COVID Isolation Project #3- A Better Portable Harmonograph

What is a Harmonograph? It is much simpler to show what it does than explain the math and theory behind what it does so here is my current design in action:

Some drawing examples:

I've used a Harmonograph for outreaches and community activities in the past but the one we use is awkward to transport and had a rather large footprint (the width is greater than many standard tables – still works great though). For a long time I’ve wanted to design sleeker version that is easier to transport but performs just as well, if not better than our larger, heavier version (it’s a work horse and has worked for many years and stood up to a great deal of punishment).
My goals for this more portable Harmonograph are as follows:

• Made from easily sourced parts (making potential repairs much easier – nothing exotic in its design)
  
• Easily portable – fold up into a flat form (ideally into a flat box)
  
• Magnetic Drawing Platform to easily secure paper (no tape needed)
  
• Sturdy – difficult to damage (stands up to eager children)
  
• Safety features
  
• Carrying case should be a "Grab and Go" (no need to take additional supplies)
  
• Carrying Case will hold:
  
  • paper
    
  • colored pencils (lighter weight, less expensive and do not dry out)
    
  • pencil sharpener 
  • I found that colored pencils needed to much pressure (meaning increased friction and drag and shorter toal swing time).  Returning to pens
    
  • extra parts and tools (if needed)
    
  • Simple diagrams for setup (affixed to the inside of the case)
    

My current design utilizes a single piece of 3/4” conduit bent into the shape of a “U”. The base is made up of 4” x 1” lumber. This prototype does not fold up but the dimensions are set up to allow it once all other design features have been met.
The current drawing platform is made up of plywood and sheet metal (magnetic) and is sized to fit standard 8.5” x 11” paper including the magnets holding the paper down.
My initial pen/pencil holder was a spring loaded one that held the drawing instrument vertically above the board.  It ended up not working well.  The spring load mechanism would get stuck at random times.  It's possible that if it was machined on a lathe it may have worked out (though that might make it to delicate). 
My next pen/pencil holder design was a simple swing arm holder. In testing it proved too wobbly and resulted in poor drawing and increased friction (it only drew a few lines). In a much earlier trial (2 years ago) I used a more precise swing arm design that worked great but it was much to delicate (good lab design but not a good practical design).
I’m now attempting a more engineered design, stabilizing the swing arm with the addition of bearings, etc. My current prototype is not very elegant but I’m keeping my fingers crossed that this design will function better than the last one.
Making something new is always an iterative process. As long as you can learn something new from a design that fails to perform then you are making progress.
This design is definitely a work in progress but it’s getting closer every day to meeting my design goals. Once I get it to how I want it functioning then I’ll have to actually make the box for transporting it (another adventure in design… that I look forward to).
What I've discovered so far:

• need a heavier drawing platform to increase momentum (resulting in longer swing time)
• enlarge the drawing platform, possibly making it square to allow different orientation of the paper.
• I would like to add a method to adjust the length of the x or y axis pendulum motion to allow other figures to be drawn