Differential for the Meccano Steam Traction Engine Supermodel

by Jacques Vuye

Overview

The proposed mechanism provides a significant improvement to the operation of the Meccano Traction Engine Supermodel.
The original design calls for a rigid axle with both traction wheels locked onto the rear axle. This results in poor turning capabilities for the model, mainly because most of the weight is concentrated on the rear wheels.

The proposed improvement is based on Bert Love's differential described in Meccano Constructor's book, but, in order to reduce overall height, it uses a toothed ring (#180) instead of a 133 teeth gear wheel (#27b).
This allows assembly of the differential components inside the ring, instead of on top of the 133t gear wheel. The proposed mechanism had less than 1" to the overall width of the model and has no significant impact on the otherwise pleasing proportions of the model. 

Assembly

Begin construction by temporarily installing a 95t gear wheel (#27c) inside the Gear Ring (1). This will be used as a centering jig for the initial assembly. It is best kept in place using fishplates, temporarily bolted on both sides of the gear ring. Use any of the elongated holes for this purpose and reserve the circular holes for mounting the spokes of the differential later on.

Lock a short rod (e.g. 4") in the 95t gear wheel's boss.  Install 4 long threaded pins (3) on a 4 holes collar (2) using locknuts. The threaded pins should be mounted in such a way that the collar runs freely on the centering rod. Install 4 short rod couplings (4) on each of the threaded pins, but do not lock the grub screws yet. Bolt the 4 short rod coupling (4) in the circular holes on the gear ring (1), using two washers as spacers and keeping the collar (2) on the centering rod. Lock the grub screws on each of the short couplings, while ensuring that the centering rod can turn quite freely in the boss of the 95t gear wheel and the collar (2). Now the collar and the differential "spine" are centered in the gear ring and the 95t gear wheel "jig" can be removed.

One of the threaded pins is now removed, making sure the three others remain undisturbed (as to preserve the perfect centering of the collar (2)). Mount a small bevel gear (6) on the threaded pin, using a number of washers (including regular ones and Elektrikit thin washers as well) for proper shimming. Mount the large bevel gear (5) on a short rod and insert in the collar (4). A number of washers are inserted between gear (5) and the collar (4) to ensure smooth meshing of the pinion. Patience is required, as it will usually take several attempts to achieve perfectly smooth operation. 

A large bevel gear is mounted on the right driving wheel and meshes with the bevel pinions in the same way as gear wheel (5). The proper shimming of the small pinion (6) is very critical, as they should not interfere with the nuts holding the bevel gear wheel (7) on the driving wheel.

 When assembly is complete and proper meshing accomplished, a coat of light grease should be applied to the gears.

December 2000