A MPD18 chassis build for OO9

[Kenton]

OK WB has been quiet for a while but Xmas is a coming and the wind is howlin' at the door.

 

This chassis (9mm gauge; 6mm RP25 wheels; 18mm wheelbase) is sold by Meridian Models - It is also available through Parkside Dundas and Nigel Lawton who has put a copy of the instructions on his site as a PDF file.

 

Now the instructions are about the most comprehensive "kit" instructions that I have come across and include small step by step photographs to help lead the builder through the kit construction.

 

So why bother with this thread?

 

Well, I thought you might like another dose of my out-of-focus-photography and might also like to see what sort of mess someone other than an expert (and related to a Chiroptera) makes of this challenging build?

 

All nicely packaged in ziplock bags in a very useful plastic box you get a fret containing the following small parts:

 

 

You also get a motor, resistor, phosphor bronze wire, a rubber belt (plus a thoughtful spare), wheel sets, pulleys, 1.5mm lay-shaft, worms, small brass tube, and an absolutely tiny copper-clad board.

 

The tools required: soldering iron (25W) will do at this size, 145'C solder, Carrs red flux (any will do), files and tweezers, some silicone grease, a small 5-sided broach, and some of this:

 

 

Oh, and a magnifying glass.

 

Having carefully counted out the parts and read through the instructions - at least twice, the build began ...

[Pinkmouse]

Interesting, I need a little chassis for a freelance narrow gauge loco for Jerusalem Works, and that might just fit the bill. Oh and you missed the "l"s off your "/url"s

[Kenton]

Oh and you missed the "l"s off your "/url"s

Thanks. Despite reviewing the post still managed to make the same typo twice!

[Kenton]

OK here we go step-by-step:

 

The Chassis Frame

 

1. The chassis frame is a simple one piece fold-up.
   
    
   
2. Don't forget to open out those fold lines slightly they are a little on the narrow side and on my first attempt I found that the fold would not go to 90'
   
    
   
3. Fold up the other side. As always fold inwards on the half-etched lines.
   
   
    
   
4. Locate the motor end spacer.
   
    
   
5. Fit into the frame at the opposite end to the "Meridian" name. The frame has been well designed so that interlocking steps in the pieces help alignment. Then solder it in place.
   If plenty of flux is used the solder will run along the frame fold lines and strengthen them. So be sure that the sides are not pressed together while holding them - they need to be at 90'
   
   
    
   
6. Locate the other end spacer.
   
    
   
7. This is located in the other end of the frame. Once again, there are interlocking tabs to set its position - as long as you didn't file them off when tidying the pieces after removal from the fret. Solder in place.
   
   
    
   
8. Locate the two cross pieces and fold over the four half-etched lines on each piece (remember half-etch on the inside)
   
   
    
   
9. Fit one at each end in the open areas of the frame. Solder in place.
   
   
   

[Kenton]

Fitting The Motor

 

1. Now the instructions would have you believe that the motor straps are provided:
   
    
   
2. and that it is a simple task to thread these though the etched loops on the side of the frame...
   
    
   
3. Sadly, for me this proved to be of no use. During the process of trying to tighten the straps through that buckle the buckle broke.
   Probably too much force on my part or simply the cutting edge of the strap on a very finely etched buckle.
    
   Anyway, an alternative method was required - and I think improved method - to hold the motor in place.
   Simply use a VERY small amount of super glue. Obviously keep well away from the motor spindle.
   
    
   
4. Locate the motor stop
   
    
   
5. Fit through the slot in the top of the frame with the broad section outside and pressed up to the back of the motor.
   
    
   
6. Bend and solder in place inside the frames.
   
    
   

[Kenton]

Running Gear

 

1. Locate the lay shaft and brass worms. Forget about those silly etched washers and replace them with 12BA REAL washers.
   
    
   
2. Test fit the lay shaft in the frame. The holes will require a slight opening-up with a 5-sided broach so that the shaft spins freely in the frame.
   
    
   
3. Slide the lay shaft through one end and as it passes through add 2 washers followed by the two worms followed by 2 more washers and finally pass through the other frame end.
   Position the lay shaft so that most of it protrudes from the frame at the motor end. Push the worm and washers at each so that they are close up to the frame and then apply a drop of that Loctite 603 non-permanent thread lock to THE INBOARD ends of the worms. It ONLY takes a small drop of the stuff on the end of a toothpick. DO NOT get it anywhere near the washers or frame ends. Once both are locked on the lay-shaft there should be virtually no end movement.
   
    
   
4. Locate the two pulleys and one of the drive belts. Check that the larger pulley fits on the lay shaft and the smaller (tiny) pulley fits on the motor shaft. The latter required a touch of the 5-sided broach - but only the lightest touch.
   
    
   
5. Position the two pulleys in good vertical alignment with the small pulley as close as possible to the motor. Once again lock them on their respective shafts by the judicious use of a drop of Loctite 603 non-permanent thread lock on the OUTSIDE faces. Fit one of the belts and check that the spinning motion of the motor shaft is smoothly transferred to the lay shaft.
   
    
   
6. Locate the two short lengths of brass tube (axle shaft adapters).
   
    
   
7. Drill two holes in each of the axle shaft adapters. I think this is best performed with a hand-held Archimedes drill rather than a powered mini-drill.
   Holding the axle shaft adapter gently in the jaws of a vice, file a flat on each end and then drill out a 0.5mm hole.
   A trick is to place these on a length of brass wire with the ends bent. This prevents them from wandering off but also stops you squashing these out of shape in the jaws of the vice.
   
   
    
   
8. Locate the worm gears. Push fit a drilled shaft adapter to each worm gear so the gear is in the centre of the adapter. These should be a tight fit and may need to be gently drifted in with a hammer.
   It is at this point that you realise those holes really do need to be at the ends of the shafts.
   
    
   
9. Identify the insulated wheel on each wheel set - the one with the black plastic bush behind the wheel. Carefully remove the insulated wheel on each wheel set using a wheel puller (or a pair of pliers and tweezers and a rocking sliding action).
   
    
   
10. It is a good idea at this stage to remove the pulley belt so that it does not fall off and get lost in the following steps.
    Check that the axles fit comfortably through the holes in the frames, opening them up a little if needed.
    Position one of the adapter and gear assemblies on top of one of the worms within the frame and feed the axle shaft through both frame holes and the
    axle shaft adapter. Check that the axle rotates freely. Then repeat for the second wheel set.
    
     
    
11. Carefully re-fit the insulated wheel on the end of each axle using a wheel press to ensure the wheel is fitted square and adjust the back to back to your liking (I use 7.7mm).
    Centre each axle shaft adapter on its axle and apply Loctite 603 non-permanent thread lock to each of the holes drilled in them to lock the
    gears to the axles. Take great care not to get thread lock on the gears, worms or near the frames. A toothpick is a handy applicator.
    
    
    

[Kenton]

Pickups

 

1. Locate the resistor, cut the lead wires short and bend as shown. (Is that an 18 ohm resistor ?) used to reduce the voltage at the motor from 12V to ??
   
    
   
2. One end of the resistor is soldered to the top of the frame at the opposite end from the motor.
   The BLUE wire from the motor is stripped and soldered to the free end of the resistor.
   I will emphasise BLUE unlike what I have shown in the photo and subsequently lead to much head scratching. (I'm not that colour blind - just stupid)
   
    
   
3. Locate the tiny PCB material and phosphor bronze strip.
   
    
   
4. Gap the PCB about 1mm from one edge.
   
    
   
5. Solder the phosphor bronze strip across the PCB and tin the other side.
   
    
   
6. Solder the free side to the inside of the frame on the side which has the insulated wheels fitted. Ensure that the section and gap are below the edge of the frame and test for electrical isolation pf the strip from the frame.
   
    
   
7. Shape and cut the two ends of the phosphor bronze strip to rub against the back of the insulated wheels.
   
    
   
8. Solder the RED wire to the PBC and phosphor bronze strip. Yes, I know, it is still wrong.
   
   
    
   
9. The kit comes with 2 different types of attachment plates. You probably need to consider which will be best for the model body you are building.
   I thought that this one is the most versatile as it presents a location point for a 12BA nut and bolt. It is simply soldered to the chassis cross piece at the opposite end from the motor.
   
   

 

As straightforward as that. Nowhere near as fiddly as I first thought when opening the box and produces a nice compact motor that with some weight (and re-wiring correctly) performs very well.

 

I have another to build and it will be even quicker without having to pause and pose for the camera. A pleasant evenings work.

[halfwit]

Neat work Kenton, and nicely explained. I've thought about getting one of these myself for a project.