In the 1940s, Swiss engineers developed a new type of zero-emission electric bus that used a large rotating flywheel to store energy instead of rechargeable batteries.

Many Swiss cities at that time used trams (powered by electricity from overhead cables) as public transport, running on predetermined routes. Installing overhead power lines on new lines is too expensive, according to Amusing Planet. Wanting to create a quieter and cleaner vehicle, not restricted by overhead power lines, Bjarne Storsand, chief engineer of the Maschinenfabrik Oerlikon company, came up with the idea of the gyrobus in 1946.

The Gyrobus is powered by an electric motor and that motor uses electricity produced by a flywheel generator to store energy. The flywheel rotates at the charging station thanks to 3 long rods placed on the vehicle’s roof. When the flywheel reaches its maximum speed of 3,000 rpm, it is fully charged. At that time, the bus can run 6 km at a speed of 50 – 60 km/h, depending on the load on the vehicle and the slope of the route. Sometimes, the Gyrobus even runs 10km on a single charge.

The flywheel the engineers used was quite large (160 cm in diameter) and heavy (1.5 tons), sealed inside an airtight chamber filled with hydrogen at reduced pressure to lower drag. Charging the stationary flywheel lasts 40 minutes, but when the flywheel is spinning, replenishing power only takes 2 – 5 minutes. The higher the voltage, the less charging time. Charging stations along the route ensure that flywheel revolutions never decrease to a level that affects the bus’s performance and speed. For example, the 4.5km route in Yverdon-les-Bains has up to four charging points.

Placing a large spinning flywheel inside the vehicle leads to two unexpected consequences. The gyroscopic effect of the flywheel makes it difficult for the bus to change direction, leading to some difficult situations, especially when the bus goes through a turn. On the other hand, the system provides a very smooth and balanced ride.

Gyrobuses were used in limited numbers in many cities such as Switzerland, Belgium and the Belgian Congo until 1960. The gyrobus buses operating in Léopoldville are even the largest with 12 vehicles running on 4 routes The road is about 20 km long. However, high energy consumption causes the system to stop working. Similarly, gyrobus services in Ghent, Belgium, and Yverdon-les-Bains also ended due to economic problems. Currently, there is only one gyrobus in existence, restored, preserved and displayed at the Flemish Train and Bus Museum in Antwerp.