Inline Motor Bracket Bracing
The classic three-sided sheet brass inline motor bracket intended for use in scratch building slot car chassis was first introduced by American Russkit in the latter half of 1965, as a scratch building part for Mabuchi FT-16 motors, including their own Russkit "22". Two versions were offered, part numbers 794 and 795:
This new bracket type is more properly described as an "Integrated Inline Motor Bracket" because it integrates the motor mounting plate and the two axle carriers into one simple compact unit, differentiating it from earlier flat plate motor bracket designs such as the Russkit 792 and 793:
This simple 70 cent retail price sheet brass fabrication had a profound effect on the evolution of scratch built slot cars, with the part number 795 eventually becoming the de-facto standard starting point for chassis design almost up to the point at which the anglewinder drive rendered the inline obsolete for pro racing in April of 1968. Even after the inlines went away for pro sports car and coupe racing, many builders would simply cut the arms off of their Russkit 795 brackets, which were plentiful and easily obtained at the time, and use them to build their new anglewinder racers.
As brilliantly simple a solution as it was, the three-sided integrated inline motor bracket, including the ubiquitous Russkit 795, was not without its problems. Not the least of these problems was that as an important basic chassis part it didn't have much structural strength right out of the package.
If you were going to build a scale model slot car, and just drive it around the track to see it move, you didn't really need to complicate your chassis building efforts by strengthening the motor bracket with extra bracing. However, if you were going to race your car competitively in a field of many other cars, you found out pretty quickly why motor bracket bracing is necessary.
The architectural evolution of integrated inline motor bracket bracing, using the Russkit 795 bracket as an example, is the subject of this article. There were other integrated inline motor brackets available from other manufacturers, particularly after mid-1967, but the bracing architecture would have been the same.
There are four basic types of braces scratch builders used to strengthen the motor bracket. Most of the time they would use more than one type, and sometimes all four, on each chassis. For simplicity we shall call them Strut Braces, Inside Braces, Outside Braces, and Motor Mount Plate Braces.
Strut braces were generally installed in pairs (left and right) and placed between the axle tubes and the motor mount plate, as shown above left. Some scratch builders eventually began using sheet brass gussets in place of brass rod or piano wire for their strut bracing as shown above right.
Inside braces were made in two basic types; round and square, as shown above left. There were however many variations, as shown above right, but round and square were by far the two most common.
Outside braces are a logical adjunct to inside braces, and were made in everything from square to a very wide "U" shape, as shown above left. Sometimes outside braces were used without an inside brace (only struts or gussets), as shown above right.
Motor mount plate braces were used to strengthen the part of the bracket that the motor is mounted on, right at the point of smallest cross section and therefore lowest strength. This was done primarily in an effort to keep the bracket from folding up in a hard crash. Basic types included a horizontal cross brace as shown above left, and "A" brace above right.
Beginning with the Rod & Custom magazine sponsored series races in 1966, the rapid evolution of slot racing chassis design, including motor bracket bracing, was documented in photos and sometimes drawings, and widely published. Presented below are historical examples of various motor bracket bracing arrangements, grouped by year.
Dates of first appearance of each example are based on the original written record (magazines, newsletters and journals) whenever possible, and are presented chronologically. Every effort has been made to present this evolution in its proper order.
Historical Examples of Various Motor Bracket Bracing Arrangements
In April, 1968, anglewinder drive made its appearance in 1:24 scale commercial racing. This put an end to inline drive for coupe and sports car chassis, and several years hiatus for open wheel chassis as well. There was little need to further develop inline bracket bracing, because the inline bracket was no longer being used. Modern slot racing classes such as "Retro-racing" have resurrected inline chassis building, mostly because it is period-correct but also because easier to scratch build an inline chassis than an anglewinder. Or so the proponents say.
Recent design advancements in inline motor brackets include being formed of thicker brass for greater strength, or being machined from a solid billet. Other advancements include shorter axle carrier arms to place the motor closer to the axle, and greater bracket width to accommodate wider chassis. Recently, some manufacturers have been purposely locating the motor shaft centerline below the axle centerline in a "hypoid" configuration, so that modern flatter motors can be mounted horizontally, keeping the center-of-gravity as low as possible, independent of rear tire size.
Advancements in motor bracket bracing, particularly for brackets made of thinner brass, include forming the braces out of larger diameter piano wire, such as .078".
