I'm doing a floor cleaning robot project. I'm using a L293D shield and 3 motors 12V, whith a power source of 9V. The motors work normally, put when i put in the floor, they don't spin and don't move the robot. What could be the problem?
You need to tell us the specifications in a lot more detail.
What are the motors? What is their voltage and current rating?
What is your power source? What are its ratings?
A L293 Shield seems very inadequate for the power you are talking about...
12 V motor, 9 V source, a voltage dropping ineffective L293.You can't but fail. Measure the voltage at the motor when you expect it to run. How far is it from 12 V?
Welcome to the forum.
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http://forum.arduino.cc/index.php/topic,148850.0.html (http://forum.arduino.cc/index.php/topic,148850.0.html) then look down to item #7 about how to post your code.
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Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Your 9V supply, is it one of these?