Drilling holes will reduce the
overall weight even further.
a threaded output shaft. If you
cannot find a suitable hub adapter,
these are a lot easier to make than
bespoke wheels, so machining your
own hubs for your commercial
wheels is often a good compromise.
The other factors to consider
are the maximum safe RPM of the
wheels, the maximum specified
load, the friction (tire) material, and
bonding methods. Trial and error
plays a large role in the choice of
commercial wheels.
Machining Your
Own Wheels
With so many types of wheels
available to purchase, why would
anyone make their own? My robot
‘Wheely Big Cheese’ uses custom
built wheels that are basically
welded titanium ‘drums’ with
domed front and rear faces, and a
keyed aluminum hub for
the titanium live axle.
Instead of tires, the
wheels have tungsten
spikes that bite into
wooden arena floors.
The entire wheel weighs
just 10 lbs and easily
survives most combat
situations. Nothing
commercially available
met my requirements for
the same weight which
is exactly one of the
reasons to justify making your own
wheels.
Rubber tire material is
bonded to the aluminum
wheel with carefully
selected epoxy adhesive.
the material from between the outer
and inner edges — and creating
what is effectively an ‘I beam’
section across the wheel — can
remove significant amounts of
weight without compromising the
strength of the wheel too much. For
further weight loss, drilling holes in
the thinner section can be effective,
but great care must be taken not to
weaken the wheel to the point that
it will warp and/or deform under
load. If you do not have the facilities
to machine a billet of material to
form a wheel this way, you can
create the same shape (or a drum
shape) using welded fabrication
methods. We recently manufactured
a pair of aircraft grade aluminum
wheels which started out as 5 lb
solid disks, then were machined out
on the lathe and then drilled on the
mill. A durable solid rubber tire was
then bonded to the aluminum
wheel, with the finished product
weighing just 1.5 lbs each — the
potential weight savings are clear to
see.
Assuming you are reading this
and you have access to a complete
engineering workshop that gives you
the option of using bespoke wheels
machined to your exact
specifications, or fabricating hollow
wheels out of any material you like,
or manufacturing custom hubs and
adapters to suit any commercially
available wheel, what should you
do? Should you make your own or
buy some ready-made wheels?
There really is no wrong answer to
this. You may enjoy making parts so
much you will invest days creating a
rolling work of art when a
commercial version would bolt right
on, or perhaps you don’t see any
benefit in spending many hours to
marginally improve on something
that does not cost so much and
could be delivered to your door
overnight. As with so many things in
the robot combat world, every
builder will have their own preferred
solutions, and if a solution works, it
can always be argued that it is the
right solution. SV
34 SERVO 09.2010
