Photo 1. DigiMix3 connected to a
Victor 883 and a potentiometer.
Photo 2. Limit switches control
up and down travel.
motor shaft. That connects to an
analog input. The signal to the
Victor 883 is driven so the position
of the lifter is equal to the position
of the transmitter stick.
With the R/C input connected
to the gear channel, it can be made
to go up fast and down slow by
modifying the travel adjustment.
This requires the least amount of
attention during a fight. The switch
is up or down. Connected to the
rudder channel, it can be controlled
as desired. This requires more
splitting of your concentration while
Programming is done in
Assembly or C. Assembler requires
very intimate knowledge of the
details of the chip. It makes the
fastest and (hopefully) best
performance code, but is not for
beginners. C is a higher level — like
Basic in some ways — and is easier
(for me at least). Performance may
not be as good, but it gets the job
I have Employed
prototype board. The control boards
connect between the RX and the
Victor 883. Photo 1 shows a typical
For the traverse with digital
limits, the switches are connected to
digital inputs for max up and max
down limitation. The R/C command
from the gear or rudder channel is
used for input. If the command is
positive and we are not on the up
limit, the signal is retransmitted.
When the up switch is tripped, a
neutral pulse length is output
stopping the motor even if the
transmitter stick is still at full
deflection. The mechanical limit
switches are mounted at the ends of
travel. Photo 2 shows limit switches
operated by cams.
1. Microchip PIC12C508. Made
traverse with digital limits. Works
well. It is an eight-pin chip that was
programmed with the PICStart
programmer and programmed in
Assembly. It works well, but it is not
easy to program for beginners to
microcontrollers. If I were to
continue with the PIC, I would use
the PICit3 programming device that
leaves the chip on the project board
while programming and debugging.
It is possible to program in C but I
never got that far with it.
Programming tools are not high
priced, but they are not free.
2. Motorola 9S12C from
Technological Arts. Made analog
28 SERVO 02.2011