Ergonomic Analysis: Hand Crank vs. Bike Pedaling
Brittany Griffin
Before I began analysis I met with Matthew Marshall, our ergonomics SME.
We first began with a discussion of our current designs and the question of whether
to power them by either hand crank or bike pedaling. The first conclusion we came
to is that leg muscles are obviously bigger than arm muscles so with bike pedaling
we should be able to produce more force/torque. This was just a general
assumption and not design specific so we went more into the kind of research that
can be done to get more specific answers.
We decided that something valuable to focus on would be our engineering
requirement that states that we want to operator to be able to run the machine
without a break for more than an hour. Focusing on this requirement made us think
that either our target is a little too high or that we would have to use a bike crank. It
was decided that I would do some further research to see if there have been any
studies done with hand cranking or bike pedaling that could give us an idea of
average endurance and/or power production.
One of the first things I came across was a military standard for human
engineering (MIL-STD-1472 F, pg.69). Below is a table from the standard that shows
the minimum, preferred, and maximum length, diameter, and turning radius of a
hand crank for light and heavy loads. This may become useful in the future if we
decide to go with our apple peeler design and find that a hand crank would make
more sense for a stop-and-go like operation.
One of the first studies I came across when searching for hand crank studies
was for the design of a portable hand crank generating system for use in developing
countries. This seemed like an application very similar to our project. As part of
their design process, a study of human power capabilities was done and the results
were put in the table below. Assuming the average daily human calorific
consumption is approximately 2500 (this would be an overestimation in a
developing country), it’s found that a person would have 3000 Whrs of energy per
day. When taking into account everyday activities they found that it would be a
reasonable assumption to say that a person would have 100 to 300 Whrs of energy
for the purpose of conversion (a hand crank generator in this case). This gives us a
rough estimate of the amount of energy a person would have to put into the
machines that we’re designing.
The next useful study I came across was “Torque Production Using Hand
Cranks in a Simulated Gear-Operated Valve Opening Task.” They used a
dynamometer and software on two computers to convert the work done by the
subjects to a torque value expressed in Nm. Data was collected for 5 males with the
following anthropometric data:
Below shows the results that were found are various angles, directions, and heights.
This gives us an idea of the torque production a person can produce using a hand
crank.
Finding studies on bike pedal power or pedal endurance was very difficult
and proved to produce little to no results. Research will continue but for now it can
be assumed that endurance will be higher when using a pedal system as opposed to
a hand crank because of the size and average strength of upper body versus lower
body. Pedaling would also be more ideal because it frees your hands to load and
secure the machine. It would limit the number of movements that would be
necessary if we were to use a hand crank.