Mechanical and Machine design

For more information about the group project, please refer to this page:

For the group project, we set out to create a wall pen plotter. In our case it was a smaller version that actually plotted on a piece of paper stuck to a board.

There would be two motors pulling the pen along the board, but there needed to be something to hold the pen in place as it moved along. So I set out to design a pen gantry that did just this.

I decided to design this in 2D and then lasercut it out of acrylic.

The idea behind it is that it doesn't just one pen, but can be adjusted to fit different pens. The strip pictured in the middle will have bolts screwed into the holes that can be used to screw down a pen.

Unfortunately, at this time the laser cutter at the lab was out of order, so I could not cut this design out of acrylic. Instead I cut the piece out on the ShopBot out of a piece of MDF. There was not a lot of scrap material around so I had to settle for a piece of 6mm MDF.

As you can see, the gantry actually turned out a little large. I couldn't find bolts that were long enough, so I inserted a shim at the bottom of the gantry hole that the pen could rest on as I fastened it with the bolts.

The gantry was then attached to the motors and the board with fishing wire, and a problem immediately became apparent. The gantry was much too heavy.
As soon as you let the gantry hang by itself, it would basically flip backwards and have the pen pointing up into the sky. That wouldn't do.

I quickly made the gantry a good size smaller and milled it out again.

Luckily, this gantry stayed in the correct position, and kept the pen quite steady. Unfortunately, it was still too heavy for the motors to drive around.
I'd still like to make a lighter version of this out of a thinner acrylic, but that isn't possible until the lasercutter is fixed.