I recently created a project that involves the control of three SG90 servo motors. I started off by controlling this through the 5V output pin of the Arduino Uno, with the Arduino powered through the barrel plug with a 9V mains power supply.

However, the servos couldn't perform the full 180° sweep, it would appear to be due to the high torque at the end of the motion for my application.

I then switched to powering the servos separately to the Arduino using four AA batteries in series. I now had no issues with the servos stalling and could perform the full sweep.

I am not sure why this is though?

Four AAs in series will result in 6V, which is not that different to the 5V Arduino output pin? And it seems the current is the issue with servo stalling? and surely the number of batteries makes no difference to this as connected in series it stays the same? Is the current of the AA battery just higher than the 5V Arduino output pin?

Any help would be greatly appreciated, I'd really like to have a better understanding of this.

  • How much current does each SG90 servo draw? How much current can the Uno 5V regulator provide?
    – VE7JRO
    May 2 '20 at 14:26
  • @VE7JRO I'm unable to measure the current directly but from some measurements I found online it appears the typical current during operation of the servo is 100-250mA with a stall current of 360mA. It appears the voltage regulator can get up to 800mA if pushed to the limit. Please note all the sources I got these values from may be inaccurate.
    – FEA42
    May 2 '20 at 14:36
  • Here's some info on the SG90: arduino.stackexchange.com/a/49755/37523 I'm not sure what type of voltage regulator on your particular Uno, but heres some info on that: arduino.stackexchange.com/a/43894/37523
    – VE7JRO
    May 2 '20 at 15:27
  • For controlling more than one/two max servo you should use a motor shield (h-bridge) or something like a PCA9865 board with external power supply. You get funny effects with three servos attached to the UNO when trying to do syncronized sweeps or high torque at the same moment in all three servos. Invest in that hardware, if there is enough Amp (1.5A and up depending on the num of servos) you could use a single PSU for both. May 2 '20 at 16:26

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