Helping 3D With 2D

There is one thing I must do before running into the workshop and start cutting up random pieces of wood into lengths that I don't know, I need to draw out a scale drawing and find out the dimensions of my chair

The centre of my chair, the mechanism and my whole project are the cogs and central column. It is crucial that I get that right first! So I cut out a full size cross section of the central column out of thick grey board and from that simply rolled different sized cogs down the side of the column and marking and cutting the teeth I was able to get the correct sized cog!

Something really important that I had failed to realise is that, for the chair to full causing the trap to shut it must be put in a raised position first. This is a problem because if the seat is too hight up the ergonomics would be wrong and the victim wouldn't be able to get onto the stool to then activate the trap. So, I found by having a smaller cog, it would mean I could get the most rotation from the smallest full of the column

I filmed this movement of the column and the rotation of the small optimum cog, which is shown here -

If you have a problem viewing this video, click on the link to see it played in better quality on YouTube, with a killer soundtrack!!

Next I needed to work out the maths behind the different sized consecutive circles that will be cut up to become the cross braces of the pod -

Both of the drawings are drawn half scale but have the full scale measurements on them. The numbers on the rings correspond to the ones of the top drawing. The diameter of ring 1 is 300mm on the outside edge and 220mm on the inside edge. The diameter of ring 2 is 510mm on the outside edge and 430mm on the inside edge. The diameter of ring 3 is 604mm on the outside edge and 524mm on the inside edge. Finally the diameter of ring 4 is 610mm on the outside edge and 530mm on the inside edge