In performance cycling, weight is vital. Not only does weight and its distribution impact a bike’s handling, but it also has a particular disadvantage to speed – especially when the road goes up hill. To meet demands, a new e-bike has been developed featuring a drive system from maxon.
“E-bikes are ugly, they’re heavy, and they don’t handle well,” said Harry Gibbings, founder of the HPS Watt Assist e-bike system. “So, we decided to create a system that would make the bike look great, maintain the right handling, and it would be lightweight.”
So what HPS has created is described as the world’s lightest e-bike motor and battery system. HPS Watt Assist is available to high-end road bicycle manufacturers to integrate into their bicycle frames, achieving the same look, size, and handling as a ‘normal’, un-assisted racing-style bike. The system features a slender drive system that fits into the bicycle down tube, while a lightweight battery is housed in a cycling drinking bottle design that sits in a bottle cage on the frame’s seat tube.
This configuration ensures that the bike’s centre of gravity remains low and central. Crucially, this means that unlike other e-bikes, the frame can maintain a standard wheelbase and fork rake. As a result, a bike integrated with Watt Assist handles in the same way as a high-performance bike. And looking at a frame equipped with an HPS system, you’d be none the wiser that it is electrically assisted.
The drive system
To achieve this design, a drive system with high torque density and low weight is crucial. “maxon’s motor provides 13.8Nm torque in a package weighing just 300g. That’s astonishing,” says Harry.
Harry learnt of maxon through the company’s exploits with its NASA projects, where its drive systems have been involved in every Mars mission to date. A maxon brushless, four-pole DC motor, optimised for torque density, is paired with a customised gearbox that achieves virtually silent operation, unnoticeable to the ear while cycling, while maintaining long-life durability.
On a normal e-bike, the battery is a significant weight contributor, but HPS overcomes this with a special design that generates 93 watt-hours (Wh), giving 1.5 hours’ use for just 722 grammes. There’s also a slightly larger version that provides 185Wh for 3 hours’ use at 1.2 kilos.
For experienced cyclists, 1.5 hours isn’t a long ride, but Watt Assist isn’t intended to be used like a normal e-bike.
“With a regular e-bike, riders typically use its power all the time, but with Watt Assist, I define it as ‘climb time’,” says Harry. “Our system isn’t designed to be used constantly. We’re targeting experienced cyclists, and Watt Assist provides that extra assistance to be used just when you need it, whether that’s helping you crest the brow of the hill, or riding into a strong headwind.”
Natural power delivery
The HPS approach to power assistance is also unique in that unlike a conventional e-bike, its input doesn’t come from a torque sensor. Instead, Watt Assist uses pedalling cadence in combination with a wheel speed sensor. This method gives the rider a more natural sensation of power assist and relies more heavily on human effort.
“You get this feeling that the power is coming from your legs and not a motor,” says Harry. “With our system, you have to be cycling at a certain rate for the torque assist to be applied.”
A button on the handlebar selects the increments of assistance. There are two modes: ‘Peloton’ mode features six small increases in torque, providing a sensitive output suited to riding safely in a group. There’s also an ‘Attack’ mode that rapidly advances to the maximum 13.8Nm assistance when sudden acceleration is required.
Precise torque assistance levels have been developed through extensive testing, including telemetry generated by riders including former professional cyclist Philip Deignan. To read the selected assistance level, Watt Assist connects wirelessly to a rider’s handlebar-attached computer screen display.
Sir Chris Hoy testing an HPS-equipped bike
Precise motor control
When the handlebar button is pressed, this communicates with a maxon electronic motor control unit (EMCU). This master controller operates the HPS programme and its corresponding modes and torque levels. In combination with the input of the wheel speed sensor, the EMCU commands an additional maxon controller that regulates motor torque and speed, and the resulting assistance that the system provides to the rider.
“We looked at other motor manufacturers, but maxon was by far and away the best. The precision engineered drive system gives us the fine control we were looking for, in a torque-dense, lightweight package,” says Harry.
Leading engineering design and development at HPS is Gary Anderson, former chief mechanic at the McLaren F1 team and the designer of the Jordan F1 car. maxon UK & Ireland engineer Matt Dean worked closely with Gary in the specification and development of the HPS drive system.
“Matt Dean has been instrumental for the entire length of the project,” says Harry. “He was a guy we could work with – and we continue to work with today. Along with the support of the head of maxon UK & Ireland, Will Mason, Matt has provided extremely valuable assistance throughout to help develop Watt Assist.”
HPS is currently working with premium bicycle manufacturers integrating Watt Assist into their frames, and we can expect to see the first releases in the next 12 months.
For more information please visit: www.maxongroup.co.uk
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