Thursday, 17 February 2011

FMP - Two (15/02/11 - 17/02/11)

First things first, I fixed the first working model:

I had trouble again trying to get the length of the heatbent acrylic right, but then I realised what I was doing wrong. The circumference I was getting was found by using the diameter of the inner circle that I was bending it around, I hadn't taken into consideration the width of the acrylic, which then knocks the diameter up by 10mm, having a great effect on the circumference. However this new circumference came up too large and struggling to think what was wrong I tried using the diamater from the middle of the acrylic, so increasing the diameter by 5mm this time (2.5mm both sides), so that the radius of the circle I'm using to get the circumference would slice the acrylic in half. This worked a treat and came up perfect but due to warping from the heat, I had to fill the tiny gap as seen in the photo below:

In regards to the trouble of the poles becoming stuck, I swapped them for thinner ones with rounded off edges to help them glide the CAM. Also pieces of rod were glued in the middle which the above base now sits on and can easily rotate. All in all there is no trouble with it, but it has highlighted a few issues. The major one being that these poles, as they hole they sit in was cut for a larger diamater, spin a lot. It's hard to keep them from doing, but I've thought about attaching small tires onto the ends which together with guides either side should prevent them from spinning.

I've also thought of placing springs into the top acrylic houses which the poles go up into, so that they're constantly forced down, thus hopefully eliminating them getting caught mid air. This is the acrlyic housing:

Moving onto a second possible design of getting to work, is the above CAM design that I mentioned in my before post. This works by having horizontal poles coming from the centre point (which is turning) which have a bevel gear attached which rotate due to a horizontal bevel gear. So that when the centre point rotates, the poles rotate along with it as well as rotating along their length. Attached to their length is an offset CAM device which, while rotated, creates a greater radius than that of the pole, this is where the vertical pole along with the horse are hung. If that sounds too confusing the following photos should clear it up:

So as the structure is rotated around the wooden base the vertical gear is rotated too:

This in turn rotates the CAM device:

I was initally having trouble making the rod and gear one piece as the hole in the gear was too large (it was store brought). To fix this I attached a copper arm which is soldered to the rod as well as slotted through the gear:

A problem I raised in my research was that the CAM device would cause the pole to go back on itself when it was rotated. The vertical pole should just move up and down with as little forward and back motion as possible. So to keep it centred but also allow it to raise, I added a secondary CAM (the inner parts in the photo below) which when rotated by the outside ones would go up or down, but being loose on one end it allowed the pole to stay somewhat centre:

The idea works fine but it's the model that is fragile and prone to these bits falling off. Just like the vertical gear, attaching these CAMs to a rod isn't as easy as I intially thought as there is little to grip onto from anything circular. For this reason I'm going to try using a sqaure bar tomorrow, which will turn anything slotted over it regardless of how tight the joint is.

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