333 Hz servo motor

[Oliver Kan]

Hi Guys,

I want t o replace the 40 Hz servos currently used on my udb to new ones

having a frequency of 333 Hz.

what parts of the code should I change ?

Thank you,

Oliver

[Guy-François MESNIL]

Hi Oliver,

The answer to your question is easier than the passive buzzer subject!

Basically, MatrixPilot is designed to use historical servo command for modelism : Up to hight servos are controlled with successive pulses of one to two ms sent every 20 ms.

If you try to send this serie of 8 pulses at 333 HZ you have not enough time in the frame of 3 ms.

So it is needed to change the servo out principle.

In the multicopter world , you need to command each motor at high rate, typically 200 Hz.

For my quad, I re-use the servoOut.c written by Mark Whitehorn.

You can find it in the branch MatixPilotMulti: https://github.com/MatrixPilot/MatrixPilot/blob/MatrixPilotMulti/libUDB/servoOut.c

He opted for the OutPut Compare capacity of the microchip microprocessor instead of the classic PWM.

Mark made the job during a previous version of UDB PCB (UDB4 if I remember).

I am not sure that his code is compatible with the UDB5.

If you have a doubt, you could have a look to my own servoOut.c https://github.com/Jeffem/MP5_QuadCopter/blob/master/libUDB/servoOut.c

This version is uptodate for UDB5 and MatrixPilot version 5.

You replace the normal servoOut.c by the MarkW's code and define the constante ESC_HZ to 333 in the options.h and GO!

Regards,

gfm

[ben levitt]

It should be compatible with the UDB5 and UDB5mini just fine, as they just changed the IMU sensor and IMU reading code.

Ben

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[Roby]

Hi Guys,

What are the benefits of these 333Hz servos?

Do they require extra power? So less battery life?

Roby

[Riccardo Kuebler]

Hi Roby,

those servos are meant especially for helicopters tail rotor, where a very high speed and responsiveness is desired to follow heading gyro.
Seems they have a really narrow deadband too.

Here are some more infos:
https://lmgtfy.com/?q=333hz+servo

I can't see any use in fixed wings. Even for very fast planes there are plenty of speed servos at 50Hz.

Any digital servo requires high current as they are capable of very high holding force.
So I can only guess that power supply has to be adequate.

Best regards,
Ric

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[Guy-François MESNIL]

Hi RIC,

My fist reaction about the interest of rated at 333Hz the servos was to refer to the time constant of the load and at the heartbeat of the controller.

But, looking at the literature before to answer, I found this artcle :

https://www.rchelicopterfun.com/rc-servos.html

The author confirm what you said!

It was not so evident at the first glance!

Thank you very much,

ragards,

gfm

Note for Oliver : If you use the MarkW servoOut.c, dont forget that the constant ESC_HZ defines the common rate for all servo outputs! 

Le jeudi 13 février 2020 10:29:45 UTC+1, Oliver Kan a écrit :