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I am using two motors ( from old two drill machines - same kind, these are 3.6v motors ), connected to arduino + arduino motor shield seeed studio v2.

I tried to use 18v/1.2a battery that was laying at home (from old machine ) what I have noticed is that motors are running for 3-5 seconds than stop, one of the red lights start blinking in the motor shield, then it stops for 3-5 seconds then it works again and loop.

Note: the motors are working when I connect them directly to 4.5 or 6v battery. But when I try to assemle everything , it doesn't work.

I tried 14v battery I noticed the same thing ( but slower, and this is something logical ), the battery of 9v don't make any move ( even by powering th arduino alone (using 9v) and the motors alone (9v) ).

What are things that I should consider here, any thoughts.

What did I miss? And what kind if battery should I use ??

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This is a hard question to answer without knowing a few more things about your components.

  1. If you run the motors at 3.6V, or close to that, how much current do they require? You could measure this using a multimeter in series with your motor and an about 3.6V power supply.

Since they run at a pretty low voltage, I'd guess the motors require quite a bit of current, or they're relatively low power machines. That's probably why the 9V batteries don't work. Regular 9V alkaline batteries can't provide much current.

  1. Is the red light blinking on your shield an overcurrent indication? Trying to run a 3.6 v motor at 18v is probably going to be bad for the motor in the long run (or not so long), and it could certainly result in a lot of current going through the motor driver and causing it to shut off.

One thing you could try is using your 18v battery, but running the motor at a very low duty cycle setting. Are you using the shield based on the MC33932? If so, it supports duty cycle control. Theoretically, you shouldn't exceed 20% duty cycle with an 18v battery (3.6/18=0.2 or 20%).

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    \$\begingroup\$ Overload of the motor shield sounds very likely. Motors from electric drills are designed as high-speed high-torque motors. They are not designed for efficiency at low speed or low load. It is quite likely to need many amps to get these motors running, and the more voltage the OP provides, the more current the motor takes. So the OP either needs to reduce the duty cycle (and torque/speed) or needs to get a stronger driver. \$\endgroup\$ – Michael Karcher Mar 7 '15 at 22:11
  • \$\begingroup\$ @PhilipOdom: Thanks for your answer. It took me some time to get a multimeter. I measured the current, and I found that the both are varying from 1.46A-1.47A, (I was surprised because you mentioned that i should find it high). I think it should be taken as 1.5A. what do you suggest now, what should I do?. The drill machine is small one (as big as a human hand). Any other suggestions are welcomed. \$\endgroup\$ – user3378649 Mar 8 '15 at 18:26
  • \$\begingroup\$ @MichaelKarcher Thanks for your answer as well. I provided details on what I found of what Philip requested. would you please shed a light on this, you might have something specific to recommend ? \$\endgroup\$ – user3378649 Mar 8 '15 at 18:28
  • \$\begingroup\$ @user3378649 This is 1.5Amps at 3.6 Volts while the motor is running. The startup current is likely much higher, especially if you run it at high voltage. For further help, please answer the question about the type of motor shield you are using. I was unable to identify the shield type just from googling for a blinking red LED on it. \$\endgroup\$ – Michael Karcher Mar 9 '15 at 0:21
  • \$\begingroup\$ @MichaelKarcher Thanks! I am using this shield (seeedstudio.com/wiki/Motor_Shield_V2.0), connected to two 200 RPM (3.6V/1.5A)motors. and Enable indicator is the one that is blinking. \$\endgroup\$ – user3378649 Mar 9 '15 at 16:09

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