by Marconi Proxy Race entrant
Larry Geddes
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1 - Chassis Theory
A live axle can interact with the track in only 3 ways - - neither tire slips - both tires slip - only 1 tire slips |
THE basic problem - Live axles tend to roll in straight lines - they
don’t want to go around curves! |
There are no other
possibilities. At any given time, only one case can apply. On the
straight, we want both tires hooked up, but what about the curves? If
both tires slip, we have a power slide & the motor is making
revolutions for no gain in distance. Having one tire providing
traction is better than none.
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Centrifugal force will see to it that the inner tire gets “lighter” & the outer tire gets “heavier”. At some point, the inner tire will slip, but only if the chassis allows this to happen.
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2 - Chassis Theory |
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If the
chassis
is too stiff, either both tires will slide or both will tend to stay
hooked up. The rear end of the
chassis
must be flexible enough to allow the inner tire to slip, & “plant” the
outer tire.
To allow the rear of the chassis to twist easily, a “spine” pivot on the longitudinal centerline is used. This is a length of 1/16 piano wire inside two lengths of 3/32 brass tubing. The short rear tube & the piano wire are soldered solid to the motor box, & the long tube is soldered to the pan assembly. It is braced with a cross rail running from pan to pan. Both tubes are let into slits cut in the motor box & nose plate, & are flush with the bottom of the chassis. There are two light torsion rails on either side of the spine. These hold the front & rear together & provide the desired amount of stiffness depending on their length & diameter. These rails are also let into slits & are flush with the bottom. The nose plate/pan assembly is one piece & has no hinges or other movements. Two small stops are added to the motor box, overhanging the pan, to limit the ultimate pan travel. |
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3 - Some
construction details
Motor box - Consists of two 3/32 square tube struts let into slits in .050 steel cross plate at front. Two 1/16 L-shaped piano wire pieces fit into struts & overlap across the back. Pillow blocks are mounted on struts with 1/16 thick spacers. This allows motor box to be as wide as possible. Struts pass underneath hubs on gear & wheel. Motor mounts - Two lengths of .055 or .047 piano wire are soldered to motor as shown. These rails sit on top of struts & rear cross brace. Gear mesh & motor angle are adjusted for best fit, & rails are soldered to motor box. Rails stay attached to motor when motor is removed. 3-point mounting is very stiff. |
