Prototype

Richards Bay 20 Aug - 3 Sep 2011

I went down to Richards Bay at the end of August to build a prototype of the wave generator. The aim of the exercise was see if there were any pitfalls I missed while working on the design. Experience has shown that there are always some points you neglect to notice which was exactly the case. This video shows the progress.

Pulleys

First off I wanted too see if it was possible to build pulleys out of PVC pipe. I when out looking for scrap pieces of pipe that builders no longer wanted. It didn't take too long to find some.

The pulleys consisted of 2 PVC pipe cut-offs, one inside the other. The smaller pipe was glued to an old CD and functioned as the bearing around which the larger pipe rotated. The pictures above show the whole process. Unfortunately these pulleys were too light-weight for heavy lifting. The main weak point is the CD as it can't handle the pressure, as expected. Another way must be found to construct pulleys cheaply and out of recycled material.

Layout

Secondly I wanted to see how all the plans fit together. The whole setup was done on land because testing in the ocean first was deemed a little too risky for a first draft.

The major change to the design was that bicycle parts were imported into the idea. The original shaft generator idea was not that practical. Too much copper would have been needed to cover a pipe of a few meters long. Also, having a rotating wheel allows for inertia. So the bicycle sprocket idea came to be. It's a cheap one-way bearing and since a chain connects to it there is no slippage. It also allows for better scalability since additional sprockets can easily be added to the rotating shaft. The pictures below show the concept better.

The pulley guides the rope from the float to the bicycle chain where it's firmly connected. As the wave pulls the floats up the rope will pull the chain which will drive the sprocket. As the wave drops the counter weight at the end will return the chain to its starting position.

Since bicycle sprockets are mass produced they are rather cheap (R25) and second hand sprockets are not that difficult to obtain. The same goes for the bicycle chain, a new one sets you back R85. I went into the first bicycle repair shop that I saw and asked them if they had any throwaways. They had no problem supplying me with everything I needed free of charge (social business already at work).

The picture above shows how the sprocket and wheel was mounted to the bottom of a work table. Thanks to Hein and all his bright ideas!

These pictures show how the second hand inner tube from a bicycle became the belt to drive the generator. The generator used was a 600watt from an old wind generator. In the end the generator only produced a small charge but this was expected. The power of the design would only start to show if a few of these were set up in series.

Lessons

There were a couple of things discovered through the construction:

Never be to attached to one design. I had to rethink quite a few concepts before things started to come together.
Welding will be needed. I really want to steer clear of this because it brings in more complexity which I hoped to avoid. There must be another way to mount the threaded shaft that feeds through the sprockets.
The pulleys used in the end were cheap pulleys I got from the hardware store. These will not last long in the ocean. I talked to the supplier and they assured me that they would last a few months but I'd rather have fully plastic ones that can't degrade. I will have to look. Ideally I want to be able to construct the pulleys out of recycled material. Back to the drawing board here.
Everyone I showed the project too was worried about the parts (ropes and pulleys) deployed in the water. The ocean is a unforgiving environment as well as a living one. Within a couple of weeks the ropes will be teaming with life. This will cause drag in the water and will weaken the ropes and clutter the pulleys. Ways to combat this will have to be explored. Getting the ropes out of the water would be ideal. During the brain storming deploying poles in the ocean was mentioned. High pressured air is often used to bury poles deep in the ocean floor. The pulleys can then be mounted to these instead. This would allow most of the rope to be out of the water. It does add more complexity though. The cost of this will have to be evaluated vs the cost of replacing the ropes regularly.
Almost everything can be scavenged for the generator. I build the whole prototype for less than R300.
The most expensive part of the setup was the rope as it can't be scavenged. A 100 meter nylon rope set me back R145. This means deploying in the deep sea will be every expensive.

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