Motors and gearbox units I do not intend to say too much about these at this stage, except for a few comments about what types are satisfactory for the suggested method of construction. I am using a couple of Portescap motors to save a little time and simply because, I had been saving them for this particular project, other locos I have already built for the project use them. They come already assembled, but can be separated between motor and gearbox if necessary. ( I must point out however that in doing so you are going against the conditions of the guarantee.)
I am not, however, going to push for everyone going down the Portescap route. Some people do not like them
claiming they can be noisy, I have
one that is, but most of the ones I have installed run very well and quietly. I have found them very reliable and have used them, from the time they came out, on many types of locomotive. The oldest ones seem to be the quieter ones. I am not here to push Portescaps or any other motor or gearbox for that matter.
The modern skew wound motors made by Maschima are powerful and efficient. I use them, much the same as most modellers, nowadays. They are powerful for their size, well made and reliable. There has been much written in past Scalefour News articles about motor speeds and gear ratios and getting the best matches, there is also some information on this subject in the Digest.
Simplistically the choice normally comes down to -
"What is the largest motor and gearbox arrangement possible within the restricted space within the locomotive body?" ( I am leaving out the possibility of fitting a drive from the tender into the loco as I would not recommend this to anyone beginning.)
I personally, would not want any of the drive unit showing and like to have a proper back head in the cab. motors up to 16mm dia. can be used in the majority of modern locomotives, especially if you buy the flat sided motors which are 14mm across the flat sides. They will slip out between the frames if you make allowance for that. Much depends on the narrowness of the firebox so check for this when measuring for the drive unit.
"Which gear ratios suit which locomotives?"
The answer to this is partly in response to "What kind of layout are you building? High or low speed?"
Passenger locos around 40:1 or 50:1 depending on the top speed you wish, 40:1 being the faster one.
Mixed traffic locos 50:1 and 60:1
Freight locomotives 60:1 to 80:1
Shunting locomotives 80:1 and higher for ultra slow
There are a huge range of gearboxes available. Some are very fine, but I have found, from personal experience, they will wear out fairly quickly . Then again I have heavy locomotives working long trains on my Grayrigg layout. I go for the more robust gearboxes. Most companies selling motors and gearboxes will give some help when choosing. Multiboxes which give a range of options are particularly useful and narrow versions are available for split axle where they are required - I hope to cover this later. Most gearboxes are good nowadays and once assembled according to instructions will function well.
If using the construction system I am suggesting, I would suggest you use a type of gearbox, which uses grub screws to attach gears on to shafts as they can be released again for free running tests. You can tell I am not keen on gluing gears either, as I like to be able to adjust and disassemble, if necessary, without any trouble.
When assembling your gear sets follow instructions and take care to
make sure all is square.
If you have gears with grub screws file a flat on the axle, as suggested in most of the instructions. This allows for tightening up without distortion of the gearwheel.
Once your gearbox has been assembled, put an axle in place and screw up the final drive gear, test that all is working without the motor's worm wheel engaged. Fit motor and worm wheel,to gearwheels, (A cigarette paper placed between the two should give a working tolerance on heavier gear sets) tighten everything up. remove the paper and try turning the motor shaft to make sure that all is turning over OK. before trying power through the power unit.
If everything is turning OK, then apply some power. The gears should run smoothly without much noise. If there is any sign of catching check to see what may be doing this under a good light and a magnifier.
1) It could be the worm wheel is not driving by its centre.
2) It could be that the worm wheel is offset to the primary drive wheel. You may have to add thrust washers to get everything in line.
3) It may be that the grub screw is catching on something.
If all is well and there is no sense of the motor or gears sticking in any way, try running in the mechanism. This can be done, while building other parts of the locomotive. I use my helping hands to do this.
To Run InPut a touch of light oil on the gears and turn the motor over slowly. Then run on half speed for half an hour in each direction.
Oil again if necessary, then run at full power for half an hour in each direction.
(In olden times Brasso was recommended for running gears in, but given the quality of gears now I would be reluctant to do this, as it will only wear the gears out prematurely.)
Modern motors are meant to get warm in operation, so don't be surprised when they do. Stay with the mechanism just in case anything works loose, you have lots of other things to do. As the gears bed in and become more polished they should become quieter and smoother. After running in try running them as slowly as you can and see the difference from how they were when you started running.
Allan