh code).
I mostly fly nitro and petrol planes, so a fuel flow sensor would be nice to have.
Do you know if the plastics used in the sensor are OK with both nitro and petrol? I don’t see fuel types listed in the datasheet. It probably is fine, but after dissolving a bung of one fuel tank in a 50cc DA engine I like being careful now :slight_smile:
Also, where do you buy the sensor from? I see lots of blurb on various sites, but no price or ordering info.
Cheers, Tridge

Hi Tridge,

Thanks for your promising answer. We have not got the fuel flow sensor yet, but I have required some quotation from a supplier, they may be a bit expensive… I will contact you again if we decide to purchase one and integrate it towards the APM autopilot.

Best Regards

Anders Be,

Hi Anders and Tridge,

I was wondering if you guys managed to get this thing to work. For an academic experiment, I am trying to connect an I2C compatible thermal sensor to the I2C port of my APM 2.5
I’m having trouble accessing the sensor from within the code and I’m also not quite sure how to integrate the measured values into my MAVlink stream for processing in my groundstation.

Any help would be highly appreciated.