UK-based Aim93 is aiming to break the world record for a human powered vehicle (HPV) with a newly designed recumbent bicycle, which they unveiled at the recent Autodesk University London event.
The small team of engineers believes they can hit 93 mph, eclipsing the current standard of 89.6 mph for an HPV. To achieve this, they’re relying on decades of experience and the latest digital design and simulation tools from Autodesk, a team sponsor.
For context, how fast can a person typically go in a vehicle operated under their own power? Most people on a conventional bicycle can easily reach 10 mph on flat terrain. Competitive cyclists can hit speeds of 25-30 mph without too much trouble.
But there’s an entire community of engineers, designers, tinkerers, and cycling enthusiasts committed to pushing the limits of what’s possible in the specialty arena of HPVs. They design, fabricate, and pilot vehicles that are technically bicycles, but look more like pedal-powered rockets.
In 2016, a team from Aerovelo set the existing record of 89.6 mph in their vehicle, the Eta.
From competitors to collaborators
Glen Thompson and Mike Burrows have both been active in the world of HPVs for years, and have competed against each other numerous times.
Thompson is a designer, engineer, and senior lecturer at London South Bank University. Having originally studied vehicle design at the Royal College of Art, his specialty is the study of aerodynamics.
His HPV racing career reached a pinnacle in 1987 when he won a silver and four bronze medals at the World HPV championships in Vancouver.
Burrows is a long-time bike designer based in Norwich. He’s perhaps best known for designing the revolutionary Lotus 108 bicycle which was ridden to Olympic gold for Britain in the 1992 Olympics.
In recent decades, he’s been focused on recumbent bikes, having developed the RatRacer and the commercially available Speedy. Famously iconoclastic, he doesn’t own a computer or a mobile phone, and eschews CAD systems for traditional hand drafting and hand crafting approaches.
Friendly rivals for more than 30 years, Thompson and Burrows met again in 2013 at the funeral for a mutual friend, bicycle advocate and author Richard Ballentine, and decided to start working together on a new HPV, one that would leave the others in the dust.
“The most important factor in a partnership like this is confidence in each other’s abilities,” says Thomson. “Mike and I have always enjoyed sharing data, knowledge, and ideas about bicycle design and aerodynamics, and at the funeral we realised the opportunity to combine our talents to build a record breaker. Our mutual experience enables us each to critique and challenge the other’s ideas constructively. The only thing we ever argued about was who is the more arrogant!”
Laid back for speed
When most people think of cycling, whether that’s a trip to the park or the Tour de France, they think of what are called “upright” frames, in which the rider is perched above the two wheels. This design has the advantage of enabling good visibility as well as allowing riders to use their own mass to drive the pedals, which is why most people stand to pedal uphill.
But when it comes to achieving maximum speed, uprights have a big flaw: the rider produces a large profile, which causes significant drag. All that wind in your hair while riding is actually the air reducing your velocity.
Not your conventional bicycle
Uprights are still used in competitive cycling because the sport is so highly regulated—innovation is purposely restricted to promote competition. They want to ensure that the riders are being tested in a race, not the equipment.
In the world of HPVs, though, the rider is secondary to the vehicle, and innovation is not only tolerated, it’s expected – in many ways, innovation is the main event.
It’s rare to see an upright bike at an HPV competition. Instead you’ll see recumbent bikes because their aerodynamic profile is so much more streamlined. And the fastest vehicles are fully encased in farings that further reduce drag. You certainly won’t get any wind in your hair riding these machines, but it’s hard to argue with the results: velocities that exceed highway speed limits reached just by pedalling.
Gearing up with generative design
To make the Aim93 frame, Burrows used his normal approach: the design started on a large drafting board in the gantry office above his workshop; it then progressed through various lash-up prototypes to a track-ready frame design built by hand by wrapping carbon fibre around foam cores.
Thompson, meanwhile, got busy on the faring, using a much more digital approach: he took the published data for the record holder at the time, Varna, and ran computational fluid dynamics (CFD) simulations on it, then started making iterative changes to achieve aerodynamic improvements.
“Aerodynamics of HPVs is a unique field because they have the lowest extreme of drag forces for any human-based vehicle (the fastest production cars at 93 mph have 80 times more aerodynamic drag),” says Thompson. “Setting up a CFD model needs highly detailed settings to arrive at reliable data.
“The software tends to underestimate forces, and for many HPV teams in the past, the move from CFD to road test data has led to disappointing results. I have always tried to work to the most pessimistic interpretation of the digital simulation. Autodesk CFD Motion, and their expert Heath Houghton, enabled us to verify our results and build confidence in the predictions.”
In 2016, the team brought in Barney Townsend, another designer/engineer and 10-year colleague of Thompson’s at London South Bank University. They had previously collaborated to develop the teaching of Autodesk applications at the University, particularly in CAD modelling and simulation.
Townsend’s role, among others, was to improve on Burrows’ hand-crafted frame using Autodesk’s generative design technology, which is now part of Autodesk Fusion 360 Ultimate, a cloud-based product development platform.
Generative design uses machine learning and the power of the cloud to generate design solutions that a human would never consider – hundreds or even thousands of them. The designer then works collaboratively with the software, choosing trade-offs to achieve the goals they establish for size, weight, material, manufacturing method, and more.
“I started out by defining the loads that the frame would be subjected to, and blocking out the areas that were off-limits, such as the space for the rider, wheels and chain set, and the outer boundary limitation of the aerodynamic shell,” says Townsend.
“Basically, once the software knows the spatial and load conditions it must work within, it fills this with material and then nibbles away at it, continuously analysing the internal stresses to remove as much mass as possible without going below the specified safety factor for the structure to do its job. It then presents the designer with a series of outcomes from which to make a decision.
“Fusion 360 does a great job of combining – fusing – elements of different software in one package,” Townsend continues. “And the fact that it’s available free to all students, as well as to companies with less than US$100,000 in revenue means that not only can I teach it in my university classes, my students can use it in their start-ups after they graduate.”
He says that it has even changed the way he reviews student work, since students can share their models with him via web browser.
At Autodesk University London, the team put their original prototype on display, the frame that Burrows crafted by hand, along with a scale model of the frame that they’ve created using generative design.
In July 2018, they’ll attempt to set a new world record in a standard one-hour HPV event. In this, the team launches the vehicle from a standing start and they see how much distance it can cover in one hour on a circular track. Mike Burrows himself, aged 73, may be the pilot.
But the big race comes at Battle Mountain, Nevada in the US, in September, sponsored by the International Human Powered Vehicle Association. There, the Aim93 team aims to set the new record for speed, period. On a uniquely flat and straight section of Nevada highway, they’ll have five miles to get the vehicle up to top speed, which will then be measured for 200m.
So far, the 90mph mark has proved elusive for HPVs but the Aim93 team thinks they can beat that significantly. “All our simulations show that we should be able to hit 93,” says Townsend.
Only time will tell whether they can do it. In the meantime, the Aim93 story shows us not only what experienced designers and ingenious engineers can do with the right tools and cutting-edge technology, but provides a glimpse of just how far and how fast people can go under their own power.