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The TX16 was set to 250mW max power, dynamic on. The Ranger was originally set to 250mW, dynamic off, but was later changed to 1000mW, dynamic on.

Results

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What we noticed was that the TX16 was constantly at 250mW, with link quality 80-100 in close range operations (< 100m). As the drone moved away, the link quality decreased to 40-60% at 1.1km. TPower never lessened below 250mW. Moving away from airport did not help.

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All in all though, RTL always worked and we only flew within capabilities of ourselves and the drone (thumbs up)

Flight Test Logs

Hotlinks

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The graph above is the accumulated MAVLink Packet received/sent in the flight controller (PX6) during a flight test

The red line represents the data sent and the green is the data transmitted

  • The key takeaway from this graph is that we know the telemetry RX/TX isn’t proportional. The RX:TX has a 10 times ratio difference shown in the graph

  • The airport uplink/downlink bandwidth ratio is balanced and unchangeable. In the future, if the ELRS airport uplink/downlink bandwidth could be customized, then the telemetry transmission quality could be further optimized.

Hotlinks

Logs (view only - must be signed in to UW account): https://uofwaterloo-my.sharepoint.com/:f:/g/personal/uwarg_uwaterloo_ca/EnmcEWaGxHdEiYuD6xJM7XMB3XnpnPPU6S26vowZ1zjkQQ?e=gwI5j1

Media: (non existent as of rn)Flight test thread: https://discord.com/channels/776618956638388305/1134564410652885002 (non existent as of rn)

Flight test thread: https://discord.com/channels/776618956638388305/1134564410652885002

Suggestions for future

Here’s some things that we should (probably) do in the future

CRSF instead of SBUS for RC

Using CRSF instead of SBUS means that we can’t use the RCIN port, but instead connect to a serial port (TELEM 1/2/3/4).

This gives us a few advantages, the biggest one being redundant telemetry over RC link. We noticed often that the RC Link was more reliable than the airport link, and having the ability to get telemetry back from ardupilot and running a Yappu script means that if our airport link goes down (more likely than RC), we still have the ability to view telemetry and fly the drone (especially verifying things like correct flight mode - RTL).

True diversity or PA/LNA Equipped RX

A receiver with a PA/LNA will have more telemetry output power (up to 1W), meaning that it’s less likely for airport LQ to degrade (especially since airport is 90% Air → Ground). It is common to run TX modules as RX for airport.

Diversity receivers help protect against null zones and interference that may be caused by the angle/position/rotation of the drone. Highly recommended and not significantly more expensive than existing RX’s.