This is a description of the hand built point motor that I use. I
believe that the original description appeared in a magazine some
20 years ago, and some improvements have been made.
The main basis for the motor is the use of a small electric motor to
drive a slider across a printed circuit board, as well as moving
the point blades. The slider and board enable automatic stopping
of the motor and automatic readiness for travel in the opposite
direction. In addition, my particular implementation allows for 3,
single pole, two way switches that are used to control frog
polarity, other point motors and any other related equipment.
If you choose to use this design, custom pcbs can be made for
particular circumstances. I have not made any custom boards, but
motors can be cascaded or run in parallel to provide additional
features.
I have not tried driving a crossover (two points) with one motor,
this would depend on the power of the motor and efficiency of the
mechanical linkage. I have preferred to link the two motors
electrically, so that one point is thrown first then the second
throws automatically. Complicated point arrangements can be
electrically interlinked to avoid conflicting movements.
Plastic sheet and strip, various sizes.
Surplus can motors; 6 - 12v according to supply voltage available
Surplus edge connectors, as available, I used S100 bus connectors.
3/16 inch brass rod, or metric equivalent
Threaded steel rod, I used 7BA, but the size is not critical
Single sided PCB for use as the slider
Phosphor bronze strip, for use as pick-ups on the slider, or
nickel silver wire, I used both.
Push fit plastic tube to connect the motor spindle to the
threaded rod, or other suitable linkage. I used telephone wire
with the wire removed.
Bathroom silicone caulk to mount the motor.
Miniature, two way, double pole switches, to control the motors,
as available.
Printed circuit board, as described later.
Jig, as described later.
The overall size of the motor depends on the Printed Circuit Board,
and this depends on the edge connector used, and the number of
switches incorporated onto the PCB. My printed circuit board was
about 2in square, and overall the motor assembly was 4.5in by 2.5in.
I used S100 bus edge connected, which are double sided and one
eighth inch spacing, and the main object is to make the motor
easy to remove and replace in case of failure. An edge connector
is not required. If the PCB is extended, wires can be soldered
directly to the board, but this limits the ability to change the
motor quickly. If edge connectors with closer spacing is used,
the boards will be smaller, and the slider may be more difficult
to construct accurately.
Three switches seem to cater for most situations, however there could
be situations that need more. If you need a 'lot' of motors, it
may be best to standardise on three, then cascade the motors or
run two in parallel. If you only need a few, then custom, hand
made boards may be practical.
I required 45 motors for my layout, so I standardised and used
cheap components as far as possible. However, to save a lot of
difficult work I had the PCBs professionally made. I produced a
mask with acrylic sheet and drawing tape, and the supplier etched
and cut the boards. The PCBs were also run through a solder bath,
this prevents the copper corroding and gives a better electrical
contact. Gold is recommended and not very expensive, but I do not
have any current prices. The supplier was most mystified because
there were no holes!
This is actually fixed to the underside of a simple board on short
legs. A mirror is placed underneath to demonstrate the unit.
Track and point are hand laid code 80 on PCB sleepers. Engine is
Mainline J72.
Last Modified: 1st December 2003