Agopengps with servo motor - The Combine Forum
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post #1 of 8 (permalink) Old 05-09-2019, 07:36 AM Thread Starter
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Agopengps with servo motor

Hello,
I am a French farmer and I have a lot of interest in Agopengps.
I thank you all for the help and support provided, you are really great.

Unfortunately I have a lot of trouble with English.
I already have an operating system, but I want to drive a standard servomotor which itself will order a hydraulic distributor (manual originally).
I can not find on the forum if someone has already tried this solution.

I of course try to connect a live servo on the PWM output, the servo moves annarchically playing with the pid, but no good result.
Would you have any advice or arduino code to offer me?
In advance I thank you.

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post #2 of 8 (permalink) Old 05-09-2019, 12:00 PM
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So the servo motor has a normal 3 wire connection?
https://en.wikipedia.org/wiki/Servo_control


In that case the position is controlled not over the duty cycle but over the length of the PWM pulse.
So you need to choose the PWM parameters to generate the right pulse length for the desired servo position.

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post #3 of 8 (permalink) Old 05-09-2019, 12:25 PM Thread Starter
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ok for the wires 2 are used to feed the servo, only 1 son is used for the signal pwm
Can you give me a direction of the lines to modfier to change the pulse length please?
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post #4 of 8 (permalink) Old 05-09-2019, 01:05 PM
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What code are you using?
But in the end you have two possibilities:
  • Set PWM frequency to 100hz (every 10ms a pulse), and the duty cycle (assuming 8 bit) from 26 (-90) over 38 (neutral/0) to 51 (90).
    I think the easiest modification (before output calculate the new pwm: newPWM = originalPWM / 21 + 38 -- assuming originalPWM is -255 up to 255, if 0 to 255 you need so multiply with -1 in one direction), but limited resolution.
  • Change the frequency and duty cycle dynamically to generate a good signal. More work.
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post #5 of 8 (permalink) Old 05-09-2019, 01:19 PM Thread Starter
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Thank you for your help doppelgrau, it is late in France I test tomorrow.
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post #6 of 8 (permalink) Old 05-09-2019, 02:30 PM
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Hello Farmtek,

I also and try to run Agopen GPS, when I've time ...
For instance I'm a bit stuck with the RTK, particulary with the antennas.
For servo motor, you need to efresh the pulse at leat every 20 ms.
Positive pulse = 1.5 ms -> -45 (CW)
Positive pulse = 2 ms -> 0
Positive pulse = 2.5 ms -> +45 (CW)
Do you have completed the whole system, is it working well ?
Best regards from France
Where are you from ? me close to Arras
francois
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post #7 of 8 (permalink) Old 05-10-2019, 04:51 AM Thread Starter
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thank you francois I will test in the WE.

for the part RTK I use chips UBLOX neo M8P and F9P associated with Xbee sx 868 (authorized in France) at home it will be the xbee pro 900.
The antennas for the M8P are talysman TW3742 L1, for the F9P I use antennas aliexpress L1 / L2 / L5 which costs 130 and works wonderfully
I made my boxes in 3d printing
If interested I will join you photos and links
p00qwerty likes this.
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post #8 of 8 (permalink) Old 05-14-2019, 03:58 AM Thread Starter
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Unhappy

I have several tests but still impossible to directly control a servo motor with the PMW signal of the arduino.
Someone already try?
I can not find the lines to modfier in the arduino code ...
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