# Voxl ardupilot issue

Source: https://forum.modalai.com/topic/1074/voxl-ardupilot-issue
Category: Flight Core and Legacy VOXL (https://forum.modalai.com/category/9/flight-core-and-legacy-voxl)
Tags: voxl
Posted: 2022-06-30 20:39:14 UTC by sergio
Replies: 2 · Views: 688

## sergio · 2022-06-30 20:39:14 UTC

Voxl communicates perfectly with ardupilot but there is big mistake.

Ardupilot expect earth frame pos and drone frame vels when voxl send out earth frame pos and vels.

So there is parameter to easily change the frame for vels send out by voxl vision px4 service ?

Or

Must you upgrade the voxl firmware to match ardupilot? There is many customers that will be happy when voxl be useable with ardupilot

## Reply by James Strawson (ModalAI staff) · 2022-06-30 23:34:55 UTC

Hi Sergio,

voxl-vision-px4 does send out drone-frame (body-frame) velocity via the ODOMETRY mavlink message which is also what PX4 expects.

A couple references:

- The section titled "Frames of Reference: Odometry" here https://www.modalai.com/blogs/blog/how-to-autonomously-navigate-with-px4

- The code where velocity is transformed from local frame to body frame before sending the mavlink message: https://gitlab.com/voxl-public/voxl-sdk/services/voxl-vision-px4/-/blob/master/src/vio_manager.c#L186

Best,
James

## Reply by sergio · 2022-07-07 22:05:07 UTC (in reply to James Strawson)

@ James-Strawson 
Im sorry but is note the case….
While just activation voxl vision px4 service from fredh resceived voxl cam, voxl output local frame pos and velocitys via mavlink.

so how to activate local to body frame velocity transformation?

Maybe with px4 this work but with ardupilot i check on mavlink analys and i make simple translations and i can ensure you that voxl send out local frame pos and vels.

Maybe you can tell me ou to force voxl to output local frame pos but body frame vels to ardupilot ?

Thank you so much.