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Is 24khz RPM filtering possible?

kutay

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I dont like the way my drone (emax tinyhawk 2 freestile) on 48 khz ESCs, it is very floaty. Is there a way to do rpm filtering on 24 khz ESCs? I tried jazzMavric firmware, even the ones that say "24" on them but still they make the sound of 48 Khz ESCs in the start up sequence. I would appreciate if you tell me what ever you know about this topic.
 

brettbrandon

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I don't have an answer to your question but just want to say, welcome to the forum...
 

coyote_dc5

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What benefit is there to adding bidirectional dshot to your build? Does it just reduce chances of desyncs or something entirely unrelated?
 

L0stB1t

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Hi kutay. Sure you can do bidirectional DShot perfectly with 24khz. Just don't use JazzMaverick firmware, there are problems with it lately. Pay a few bucks for JEsc licenses and you're good to go. I'm not sure if 24 and 48khz firmwares make different startup sounds, I think there's only a difference between BLHeli_S, JEsc and JazzMaverick sounds. Also I'm not sure if you'll notice a big power difference going from 48 to 24khz. I'm running 48khz on my 2.5" and 3" kwads, it's been a while since I tried 24khz.

coyote_dc5, bidirectional DShot sends the exact RPM of the motors back to the FC, which can use it to put some very precise gyro notch filters on those frequencies (and its harmonics). This results in less filtering delays which makes the PID controller react faster. This is good for tighter control and better propwash handling.

You can read all about it here: betaflight/betaflight . There are quite a few good tutorials on YouTube also.
 
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coyote_dc5

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Interesting, so basically you need ESC telemetry to do this? So what are dsyncs and prop wash exactly and are they linked at all?
 

L0stB1t

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Interesting, so basically you need ESC telemetry to do this? So what are dsyncs and prop wash exactly and are they linked at all?
Well as far as I understand, Bidirectional DShot is a "kind of" ESC telemetry that doesn't require an extra wire back to the FC. The ESC will simply send the current RPM (or actually the eRPM, which is the RPM multiplied by the number of magnets on the motor bell) back to the FC after every DShot command, on the same signal wire.

It won't give you ESC temperature or current draw information like "real" ESC telemetry with an extra wire would (How to setup BLHeli32 ESC Telemetry & Current Sensor - Oscar Liang).

A desync happens when an ESC can't figure out the motor bell position. Normally it can detect it by sensing the reverse current in the motor windings caused by the passing magnets (yup, the motor is a dynamo for a fraction of a second), but it can get confused for a number of reasons. The most common one is when you have a low Motor Idle Throttle Value set in BetaFlight; if wind and turbulence slow down the props faster than the ESC expects then it can lose sync. Simply increasing the Motor Idle Throttle Value by one or two percent can fix this because at slightly higher speeds the ESC has more power to keep the RPM constant. A better solution is to set up Dynamic Idle (betaflight/betaflight , "Dynamic Idle" the most useful Betaflight feature you never heard of) but it's more complicated to set up AND it requires Bidirectional DShot. So yes, this is where having Bidirectional DShot can help you prevent low RPM desyncs.

Propwash is the "dirty" turbulent air under your propellers. If you fly into it, you'll get all kinds of oscillations while the FC is trying to keep the kwad stable. You get it when flying fast forward and then suddenly turning around and flying back where you came from. Or when dropping vertically and applying a throttle boost. A well-tuned kwad (correct PIDs and low latency filtering) can keep the oscillations to a minimum, but it's better to learn to fly avoiding the propwash. Obviously the turbulent air can push the props and slow down the motor RPM too much, causing ESC desyncs...
 
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coyote_dc5

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Great explanation so thank you. If I could reward a gold star I would :p I'll follow those links tonight for home work too ;)
 
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