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Automatic 4-speed Transmission

Automated version of my 4-speed transmission.

Having designed a robust 4-speed transmission that could be shifted instantly using a Control+ motor, and combined into a single 16-speed transmission, I saw a possibility of making it automatic by installing a torque detector on its output. The detector consisted of a simple differential connected to the shifting mechanism, with a lever pulling a rubber band. The transmission output’s shaft went into one end of the differential and the other end of the differential served as a final output, so as a result the differential was reacting to a difference in resistance between these two output. When the final output met enough resistance, it made the differential rotate in one direction, and when the final output’s resistance decreased, it would make the differential rotate in the other direction. Coupled with the rubber band and the lever, it meant that with no resistance on the final output the differential was pulled so that the transmission was shifted into 4th speed. Then, as the final output’s resistance increased, it would gradually shift down to 3rd, then 2nd and finally 1st speed, depending on how much resistance there was.

The mechanism worked reasonably well but suffered from jerky, intermittent shifting. The reason was that the driving rings needed to be disengaged briefly to shift the speed, and disengaging them meant that the transmission’s input and output were momentarily disconnected. With no connection, the transmission’s output stopped and the differential “tried” to return to the 4th speed. In practice, it usually meant that it didn’t shift on the first try but only after a few attempts. The mechanism could also shift up when the resistance decreased, but it proved tricky, as the only way to shift back up was by having the rubber band effectively drive the vehicle the transmission was in. As a result, the shifting up was usually only possible when going downhill, when the output’s resistance was negligible.

There are no instructions for this variant of the transmission – instead, use the instructions for the regular, non-automated variant and just add the differential and the rubber band, as shown on the video.



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