Friday, August 23, 2013

Anton's 75' turntable motor and gearbox replacement

I have not been happy with the noise and operation of the motor/gearbox combination supplied in the Anton's 75' turntable. For some time I have been contemplating replacing the motor/gearbox with a combined 12v DC motor and gearbox available from Jaycar Electronics. In the intervening period I was given a similar motor/gearbox from a friend so I recently pulled the original motor/gearbox out and did a simple replacement. I retained the pulley system and the increased torque available from the new motor overcame the turning hesitation that was sometimes evident with the original motor/gearbox.

The current Jaycar motor/gearbox ($19.95) should be quite OK to use although the hole in the small pulley will need to be enlarged with a 4mm or No.18 or 19 drill as the Jaycar gearbox has a 4.2mm dia. shaft. This motor is 12v DC and runs at 36RPM so when wired in using the original motor wiring including the capacitor across the motor terminals, the trim pot on the existing circuit board can be used to adjust the table turning speed. The existing pulley ration of course means that it should run nice and slow.

As can be seen from the photo below, I simply used a wire twist tie to hold the new motor in place, the wire passing through the original motor mounts. I will replace this of course with something a bit more professional. The original set up has a nylon adjusting screw that pushed the bottom of the motor/gearbox away from the mounting frame thereby tightening drive belt on the small top pulley. I managed to lose the small nylon screw but had a suitable metal replacement (2mm metric bolt I think). The new motor wanted to slip sideways off the tensioning screw so I made a 'saddle' from a piece of brass tube to which I soldered a larger nut, the end of the tensioning screw sitting inside the nut. While the nut can't be seen in the photo a little study will show why it is required. This saddle could be made from a piece brass sheet.

The outcome was a very quiet drive with enough torque to eliminate the turning hesitation (slipping/almost stopping at times when turning) of the original drive.

Here is a video of the drive in action, the video camera is sitting on the baseboard and the drive is under the turntable, you have to listen very carefully to hear anything in the video. The drive does make a little noise in operation but nothing like the high pitched noise of the original.

Friday, August 16, 2013

Modification to the Weight of an SDS Models Rail Tank Car

During a recent operating session we had trouble with multiple derailments of an SDS tank car which was placed in the middle of No.81 Goods which was being banked from the rear. The driver of the bank loco has worked this train many times so was not the reason for the derailments. It got so bad that the offending tank car was removed from the consist. After the session I had a look at the tank car and felt that it didn't feel heavy enough. On checking, it was found to be 63 grams which under the weighting rule used on Bylong of 2 grams/scale foot over buffers or headstocks meant that it should have been about 90 grams. No wonder it was giving trouble. A survey of the other SDS Models tank cars I had produced the same 63 gram mass for each.

I decided that extra weight was required so I proceeded to find out how to get into the tank.

The process is simple enough and was carried out on an Esso tank car as follows:
  • Ensure that you layout all of the parts similarly to the photo below so that you can reassemble the tank car with all the details correctly placed.
  • Unscrew the bogies.
  • Unscrew the three screws holding the tank to the underframe
  • Remove the three unloading pipes from the underside of the tank.
  • Carefully disconnect all ladders, strapping etc. connected to the tank from the underframe
  • Unscrew the two small screws holding the underside of the tank.
  • Glue four small lead fishing sinkers along the centre of the existing metal weight.
  • Reassemble carefully, particularly when aligning all the ladders, strapping, etc. between the tank and the underframe.

Exploded view including the fishing sinkers

I should mention that these SDS Models rail tank cars are the ones that are/were available as singles from the first manufacturer (considered unsatisfactory by SDS Models). The later three pack tank cars from SDS Models may not have this weight issue. If some one could weigh a tank car from a three pack and let me know the mass in grams that would be useful.