“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 con dent that we have a fully
safe vehicle.” Doing so nearly doubled its
weight, to 33-4kg.
Main: CAD assembly of the
original bike
Right: The full 2019 Aim93 Team
NEW FEATURES
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 ow
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 icks a switch,
and the spring-loaded support wheel rod
retracts. A newly-designed hatch, with
magnets in the outer ap, helps improve
the aerodynamics around the assembly
by covering the hole. This year’s bicycle
materials bill was about £3,500, 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;
the axle
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 ght
for that is quite a signi cant 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.”
Turn over to see how the team fared
Bamboo bikes
A spin-off from Aim93 is another bicycle project
at London South Bank University for rst-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 ve, the students have two weeks to
convert the upright bicycles into recumbents using
bamboo and breglass. 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 bikespeci
c 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 F1 in Schools project; some kind of schools’
league of bamboo recumbent bicycles.”
www.ied.org.uk 11
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