Aim high: A London South Bank University project to develop a high-speed competitive recumbent racing bicycle has successfully moved from faculty research to student extracurricular initiative, and has its sights on reaching 93mph.
While Burrows made the carbon-fibre bicycle frame, Thompson focused on the fin-shaped faring. His starting point was the published dataset of the Varna, a series of record-breaking human-powered bicycles devised by Georgi Georgiev, which Thompson used to set up and validate the computer model. A simulation included 12 million elements. Then began the work to refine key areas: nose, footbox, tail, wheel openings. He worked particularly on the zone where air flow changes from laminar to chaotic, where drag forces are high.
Last September, their finished design, dubbed the Soup Dragon, competed. The World Human Powered Speed Challenge runs on a five-mile long stretch of straight, level resurfaced public road in Battle Mountain, northern Nevada. Each team gets a total of 10-12 runs over the week long competition; speed is measured in the final 200m.
The 19kg vehicle consisted of a carbon fibre frame with recumbent rider's seat and steering stick, toothed chain-ring mated to the front wheel in a direct-drive configuration, huddled--with rider--inside a thin exterior shell viewing the road ahead on two battery-powered redundant video cameras and screens. The end result of years of work was a fantastic first result 53mph.
The attempt marked the end of the beginning; both men retired from the project, and Thompson retired from LSB University. His former project assistant, Barney Townsend, senior lecturer in product design, stepped up to guide the project, led by an entirely new project team: students.
PASSING THE BATON
Townsend explains: "The whole idea of the project from the outset was to get it started and hand it over to the students as an ongoing extracurricular project in the vein of Formula Student--which was exactly what he did."
"Getting to that model to that level in the first place took many years of high-level research. Once we've got that, you can, at an undergraduate level, discuss the principles and introduce them to what's going on, and explain various different factors, and then it's quite easy for them to further explore iterations in the shell shape and so on."
Over the past year, Townsend and the students have been adjusting the design, with a new, one-race focus. He explains that last year, the design competed in a second race, the British human-powered speed records, which take place on a circular track because of the lack of empty straight roads in this country. The lightweight design of the vehicle helped to reduce the effort required to get to top speed.
But by reducing weight in the vehicle, the designers also reduced its structural integrity and stiffness. As a result, the single-skin fibreglass airfoil with stiffeners actually deformed under aerodynamic loads when it was raced in the Nevada desert. "Having got there, and seen the event and the track, it was clear it could be unsafe in a nasty accident." In addition, the rider, Russell Bridge, a veteran competitor of human-powered races, complained that at top speed steering felt loose, floppy and wobbly: a scary feeling at any speed, much less highway velocities.
"That's not necessarily a fault in the design; we couldn't test it at those speeds because we have nowhere to do so in the UK with enough length of track to get up to that speed. And time constraints- we had limited time to test before we went anyway."
This time, blasting through the desert is the only goal. A quirk of the course is that it dips by just under 1% toward the end; that means that competitors will not be punished by additional vehicle weight.
So, although the team has kept actual shape of the shell identical citing their lack of experience with it, the construction of the shell they have changed utterly: it is now a stiff, dual-skinned carbon composite epoxy and polyurethane sandwich with Kevlar to protect in case of a crash. That makes the vehicle essentially a monocoque design, meaning it is structurally supported by the exterior frame. Embedded in the shell is a keel section consisting of two triangular wedges that form a base on to which everything is attached, including the transmission; the frame also now includes a roll cage to further protect the rider.
"The big learning point when we got to the event last year was that we had designed a bicycle and brought a bicycle with us, but actually with the speeds that we were achieving and the conditions, it should have been more like motorcycle engineering. That's the philosophy: we're trying to over-engineer everything this year to be confident that we have a fully safe vehicle." Doing so pearly doubled its weight, to 33-4kg.
Two other design elements were tweaked this year. One of Burrows' original innovations was the transmission: to remove the derailleur and cassette and make the bicycle direct-drive on the front wheel. New drivetrain parts for that were made this year. Although the design reduces weight and complexity, it also removes gears. Two consequences flow from that. First, the strongest rider in the world could not drive a 150-tooth main chain ring from a 16-tooth sprocket powerfully enough to accelerate to a stable speed before tipping over. (In fact, the team hopes to reduce the sprocket to 14 teeth for an optimal high-speed ratio).
Partly, the race organisers help here by allowing a 15m push start. But even so, the vehicle still needs a stabiliser wheel for lateral support for an additional 50-100m. Once fully stable, the rider flicks a switch, and the spring-loaded support wheel rod retracts. A newly-designed hatch, with magnets in the outer flap, helps improve the aerodynamics around the assembly by covering the hole. This year's bicycle materials bill was about 3,500 [pounds sterling], including testing and prototyping.
Second, the direct drive mechanism interferes with steering, which is also accomplished with the front wheel. On most bicycles, drive and steer are handled on separate axles because of the precision required in the drivetrain; turning the axis of either pedals or chain-ring pivots the drive sprocket, side-loading the chain. Instead, the whole axle pivots on a cylindrical bearing inside the centre of the sprocket; goes through the wheel to the left hand side, and is then pushed backwards and forward by a drive rod from the steering column.
The stated aim of the team is to break the human-powered vehicle record of 89mph--in fact, to hit 93mph. Townsend says that he believes that this remains a realistic target, as it was borne out of simulation data and detailed calculations.
Contends Townsend: "It is a goal in the sense that it has a nice challenge to put us not just ahead but is something to fight for that is quite a significant improvement on the current world record that may one day be theoretically achievable. I don't think that we will achieve it this year. I don't think that we have enough experience yet. These kinds of projects take years of development and experience to tune them to the state that you will actually eke out those absolutely last percentages of power to break over the limit. My personal goal this year is the British speed record, which I think stands at 76mph; I think that we have a good chance of breaking that."
The drivetrain of the Velociraptor was one of the areas that the team had reengineered in the year-long run-up to the race, including supporting the steering column at both ends and changing the bearing surfaces on the left-hand end of the steering axle to travel on rails. Although that stiffened the steering, it also highlighted the major significance of the effect of the offset steering. The team had known that it would affect the bicycle's handling; bumps in the road are trying to push the wheel backwards and turn the bike to left, forcing rider Russell Bridge to steer it back to centre. Barney Townsend, the South Bank University project lead, explains: "On the road tests that we had done in the UK, it hadn't seemed a problem; it felt perfectly stable. That said, in the UK the only tracks that we had access to were a mile or a bit longer, they don't give us the ability to get It up past 40mph.
"In Nevada, the bike ran the 2.5-mile course happily enough, but with a bit of weave. And then we got on the five-mile course, and it was getting up to well the other side of 50mph--55, 56mph--and he was really struggling to control that steering." Eventually he crashed, at greater than 50mph. Fortunately, Bridge was fine; the new heavy composite shell and carbon roll cage protected him, and the integrity of the vehicle. Had the same thing happened with the previous design, Bridge could have been injured or even killed from road abrasion.
Although the crash didn't threaten Bridge, it did threaten the team's medal hopes. Continues Townsend: "We did some head scratching. We knew we could tune it a bit, and keep racing; we could shorten the steering arm to make it less sensitive, and things like that. But, ultimately, the problem was exacerbated by speed, so It would only get worse, and if we managed to tweak a few more miles an hour out of it, he would only end up crashing at a higher speed. Ethically, we thought the best thing was to have a big rethink."
The team knew it would be impossible to rig up rear-wheel steering; that is said to pose big problems with stability for any bicycles, but particularly recumbents that feature a lower centre of gravity. And it also knew that, since the crash happened early In the competition, it had a (little) time to try a fix.
CAR PARK ENGINEERING
"We had a team of engineers here, and a reasonable toolkit, albeit our workshop is the motel carpark," reasons the engineering lecturer.
"In the space of three quite intense days, we transformed that bike from a front-axle steered, front-wheel driven, rear-braked bicycle, to a rear-wheel-driven, front-fork steered, front-axle braked bicycle. It was quite a significant rebuild of all of the mechanical components."
The transmission unit and front wheel were housed in between two side panels of carbon and then an upright front column that held the front bottom bracket and chain-ring axle and the cranks. The team reconfigured the frame, cutting the side panels in half and rotating one upward, and built a new upright column sitting between the wheel and the rider, and mounted in that a pair of bike forks pirated from a new bicycle bought from a shop an hour down the road. The main chainring was kept in the same place, offset far enough from the front wheel to enable a degree of steering. It drove the 8mm machine drive chain, lengthened with spares, running all the way underneath the rider to the back wheel. The chain was guided along the central rails of the monocoque chassis by using two pairs of spare sprockets as idlers, one set each on drive and return. The previous front wheel, with its 16-tooth hub, was swapped to the rear; and the rear wheel came up to the front, braked using discs, thanks to mountings that came with the new fork.
JUST IN TIME
"We completed it in just enough time to race on the last day, which was fantastic," continues Townsend. "Again we did the 2.5 mile course in the morning, and then got on to the 5-mile course in the afternoon. Which infuriatingly had a big crosswind; it wouldn't have been a legal run anyway, with a flat crosswind of about 15mph. But they were letting bikes down the course. The top of our logged speed was about 55mph on this brand-new bike. But even some of the top guys who had been doing 80-plus mph during the week only managed that in the same heat in that wind. So that was a big success as far as we were concerned. And, likewise, Russell felt safe in the bike."
"So it was a mixed review. We didn't break any records that we were hoping to. But we won an award for the hardest-working engineering team, for this intense period of work. We got a lot of respect from the community about what we were able to achieve in three days. From my perspective, it is as much about the student experience as the project and the students' experience of participation. It was really inspiring to see this group of students, who had worked together all year on the project under less pressure at university, really come together. Also, for them, to experience that level of highly pressurised teamwork, and simply doing whatever it takes to deliver on engineering projects within the time available."
In fact, their dedication won over the leader of the French team, who was staying at the same motel--their place on the final night heat on the five-mile track was given by him. That epitomises the enthusiasm and sportsmanship of the event, contends Townsend. "The whole event is a very interesting community of like-minded techy, quite nerdy but also sporty, engineering-type people. It's a group of passionate amateurs, all sharing knowledge."
So, back to the drawing board. As most of the team were third-years or graduates, one of Townsend's first tasks is recruiting the next cohort. He concludes: "Next year, the plan is to go back fighting. I've got my eye on the 80mph hat; I want to see it on our rider. There's no question of stopping. I'm not disheartened at all; we are the young upstarts; it's only our second year. Good design is about learning from what works, and what doesn't and improving on that as a result."
A spin-off from Aim93 is another bicycle project at London South Bank University for first-year undergraduate engineering design students. This starts with a consignment of 40 old bicycles from a charity, and a pile of bamboo struts. Working in teams of five, the students have two weeks to convert the upright bicycles into recumbents using bamboo and fibreglass. The winner Is decided during a race down the road outside the university. Says Townsend: "It was a very cheap project to run and easy in terms of implementation, and the students absolutely loved it. We got some great footage of the joy on their faces as they are pedalling their newly-built recumbent bicycles down the road. They learned so much; most of them had never disassembled a bicycle; never used any of the bike-specific tools; never really examined the way the drivetrain works and the precision that you need in alignment of components. That's something that, longer-term, we'd like to think about rolling out, as a kind of Fl in Schools project; some kind of schools' league of bamboo recumbent bicycles."
Sponsors and supporters
Although the materials bill for the bicycle was relatively low--about 3,500 [pounds sterling]--sending a dozen students to Nevada for two weeks is not. This past year, the team benefitted from a number of sponsors.
* Airgrind produces a nanotechnology coating for aircraft; it seals every pore in the surface to reduce drag.
* Blue Hippo Media is producing a documentary about the project. "Glen and I had it in our minds that one of the big aspects of the project is engagement in STEM. The project has got so many touch points at school level that can be used to inspire the younger generation, and explain that this is what real engineering is."
* IT company lllumit, one of whose directors is a keen cyclist, sponsored production of the documentary.
* Rayvolt, the Spanish e-bike company, donated a 1,000W hub motor that the team anticipates using next year to help accelerate the bicycle to high speeds on short tracks.
As the new academic year starts up, the team will again be looking for sponsors.
Caption: The original steering/transmission unit
Caption: First morning run
Caption: Main: CAD assembly of the original bike
Caption: Right: The full 2019 Aim93 Team
Caption: Arrival at finish line on final evening after a Successful five-mile race on new bike
Figuring out the chainline in the new configuration
The punishment inflicted by a 50mph crash on the composite shell
Caption: Last evening run
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|Title Annotation:||HIGHER EDUCATION|
|Date:||Nov 1, 2019|
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