No tyre, no problem: James Bruton rides on a sphere
British inventor and YouTuber James Bruton has built an electric bike that balances on a red circus ball and can move in any direction. What sounds like a gag is actually full of serious engineering work.
James Bruton is no stranger to the maker scene. The British engineer and former toy designer has made a name for himself by pushing the boundaries of robotics and locomotion with unconventional ideas. His latest design eclipses everything that has gone before: an electrically powered bike that rides on a single ball.
It looks spectacular and challenges physics, electronics and riders alike.
From two spheres to one
A year ago Bruton surprised everyone with a vehicle that used two large spheres instead of wheels. Now he is going one step further: the new model balances on just one sphere measuring around 60 centimetres, on which an aluminium frame with a seat and technology is enthroned. A YouTube video shows that the construction is actually stable enough to carry an adult rider.
The entire drive sits above the sphere. Three vertically mounted omnidirectional wheels form an equilateral triangle and press against the ball from above. Each of the three drives is operated by an ODrive-S1 controller (a high-precision control unit for brushless electric motors) with an output of around 2 kW. They move the ball forwards, backwards or sideways at different speeds. The principle is similar to robotic drive technology, only in a much larger, more delicate version.
The most difficult part: remaining stable in two axes
Unlike its predecessor model with two balls, the single-ball bike has to be stabilised in both longitudinal and transverse directions at the same time. This makes it significantly more complex than conventional balancing vehicles such as Segways, which only correct in one axis. A central microcontroller (Teensy 4.1) constantly reads inclination data from a motion sensor (BNO086). A precise control algorithm (PID controller) controls the motors and makes corrections in the millisecond range to prevent falls.
Source: James Bruton / YouTube
The energy is supplied by six 6S lithium-polymer batteries, which together generate a system voltage of 50 volts. The frame and many components come from the 3D printer.
Theoretically elegant, practically extremely sophisticated
On paper, the steering seems logical: if the bike is to travel straight ahead, the forward-facing Omni-Wheel rotates more, while the two side wheels run at reduced power. These ratios are varied for direction changes. However, steering is anything but intuitive in practice.
In the two-ball bike, Bruton was able to drive the balls against each other. The new model does not have this advantage: a single ball cannot simply be controlled differentially.
Bruton therefore came up with an unusual makeshift solution: a laterally extendable wing made from a wooden stick and foam. If he holds this in the airstream, the air resistance causes the vehicle to turn. A makeshift but functional solution that shows how far the design is from a steering system suitable for everyday use.
Wheels off the shelf? Not a chance
The omnidirectional wheels themselves presented a further hurdle. Commercially available models were unable to withstand the forces and friction that occurred.
Bruton therefore developed its own wheels with an aluminium core and 36 passive rollers (18 per row). However, each of these wheels also contains a large number of smaller rollers with their own bearings, so that the total number of these mini roller elements in the entire tricycle system is 216. This means they run with low friction and do not block even under high loads.
Source: James Bruton / YouTube
The electronics were similarly experimental: In the gym, static electricity - caused by the friction between the ball and the floor - caused the control system to partially fail. Bruton is already investigating countermeasures.
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