Hi guys. Please I need help.
So I made my new robot to be controlled by Arduino. Since I am a beginner, I have limited resources so I had to improvise to make it happen. I faced a problem with the power supply as I do not have 12v battery for my robot.
My project is as following:
Four wheel robot with four DC geared motors linked to arduino via motor drivers (2 pieces, each piece operating two motors) .
Regarding the battery, I have linked two batteries (9v each) in series and I got 18v batterie. Between the battery and the motor drivers I used a step down module in order to get 12v. Then I powered Arduino with a separate 5v power supply and I shared the ground between them all.
Now the problem I am facing is:
When I measure the voltage for the both motor drivers while the Arduino board is off, I get 12v for each. However, when I turn on Arduino board, and I measure the same, I get only 3.7v for each motor driver. I couldn’t understand what is exactly the issue and what does the Arduino board has to do with this sudden drop down voltage as it has its own separate power supply! Please anybody can give a hint?
This is the problem. 9V batteries are not suitable for motor circuits.
For 12V, try 8x AA or C batteries. If using NiMH rechargeable, you may need 10x batteries.
Thank you for the reply. But as I mentioned, I linked two 9v batteries together in series and I got a battery with almost 17v. Then I used a step down module to control the voltage and I regulated it to 12v . Does this still cause a problem? Or do you mean that the 9v batteries are not suitable in general whether we changed their voltage by linking them together or not?
Yes.
Yes, exactly. Voltage isn't the problem. When selecting a battery you need to consider both voltage and current. 9V batteries can provide only a very small current. Enough for a smoke alarm. Not enough for motors. If you try to pull too much current from a battery, it's voltage will drop
Okey I got it. My mistake I did not measure current 
. Thanks for assistance
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