Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422
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Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by Labomedia on Fri Nov 30, 2012 7:38 pm

Hi...

We're trying to use 50 servos HS-422 from Hitec with 4 Adafruit 16-Channel 12-bit PWM/Servo Driver.

First, we tried with only 1 Adafruit card with 16 servos driven by a RaspberryPi with Adafruit distribution and servos are becoming mad after a very short period (servral seconds)...
Basically, they're shaking but all in the same way...

If we kill the python script, they're still shaking...
If we unplug the Raspi, they're still shaking...
If we turn of the power of the Adafruit card, they're still shaking...
If we turn of the power of the servos, they stop shacking (of course), but if we turn the power on again... they're starting shaking in the same way...

After a while, everything becomes normal (I mean, they stop shaking and we can make other tests).

The pb seems to be stronger when we try to use multiple servos at the same time.
If we put a time.sleep between action, it seems to work, but, every time, after a while, the issue reappears...

For info, if we try to use only one servo, no matter where it is plugged on the car, it works...

What did we miss ?

What should be the C2 value of the capacitor on the Adafruit board in our situation ? (do we need one ?)
Has anyone already encountered the same problem ?

Thanks for any advices...

Cheers...

Labomedia's team
(sorry for our english)
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Re: Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by adafruit on Sat Dec 01, 2012 10:14 pm

how are you powering the servos?
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Re: Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by Labomedia on Sun Dec 02, 2012 7:20 am

Oh oh oh... :lol:

We've made some (stupid) arithmetics based on the information that each servo needs 100-150 mA on rotation...
As we don't need more than 10 servos at the same time, we decided to use a 3A-6V...

Last afternoon, we've tried with a 32A-5V... and it has worked fine with 8 servos synchronized... :D

We wanted to test with the 4 boards and the 50 servos before "solving" this thread...
We're going to try today...

We'll let you know our result...

Thank for replying us on a sunday... :wink:
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Re: Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by adafruit_support_bill on Sun Dec 02, 2012 8:26 am

each servo needs 100-150 mA on rotation.

That is a reasonable estimate for an HS-422. But there is typically a spike in current demand at startup, so the instantaneous current demand with multiple servos moving at the same time can be quite high. If you run into problems with more servos connected, you can try adding some capacitance on C2 to help handle the startup surges. The value is not critical, but I'd use 1000uF or more.
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Re: Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by Labomedia on Tue Dec 04, 2012 10:43 am

Well...

The installation is working fine... :D
And we don't use any capacitance on C2.

Here is a little vidéo.

Thanks for your help. :)
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Re: Adafruit 16-Channel 12-bit PWM/Servo Driver issue with servos HS-422

by adafruit_support_bill on Tue Dec 04, 2012 10:46 am

Very nice! :D
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