There seem to be a lot of different two-motor chassis around.
I see them in the old magazines about every third month,
plus Graham sent one,
and Don sent one,
and I've got one (I'll post it soon),
and they are, as we know, quite popular on ebay!
There are probably a lot of reasons why you see a lot of 2-motor chassis.
For one thing, Mabuchi came along and
made significant improvements to their motors. Russkit (and every other
manufacturer) liked the improvements and said, "Sure, sign us up!" Russkit
called the new motor a Russkit 23. Meanwhile, they had a bizillion of the
older style Russkit 22 motors left over. Russkit made the dual motor slot
cars, that are so popular on ebay, with those older 22's just to deplete
their inventory of those motors!
Plus, have you ever seen the Russkit motors in
Olsen packaging on ebay? It seems, at the end, Russkit STILL had a surplus
of their motors on hand, and sold them to Olsen just to get rid of them!
Another reason for 2 motor slot cars was experimentation. The
explosion of the slot car hobby was at its peak in 1966. People were
experimenting with EVERYTHING in slot cars - all in the name of speed and
getting to the finish line first!
Nobody knew if 2 motors were better than
one, so a bunch of people tried it. Some cars were built with 2 motors side
by side in the rear in an inline position. Many were built simliar to the
way Russkit built theirs. A few were sidewinders with both motors at the
back. Still others were a front and rear sidewinder setup. Some were more
successful than others, but after it was all over, the single motor won out.