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Forum Index : Windmills : Help with a school project
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
This is really starting to look like something. It may be difficult to find a way to use the original bike wheel bearings with a paddle wheel arrangement, but two bike wheels and wide paddles are probably still the best way to go. You may need to remove the guts from the original wheel bearings, and slide the wheel hubs onto a suitable length of metal pipe. Both bike wheels will need to be very solidly attached to this axle tube, or your paddles will just collapse. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Not sure it would be that hard to retain the bearings if required- get a length of tube of the right length to run between the two rims- hammer one of the nuts that held the rim on the frame into the tube (That means testing tube sizes until you find one that is just the right size- then on the other side use right angle steel to form the upright from the float- drill hole and tighten other nut from bike frame to hold axle in place Come to think of it- if the floats are held fore and aft with rigid bar/angle- I dont really see the need for the center axle at all (between the two rims)- just the one side held would probably be enough Another option for a center axle is the threaded rod found at hardware stores with the same thread as the bike axles- They also have 'joiners' that allow you to join two threaded rods together (like a really long nut) joiner connects bike axle to threaded rod- then keep joining until you get to your required length- then another joiner to the other rims axle example of joiner at bunnings joiner Threaded rods of various sizes/threads threaded rods obviously you would select rod and joiners of the same size/thread as your bike rim axles |
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| Brady Newbie  Joined: 17/08/2017 Location: AustraliaPosts: 8 |
So, I've have been with my group today, and they are really supportive of the floating paddle wheel. We have begun construction of a very small paddlewheel model. It's not going to be much, it's only made to see how fast the water is, and puts it into perspective of what we have to build. We have cut out 8 wooden paddle things, around 11 cm long, 8 cm wide. The paddles will be attached to a wooden axis, the paddle would floats amongst two small plastic water bottles. We will throw it into the water and see what works.  After that, we'll go onto our main model. Which will be able to produce electricity. Very excited for the testing phase. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
To measure the speed of the water, all you need to do is toss a floating object into the water and time it with a stop watch over a known distance. Between a convenient rock or a tree and your bridge for example. From that we can work out from the diameter of the paddle wheel how many turns per minute a given diameter paddle wheel is going to turn. When you eventually get an electrical generator to test, you can turn that by hand to see how fast it needs to spin to do the job. A lot of things can be measured and worked out and anticipated, before actually testing the final completed turbine in the water. Building a small scale model first is a very good idea. It can tell you what many of the unexpected difficulties might be, before you start work on the final full sized turbine. Once you have made something, its always very easy to look back and think how you could have done it better, or made it simpler. If its only a small model, you can trash it and start again and use your improved ideas in the next improved version. Cheers, Tony. |
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| Brady Newbie Joined: 17/08/2017 Location: AustraliaPosts: 8 |
Ok, right that makes more sense. By working out how fast the water goes, and how much it takes to produce electricity. I can find out what motor and it's gear ratios to use? I will most certainly do that if I can work all of that out with just a bit of testing!  Thanks |
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| Brady Newbie Joined: 17/08/2017 Location: AustraliaPosts: 8 |
 UPDATE: progress has been a bit slow. Sorry for that.. We have completed the testing model, it's quite small. But it's only made to test the speed of the water. Testing phase will be tomorrow. Going off of the suggestions from this form, tommorow we will a) test the speed of the river. B) find out the rotations per minute for our system, and C) find out the tides will be at that time. By working these three out, we should be able to predict how fast the water will go at its peak, and how much power it can produce. Then we can go into our working model. Hmm it won't let me upload the image of the model... got it. |
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| flc1 Senior Member  Joined: 20/11/2011 Location: New ZealandPosts: 242 |
looks like your on your way Brady , good stuff,maybe a little bit of bracing wood between the base of each paddle by the shaft? |
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| Brady Newbie Joined: 17/08/2017 Location: AustraliaPosts: 8 |
Uh, sorry, another late reply. The test was sort of disappointing, the river was moving incredibly slowly. Using a measuring tape, we measured out 20 metres from the footbridge across the bank. From the footbridge, we dropped a plastic bottle (tied to string) into the river and timed how long it took to get to that 20 metres. I found out that the water speed was 0.385m/s. Very slow, I know. After that, we tested how many rotations our system would do in one minute. We got around 22 rotations per minute. I observed some things, for one, the system was tilted at an angle, as we only used a single piece of string to hold it. The paddlewheel would also stutter, it would have trouble climbing, and then decline fast. Most likely due to unbalance. There are quite a few things that I think may have got in the way of a much better result. A) The device was not in the fastest part of the river (the centre), as this was only a model, and it wasn't attached to the gate pole. B) We simply dropped the system into the water using a single piece of thick fishing wire. Because of this, the system was always at an angle, and it never got the full power of the river. C) The river was running abnormally slow, however this was a natural challenge, and we obviously aren't at fault for this one. D) I also believe there may have been a bit of friction on the shaft, preventing the paddle from moving faster, we did oil it, and sand paper the wooden shaft before hand, but I believe there is room for improvement. E) The paddles were unbalanced. While they were cut as evenly as possible using machinery, there may have been some unbalance. The hot glue may have caused unbalance, and they may have not been glued on evenly apart. We also added tape on one of the paddles to distinguish one rotation, I believe I put too much tape on. F) around half of the individual paddles on the paddlewheel didn't touch the water. I'm wondering if the useless parts of the paddle added unnecessary weight, in which lowered the rotations. The system, in the end, floated and rotated, without any leakage occurring after the testing. There are obviously many things we will need to improve on to get the most efficient design. But, it was a success at least |
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| Brady Newbie Joined: 17/08/2017 Location: AustraliaPosts: 8 |
The green line is where I want some sort of plank or pipe for the system to rise up and down. Also you can see how tiny our model system is. My hope it that we'll get it a lot larger.    Quality is kinda potato, but we put in tiny bent nails in the shaft to stop it from moving side to side. Flc1 is that what you meant? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That test was a great success in that you have learned a great deal about some of the problems to expect when developing the next prototype. Probably the first thing is a means of keeping the turbine in a stable position in the fastest part of the flow. Your two floats need to be placed as widely apart as practical to prevent the turbine from tilting sideways, especially in choppy water. So the whole turbine probably needs to be a lot wider than it is tall so it always floats fairly level. And if the whole thing was mounted on a fairly long trailing arm, that should keep it steering straight and in the centre of the main flow. Because it turns so very slowly it needs to be made quite large, otherwise as soon as you place any significant load on it, its just going to stop turning. Its one thing to just make something that turns, but to charge a battery, it also needs to generate some useful mechanical power. To get a nice even turning, there need to be several blades in the water at the same time. The amount of "pull" the water can exert on the blades depends on the surface area of the blades. Very wide blades will generate much more force than narrow blades. Speed is pretty much fixed by the flow velocity, so to extract more power, the paddles need to be made deep and wide. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I suspect your prototype has a lot of friction in its 'bearings' (where the rotating axle goes into the floats) which would slow its rotational speed significantly as well A set of bearings would probably show a major speed increase (if you have a pair of those spinets things like these (spinnets) - use one bearing for your axle to go through, and the other two bearings to put screws/bolts into your float) As suggested, making your axle and paddles wider will make it more stable, and develop a lot more power as well |
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| flc1 Senior Member Joined: 20/11/2011 Location: New ZealandPosts: 242 |
Gday Brady, like your pics, I was just hinting at putting a small bit of wood between each blade down by the shaft, to give a bit more sapport to the blades.But its probably not needed, keep up the good work. I look forward to seeing it finnished and charging your battery.  |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I have been thinking about what to use as an electrical generator. Check out these low cost Chinese hand crank generators on e-bay. For only a very few dollars you might find something that can easily be adapted for pulley drive. This is just one example, there are several different sizes, styles and types of hand crank generators advertised on e-bay, all of them cheap. http://www.ebay.com.au/itm/USB-Emergency-Charger-Dynamo-Hand-Crank-Generator-For-MP3-MP4-PDA-Cell-Phone-/201985181592?va r=&hash=item2f07414798:m:m1ccfcM4LvPiMnM_MksIIQQ Hand cranking suggests about one turn per second ? But I have no idea what speed you will finally end up needing, or how hard these are to turn. No specifications provided unfortunately, only way to find out is to get one and do some testing. A standard BMX bike rim is usually 20 inches or very close to 500mm diameter. Circumference will be around 1.57 metres. Flow is roughly 23 metres per minute. So a bike wheel might turn perhaps 14 turns per minute. If you can work out how many turns per minute a hand cranked generator needs to turn, that will give you a reasonable starting point to further experiment with different pulley ratios. Cheers, Tony. |
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