13. Mechanical Design Assignment

Mechanical Design Assignment

This assignment was very important facing the final project design, because, as its name says, it deals with the mechanical aspects of the project. I made this first approach to a workflow before starting:

For my final project, there are a number of definite constraints that have to be addressed in order to succesfully get the airship to move. These are the following:

Weight: the frame containing the project's hardware must be as light as possible.
Symmetry: If possible, the design must be Symmetrical in order to better distribute the load within it.
Balance: The model should be balanced in order to glide properly.

So, I proceeded to tackle these issues for the final project, first the Frame design. The objective was to create a frame light enough to be lifted by an Array of Helium Baloons and be able to glide autonomously or via an external control device. The first idea was to leave enough room in the middle so a camera could be set there. This first approach was designed in inventor:

First Frame design

As the Final presentation Day approached I started to work through this idea, then the camera was out of the way and a lighter design could be made, this time, took a direct approach and cut the shape from foam. This frame designed was shown in the final presentation day.

raw foam

Airship Canopy

The idea behind the project was to use Helium gas to elevate the frame/canopy containing the electronics and propellers. I sourced locally a canister of Helium por party baloons as well as fifty baloons to lift the set.

Helium

The initial tests with the Helium indicated that each baloon could lift around 5 grams of weight, so to lift the whole canopy including electronics and motors (140g) we would neer between 25-30 baloons to get the job done.

To fabricate the frame, We started from a spare foam block and cut it using a heat gun-heated cutter we had at the lab.

cutting foam

After making the frame, it was time to cut the space for the moving parts, being specific, the steering servomotor, but, in order to get the servomotor to steer effectively, I needed to design a simple mechanism to work with the servomotor in order to carry thre DC motors and steer the airship, the simplest way this could be done is by designing a piece that could press-fit the servomotor, for this, I used inventor and cut it using the laser cutter, the basic design is just an extension arm for the servomotor.

blimp articulator

Widening this concept, I duplicated the arm and rotated it, creating a sort of incomplete triangular piece, this would help me better steer the airship:

sensor boards, after soldering, ready for testing

Since "closing" the triangle would need and additional piece and fixating elements such as bolts or screws, I went on to design a single piece to steet the airship. this one would press-fit with the servo and have the DC motors attached in the other side.

Final Articulator

The Assembly was tested attaching one of the DC Motors to the piece using a cord and a small servo on the other end.

Testing articulator

In the next image the evolution of the design can be seen, including a more detailed take on the final piece:

Blimp articulators

steering piece

After testing the first blimp design in the final presentation day, it was made certain that some changes needed to be made for it to work successfully, for instance, the first canopy area was to large, making it harder to balance, so a new canopy design was in order, for this I went two ways, one, assuming that the project could behave in a way similar to a Hovercraft over water, and taking this into account I designed a new canopy:

hovercraft inspired canopy designed

This meaning that the project's hardware would be placed upon the "platform" made in the depressed zone. I exported the design and made an attempt to mill it in the shopbot using Partworks 3D. At the time, the Shopbot had 12mm Plywood on it, so I had to scale the model to mill it, the result was not very functional, So I had to make something else. Hover Shopbot Test

I Used Rhinoceros for Modelling a new press-fit canopy, here is the DXF exported prior to laser cutting, the cut model can be seen in a photo in the Project Development page:

Canopy Press Fit Design

After cutting, it was cleat the the enclosure built was too bulky and heavy for the airship, so, in order to light the parts I introduced an array of geometrical forms to be cut with the model.

Press fit canopy final design

The assembled canopy model can be seen assembled in the following pictures.

Final Canopy

Final Canopy 2

Final Canopy 3

the design files for this assignment can be found here

Conclusions?

Design is everything in this assignment.

Second, it's always about what needs to be designed

Third, sometimes, making things really simple can be daunting. Keep that in mind

Fourth, as previously stated, take into account Hofstadter's law into assignment planning, it -painfully- works.