I have a project for engineering, and want your thoughts on it.
For the project, we are asked to build a horizontal or vertical blade windmill that is able to generate the most amount of electricity while also lift the most amount of weight. A fan set to high speed will be the “wind source”, and it will be four feet away. We are given panels, dowels, disks, a motor for measuring electricity, and mounts. Materials available are 1x2 wood,metal braces, vex gears, and pulleys (can be vex). I asked If we can used vex motors, a cortex, and a pneumatic transmission, but she yelled at me and said no. lol I was thinking on using a transmission though for a high speed, and high torque setting. What do you guys think, and do you have any tips
so any ideas?
I mean if it’s a windmill you shouldn’t need a motor to power it. I would probably make the lightest fins possible because those would be the easiest for the fan to move.
Okay. would poly carbonate sheets be fine. They are pretty light and thin.
mmm, I think in this case because you not using a particularly powerful source ( I would assume, unless you have a jet engine fan ), a smaller and lighter design that can spin really quickly could be beneficial, as oppose to a heavier more powerful design with higher gearing.
Lift the most amount of weight? Is this meant to model something like those airborne electric generators that some people have been working on?
Or was your teacher talking about generating the most amount of torque?
That seems fairly wimpy, so I’m even more confused about the “lift the most amount of weight” requirement.
When you say they gave you a motor to measure electricity, do you mean the motor is being used “in reverse” to act as an electric generator? Or are you given a generator and the output of the generator must power the electric motor?
Because of the probable weakness of your wind source, I would try to reduce the number of gears to a minimum so you can reduce starting friction as much as possible. But be aware that power in generator systems like this is related to speed x torque. Think of how your torque-speed curves look for your 393 motors. You get the maximum power at some value “in the middle” between your max torque and max speed. In the “middle” is the zone where you want to run the generator itself. The “attack” angle of the vanes will dictate what your speed will be and the overall size of the windmill will dictate how much energy you can extract from the moving air.
Knowing what are the power generation characteristics of your generator might be a good place to start. If you don’t already know those specs, maybe you could hook up to the generator a Vex 393 motor, an encoder, use a multimeter on your generator, and through a Cortex derive a power speed curve (looking at the speed and torque curves of the 393 motors). From there, perhaps you can think about optimum speeds, etc.
For attack angles, you might consider making a vane system with adjustable angles, hooking an encoder + Cortex to its shaft, then run experiments to see which attack angles give you the most speed. Then vary the frictional torque a little and see how that affects the system.
Just thinking out loud, here.
Yes It has to lift the most amount of weight.
This also is correct she will attach a voltage tester to it to measure electricity generated.
Could you explain this pls, and how would I derive that chart.
Perhaps you could first attach an encoder to the output shaft of your windmill and read the encoder (via the Cortex) to get rotational speed of your windmill when the fan is turned on. I’m guessing you could think of this as your system’s no-load, free-wheeling speed. If you want, you could adjust your windmill vanes (varying attack angles, distance from the hub, vanes sizes, etc.) to see what it takes to get the maximum free-wheeling speed. Doing just this will probably give you the most bang for your buck as far as trying to find out how best to design your system.
To see what your max torque output could be, you could attach a weight to a string, which is attached to the hub of your windmill. The weight will impart a particular torque on your windmill’s shaft. By varying the weight and/or position of the weight (position = its radial distance from its shaft’s turning point), you can vary the amount of torque on your windmill shaft and make adjustments until you get a torque value at which the windmill will spin neither one way or the other - this would be similar to a stall torque (which is the max torque output your windmill can provide).
Somewhere between this max torque situation and the max free-wheeling speed will be the max output power of your windmill. Knowing these limits will help you decide how to gear the system or how best to configure your vanes. Essentially, you want the highest speed you can achieve at the highest torque, roughly speaking, since Power = torque x speed.
To get the generator speed-torque characteristics, you might consider this:
(EDIT: I changed this from my original post because I forgot that we have a 393 torque-speed curve only for max power.
Hook up an encoder to a 393 motor shaft so you can use your Cortex to monitor the speed of the shaft. Give the 393 motor a command of max power, 127, and see what your output speed is. It should be close to the motor’s no-load speed of about 60-100 RPM.
Next, hook up that motor shaft to your electric generator without there being an electrical load on your generator. Now give the 393 motor a command of max power, 127. The speed difference you see should be a result of friction in the generator. By looking at the 393 speed-torque curve, you should be able to associate the speed with the torque.
Taken from Pearman: https://vexforum.com/t/motor-torque-speed-curves-rev2/21868/1
Next, by connecting gears to your system, you can evaluate the friction in those gears by watching the speed drop and again using the 393 speed torque curve as a reference.
This will give you some idea of what sort of frictional characteristics your motor/gearing/encoder/generator system has. You might notice that it is non-linear and has a zone where friction suddenly shoots up. Note well: this is without any electrical load on the generator, so most of the power that is being consumed at this point will be from friction, I think. Your electric generator will give you a voltage reading but what’s ultimately most important to you is how the generator will behave when it has an electrical load applied to it, like a motor or light bulb or resistor.
Be aware that you can spin an unloaded generator at speed S and get a voltage reading. But as soon as the generator experiences an electrical load, the generator will require more torque to maintain that same speed S. So there are load and no-load conditions on generators.
So the next thing you can do is apply the electrical load to the generator and see how the speed drops. Again, using the 393 torque-speed curve, you should be able to get some rough ideas of the frictional + electrical load characteristics
I think you could be able to use this kind of motor/encoder/generator set-up to get a feeling for how your system will behave under various electrical loads for various gearing ratios, etc. if you decide to use gears. However, I know it all sounds a bit complicated, and I’m guessing you don’t have enough class time to do all of this, but doing some portion of this might help you, if you are really trying to find the sweet spots in the design. Trying to optimize the aerodynamics along with the gearing to match the generator output characteristics would probably be way too much to do.
You could even hook up the entire system (windmill, generator, etc.) and drive the whole thing with the 393 motor to turn it into a fan and see how it “blows” (effectively running your windmill in reverse to get some idea of its behavior).
If nothing else, maybe consider just using the encoder on your windmill shaft (mentioned in my previous post) to see how to get the most speed for various vane configurations. That would probably help the most to get you in the ballpark. Then if you have time left over, you could dive into finding the characteristics of your generator, etc.
I hope that helps rather than confuses you.
I forgot we have 393 torque-speed curves for only the motor commanded at max power, 127. See the newly edited post above. :o
How would I know it I am this point.
Sorry about the confusion with that - I keep presuming we have torque-speed curves for motor values other than 127. So running your 393 at the commanded 127, I guess the only thing you could do is compare how much torque your system requires as you try different configurations, different gears, bearings, etc. and see which ones gobble up less power via friction.
Thanks a bunch. What shape should I use for the blades?
and what materials
Would a carbonate sheet suffice.
According to this article, the best number of blades is three, but four is slightly better, though it decreases cost-efficiency and requires thinner blades, so three would be fine.
I didn’t really read through the article (I probably would if I didn’t have an essay), but a carbonate sheet might be okay. It would need to be pretty thin (I’ll assume 1/16~1/32 inches), so you’ll probably need to buy some since cutting sheets in half would probably be almost impossible. Bending the sheets will most likely be a tough job, too.
I would suggest maybe a cardstock blade if all else fails because paper is simple to manipulate. Good luck
You mean like polycarbonate? I’d try starting out with some cheap stuff, first - cardboard, stiff paper, etc. to get a feeling for things. Then, if you really think you’ve got it figured out, you might try some plastics. I’m not sure about polycarbonate, but I know you can use a heat gun on Delrin to bend it into some useful shapes, so long as the angles are gentle enough.
Surely there must be some good forums somewhere on DIY windmill generators. There are all sorts of people into survivalism, surviving zombie apocalypses, etc. that have probably figured out the DIY windmill thing.
I’m not endorsing this one, but it’s what popped up when I googled it: