String Kit: 

1) the principle your toy is based on: The main principle that I wanted children to take away from this toy was of geometry and how you can start visualizing geometric shapes in your head. 

2) how will the child interact with the toy: The child will start off with the assembled structure and follow the instructions to create the final 3d shape (like a draw-by-number book, except in 3D). 

3) construction cost, durability, safety: I think the construction cost will be very minimal - we are talking about maybe a couple pieces of wood glued together and some string. Durability also shouldn't be an issue as nothing actually moves - as long as the wood is well attached, there shouldn't be any issue of the piece breaking. Safety however poses a challenge as string is involved, so this forces the age group to be a bit higher up (maybe in the 8 year old range). 

4) what I learned from the experience: One thing I struggled with in Calculus 3D and even CADing is that sometimes I can't visualize certain geometric shapes in your head. I wanted to see if I can help children get started on that using a kit-toy system. One of the big examples I had for this was the kits that had printed lines on them for famous moments/pictures, and if you used the etching pen to etch away at the lines then you could see your picture in silver illuminated against the original black. I loved those pictures and I learned a lot about monuments from them. However, after discussing about the presentations on Tuesday, I realized that most kids probably won't find this activity fun. It would only appeal to a small group (who perhaps enjoy art at the time), and doesn't really apply itself to a larger audience.