#25Hz for extreme long range, does it makes sense ?

11 messages · Page 1 of 1 (latest)

trail needle
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Yo guys, recently switched my 1.8m glider from CRSF to play around with ELRS 0.9.

I’m hitting pretty incredible range and flight time with this thing in thermals and I was wondering if running the lowest packet rate possible would make sense on such a platform ?

I don’t need crazy low latency, <30ms would be plenty, so I’m thinking running the lowest packet rate to run it as easy as possible on the hardware (power consumption, heat etc) seems like a win-win situation.

I guess I’d have to play with RC Smoothing quite a bit to get it to work well because for now it’s very stuttery, but I’d be curious to hear your opinion on wether it’s a good idea or not.

Thanks !

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rich aurora
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What do you mean with ELRS 0.9? Current latest release version is v3.4.3 https://github.com/ExpressLRS/ExpressLRS/releases/tag/3.4.3 with v3.5.0 being in second release candidate phase: https://github.com/ExpressLRS/ExpressLRS/releases/tag/3.5.0-RC2

Long range flying is mostly calm flying backed up by stabilizing autopilot to smooth out any signal loss phases, thus one does not need a high update rate at all. You can pick the lowest update rate for the ELRS system and that is already IMHO more than enough.

If you want to further optimize your antenna setup, you could consider moving the antennas to the tips of the wings as far away from (other) cables, carbon or other RF shielding materials, as possible. Try to match one of the antenna orientation with the ground station antenna orientation. Using a directional ground station antenna at an elevated location will also give you a great increase of range (typically combined with AAT and/or a relay station).

trail needle
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0.9Ghz, 900Mhz. Gliding and thermaling does require a decent refresh rate because a lot of manual flying is involved unlike hitting cruise mode on a wing and waiting some hour before hitting RTH.
Alright thanks for your answer, I’ll try a few settings and figure out what works best

unkempt gulch
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It can make sense if you want long range.

jolly jackal
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99.9999% of users should not use 25Hz

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It has other downsides that make it bad for, well, anything else.

simple badger
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Is that plane big enough for a flight controller and a camera?

jolly jackal
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@trail needle for your use case, the lowest I'd go is 100Hz Full mode with 16ch/2 channel setting. That gives you exactly 50Hz (which is what your servos will want) and range enough to exceed 100km easily if you do want it.

grand gust
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Btw just so you know the way to compute the maximum range gains you go to https://www.expresslrs.org/info/signal-health/#rf-mode-indexes-rfmd
Note down « Sensitivity Limit » and go ask chatgpt this;

At 914Mhz using FSPL at 250mw transmit power and -120dBm minimum what is the maxium range you can get ?

Compute using python and proper speed of light.

Replace 914Mhz with 868Mhz or 2.4Ghz as needed.
Replace 250mw with your TX power.
Replace -120dBm with the value you noted.
You can also subtract your RX and TX antenna gains if you have any (so if you are using a 2dBi antenna on your TX you write -122dBm since the table gave you -120dBm).

The maximum theorical distance at 50hz is 412km at 25hz is 655km so unlikely to be significant.
Note that this distance is in free space, obstacles in your way, particularly the earth curvature is gonna cause issues before any between 50 or 25hz will reach their limits.

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The 3dBm difference is also marginal, you could do better with a good 5dBi antenna and 50hz (this is make the signal more directional along the horizon, but I doubt you are flying your plane orbit level highs in the first place).
Also nothing stops you from having both a 5dBi antenna and 3dBm gain from 25hz.