Traditional Onager

[aidenpons]

Well, I've had a liking in projectile launchers for a long time. And since obtaining copious quantities of elastic bands I've been able to create an onager that gets most of its power not from the "Hand of God," but from elastic bands. *cue dramatic front view that is in very nearly all of my MOC topics*

 

Okay, it looks more like a siege tower than an onager, but shh =P

 

 

There we are: that doesn't look like a siege tower now, does it? =P

There are four important things to notice here.

1) The double reinforcing on the beam. 2) The copious quantities of elastic bands. 3) The extension of the front, to prevent it from flipping over thanks to its torque (it was extremely amusing to watch though =P). 4) The gear in the bottom left.

Regarding number two:

That's one side of one beam. It has 4 elastic bands on it. = 16 overall. See why I wanted copious quantities? =P

 

And regarding number 4: That's what makes this model special, and not just some random thing you pull down and watch fire.

 

This may look vaguely similar to the mechanism on the Viking longboat. especially the gear and the little bar. I understand it's called a "ratchet," but what I don't entirely understand is how it works. I think the small bump out on the arm (The whole mechanism is called a ratchet, I think) digs into the gaps between the teeth on the gear, stopping it from rotating one direction ONLY. It can rotate the other way because instead of jamming, it will simply bounce the ratchet up (bounce is indeed the correct word to use). Now why would I want that? There's something else important here: the small red and black thingy. It's connected via fishing wire (an excellent choice if you want some form of string for your MOCs) to a reel (no, not a full-size fishing reel, the small one in the center =P) that's hooked up to the ratchet via gears.

What that means is that the ratchet will allow the wire to increase its length as the gear rotates, but not decrease (or vice versa). Why is that useful? Well, first you plug the red thingy into the main arm.

 

You then turn the gear (that's what those blue thingies are on it for) to decrease the length of the wire/tighten it.

 

You will notice my hand is not in that picture. You will also notice that the rubber bands are extremely stretched. You will assume (yes, you will assume, ASSUME OR DIE =P) that this is entirely stationary and can sit in that position for days.

You would be correct. The ratchet stops the gear from rotating which stops some other gears from rotating which stops a bar from rotating which stops the reel from rotating in the direction that would loosen the string.

Once the whole arm is down, you put the projectile in. (If you put it in earlier it just falls out)

 

Now, there are three ways to fire this.

1) Cut the nylon. Expensive but the least energy is lost to friction, and scissors are rarer than erasers in the human household =P

2) Lift the ratchet up. Easiest to do, but LOADS of energy is lost to friction on the gears.

or 3) Remove the red/black bit. That can require a bit of force on the bars (which can be seen poking through what it's connected to) but very little energy is lost to friction.

I go with the third option, unless the ratchet is in a bad mood and decides to autofire. =P (Surprisingly rare, if you rotate the gear slowly it only happens 1% of the time (as in 1 every 100). If you rotate the gear quickly it does have a higher chance: about 20%).

In any case, whatever you do, the arm is released and goes flying, until the bottom of it hits the rest of the frame. At that point in time, if the extension of the front is not there, the onager will simply continue with its rotational movement, but rotate the whole onager as well around what is the middle wheel (the front one if no extension). However, with the extension it has to try and rotate around the front wheel, but the force is not in the optimal direction for that and it just rocks a bit (okay, more than a bit =P).

And what happens to the seventh* wheel, the one we put in the ammunition slot? (* Technically the 23rd, as you can see from the picture that other wheels are included that do not touch the ground. There's three wheels per back/middle wheel (one for the outside, one to touch the ground (the big spiky one), and one on the inside to keep the other wheels a good distance away from the main frame), and five for the front wheels (one to touch the ground, one on the outside, one on the inside and then two on the inside of THAT to stop the whole thing from falling out its socket). The inside back wheels aren't easily visible, but in the above picture you can see all five for the front right wheel. The reason none of the wheels that touch the ground aren't connected to the same axle (well the middle ones are, but they have a different connector that allows them to rotate individually) is to allow the whole thing to turn. To turn, one wheel must either a) change direction (hard to do here) or b) go at a slower speed while the one across it goes faster. If they're connected to the same axle then the first is next impossible (turning the wheel means the centre isn't pointing towards the other centre), and they can't go at different speeds (as the axle has to go the same speed as the wheel). So they're disconnected from each other.)

Well, the seventh twenty-third wheel that's the only one that isn't black, goes flying thanks to inertia, and the fact that the casing for it is high enough to not let it roll out at the top but small enough to not stop it from going anywhere at all (apart from with the rest of the arm, but that's obvious =P). I've found the projectile to travel a cosy 2-3m to when it first hits the ground, but being a wheel it usually goes on rolling from that for a long way.

 

Okay, it does need the Hand of God to turn the gear, but a couple of minifigures could grab onto the arms of the gear and pull it down with their weight, hmm? =P Plus, a comparatively lousy 1m for a shot is half a mile (cue correction from somebody) to a minifigure. =P

Edited May 17, 2015 by aidenpons