design

This week, I wanted to advance my final project and create the squishy head for my octopus robot. I wanted it to be nice and round, palm sized, squishable, and arguably most importantly, PINK!!!

So I got started on the design!

I knew I needed a way for it to connect to a lower frame that holds onto the tentacles:



So I designed a mushroom head thing that would sit on top of the frame perfectly, while also fitting into it securely.



As you can see, there is a little lip that will fit into an indent on the frame.

Now I know what you're thinking... Abby there is an overhang :(
I too was rather cooncerned about it.. figuring out how to even mold this thing. I tried just splitting it in half... fail. I tried using only two parts... fail again. But finally I discovered a solution!



I split it into three parts: the top of the head, the indent, and the hollow middle + lip. Since my octopus head is supposed to be squishy, I decided to just print the mold out of PLA and cast it directly there.

I originally designed it to be 12 cm in diameter, but I realized that I had limited printer space and time in the day.. so I did a quick test to see if 1) if the material works (because some people were saying the food safe one was not) and 2) if I could print it in PLA since the instructions said to do a test.

casting

I did not document the little on very well but here I am sanding it down a bit. This is also when I realized I accidentally printed it out of TPU instead of PLA..... But it honestly didn't seem to make a huge difference. The middle piece is missing here because it failed out of TPU, so I printed it with PLA.



Then I mixed my silicone - 1:1 by weight, dyed it pink using alcohol dye, and then clamped everything to the table to pour. I also had to drill pour and air holes into it, as I forgot to put them in my design.. (and I forgot again with the big one). But anyway, I poured my silicon in, let it sink in, and then poured more. I did this over and over again until it stopped sinking in.

***TIME SKIP***

So tada! It is the next day and I came back to see my lovely creation!



Oh... no it is great! IT IS BEAUTIFUL don't worry!

Foolish foolish me. I did not fill it all the way < / 3 I think it was because my holes for pouring were too small, and I also just did not really shake it around or anything. Also, I noticed after the fact that it was kind of seeping out the sides...

But no worries! I had a new print of my bigger one ready to go!



Wowwww.. she is beautiful. BUT NOT READY YET! I spent a very long time sanding to perfection. or almost.



I used pieces of the orbital sanding pads - one larger grit to get the big ridges and one smaller to clean up. I also then had to drill holes for pouring, but this time I drilled them through the convex part instead of the concave, because the convex is inside and doesn't really matter. I want the top to be nice and smooth.



So once again, I prepared my silicone and poured it in. My holes were slightly bigger this time, and I was able to get a clean pour in without hitting the walls. I poured and checked and slapped it around a bit until it was no longer sinking down. I stayed for 30 mins and would pour a little more in if I saw it went down a bit in that time, but the silicone has a 40 minute working time anyway. And then I left her to cure!!!

****TIME SKIP****

The next day I came back and removed it from the mold (with great effort and many a screwdriver and chisel).



When it was finally expelled from the mold, I discovered a large (and also many teeny tiny) air bubbles. I did not put it in the vacuum, so maybe that was why, and I also did not shake it around enough maybe.



But otherwise it worked out! Nice round ball, fairly smooth. But as I say there were many small bubbles that I will fix for the real big version.



The lip also worked out other than the bubble, and I printed a little holder to see if it fits in nicely too.



But squish factor: 7/10, a little firmer than I was expecting, but still nice. Color: a little too bright, will fix for next time. Will also remove the bubbles better and make it a little thinner.