On our etrikes, the motor powers the front wheel and the pedals mainly power the left rear wheel. By design, the pedals primarily power one rear wheel to allow the rear wheels to spin freely of each other when turning. The right wheel also receives some power, but it is allowed to rotate at its own speed. In a tricycle or a car, each wheel in a pair must rotate at its own speed when turning. In a car, this is achieved with a sophisticated gearing system called a limited-slip differential. Here's a link to a great video we found that explains how this works!
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