A drive train is the name for the part of the kart that sends power
from the driver’s feet to the wheels. The drive train is made
from two wheels joined by a chain just like on a bike. This section
explains how we can use gears to increase the speed of our kart
around the course.
Gears on our VROOM karts work in the same way as gears work in
cars and bikes. The driver's legs (or an engine in a car) produce
power most efficiently by going round at a steady rate. This might
be twice a second for leg power (and 50 times a second for an engine).
However, during the race the kart moves at different speeds - slowly
around corners and quickly on the straights. Gears ensure that you're
always peddling efficiently.
Here's a picture of two different sets of gears. The pedals are
attached to wheel A and the kart's back wheel is attached to either
B or C.
In the top picture, when the 'force' from the pedal makes wheel
A rotate (turn) once, wheel B also rotates once, as it is the same
size. However, in the second picture when wheel A rotates once,
wheel C will rotate twice, because it is half the size of wheel
A.
This means if the driver's legs are turning the pedals at A twice
every second, B will also rotate twice per second, but C will rotate
four times per second.
So what speed does the kart travel at? If the back tyre has a circumference
(the distance around the circle) of 0.8 metres and the driver pedals
at two rotations per second:
- In the top diagram wheel A rotates twice per second this makes
wheel B rotate twice per second.
The back tyre is attached to wheel B so it also goes round twice
per second. Therefore the distance the kart travels each second
is two times the circumference of the tyre:
2 × 0.8 = 1.6 metres per second (about 3.5 miles an hour)
- In the bottom diagram wheel A rotates twice per second making
wheel C rotate four times per second.
The back tyre will now go round four times per second. Therefore
the distance the kart travels each second is four times the circumference
of the tyre:
4 × 0.8 = 3.2 metres per second (about 7 miles an hour).
From the explanation above it looks like you should always use A
and C because you will go faster. However, when accelerating using
the same 'force' from your legs, A and B will accelerate you twice
as fast as A and C.
Using both of these gears at different times on the course gives
your kart the flexibility to be both quick to accelerate after corners
(using A and B) and fast on the straights (using A and C).
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