Friday, July 23, 2010

Old BBQ = water rocket launcher!

P.S. I'll be adding more build pics as I upload them....

So a friend was having a "water rocket party" and we, as dads, were going to build water rocket launchers. It wasn't a competition, per se, but rather a way to have enough launchers that even if one or two failed, every kid would have a chance to launch their rocket.

His idea was to take a bunch of 2 litre bottles and spray paint them white, then allow the kids to use Sharpie markers, duct tape and other craft items to customize (decorate) their rockets. Great fun, because every kid has a chance to do their own thing and yet have fun with the other kids, and a good chance of getting really wet when we launched the rockets.

During my design phase, I researched a bunch of launchers on the internet. Trust me when I tell you that there are alot of different designs to choose from. They all were practical and easy to build, but they lacked 2 things:

1. They were not built very "heavy duty". They were built to be used a few times and then discarded or rebuilt.
2. They were slow to load. Most of the designs required pouring the water into the bottle prior to being put on the launcher, then required connecting the compressed air and pressurizing.

My problem was that kids wanted to enjoy this, so it had to handle a certain amount of abuse. It had to be quick to load, because kids aren't typically known for having a great deal of patience.

When I was in high school shop class, we built this monstrosity of a water rocket launcher, with a welded steel frame and plumbed water and air feeds. It was great for a launching alot of rockets quickly and certainly was tough, but I didn't have the resources to build something like that in my garage.

My solution?

Retrofit my old BBQ to be used as a water rocket launcher! I'd use the BBQ as a frame and then use common hardware store items to create a "simple to use" water rocket launcher.

First, I separated the BBQ from the rest of the BBQ parts. Then, I used a drill and bolts to connect one square pipe running end to end.

Next, I confirmed that an outer square pipe fit around that first square pipe. This second pipe (they call it C channel?) would be my sliding mechanism and eventually act as a release for the bottle.

Next, I drilled a hole in the inner square pipe and installed a T fitting upside down. One input would be water, one would be air and the output (pointed up) would be the bottle. When building this T piece, I took a 2L bottle with me to the hardware store (in my case Lowes) to make sure what I was building actually fit. This would now act as my launch mount.

I bolted the launch mount loosely in place. At the hardware store, I purchased 2 ball valves, for controlling the input of both the water and the air, as well as some air hose (which would handle the necessary pressure) and connect my inputs to my launch mount.

Adding a bit more control, I installed a pressure gauge just beyond the input air valve so that I could measure the air pressure I'd be adding to the system.

Placing the bottle on my launch mount, I took an old metal tool and trimmed it with a hacksaw to act as a fork that would be able to hold and lock the bottle onto the launch mount. Using a carefully crafted piece of 2X4 wood, I was able to attach the fork onto the sliding mechanism using wire ties (AKA zip ties). I now had a working lock and release and decent inputs.

A few wire ties later (to attach the ball valve inputs to the frame) and I had a working mock up that I could actually demonstrate.

Please note: If you attempt anything like this own, you do so at your own risk. For example, the pressures involved can be unsafe for the 2L bottle, not to mention if you accidentally pressurize your home's water system. Understand the risks before proceeding with anything.

After I tested the mockup, I decided to change my launch mount so that it withstood slightly more pressure. After a trip to Lowes & a helpful employee named Vern, I used a few additional PVC fittings and a stack of rubber O rings and was able to get a pretty decent seal on the bottle. This required me using a taller 2X4 wood piece.

In the end, I tore everything down and painted the frame with some good Rustoleum paint (hammerlite finish to hide the imperfections). Putting it back together, I used wire ties to secure the air hose to the frame and used the right size of hose clamps to hold the input valves to the frame, the fork to the sliding mechanism, and each air hose on its respective fitting. Two more hose clamps to connect a handle to the sliding mechanism and I was ready! And I didn't forget to leave an air compressor quick connect so that we could easily connect and disconnect the compressor.

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  1. Beautiful, elegant, and excellent design. Wish I had thought of it.

  2. good design for filling and pressurizing, however launching mechanism needs reworking. bottle does not get disengaged from all sides at the same time,resulting in a launch that is diverted to one side,