Page last updated at 15:53 GMT, Wednesday, 20 January 2010

Design for an autonomous unicycle

By Doreen Walton
Science reporter, BBC News

The model mimics the actions of skilled unicycle riders

An engineer from the University of Surrey has spent a year perfecting the design for an autonomous unicycle.

Professor Robin Sharp used mathematical models to simulate the challenge of riding a unicycle and to work out the controls necessary to stay upright.

His work is published in the Proceedings of the Royal Society.

But Professor Sharp said he has never ridden a unicycle himself. "I've ridden bicycles and motorbikes quite a bit but I'm 72 so it's a bit late to start.

"Inevitably when you start to ride a unicycle you're going to fall off quite a lot".

The design is an extension of the professor's previous work on on driver behaviour and the control of machines by people.

It includes work with the Williams Formula One motor racing team on optimal driving for race cars and on modelling for virtual driver controlled cars.


Professor Sharp explained that the unicycle research has no real application and was just for fun. "I'm a bit obsessive and I got obsessed with it until I'd finished it."

The study is based on what real riders do. "If you're falling over forwards you need to pedal forwards and if you're falling over backwards you need to pedal backwards."

Professor Sharp said he spent a lot of time on the internet looking at what people can and can't do.

His respect for unicycle riders has increased.

"They can do the most remarkable things. They've mastered this very elaborate control and can do things like jumping over obstacles.

"We learn these things by trial and error and get to be able to do things when we've really no idea how we're doing it," said the Professor.

Better model?

The unicycle and rider are modelled with a wheel, a rigid frame which includes the lower body of the rider and an upper body attached by a spherical joint.

diagram of unicycle
diagram of unicycle

The model can follow a path and move inwards in a spiral but it cannot jump. "Jumping is excluded from the modelling envelope," said Professor Sharp.

The Professor expects the work to be of interest to a select audience. "Cranks and nuts and anyone interested in stability and control and man machine interaction problems."

He believes his model is an improvement on earlier designs and it's just a matter of time before someone builds a new rider-less unicycle. He hopes that anyone attempting it will use his design.

"They would be very foolish to do it without reference to my paper because it should guide them to how to design the systems and controls and how to get it right first time," he said.

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