boards. As a project engineer, I used
to sign off drawings with a note, “Do
not scale drawing.” If a drawing had
a missing dimension, the machinist
had to call the mechanical engineer
to correct the drawing so that a bad
part would not be made. If you have
a good 1/1 scale print, then
dimensions may not be necessary.
The second optimum layout is
shown in Figure 2. The best design
used a 55 degree arc for the cam. If
you use 60 degrees, two lights will
be on at the same time. The idea is
to have one light turn on when the
other goes off. If your cam has two
lights on at the same time, it is easy
to sand the corner off the cam to
allow fine adjustment on the light
timing.
I added a toggle switch in series
with the motor power line; the user
can stop the motor movement so
one light might be on all the time.
The mechanical design was
the least expensive of all the
controllers because I was able to
find a surplus 50 RPH gearmotor
for $1.89 (Resource 2) and the
limit switches for $0.75 each
(Resource 3). I also found a 12 x
12 x 1/8 inch plywood board at
Tower Hobby for $2.98.
The cam can be made from
this plywood plank or you can
use a 1/8 inch piece of clear
plastic to fabricate the cam. Using
limit switches solves the current-handling problem while providing a reasonable cost to
implement an effective circuit.
The TurboCad 18 dimensions for the mounting holes
are shown in Figure 3, Figure 4, and Figure 5.
March 2015 33
■ FIGURE 4. Controller board installed in traffic light assembly.
■ FIGURE 5. Schematic of traffic light wiring.
ITEM QTY PRICE TOTAL SOURCE
Limit Switch 3 $0.75 $2.25 www.allelectronics.com/make-a-store/item/SMS-309/10A-SNAP-ACTION-
SWITCH/ 1.html
50 RPH Gearmotor 1 $1.89 $1.89 www.surpluscenter.com/Electric-Motors/AC-Gearmotors/AC-
Gearmotors/50-RPH-115-VAC-INLINE-GEARMOTOR-10-958-A.axd
Mounting Board 1 $0.50 $0.50 1/8 plywood board from local hobby store — use to also make cam
Lugs 9 $0.16 $1.44 www.newark.com/molex/05-06-0301/unknown/dp/54H5270
Power Cable 1 $2.49 $2.49 15 foot extension cord from local hardware store
Motor Switch 1 $1.25 $1.25 www.allelectronics.com/make-a-store/item/mts-4/spdt-on-on-mini-toggle-
switch/ 1.html
TOTAL $13.82 Prices subject to change without notice. PARTS LIST
