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Running multiple high-current-draw servos from an Arduino
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Running multiple high-current-draw servos from an Arduino

by NullPointerException on Thu Feb 07, 2019 12:59 pm

Hello,

I'm on an FTC robotics team and I'm trying to retrofit one of our older robots with an Arduino instead of the stupid Android phone-based control system required for official competitions. I've managed to secure some of the legacy (pre-2015) FTC electronics from the Mindstorms NXT era such as the "HiTechnic DC Motor Controller for Tetrix" motor controllers and gotten them up and running with an Arduino Uno after (annoyingly) having to change the I2C speed to 9600 baud.

Unfortunately, I haven't been able to secure more than one of the "HiTechnic Servo Controller for Tetrix" servo controllers, so I was thinking about a more standard route, like using an "Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface", however I have a couple of questions:

  • Would the Adafruit controller work at 9600 baud I2C speed?
  • If not, do you guys stock another controller that could be used with the Uno through SPI or some other interface?
  • Would the Adafruit controller be adequate for powering 4-6 high-current-draw servos?
  • If not, could the issue be remedied by using one of these? http://www.revrobotics.com/rev-11-1144/

Thanks in advance!

NullPointerException
 
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Re: Running multiple high-current-draw servos from an Arduin

by adafruit_support_bill on Thu Feb 07, 2019 1:09 pm

The PWM/Servo Shield should work fine at the slower NXT bus speed. And it should handle 4-6 'typical' high-torque servos. If you are using something like 1/4 scale servos with even higher current requirements, you should consider something like the REV power module (or a home-made wiring harness).

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Re: Running multiple high-current-draw servos from an Arduin

by NullPointerException on Thu Feb 07, 2019 2:16 pm

adafruit_support_bill wrote:The PWM/Servo Shield should work fine at the slower NXT bus speed.


Awesome, great to hear that :D

adafruit_support_bill wrote:And it should handle 4-6 'typical' high-torque servos. If you are using something like 1/4 scale servos with even higher current requirements, you should consider something like the REV power module (or a home-made wiring harness).


Hmmmm. Ok, so just to clarify I would be using 4-6 of these "grade/caliber" servos: https://ebay.us/q0wgQM

Assuming that would be OK, the one other question is, what should I do for power? The robot will be running off a 12v 3Ah battery pack. Would this be a good choice to run the Arduino + Adafruit servo board off of? https://www.amazon.com/dp/B01CUA4KK8

NullPointerException
 
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Re: Running multiple high-current-draw servos from an Arduin

by adafruit_support_bill on Thu Feb 07, 2019 2:33 pm

The servo specs don't mention current requirements. At 291 oz/In @6v, I'd estimate the stall current to be in the 3A range. Normal operating current is probably around 1.5-2A when moving under load.

4-6 of them going at once would be pushing the current carrying limits of the traces on the board. You probably would want to use something like the REV power module.

The 10A DC/DC converter is probably sufficient - unless you expect to be pushing all 6 servos hard simultaneously. In that case, you may want to go with the 20A version.

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Please be positive and constructive with your questions and comments.