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Gearbox principles (2014)


I was a little afraid before building the gearbox. But as it is in math, man must think first and start solving the problem afterwards. Having it thought over, the solution is quite simple. So, let’s construct it and thing about mechanical realization.

We can build a synchronized version thanks to the wide pallet of Lego Techic parts. This significantly reduces wear of the gears.

Since my gearbox has 6 speeds I need three shift rods. Each such rod has three possible positions where in the two positions it is connected to one of the outer gears. Motor (input) is driving all the shift rods. Output is connected to all the outer gears of the shift rods. Moving the ring (clutch) connects the shift rod to one of the outer gears and thus it connects the input to the output.

Now it is time to think about how to make all the gears arranged so each change of the shift rod causes different angular velocity on the output. I connected all the shift rods with gear ratio 1:3:9. Each shift rods has two different outer gears, so it is desirable to connect both the gears with a ration different than 1:1. I connected both sides with gear ratio 2:3.

It is important that the both sides of the outer gears are connected together with lower gear ratio than the shift rods. This way the gear would change incrementally as we are used to. All the gears and the angular velocities are closely described in the video bellow.

Click the image to show it in higher resolution
Wrong usage of gear ratios
Version 1 of the 6 speed gearbox
Version 2 of the 6 speed gearbox
Version 2 of the 6 speed gearbox, bottom

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