Variables: The Piston

This week I started working with the design of my piston again and drew up some more variables for when I actually start measuring the dimensions of the parts. The drawing uses both, the variables that I used in last weeks diagram with added new ones, so, for this reason, I am re-uploading the picture from last week so that it will be easier to refer to both at the same time.

The dimensions from last weeks picture used in this diagram are x and z, where x is the length of the individual segments of the piston, and z is the number of segments in the piston. These are used in combination with a new variable r, which is the radius of the first segment, and q, which is the distance between segments, to find the radius of the last segment. As seen in the diagram, when moving to the next segment, the radius is reduced by two times that of q, the distance between segments. Therefore the radius of the last segment is the radius of the first with two times q times the number of segments, z, minus 1.

First Steps: Variable Measurements

Before I can start building the parts to my mechanism, I need to know what parts I need, how many I need, and their dimensions. So this week I have been thinking about the relative dimensions of the parts for my mechanism. By this I mean that the dimensions are variables, and therefore, it does not change what the equation for the other dimensions are, if the actual dimensions change.

These dimensions are needed to find z, which in this diagram, is the number of segments in the piston. This is important information to know early because the different parts all need to fit into one another, meaning that all the pieces are consecutively smaller than the last piece. Knowing the number of pieces needed to build the piston will tell me how wide the radius will be for the largest and smallest pieces, and then all the ones in between.

First Steps: Doubling Up + Tech Shop

During the night I realized something important about my design. As a test, the arm should be able to allow me with ease to lift myself on a bar with that one arm. Because of how one’s arm moves to lift oneself while doing a pull-up, I have made the observation that I will need to double up and have two pistons per arm, not one.

This picture is of my arm before and after lifting myself for a pull-up. As one can see, my bicep and my forearm are not the only muscles that pull closer to each other in my pull-up; my tricep is also pulled closer to my side. Therefore by using two pistons I can minimize the stress on the users muscles, as it gives support to both groups of muscles that are working during the pull-up.

On a side note, I have recently visited a place known as Tech Shop. Tech Shop is an organization where one can pay for a membership and have access to a wide variety of machines and parts needed to build projects like my own; however, their building that is closest to me is closing down, and it will take a few weeks for them to find a new plot for their building. This will hinder my ability to actually build my arm, but I can spend more time on the design of my arm and work on the design of my supports and testing instruments.