Saturday, 12 October 2013

Kinetic ghosts ... ...

Another Halloween themed toy, this one however incorporates a bit of physics, it's basically a Halloween take on the old woodpecker toy, the one that slides down a pole when you move it.

Here's a picture of the ones I made -

Look familiar ?

These toys have been around for many years, and more traditionally they were wood peckers, but seeing as it's coming up to Halloween I thought I'd see if ghosts would work seeing as the principle is the same.

All you need to make these are some bits of wood and a spring, one from a pen would do, but you can buy packs of springs from hardware and diy shops, and it's always handy to have a variety of springs lying about.

Ingredients - 

Few bits of wood and a spring.

Basically you need a piece of wood for the base, a small piece of wood for the ghost, or you could make some other shape (a pac man shape for example) a piece of thin dowel for the pole (I use 6mm dowel) and another piece of dowel to make the collar (I used 15mm dowel)
Dowel in a variety of lengths can be picked up for around 99p for a short length from most diy shops, and lastly a spring, like the ones you get in pens, but again springs can be bought in packs.

Okay, in the piece of wood you use as a base you want to find the centre, if you have a square / rectangle piece of wood draw lines from each corner diagonally and this will give you the centre of the wood, then measure up from this point about 2 or 3cm and drill a hole just big enough for the dowel, so if you use 6mm dowel use a 6mm drill bit, you may need to sand the end of the dowel a little to get it in the hole, and use a spot of wood glue (pva) to make sure it doesn't come out.

Finding the centre -

Ignore the other marks, it was scrap bit of wood.

You can just make out where I made the mark for the dowel, just above the centre mark.

Hole drilled and wood sanded to get rid of the pencil marks - 

Next the dowel and a drop of glue.

Okay so once you've drilled the hole go ahead and stick the dowel into it, the length of the dowel can be what ever you want, I made mine 22cm in length, this allows for the bit that is stuck into the base.

So you should have something that looks like this - 

That was easy, what's next ?

Now the next part is making the collar, this will be the part that the spring attaches to, I used a bit of dowel and I drilled a small hole in the side first for the spring to fit in, then I drilled a 6mm hole in it for where it will sit on the pole.

It's best to use something to hold the wood still while drilling, and if you can get hold of one use a post drill, or a vice of some sort to hold the wood while you drill it, one it's safer and two your holes will be more accurate.

Holes drilled, one at a right angle to the other - 

Reading for fine tuning.

Before you glue the spring into the hole you made for it you'll want to check to see how the collar fits on the upright piece of dowel, I used a 6mm drill bit which meant I had to sand the inside of the collar a little to get it onto the dowel, stop sanding once the collar will go onto the dowel easily and will slide all the way down if you let it go, if it's too loose it will just fall straight down when you try to use it with the spring and ghost attached, if it's too tight it won't move at all.

This is the collar, you can see where the holes need to go - 

Bit blurry but you get the idea.

Next the ghost, this was the easiest part, I took a roughly cut small block of wood and using a couple of triangular needle files I made grooves in one end of it.

Like so - 

Needles files are cheap and handy for wood working.

Then the next thing to do is drill a hole in one side of the ghost shape, again use the same sized drill bit as you used for the hole in the collar where the spring will go, I used a 5mm drill bit as my spring was roughly 5mm.

Ghost finished, just needs a paint job - 

Kind of pac-man esque.

You can see the hole where the spring will go, the next step is to fix the spring to the collar and the ghost shape, I'd recommend a glue gun, or some kind of quick drying glue, and when you do glue it make sure to keep everything as in line as possible.

Assembly complete - 

Ready for some decoration.

As I'm going for a Halloween theme I painted them white, and gave one googly eyes, and the other I just coloured in with a black marker pen, I've used the same water based white enamel paint on these as I used on the jumping jacks.

All done, I could have painted the base and pole, but decided not to - 

Very spooky, well maybe not.

I've included a short video of them in action at the end of this post, but first a little bit on how these work, see it's all to do with friction and gravity and the momentum of the spring.

The spring and the weight (in this case a ghost) cause the collar to sit at an angle on the pole, this causes friction and stops it from falling, which is why you don't want to make the hole in the collar too big, if you did it would just drop, due to very low friction.

So how does it move down the pole ? well when you set it off, by making the ghost go up and down on the spring this causes the collar to move as well, and there's a point where the collar is in line with the pole, then gravity makes it fall a short way. 

So the collar rocks back and fourth in such a way that it will align with the pole and gravity makes it fall, the weight (ghost) causes the spring to rock one way and then the other, and in turn this causes the collar to rock one way and then the other and the inertia of the weight (ghost) keeps the spring moving.

In theory if you could some how keep the pole on a loop this would run forever once you started it off, it's because it has a base that it stops, if you made the pole say 100 metres high this would in theory run until it hit the bottom.

Here's a very rough gif animation of what's going on - 

The red stars show where friction occurs.

You can see in the animation where the collar lines up with the pole, and gravity then makes it fall a short way, you can always search online for 'Kinetic woodpecker toy' which will yield much better descriptions of how this works than mine.

And if you feel like making something similar to this (it works on the same principles) then have a look here - Oscillating Woodpecker (opens in new window)

And here's the video of these working -

Thanks for reading.

Homemade Thursday

1 comment:

  1. Oh these are so cool!!!! They'd make great presents wouldn't they!
    Thanks for linking up! Loving your posts as always xx