How to make an Onager ... ...

So carrying on from our Trebuchet project we decided to make another type of siege engine, this time an Onager (sometimes referred to as a Mangonel) which is a type of catapult, but instead of using a large weight and gravity to fling an object this uses a different kind of method, the torsion bundle.

The name 'Onager' comes from the Greek word for ass (the donkey type) the reason they gave this device that name is because it kicks when it's fired, much like a donkey (ass) these types of devices were used as far back ancient Greece, and were widely used by the Romans for siege warfare, I also found references to small devices similar to the one we've built being used in the trenches in world war one, for firing hand grenades into enemy trenches and into no mans land.

Here's our finished Onager - 

This is the Mk 2.

The picture above is as it says the Mk 2, the Mk 1 needed a bit of tweaking due to a range issue, that being it didn't actually have much, the Mk 2 on the other hand does, and as a result I've kept the torsion quite low, we can almost clear the garden with this one, any more power and we'd be in trouble, how ever I do plan on taking it out to an area where we can really see what it's capable of, and adding more to the torsion to see just how far it'll throw an object.

Building one is not that hard, it does require some basic wood work skills (like the Trebuchet) the most problematic part for us anyway was getting the torsion right, and as I mentioned we had to tweak it to increase the range.

The basic frame work (made from 3.5 inch x 1.5 inch timber, 32mm x 82mm) which you can buy from most diy type places, the bit I used cost £4, I've used 3 inch screws to fix it together, and once again I used dowel to plug the screw holes, the cross bar in the middle is to help stop the torsion bundle from pulling the two main sides inward.

The basic frame - 

Easy peasy.

I was going to use thinner wood, but I felt better making it a little more sturdy, for the holes for the rope to go through on either side, I drilled using a 22mm spade bit (you could use a forstner bit, or large drill bit) the main reason for making them that size was because I decided to reinforce the holes for the rope with 22mm copper tubing, which I made two eyelet type section with, then made two flat plates to fix to the wood.

The copper parts for reinforcement - 

You don't really need to do this.

I made the eyelet by folding over the end of a bit of tube with pliers, then tapping it with a hammer, the plate is made from tube I cut then flattened out, then I made a hole in the centre for the eyelet to go through, these parts then fix to the main frame.

Here they are fixed into the main frame - 

Just needs securing in place.

And in the next picture you can see I've fixed the plate to the frame with copper nails, I've also drilled two holes diagonal to each other, these holes will hold small bars that will stop the rope unwinding.

Plate and eyelet nice and secure - 

All done, onwards.

It has to be said that on a model of this size I could have just used some thick plywood instead of going to the trouble of making parts out of copper, but if I'm honest I was going more for the look of it, but these do help to stop the wood getting chewed up.

Here's a picture I took while I was making sure it all worked - 

You can see how the brass pegs stop it all unwinding.

Again where I've used brass bar, you could use bolts, or wooden dowel, but although the brass is pretty sturdy, it won't snap, I was going more for the look, I could have just as easily used the steel rod I have, or indeed wooden pegs.

Here's another picture I took while testing things - 

I was using a bit of elastic to make sure things were secure.

Now a bit more wood work and it's done, all we need to add is a bar that the throwing arm will hit, this will then launch the projectile, it also makes things a little safer as you know exactly where the throwing arm will stop.

For the stop bar assembly all you need are two uprights with a bar across the top, then two angled pieces on either side to help absorb the impact and add some extra strength, after all you don't want the frame shattering when it's fired.

The stop bar assembly - 

It's just a spot of simple wood work.

Here's a picture with the parts labelled -

It's best to put the extra supports at a 45 degree angle.

Here's the frame work from another angle - 

The string on the stop bar is just for show.

You will want to have the frame work for the stop bar assembly to be roughly at the point where the throwing arm is vertical (or as close as possible) so it's a good idea to build the stop bar assembly and before you fix it in place mark where it needs to be in relation to the throwing arm.

As for the trowing arm, it's pretty simple to make, I had to glue and screw two bits of batten together, and in total the arm is 23 inches (58.5cm) long, I've gone with the three peg method (the same as the Trebuchet) although this wasn't the original idea (hence the Mk 1 and Mk 2) I also made a groove about an inch up from one end of the throwing arm for the rope to sit in, again you don't have to do this as the rope will hold it in place.

The end of the throwing arm - 

You can see we have room for a larger bundle.

Okay so we've almost finished, now we should really add a method of firing this thing, one that means we can be out of the way when we fire it, this I found was an easy problem to solve with the help of four eyes (four eyes really are better than two) I screwed two eyes into the main frame, and made a firing pin from another eye, to which I tied a length of string.

The main section of the firing system - 

I had to file the thread of one of the eyes.

I could have not bothered with a firing system, but even though this is a small device it still packs a punch, and I figured safety was a good idea, especially as the kids will be using it in the garden no doubt, and besides it's more fun this way.

The next part of the firing system is the fourth eye, which is fixed into the throwing arm, the idea being that when the device is loaded the eye on the throwing arm fits between to two eyes on the main frame, the firing pin then goes through the three eyes to secure it, the principle being that giving the string a good yank will slide the firing pin out and fire the device, you can see it in action in the video I've included at the end of this post.

Here's a picture of it loaded - 

A simple safe solution.

As an added safety feature I also drilled a hole in the end of the firing pin so that I can put something through it when the device is loaded that will prevent it being fired by accident.

More safety - 

Just in case the kids get too eager to unleash hell.

Here's some pictures of the three pegs at the other end of the throwing arm, it's basically the same design as the Trebuchet we made, with a slight difference. We added metal rings to the sling, we found this gave it a better motion and in so doing gives us a good range, I had to add extra bits to the side pegs to stop the metal rings sliding off.

The sling end of the throwing arm - 

I used bits of dowel for the pegs.

The metal rings are garden wire I bent into shape.

The little stoppers are larger dowel I drilled out to fit on the pegs.

Here's a picture of the method we used to add more torsion to the bundle -

The way this works is that when you twist the rope the throwing arm stops it from unwinding, you can then use this torsion to make the throwing arm move and fire a projectile, the rope we used was 6mm cord we got from one of our local diy shops, any man made type cord or rope should be good for this.

Here's a short video where you can see the twisting motion as the throwing arm is pulled back, you can see how the rope wants to unwind, but can't.

Once again my lovely wife made the sling out of crotched string, she also made the basket for the Mk1, however due to a slight error on my part the Mk1 didn't have any range, in fact the furthest away from the device I could get anything to travel was about four feet, not good.

The Mk1 - 

The Mk 1, or as my son would say 'Epic Fail'

We'd originally figured we'd make a basket type set up, like a catapult, so I made a wooden ring, and my wife made the basket, but it wasn't very good, and it seem that after a bit of reading the basket type catapults might actually be a spot of miss-direction as it would appear that although there are numerous drawings and accounts of catapults being made with baskets or small bowls on the ends of the throwing arm, most used slings, and some have speculated that this might be down to siege engine builders trying to keep the secrets of how they made things, well a secret, after all you can't have everyone making them, and there is a big difference in how the basket and the sling perform in terms of range and speed.

And that's how to build an Onager, all be it a rough guide, and below is a video of it being loaded and fired by my kids, I plan to make another more powerful torsion bundle for it, but I'll have to test it some where with more space, so I'll update this post with another video once I've done it.

On my command unleash hell ! - 

Thanks for reading.

Home made dribble bar ...

I can hear you saying what on earth is a dribble bar ?

Well it's basically a bar shaped attachment for a watering can, farmers use tractor mounted ones, but they are more or less the same thing, as to what one might use a dribble bar for, well I've been reading a lot of books lately, gardening books,books about growing food on allotments and other plant related books, and most of them mention dribble bars for either applying weed killers or applying liquid plant feeds.

Seeing as we don't use any type of weed killer on our garden, but we do use feeds, natural ones made from nettles and such like I figured I'd make one, and because I failed to find one in any of our local gardening centers.


Here it is, it cost £2 (for a pack of plastic T's, couldn't find them in singles) -

It couldn't be simpler.

Using a bit of old 22mm plastic over flow pipe I had and a 22mm plastic T, it took about 20 minutes to make.

Ingredients - 

It's a basic plumbing job.

I took two bits of the plastic pipe, one short length for the spout of the watering can, and a 16inch piece to make the bar with, the two small bits of wood are to block each end of the bar, you could use stop ends, but I would have had to buy them, which would have put the price of the whole thing up.

To get the short bit of pipe to fit onto the watering can spout, I just heated it up with my mini blow torch, a lighter or a candle will do just as well, you want to just warm up one end of the pipe so it's a bit more flexible, then work it onto the spout of the watering can, the watering can I'm making this for is metal, for a plastic watering can you can either use something to stretch the end of the pipe, like a pair of pliers, or maybe the T fitting will fit the spout already.

The short pipe fitted on the watering can - 

About an inch should be plenty.

Once the plastic pipe cools down again it will contract slightly making a nice tight fit.

Next the bar section, for this I took the 16inch piece of pipe and cut it in half, then stuck each bit in either side of the T section, the fit is pretty tight so I won't need any glue.

Like so - 

Simple, now to block up the ends.

On to blocking the ends, I've just used a couple of bits of a small branch, I sanded them down a touch so they just fit into each end of the pipe with a little tap from a hammer, again as it's a tight fit I won't need glue.

The stop ends - 

Now just needs a little tap with a hammer.

After a bit of gentle persuasion - 

Sorted, no leaks here.

Nearly done - 

Now for some holes.

All you need to make the holes is a drill, with a 3mm drill bit, if you find the holes are a bit small then try a 4mm, it's easier to make a small hole bigger than it is to make a big hole smaller.

I used my mortise gauge to score a line roughly along the length of the bar, then measured out where I was going to put the holes, I made them an inch apart.

Mortise gauge (in case you were wondering) - 

Very cheap, and handy to have.

Ready for drilling - 

More or less in line (honest)

Once I'd drilled the holes I had to clear some of them out as they had bits of plastic in them, I just used a small screw driver, but any pointy type tool would do.

Holes cleared, ready for testing - 

Done, could easily be made from copper as well.

Here it is in action, it's not very easy to see, but it does work well - 

It was a bit windy.

It cost very little, the cheapest I could find online was £4.99 for a plastic one, admittedly I had the pipe already, but you could always see if anyone is having any plumbing done in your area and ask them if they have a spare bit of pipe, or just make one for the hell of saying I made that.

Thanks for reading.

How to make a Trebuchet ... ...

Recently we paid a visit to our local museum (well one of them anyway) and as it's a castle of course it has a siege engine (all be it a small one) so we decided we'd have a go at making our own, you can read about our recent visit on my wife's blog - here (opens in new window)

For a rough guide on how to build a small Trebuchet read on.

All you really need to make a Trebuchet is a bit of wood working / diy skill as it involves sawing wood and such like and some tools and a bit of wood.


With a bit of luck you should end up with something like this -

We're very proud of our baby siege engine.

It's not complicated to make, and as to how big you go, well it's up to you, but remember this is designed to fling objects over large(ish) distances, and the bigger you go the further it'll throw (see what I did there ?) I've added a short video at the end of this post so you can see it in action.

Basically I've taken an off cut of an old pine sheet and fixed to it some battens to make a frame, it's a simple triangle shape, with one upright that holds the pivot for the throwing beam, and two supports on either side, clicking on the pictures should bring up a larger version.


The basic framework and base -

You can see that four bits of wood make up the main frame.

From the picture above you can see that the upright ('B') is fixed into the middle of the base, and fixed from underneath and then fixed to part 'A' parts 'C' and 'D' are then cut with 45 degree angles at each end and then fixed to part 'B' and part 'A'

I used screws and wood glue to fix it altogether, and obviously you need to make two sides that are identical.

If you're not too good with cutting wood at angles or the kids are having a go at building something like this, then I'd suggest getting a mitre saw, these can be picked up for about £20 from diy shops, and they come in handy for picture frames and such like, it also means you can do small jobs in the house, I normally use my electric mitre saw, but it's not allowed in the house.


Here's mine, which the kids are getting pretty good at using -

Really easy to use bit of kit.

We added wheels to our trebuchet, but again this is up to you, I added some extra bits of wood to the base so that I could add axles to the back and front, for the wheels I used my largest hole saw, which also leaves an 8mm hole, which is good as I was using bits of 8mm dowel for axles.


Hole saw -

This one needs a sharpen.

Hole saws are great for making wooden wheels, although they do need a bit of sanding to remove any bits of wood that might cause splinters.
In the next picture you can see the wheels, and the extra bits of wood I added to the base.


Wheels (well a wheel anyway) -

We even used small skewers to make pegs.

If you decided to go with wheels you should now have something that looks a little like the next picture, a basic frame on wheels, we'll get to the business parts in a minute.


Basic framework done -

There's really not that much to it.

Originally I was going to use just one piece of wood on each upright, but as the wood I was using was quite thin I decided to go with two bits of wood for each upright.

Like so - 

I could have left it as one piece, but two seemed better.

You can see from the picture I just butted the extra piece up to the framework, rather than adjust everything.

For the the throwing beam and the counter weight pivots I used 12mm dowel, now whilst you need to take care to get everything in line the throwing beam setup needs to be quite accurate, if the holes don't line up and aren't level then it won't throw very well, if you have a post drill then all the better for drilling nice straight holes, but if you don't you can still get things in line by taking your time and using a bit of masking tape (other tapes will do)


Taping two bits of wood to get the holes in line -

A bit of tape works wonders

 You can see in the picture above that I've already drilled one hole, but because I decided to add extra bits of wood I then had to drill holes through them, the masking tape helps to keep everything in line.


Ready for drilling -

Post drills make this kind of thing easier.

 You don't need a post drill, taking care with a normal drill should keep everything in line, and you can buy guides for drills that allow you to drill straight holes.

Once you have the main frame built, you can then move onto the throwing beam and counter weight, these are simple to make, but once again you'll need to keep the pivot holes nice and straight.

For our throwing beam I've used two bits of the batten fixed together, again this is because I felt one piece was a bit too thin, so all I did was fixed the two bits together with screws and some glue, then I drilled two 12mm holes, one almost at the end of the beam, and one 4 1/2  inches (about 11.5cm) further along the beam, you don't want the main pivot hole in the middle of the beam as it'll work more like a seesaw than a Trebuchet.

Our throwing beam ended up being  19 1/2 inches long (about 49.5 cm) with the hole for the counter weight  box 1 1/2 inches (about 3.5cm) in from the end, then the hole for the main pivot 4 1/2 inches (about 11.5cm) further along the beam.


You can see the distance between the two pivot points in the next picture -

It's all down to leverage.

The counter weight box is, well a box, not hard to make, the only difference is that you want to make two sides come to a point (roughly) where the pivot point is, this will allow for more clearance when the Trebuchet is loaded, I miscalculated a little and had to cut a notch out of the counter weight box.


The counter weight box -

Think along the lines of a simple house shape.

Here's the notch I had to cut out of our counter weight box - 

I may rebuild the counter weight box

Again take care when drilling the holes for the pivot, they need to be in line and straight, or the counter weight will sit at an angle, and it'll affect the stability of the Trebuchet, again using tape to hold the two sides when drilling will help keep things straight and in line.

Finishing the two sides of the counter weight - 

We went with a curved design in the end.

We chose a curved design for the counter weight, I'm just finishing it with my homemade spindle sander in the picture, but a simple house shape would do, or even a triangle, but remember to make the box big enough to hold plenty of weight, it's easier to have a box that's too big and have to take some weight out (we used sand,stones and clay) than it is to add weight to a box that's too small.

We used small wooden pegs (made from skewers) to keep everything in line, once we had things where we wanted them we used the pegs to keep things in place, like the counter weight box and the throwing beam, we just drilled (using a small drill bit) either side of the beam and counter weight, then used a small hammer to bang the pegs in, it kind of gives it a more authentic look (well we think it does)

The pegs (on the beam) - 

The pegs make it easy to take apart, should adjustments be needed.

The pegs (on the counter weight) - 

Again the pegs make things easier when it comes to adjusting the weight.

Here's the counter weight box, already weighted - 

We found 1.2kg to be heavy enough.

The clay on top helps stop things flying out of the counter weight box, we found 1.2kg to be about enough on our Trebuchet, but you can experiment with different amounts to see how it affects the range of what ever you use as ammunition.

If you do use screws I'd suggest counter sinking them, and then using some dowel to hide the holes, this is just a case of knocking a bit of dowel into the hole and then cutting it off.

Screw holes hidden - 

An old trick, but it still works.

Apparently these next bits were the most important, least that's what the kids said, I have no idea what they do.

Decoration maybe ? - 

Design features ?

Now comes the important question of the firing system, Trebuchets use a variety of methods, like a wooden basket or a sling, so we've used two different methods, we didn't go with a wooden basket, but we did make a sling (or rather my wife did) she crotched a net from string, which we used to fire the golf ball, the other projectile is a wooden ball on the end of a bit of string, so it works kind of like the hammer they use in athletics.

The projectiles - 

You could use a variety of things, see what works best.

The sling, expertly made by my wife - 

You could always make one out of a bit of material

The next part to the firing system is quite simple, it consists of three pegs, one of which is angled in a specific way, so that the net or the hammer don't release until the throwing beam is upright.

The pegs - 

The one on top at an angle is the important one.

The pegs on either side are where the net fixes to, they aren't used with the hammer, that only needs the angled peg, which is angled in such a way that the net and the hammer won't come off the peg until the beam is upright, otherwise the projectiles would end up go either straight up or actually behind the Trebuchet.

This is how the net fixes onto the pegs - 

A simple sling shot basically.

Hopefully this rather long winded post will go some way in helping you to build your very own baby siege engine.

Here's a short video of it in action, using both the net and the hammer, not the best video in the world, note to self, hold phone other way next time (I may re-do the video)

I'm happy to answer any questions about the Trebuchet, thanks for reading.