How are <1.5 sec Minibots doing it ? Gearbox mods allowed ?

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I still can't figure out how those super fast robots are doing it. The rules give you 3 alum. gears but none of them look big enough to have the 120t gear in use. There is some talk of bypassing 2 gears in the motor gearbox but that sure looks questionably legal.

Also, what are they using for traction material on the output shafts (like 118) ? (Electrical) Heat Shrink ? Surely there is no "hard" surgical tubing ?