One of the many gems hidden in the Oshawa Military Museum's "boneyard" is this M3 halftrack. Despite its rather battered appearance, I was assured that all of the parts necessary for a full running restoration are in hand, and that this vehicle will be restored in the not too distant future. Because of its condition, I was able to get some particularly clear photographs of the suspension's details.
We'll start at the front, in this case the drive sprocket. Notice the open nature of the sprocket, and the final drive housing behind it. The key difference between the sprocket and idler is the toothed sprocket in between the two halves, which appear to be interchangeable between inner and outer halves, as well as between sprocket and idler. The other main difference is the much taller hub, which portrudes all the way to the outer edge of the sprocket. The brake drum is also visible behind the inner portion of the sprocket.
The roadwheels and their suspension arms can be seen here. In particular, note how each pair of wheels pivots on an arm, which then in turn can pivot on the mount. There are stops attached to the mount to limit the movement of the suspension. The return roller should be fitted to the top of the mount, but is missing here.
Here is the left rear idler assembly. The very open nature of the M3 series idler and sprocket can be clearly seen here. I personally do not think that photoetched pieces can adequately capture this frailty; cast brass or resin would be a much better alternative. The smaller hub is also evident. The large coil spring is part of the idler tensioning assembly.
Finally, we examine the M3 series tracks. They are unusual in being not a series of links, but a single piece of vulcanized rubber over steel. No individual links necessary here! An ideal medium for reproducing these on a model would probably be the flexible resin used by Cavalier for its zimmerit, or Cutting Edge for their new sets of seat belts. As the tracks get worn, as at bottom left, the steel becomes evident. Visible to the left is an idler or sprocket half, resting on a pair of roadwheels.