# m500 outside hovering precision

Source: https://forum.modalai.com/topic/894/m500-outside-hovering-precision
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2022-04-27 13:04:09 UTC by janis_blank
Replies: 3 · Views: 975

## janis_blank · 2022-04-27 13:04:09 UTC

Hello,

under [https://www.youtube.com/watch?v=g2lub_OCbok](https://www.youtube.com/watch?v=g2lub_OCbok), you can see a video of an m500 (it's an m500, isn't it?) hovering highly stable, almost without sway. Most self build drones equipped with only GPS introduce a sway of around 1-2 metres in every direction when hovering, at least to my knowledge.
How is this precision achieved (optical flow analysis with the tracking sensor, maybe)? And would this precision also be given outside in a height between 10 and 30 metres, when the tracking sensor has no close orientation points (I assume it sits in the front of the drone)?
If not, is it possible to mount optical flow and range finder modules (e.g. PX4Flow) to improve stability?

## Reply by Guest · 2022-04-27 18:26:33 UTC

Hi Janis,

Yes, this was done with a visiual/inertial fusion, see [voxl-qvio-server](https://docs.modalai.com/voxl-qvio-server/). This is mainly used for indoor flight, but can work outside in certain circumstances. Generally, It won't work if you're flying too high (where the camera can't reproject to 3d within a good enough margin of error) or when the camera can't see distinct features at all within it's field of view (such as flying over a grass field). That being said, we have done successful outdoor vio flights when flying low and over feature-rich areas like sidewalks and parks

## Reply by janis_blank · 2022-04-28 09:24:14 UTC

Hello Alex,

and thanks for the answer. 
The drone will do surveillance on feature rich areas with a downward facing camera. However, the front cameras will problably be looking a at very boring horizon all the time. I guess I'd really need these cameras facing downwards instead of frontal. That wouldn't be doable, would it?
Also, would your flight core support the addition of a bottom range finder as outlined on [this](https://docs.px4.io/v1.12/en/sensor/rangefinders.html) page (I need to do precision landing and therefore need exact height values)?

Thanks and regards

## Reply by modaltb (ModalAI staff) · 2022-04-29 22:55:30 UTC

Hi @janis_blank ,

A quick browse of those range finders showed some with I2C interfaces.

Now, we don't have all drivers possible starting in PX4, so this might not work out of the box.  Here's the drivers available: https://github.com/modalai/px4-firmware/blob/modalai-1.11/boards/modalai/fc-v1/default.cmake#L17

There's a spare I2C port though likely available on the hardware for you, J13 on FlightCore:
https://docs.modalai.com/flight-core-datasheets-connectors/#j13---i2c-display--i2c2-bus--safety-switch-connector

You may need to enable drivers and then alter startup to get to work, here: https://github.com/modalai/px4-firmware/blob/modalai-1.11/boards/modalai/fc-v1/init/rc.board_sensors

But in theory using I2C you should be able to get data from the range finders (it wouldn't be integrated into voxl-* tools, rather just used by PX4 though)