David Olson wrote:

> This idea is much more simple - 1 servo driven from 1 rheostat.

  The simple answer, is to use a standard 7555 (CMOS 555) circuit

  +6V o----+--------+------+
           |     ___|______|___               C  = 15nF
           <    |   8      4   |              R1 = 220k
        R1 <    |              |              R2 = 8k2 in series with
           |    |              |    |\             10k control pot
           +----|7            3|----| o--o Out
           |    |              |    |/
           <    |              |   Inverter
        R2 <    |    7555      |
           |    |              |
           +----|2             |
           +----|6            5|--+
           |    |              |  |
        C ===   |              | === 100nF
           |    |              |  |
           |    |___1__________|  |
           |        |             |
  Gnd o----+--------+-------------+

--
  Cheers,
        Paul B.