Can I run more than 2 servo motors smoothly, connecting their power to regulated limit voltage and signal wires to the digital pins of the arduino?

Question

Now my next project is going to be about Servo Motors and for that, I don't want to buy any shield or motor driver for Servos. So I have designed a circuit, to drive 12 servos at a time without any interruptions. I haven't got any Servos yet, well my order is shipped already...Keeping that aside lets head down to the connection..

The Screenshot was taken from a circuit designed by me at tinkercad.com.

Parts:

1. HiWatt Battery (Standard 9 volts battery blue and white coloured)

2. SG90 Servo Motor
   (6v 400mah max) (Resistance of each of them is 1.4kohm, when connected power and ground of multimeter)

3. Arduino (Required amp is 40*12)

The circuit Explanation:

1. The Orange wires of servos are signal wires connected to the pins of Arduino.

2. A 750 ohm resistor is connected to the positive terminals of each motor, from which, voltage is regulated for the motor.

3. The motor grounds have been connected to the ground of the battery.

4. Ground of Arduino has been connected to the ground terminal of the battery. So now, ground of the battery and the Arduino is same.

5. All the motors are connected in parallel connections with 750 ohm resistors at the positive terminal of each motors

So now my question is, How many servos will I be able to run when I power them parallel-ly using a standard 9 volts battery (HI-WATT, Blue and white one), if no, Which will be the best battery for doing it?

I need to run 12 Servos uninteruptedly.

Thanks for your precious time....

Answer 1

So now my question is, How many servos will I be able to run when I power them parallel-ly using a standard 9 volts battery (HI-WATT, Blue and white one), if no, Which will be the best battery for doing it?

Unfortunately: Zero motors with your current circuit. Maybe one motor with a better circuit and the same battery. Here is the explanation.

• You should ditch the standard 9V block battery. These batteries are made for low power applications (like IR remotes or smoke sensors) and cannot provide enough current for driving all those motors. They might be able to drive one servo, but still will be drained very fast. You should use a battery, that can provide much more current. Which battery you choose also depends on your other requirements. A series of AA alkaline batteries can give you enough current. Or you can directly buy a LiIon or LiPo rechargeable battery (including a fitting charger board). They can provide way enough current.

• You cannot just use simple resistors as voltage regulators. That just doesn't work for loads, that can draw a changing amount of current (like a motor).

  • The voltage, that the motor gets, depends on the current, that the motor draws. When the motors stands still, it will draw very little current. Thus the motor is getting the full 9V in that case. As the drawn current rises, the voltage will go down, until the motor gets not enough voltage to operate correctly.
  • The resistor of 750 Ohm restricts the current draw of the motor. Even when we (for the sake of calculation) treat the motor as a short circuit, the maximum current through the resistor with 9V will be only 12mA, so way way lower than the 400mA, that you stated in your question. You won't be able to move the motor much with that little current.
  • Even if you used a smaller value, you need to be careful with the current. I guess you are using standard resistors there, which typically have a power limit of about 0.25W. These are meant for rather low current circuits. With the 400mA @ 6V, that your motors need, you are in the region of 2.4W (that is not necessary the power for the resistor, just a value for you to see the relation). You can easily burn away a little resistor that way. When you need a resistor with a higher power limit, you need to buy one, which can handle it (and these are typically multiple times the size of a standard "signal" resistor and still can get very hot, when used in the realm of their power limit).

  Instead you should buy a proper voltage regulator. At that current, buy a switching buck regulator, as they are way more efficient than linear regulators. Which regulator you need to buy also depends on the voltage of the battery, that you choose. Be sure to buy a regulator, that can provide significantly more current, than we need in total for your circuit. This is important, because regulators are typically described with a maximum current, at which they already need extra measures for cooling. When you stay well below that, you can avoid thinking about fitting cooling for it.

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So , will it control the motors as good as 16 channel servo drivers?

Yes, it can. Though you need to think about how you are controlling the servos on the Arduino. The standard Servo library supports up to 12 servos with one timer. When you can change the library to use 2 Timers for supporting more servos, then you have it. You could also try to search for other libraries, which support more servos, or write your own library. I would say, using the driver would be simpler. The driver does not switch the power for the servos. It has a chip, which can output 16 servo control signals and is controllable over an interface like I2C or SPI.

If you want to use such a driver is up to you. You might find it more important to have as few electronic parts as possible.