As for the foam, I transplanted the complete soft-mounted FC “tower” to the new frame. On F405-CTR, the barometer is on the bottom of the FC, and I’m pretty sure I put some foam there when I originally mounted it a few months ago.
It’s a bit difficult to check at the moment, but on the old frame I was even able to use Altitude and Position Hold with no problems (as long as no interference/glitch occured), so the baro must have been working ok then.
The AUW is 390 grams with 3S 1800mAh lipo. Even on the smaller frame with the tiny 1106 motors I was able to fly with a 3S 1300mAh battery.
I did see that baro curve but first the quad has to be able to take off. Could the dropping curve also result from the airflow of the props on the ground?
The motors are 2550 kV (https://betafpv.com/products/1805-brushless-motors) and supposedly “great for 4S power”, but even then the lift should suffice to take off on 3S? These are meant for racing so there must be lots of spare power?
Of course I could try 4S but it seems like a brute force solution to a problem that I still believe must lie somewhere else, so I’d rather like to solve that instead of just increasing the voltage.
I don’t think it lies elsewhere. BetaFPV’s own website suggests 4S with 5" tri-blade props. You have 3S with 4" props. Of course weight is a consideration but even eCalc shows insufficient thrust.
Ok, live and learn, I really didn’t expect it would make such a difference. And yes, my props are 2-blade only, probably adding to the problem. So 4S it is from now. Thanks!
FWIW you don’t always have to follow manufacturers guidelines. I have a sub 250g with BetaFPV 1404-3800kv on 2S with 5" low pitch props. It performs great. Not a speed demon by any means but a good flier.
TBH I didn’t give the whole thing much thought. The quad I’ve been using the most in the past 2 years is on a ZMR250 (“retro”) frame with 2306 1600kV motors and 2-blade 6" Emax Avan props and has never been running anything else than 3S. And I mostly use 4000 mAh on it. I’m pretty sure the calculator wouldn’t like that setup, but I never checked as it works fine.
Small-talk: The only problem on that quad was that it was my last INAV craft, and after some totally crazy “emergency landing” two weeks ago (which was actually more like an inexplicable random drift downwards), I’ve had enough of INAV oddities. It’s now grounded and waiting for AC conversion.
The motors were actually still spinning on the ground, as the quad apparently hadn’t even realized it had landed! Disconnecting a battery that way is not something you want to do twice…
The barometer problem on the 405 CTR is known, but nothing has ever been resolved. If you search the forum you will find other cases of incorrect reading. My 5 "quad 200 uses the 405 CTR and has a reading between 5 and 7m above the true altitude. Despite this it flies well, yesterday it flew 18 minutes with a 4000 3s lipo
I can absolutely confirm this. I now remember I had baro problems before with this quad, on BF, INAV and AC, with F405-CTR, even replaced the FC, no change.
The barometer on the earliest F405-CTR I owned and used on another quad always worked perfectly though. Maybe the problems were introduced in later revisions.
Could the dropping curve also result from the airflow of the props on the ground?
