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.