🚀 go-pugleaf

Robert,
  You want to control a model car with a 68HC11. You want the normal
  transmitter to control the car most of the time but the HC11 can
  "Take over" control whenever it wants to.

  Here is my suggestion:

  1)  Buy a "real" Radio-controlled car.
    - Get a two channel car. One channel for steering and one for throttle
    - A cheap radio will do fine.
    - Make sure its a standard type RC radio. Futaba is what I use.
      No funny business here. If you get a radio that can have different
      servos plugged into it you are on the right track.
    - You can get a car with the radio included. It will be cheaper.

  2)  The car's two servos are run by one digital signal each.
    - It's a standard 0 to 5 Volt pulse. The width of the pulse determines
      the position of the servo. The pulse repeats at a particular rate.
      The pulse is pretty easy for a HC11 to produce.

  3)  Run the servos like this: (One channel as an example)

      +----------+
      | Radio    |
      | Receiver |
      +-+--------+                                   +------------+
        |                                            |            |
        +-------------+                              |  Servo     |
                      |        +---------------------+            |
                      |        |                     +------------+
                      |        |      
              +-------+--------+-------+
              |       I        O       |
              |       C        C       |
              |       1        1       |
              |                        |
              |     MC68HC11           |
              +------------------------+


      Here's the idea:

      The HC11 measures the pulse width on it's IC1 line.
      The HC11 produces pulses on it's OC1 line to match the input
      When the HC11 needs to control the servo it will modify the
      pulse going out the OC1 line to be the desired duration.
      When the HC11 no longer needs to control the servo it goes back
      to duplicating the IC1 pulse on OC1

                          -Alan Kilian

-- 
 -Alan Kilian           kilian@cray.com 612.683.5499 (Work) 612.721.3990 (Home)
  Cray Research, Inc.   655 F Lone Oak Drive, Eagan  MN, 55121 
                        "It's based on actual math". -Dilbert