The 2.5-axis system was an assignment to design and build a mechanical system which operate on 2.5 degrees of freedom. This meant that something could move in a plane of x and y, and then at any location of that plane, it could turn on or off (i.e. "do something"). 

In the beginning of the assignment we had to create a linear movement system using a screw and a motor driver. Then that linear movement system had to be redesigned into a 2 axis motion system. The total work volume of the action was to be constrained to a 2.5 cubic inch.

The design challenge was for the whole system to be compact and easily carried around. The whole device did not have to be able to fit into a backpack but the components did. The whole system had to be able to be assembled/disassembled in less than ten minutes. The main mechanical elements given were stepper motors, servomotors, pulleys, belts, and aluminum linear 80x20 guides. 

As with all our projects, we started from some sketches again, and moved from there. With the time constraint to build this system, our team decided to design something as simple as we could. We came up with a basic idea of a writing machine. The machine would function as a 2D printer, moving a pencil or pen around a plane of surface, and then making contact with the page (on/off) whenever it needed to write. And so we began.

We had to dimension parts such as bearings and the stepper motors to ensure our pieces we made to fit them would function correctly. We had already done a linear motion system, so we decided to build on top of that. This system would incorporate the stepper motor and a rod for the first axis motion, and then a belt and pulley system set up above for the second axis motion. 

After all of us were on the same page, each member of the team was assigned different parts of the system to design. Since we had very limited time and each component of the system demanded a lot of attention on designing, we all had to work separately on each component.

I was assigned to design the first axis motion, and the way that the plate would be secured and move along this axis. To do this, I designed two end pieces to hold the rod and bearings, and a box shape to move along the rod and to support the plate that would be written on. This would be secured to two small squares of plastic that slide along the grooves of the 80x20 aluminum.

On the right is an image of one of the parts I made, as well as a closer look at the final product of the first axis motion after it was put together. 

The second axis of movement was designed by another teammate who made a piece that would hold the entire pen-holding assembly, and slide along the 80x20 frame that was mounted above the writing surface. It moved in this axis with a pulley and belt system, which turned out to work quite nicely. There were definitely challenges here, since the massive part that slid along the 80x20 was first designed to fit exactly in the shape of the aluminum frame. That fit was extremely hard to make correctly with a 3D printer, so after multiple attempts it was fixed by just creating a square shaped hole that could slide more simply with more space to move. 

The 3D printed housing for the pulley motor also had trouble fitting due to tolerance issues. It was then reprinted with dissolvable supports, however the piece was so brittle and still too tight, that it broke when fitting the motor. Eventually this was fixed also. 

​The pen or pencil holding tool turned out to be the most difficult thing to design correctly. The initial design done by a team mate would simply rotate the whole assembly of the pen holder up and down with a servo motor, to make the pen lift and make contact with the page. This proved to be dysfunctional during testing, since the pencil was always at an angle and not normal to the surface of the page. When it moved in one direction it was fine and would write, but in the opposing direction to the tip of the pen or pencil, there would be too much friction at the surface, and the entire system would get stuck. This needed to be redesigned so that the pencil or pen would always be normal to the surface and just move up and down. It is a challenging thing to design that with a servo- essential transforming rotational motion into linear. 

​A new plan was implemented to fix the pen issue. This design used a bigger square housing for the pen itself, and an arm that would push the pen down from the servo. That too, gave problems of an angled tip at the surface of writing. 

Finally the final attempt of a pin and slot mechanism with new parts that pushed the square housing worked. This would ensure that we get the linear motion from the rotational servo motion.

The slide show on the right shows the process of trouble shooting the pen attachment. 

The final product turned out great and although we didn't get to witness the testing of it, we are sure that it worked perfectly. Both the axes of motion were definitely already functioning, and with the new pen design, there could be no issue of it not writing. 

This process showed us how a simple idea can be very hard to execute, and how multiple designs and prototyping always takes more time than expected. It was great to use so many intricate details and design ideas in the assembly and building of this entire system, and our team was happy with how it turned out in the end.