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Hatra Ballista Jr: Deployment
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Hatra Jr is easy to deploy. That's one of the reasons it took so much extra time to build the thing.

Trevor helped put together a set of wheels for a custom dolly for moving the spring frame around.


Trevor and Owen roll the completed Hatra Jr out of the basement for the first time. The wheels worked well, but did slip a bit on the frame. I'll have to rig something up to prevent that.


Lift the spring frame onto the sawhorses. Getting one edge onto the horses by yourself isn't bad. Lifting the second half up by yourself is a bit more challenging. Trevor tried to help, but isn't quite big enough to handle half a spring frame on his own.


Next, the tree is hooked on using door hinges. You can see a canopy was up. We were due for rain this day but it never came. I had hoped Hatra Jr would fit under the canopy, but the canopy wasn't tall enough.

Off in the background, Mista Ballista stands waiting...


Stand up the spring frame on the very edge of the sawhorse, and use the rear-stand to hold up the tree. The arms were installed while it was lying down, and just enough torque was added to keep them from falling out.

Owen was taking most of these pictures, so not all of them are straight.


The scapus (the bottom part) slipped on next. You can see the brackets from Owen's point of view clearly here. The transverse regulea then just sits on top.


Add one winch. In this picture, you can see that almost everything was assembled, but none of the locking pins were inserted. The next step here is to add a locking pin for the winch, and another for the scapus to regulea connection.


After inserting the pins, the top-clamp goes on. Another picture from Owen's point of view, I must be asking someone for the big bolt that goes in the clamp.


Pull the rear stand, and it points skyward like a champ! All we need now is a bowstring, and a projectile of some sort.


Add the bowline, a little torque, and some apples, and lets see what happens. As it turns out, not much. The apples got a little lost in the pouch, but one made it over the fence, perhaps 70ft away.


A view of the pouch pulled mostly back, this time with a water bottle. The water bottle wasn't a good idea. It kept slipping out the side of the pouch.


A different attempt with a water bottle. Changing the orientation didn't help. This view is pretty cool though.

Eventually, we got some pumpkins, and the pumpkins worked well, almost like this machine was designed for them! Our first pumpkin went 210 feet at low torque.


Additional Pages for Hatra Jr
Hatra Ballista Jr After building and testing Baby Hatra Ballista, it was clear this design was worth pursuing. Eric decided we needed a mid-sized model which we could then enter into the World Championship Punkin Chunk in the 10 and under category.
Hatra Ballista Jr: Spring Frame A Hatra Ballista Spring frame is a bit different from a Straight or V spring ballista.
Hatra Ballista Jr: Scapus Frame There wasn't much to go on with historical references for the Hatra Ballista, just a meta spring frame covering, and an artist's rendition in the book Greek and Roman Artillery 399 BC-AD 363. As such, I opted to go with a mix of what we did with Mista Ballista in metal, or Baby Hatra Ballista.
Hatra Ballista Jr: Torsion The load bearing parts for Hatra Ballista Jr are very similar to what I made for Onager Jr, though I've made several changes to help assist in the operation and use of the machine.
Hatra Ballista Jr: Arms and Bowline A hatra ballista has inward swinging arms that allows for 90 degree's of rotation during the throw. Our model has 3 foot long arms. For our first year, these arms were made particularly strong.
Hatra Ballista Jr: Deployment
(This Page)
Hatra Jr is easy to deploy. That's one of the reasons it took so much extra time to build the thing.
Hatra Ballista Jr: Shooting Various pictures and stories of launching Hatra Ballista Jr.


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Twas' brillig, and the slithy toves did gyre and gimble in the wabe...
Last Modified: 09/17/10