As I have previously described the railcar ran forwards and backwards along the same piece of track with magnets placed on the track to make it stop and then go in the reverse direction at each end. I was aware of the fact that this ?reversing manoeuvre? was very unrealistic, with the prototype being turned at each end via a turntable.
A successful hunt through the garage for appropriate wood scraps and electric motors, etc. prompted me to have a go at upgrading the system. It had to be automatic in operation, and thus based around a delay timer, reed switch and magnets, similar to the railcar. This would also have to be modified slightly to fit in with the turntable cycle.
The actual turntable was roughly cut out by wood saw and then made round and true using a sanding disk with a suitable shaft at the centre point of the table.
The centre bearing was originally only a hole drilled in a piece of aluminium, but after some use (and wear!) this was replaced by a small ball bearing race. The underside of the turntable also has two contacts connected to the reed switch.
The table is supported by three equally spaced old-style curtain rollers running on short axles mounted across holes drilled in the base board. Two wiper contacts connect with the reed switch at each ?stop? location.
The electric motor (ex photo copier I think) was ideal, having built-in reduction gearing and a suitable output wheel. Drive to the turntable is via an idler disk, with suitable sized O ring, which is spring loaded to maintain pressure for operation. The direction of rotation is such that under load, the idler tightens. A good idea I thought, except for when things get out of alignment, hence the improved centre bearing.
The ?Ladies & Gents? building conceals the main drive motor and circuit board.
The overall operation is as follows: Railcar arrives at turntable, passing over a magnet mounted just before the actual table. This magnet closes the reed switch under the car which turns off the power to its motor and starts a delay timer (approx. 50secs).
Momentum carries car onto the table where a magnet mounted under its front axle closes a reed switch located at the centre point of the table.
Car stops before running off end of table (ideal situation). This switch starts a 555 delay timer (approx 15secs) after which power is momentarily applied to the second electric motor. This ?pulse? winds a cord up and pulls the ?latch? lever out from the table and also starts the main motor via the micro switch.
The table rotates 180deg (takes approx 12secs) and stops when the ?latch? lever returns to a home position in one of two recesses in the circumference of the table. These are slots filed into pieces of aluminium plate. The micro switch turns off the motor drive at the same time. After the balance of the original 50secs has expired the car starts again and leaves the turntable passing over the magnet. This is ignored by the car because of a second delay timer (4secs) inhibiting the reed switch circuit.
Having now turned the car around, rather than going through all of this construction a second time, I opted for the easier solution of putting a ?balloon? loop at the other end of the track. The 12 pieces of a 4? diameter circle are arranged as shown.
I have made a symmetrical, spring biased point for this purpose.
Intermediate station stops for the railcar can be organised by placing more magnets on the track.
Other aspects of the project include, increasing the stop time of the railcar from 12 to 50secs, and changing the logic so that it does not reverse direction. I have fitted a two-way switch inside the railcar to select between the two modes of operation. (shuttle or turntable).
So far the whole setup has been very reliable with few problems.
I do have to adjust the position of the turntable magnet periodically, moving it closer to the table, to compensate for the decrease in railcar speed, and resulting momentum, as the batteries expire.
I could come up with a circuit diagram if anyone is interested.
