DC MOTOR DIRECTION CONTROL

[CHARLESCRANFORD]

I AM WANTING TO START A SMALL 1.5-3.0V D.C. MOTOR BY SPINNING IT. IS THERE A SIMPLE WAY TO DO THIS? AN EXAMPLE WOULD BE TO HAVE A MOTOR HOOKED UP TO A MODEL CAR WHEEL SO WHEN THE CAR IS PUSHED FORWARD, IT WOULD MAKE THE MOTOR START DRIVING THE CAR IN THE FORWARD DIRECTION. WHEN THE CAR STOPS, THE MOTOR WOULD STOP. LIKEWIZE, IF THE CAR IS PUSHED IN THE REVERSE DIRECTION, THE MOTOR WOULD START IN THE REVERSE DIRECTION.
I HAVE A SMALL AMOUNT OF ELECTRICAL EXPERIENCE. I WAS THINKING THAT THE CURENT GENERATED BY A SPINNING MOTOR WOULD BE ENOUGH TO ACTIVATE A TRANSISTOR THAT WOULD SWITCH THE POWER FROM A BATTERY TO MAKE THE MOTOR SPIN IN THE REQUESTED DIRECTION. IF SOMEONE COULD HELP ME WITH THIS, IT WOULD BE GREATLY APPRECIATED.

 

[jbartos]

Suggestion: It will be much easier to control your motor via standard motor control circuits and control devices. Your concept could work; however, it is not used since it is not that practical.

 

[DrivesGuy]

Well, I was thinking about this one, and it occurred to me that a small problem exists. The voltage generated by the motor will be of the opposite polarity to the voltage needed to drive the motor. So, there would have to be a switching scheme in addition to the "transistor turn-on."

And you would have a slight problem with the turn off when it "stops" because that would be a zero crossing of some sort when the "push" and "drive" switch. You hit those when you change polarity. Add a switch to disconnect the source (recognize a "stop&quot, maybe on the "bumper," or possibly some type of delay to compensate for the zero crossover time. And don't forget to do something with the "turn on" transistor since the polarity to its base/gate will also switch.

I was thinking, instead, of a shaft-mounted magnet of some sort with a timer, once the RPM's get to a certain level, turn on the supply, and turn it off when the RPM's decrease again. I think a 555 timer would work. The shaft-mounted magnet could just be a second small motor that is always used as a generator. Or it could be part of a Reed Switch assembly and the pulses used with the timer. There would be less drag (read "battery drain&quot this way.

Just some random thoughts concerning this toy.

 

[jbartos]

Suggestion: This appears to be more link to robots. There are some built and working. I mark my comment by <<

Well, I was thinking about this one, and it occurred to me that a small problem exists. The voltage generated by the motor will be of the opposite polarity to the voltage needed to drive the motor. So, there would have to be a switching scheme in addition to the &quot;transistor turn-on.&quot;
<<Generally, if the voltage is of reverse polarity, then it is usually inverted by the voltage inverter.<<

And you would have a slight problem with the turn off when it &quot;stops&quot; because that would be a zero crossing of some sort when the &quot;push&quot; and &quot;drive&quot; switch. You hit those when you change polarity. Add a switch to disconnect the source (recognize a &quot;stop&quot, maybe on the &quot;bumper,&quot; or possibly some type of delay to compensate for the zero crossover time. And don't forget to do something with the &quot;turn on&quot; transistor since the polarity to its base/gate will also switch.
<<Perhaps, a Stop ...Start with a pneumatic piston or electronic delay could be considered.<<

I was thinking, instead, of a shaft-mounted magnet of some sort with a timer, once the RPM's get to a certain level, turn on the supply, and turn it off when the RPM's decrease again.
<<This is usually sensed by a speed encoder that senses speed and sends the signal to speed controller. However, the toy may need a great simplifications because of weight of those off the shelf devices.<<

I think a 555 timer would work. The shaft-mounted magnet could just be a second small motor that is always used as a generator. Or it could be part of a Reed Switch assembly and the pulses used with the timer. There would be less drag (read &quot;battery drain&quot this way.
<<Again, the encoders, or tacho dynamo are there.<<

Just some random thoughts concerning this toy.
<<There appears to be many possibilities depending on many factors. I think that a lot of experimenting will need to be done.<<