Transmission Car
Transmission Car
Author's Notes
Posted By silcantar on 08/29/2008

I intended for this car to be capable of breaking the 5mph record for the fastest unassisted robot, but I had a few technical difficulties. Still, it is a pretty good design. It features one of the most compact automatic Lego transmissions I have seen. Unfortunately, it requires a rubber band with a VERY specific strength, and I couldn’t find one.
Two motors power one end of a shaft that goes into a differential at a 3:1 gear ratio. The gearbox is on the other side of the differential. It has 3 gear ratios: 3:1, 1:1, and 1:3. The power then goes through a few more gears, which have a total ratio of 1:1 (actually 3:5:3). Therefore, the whole transmission can have a gear ratio of either 1:1, 3:1, or 9:1, resulting in a robot capable of moving very fast. In order to switch gears, the resistance on the output axle of the differential must be greater than the resistance to turn the differential (provided by the rubber band). When this happens, the differential turns, and the mechanism for sliding the output axle of the gearbox moves, shifting the gears to a lower ratio. Unfortunately, the rubber band must be of a very specific strength, so that the gears do not shift too early or too late. Because of the variety of gear ratios, the car is able to overcome inertia in the lower gears, and then switches to high gear when there is little resistance to maintain velocity. This, plus the big wheels, enables it to move at a very high speed. Unfortunately, my camera is not very good quality and does not focus well, so the pictures are blurry. Hopefully you can see well enough.

Comments (3)

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#1 mike1
Posted on 08/30/2008
Great idea for making it a adjustable transmition that feels when it needs adjusting. I was always using a worm gear and a spring though I found no practicle use for it. I think you did a great job on using this kind of device! BTW you got me inspired for a speedy robot and now it is complete waiting for my program!
UPDATE: My robot was blazing fast! I had to sprint to stop it from crashing onto the shelfs. Can’t wait to test it tommarow.
#2 Evan
Posted on 08/30/2008
Nice job on the custom gear shift even though you couldn’t get the right rubber band! ->
#3 megamindstorm101
Posted on 09/07/2008
i like rcx and you really show what its made of. I like it.

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