Sunday, 27 July 2014

Mini onager...

I have been meaning to write a post about the mini onager / catapults I made for some time,I actually made the first one last year as an experiment to see if I could make a small scale siege weapon,that would be a little easier to make than the others we've made.

There are some links to the other siege type weapons we've made at the bottom of this post and there's a short video of me making one of these (I was messing about with time lapse videos) and firing it in the garden as well.

Here are the finished onagers (one for each of the kids) -


Simple and cheap to make.

These are powered by a piece of slingshot elastic,but you could use large rubber bands,bungee cord or something like shock cord or indeed anything that's stretchy.

Construction is easy,it's basically a rectangle shaped frame with a few bits added for support and because these don't use the torsion bundle system like the larger onager we built,the throwing arm uses a pivot and a couple of bits of wood either side that act as guides,other wise the throwing arm would flap about all over the place,and even though these are small they can still give you a bit of a nip if you get your fingers in the wrong place.


Here's a picture with some of the parts marked - 


Click on the picture for a larger view.

These can be built in a similar way to the larger onager,but because of the pivot point I'd recommend making the frame first so that you can work out where you want the pivot point,and then drill it out before you make the other parts.


Quick diagram of the basic frame (sizes just for reference) -


There's no reason these can't be made much larger.

Once you've worked out how big the frame work will be and marked where you want the pivot to go you can take the 2 longest sides and drill straight through them both,this should mean the holes for the pivot will line up,I used a bit of 8mm dowel for the throwing arm to pivot on,but anything straight and round will do.


Below is a picture showing how the throwing arm pivots on the dowel - 


Simple but effective.

The guides either side of the throwing arm serve to keep it straight and they also help make sure it fires smoothly and doesn't twist,these aren't really needed but they do help keep everything in line when firing and they do seem to help with the accuracy of the onager.

To work out where to put the stop bar and other parts what I did with this and the larger onager is to work out the point at which the throwing arm is upright and at around 90 degrees to the frame work,from there you can mark the frame and work out where to put the stop bar etc,you'll also need to work out how long you want your throwing arm,I made mine about 20cm (8 inches) and from that I worked out the height at which to put the stop bar,which in my case is at about halfway up the throwing arm.

To stop the elastic from getting caught up and to keep it in line when it's loaded I've used some small eye hooks,this also gave me a point I can tie the elastic to,I also used an eye hook on the throwing arm to stop the elastic slipping down the arm when it's loaded.


Loaded - 


Ready for action.


Closer picture - 


There are other ways I could have done this,but this works.

The trigger is the same as the one I made for the larger onager,it basically uses 3 eye hooks and a pin and a length of string,again this one of a few ways a trigger could be made, but this works and it's simple to use.

What you use as a holder at the end of the throwing arm for your ammunition is what ever works I guess,you could use a sling type holder,like I've done with the larger onager,or a cup like I have used with the smaller onagers,I just used what I had lying about in my shed from various wood turning experiments,half the fun of making things like this is to experiment and see what works and what doesn't


The trigger (you can also see the eye hook that stops the elastic from slipping down the throwing arm) - 


Doesn't really need to be more complicated than this.

Video of it being assembled and fired - 




And that's about it really,these aren't super powerful,although it will depend on what you use as a power source,be it bungee cord or slingshot elastic,you can use variety of things as ammunition,I used a small ball of baking foil in the video,but almost anything will do,and I've since discovered that with a tweak to the elastic these are pretty good water balloon launchers.


Links to other siege type weapons we've made - 

How to make an onager (opens in new window)

How to make a trebuchet (opens in new window)

Hand held ballista (opens in new window)


Thanks for reading.


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