Tag Archives: mechanics

Hero’s Fountain – Test 1

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By the end of August, I intend to build a working Hero’s Fountain.  I made my first attempt the other day.  It didn’t work, but I identified a number of ways I can improve it for my next attempt.

Below is the test apparatus.  It uses a plastic bowl and two milk jugs for the water vessels.  The nozzles are pieces of copper tubing and are attached with plumber’s epoxy.  The hoses are simple nylon (I think?  The material for that isn’t really important.) tubing and are attached to the nozzles with twist ties.

Hero's Fountain Apparatus 1

Hero's Fountain Apparatus 1

Hero's Fountain Apparatus 1 Internal

Hero's Fountain Apparatus 1 Internal


The first mistake was using the plumber’s epoxy.  I used it because it’s simple and fast and I’d seen it used successfully in a similar application before.  Unfortunately, after I was half done attaching the nozzles I saw the instructions said it’s not recommended for use with polyethylene, which is what milk jugs are made of.  As you can see, the epoxy didn’t bond with the milk jugs, which broke the air seal. This is most visible on the leftmost nozzle in the picture above.

Beyond that first failure the rest is more speculative.  My apparatus has both lower chambers at the same height, which means the water has a long way to rise from the blue topped milk jug to go through the fountain spout at the top.  The air moving between the pink chamber and the blue chamber will rise much easier, so I believe raising the blue chamber to shorten this distance will improve performance.

Also, it takes a substantial amount of water to fill the tubes between the chambers, at least compared to the amount of water in the red bowl.  Priming the tubes with water would probably improve performance, but hopefully that will prove unnecessary.

Finally, as the water drained from the red bowl I didn’t consider that it would form a vortex.  That pushes some air down the tube as well as water.  I don’t think that’s a problem, in fact it might make the machine run a little longer, but it’s something I will pay attention to in my next attempt.

New Type of Engine

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I thought I’d at least heard of pretty much every type of engine there is, but this one was new to me. It’s probably what the infamous “air car” uses. I like it, it seems pretty simple, and it could run just as well on steam. Check it out here. He has diagrams of other types of engines that are also very interesting, you can see them here.

You know, the engines are the title discipline in engineering, maybe I should do a talk on the various types of engines? I imagine I wouldn’t have much to say that isn’t on these pages, but I’d still do it if there’s interest.

Ballista Trigger

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A month or two ago I was reading a book on Greek and Roman engineering and was inspired to make a ballista. It was pretty simple and worked reasonably well for the nonexistent amount of planning that went in to it. Pictures can be seen here. The only engineering hurdles it didn’t accomplish were adequately maintaining and adjusting tension in the springs, and a trigger mechanism to hold the string until it’s ready to fire.

I just finished a design for a trigger that uses only parts that were available in ancient times (maybe not quite, but if this were the size of real ones it could be).

Ballista trigger design

The only thing that worries me is the placement of the rod in the slider. Since the position in which it holds the most tension is where the rod tries to slide forward, I’m afraid it will be easier for it to slip slightly out of position without having to move the slider down. Regardless, this will just be minor slippage so it shouldn’t be a problem. If it works well I might make two of these, one from wood for the actual weapon, and a second from plastic for demonstrating how it operates.

Speaking of ballistae, does the maker faire catapult competition sound awesome to anyone else? I would have gone just for this had they made it known with more time before the event, but alas they didn’t. Is anyone interested in doing something similar in Chicago? I bet there’s enough nerds in Chicago interested in making weird stuff to have a decent competition.