Robotics series page 1

Primary stall sensor.
Under normal forward drive conditions the motor current would flow from positive supply
through the series 2-6 ohm resistor causing a small voltage drop to be seen across it
than through motor and through its drive circuitry to ground.


(I'm so used to analyzing circuits with conventional current flow that it just sticks with me even when I'm explaining electron cuttrnt flow too)


Thus the robot moving forward, however when robot gets caught and can't turn
to the left or right. then the motors begin to stall. causing more current to flow through the series resistor making a large enough voltage drop around 2 volts which causes the mosfet to conduct current to the opto iso. which in turn sends a signal to the transistors to turn the reverse motor circuitry on so robot can back straight out turn and go forward again.

To prevent false triggering when motor current increasses during normal running, the resistor capacitor network is inserted between the opto output and the transistor switch input, to allow enough delay for the motor to recover when no stall is present.

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