Andy, I'm also hacking a Radio Shack R/C car to turn it into a robot. The
best way to control the motor is to use an H-Bridge. There are many variants
and several things to consider. The following links have a lot of info
and/or links to other sites.

      Portland Area Robotics Society. Links to many sites.
      http://www.rdrop.com/~marvin/

      Chuck McMannis. Good theory and both Bipolar and MOSFET H-Bridge ckts.
      http://professionals.com/~cmcmanis//robotics/servo.html

      Bob Blick's site with a good Bipolar-based H-Bridge project.
      http://www.bobblick.com/bob/projects/

      Good theory with circuit examples of different types of h-Bridges.
      http://www.cadvision.com/blanchas/hexfet/

      James excellent Techref site with links and PIC code examples.
      http://techref.massmind.org/

   As far as my robot, I used a modified version of Chuck McMannis' H-Bridge
using N-Channel MOSFETs with built-in diodes (see link above). Since the car
has both 12V and 6V for the motor, I didn't have to hassle with a charge
pump. It uses a quad opto-isolator controlled by a 16F876. I hacked the
motor shaft to add a Hall-Effect sensor for a tach. So far it goes forward
and backward with some intelligent (PID) control and has bumper switches and
an IR proximity detector. This is a spare-time project...

   - Tom

At 08:58 AM 11/7/00 -0500, Andy Kelley wrote:
>Hello,
>
>I have an RC car that does not have a radio and i would like to make
>it into a roving robot like thing.
>
>I am stuck with this:
>how do I control a motor from a PIC using one side of the motor tied
>to 1/2 rail(2.5v) and either grounding or connecting Vcc to the motor.
>Now is the problem:
>
>I dont know how do this and I have already destroyed a few 2n222's
>
>the motor draws 6/10 of an amp.
>
>@ 2.5 volts that is 1.5 W.
>
>I tried a fet like this
>
> -/\/\/\/\- Gate
>
>
>Source
>__|_
>/  /  /
>
>Drain - motor - 2.5v
>
>and all it did was make the motor spin in one direction.
>
>Also i have another motor i need to drive at full 5v so i need to
>reverse both wires on the motor if i want to go in reverse
>
>How can i do this???
>
>Thanks
>Andy N1YEW


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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