Meridian Models/Mosskito Narrow Gauge MPD18 chassis

This is a nice little power unit with an 18mm wheelbase, designed to be used under a couple of Meridian Models loco kits, namely the Armoured Simplex and Billard T75D. These are now available under the Mosskito Narrow Gauge banner and are available from Narrow Planet (mine is an older Meridian kit, bought from a secondhand sales stand at an exhibition). I've wanted to build one of these for a while now as they look to be well designed and reliable, following the tried and tested band drive/layshaft/Tenshodo gears format.

The kit is etched in nickel silver, and includes everything that you need barring glue and solder;

The instructions cover 4 sides of A4, and can be seen here in pdf form.

The first job is to assemble the layshaft in its etched bracket;

To help position the worms and bearings there's some helpful markings on the etch;

The layshaft runs in roller bearings, I used my lathe to help push the bearings and worms onto the steel rod.

Next one side of the main body is folded up;

The layshaft assembly fitted into place;

And then trapped in position;

In the above photo can be seen the keeper plate, which clips in place under the chassis and allow the wheelsets to be removed. There are tabs etched onto the layshaft carrier which locate in the sides of the main body, once the unit is assembled these are bent over to hold the unit together without the need for solder.

One wheel on each axle needs to be removed, with a suitable puller to allow each wheelset to be built up using an etched washer, a sleeve for the worm gear to sit on, and two bearings. The sleeve needs to be glued in place, I used Loctite 603 but cyano or even a thin smear of epoxy would work if applied sparingly with care. One of the bearings in my kit was oversize, to save time I made up a new one on the lathe, which would have been much quicker than contacting the manufactorer for a replacement;

Wheels are by North West Short Line, and run on brass axles. Having brass axles running in brass bearings is considered to be bad practice, so it will be interesting to see how this chassis fares in the long term.

Here's the wheels and keeper plate test fitted;

On the etch there's a pair of T shaped parts. These aren't mentioned in the instructions, but fit into slots in the sides of the body;

They're not mentioned because you they're not needed. I found this out after fitting one thinking it would help when fitting the pick-ups, it doesn't so ignore them. I made this mistake so that you don't have to!

The motor is from Nigel Lawton's range, and as its rated at 10 volts a resistor is supplied to allow it to run on 12v. Its held in place with an etched strap on the top of the unit;

Pick-ups are made from phospher bronze wire soldered to a small piece of copperclad board which in turn is epoxied to the main unit, and are only fitted to one side as the wheelsets have one live and one insulated wheel.

Here's the other side of the unit, with the one end of the resistor soldered to the body and the other attached to the motor wire;

Note how on both sides I've trapped the wires under the motor strap.

The complete unit;

To attach the chassis two etched mounts are supplied to suit either the Simplex or the Billard. I'm building a Billard, here's the mount folded up;

There needs to be a 12BA (not 10BA as the instructions state, you'll need to know that when you lose one and have to find a replacement!) nut soldered to the top of the mount, if its fitted underneath it will foul the end of the layshaft. Guess how I know that...

The instructions don't cover making up the mount or fitting it to the chassis, however it is pretty straightforward, the pulley end of the chassis clips into the folded part that hangs down and a screw runs through the keeper plate and body and locates in the nut soldered to the mount;

I did have to take a file to the mounting plate, a little more clearance was needed at one end (left hand end in the above photo) to clear the motor when fitting the unit.

Another view;

Very few problems were encountered in this build. The holes for the screw needed broaching out, and I had to slightly modify the mounting plate. I spent a fair amount of time scratching my head about those little T shaped mounts that weren't in fact needed, and my I had to solder wires together, which I'm not very good at. Soldering brass I'm fine with, soldering electrical stuff makes me swear. Work that one out. Another problem was that one axle was out of alignment so the unit rocked when on a flat surface due to my leaving a little cusp behind when cleaning up the etch. A quick stroke of the file sorted that problem out. And I feel that the motor strap could be a touch longer, a little more strap poking through the buckle would be easier to grab with pliers when tightening.

It runs nicely. Very nicely in fact, even with no weight on the unit. With a body in place it will I'm sure be a superb runner. I've enjoyed building this, it has lived up to my expectations, and I will at some stage build another just because its so well thought out.

And finally, this is the mark 2 version of this chassis, see this post by Michael for a comparison between this and the earlier version.

Paul.