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Old Nov 19, 2005, 03:08 AM
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Toronto,ON
Joined Jan 2002
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Hand carved balsa props

Thought i'd try my hand at forming a balsa prop. Carved one out of 3mm thick balsa. It seems to have worked out pretty well for a 1st attempt but I think I want a sharper angle. I plan for it to be mounted without any gearing.

I'm wondering why geared setups are so popular. Can't thrust and load be controlled by changing the prop pitch?

I suppose a carbon fibre prop would be lighter and more effective (perfect design) if it were moulded from a purchased plastic prop. Unfortunately my local hobby shop doesn't carry carbon fiber cloth. In fact, they don't even carry small props to use as the mould. And I'd rather try to get things done with local solutions rather than ordering from the net. I found a great local supplier of pager motors but tiny props aren't very popular.
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Old Nov 19, 2005, 08:44 AM
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USA, FL, Fort Lauderdale
Joined Feb 2002
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If you really want to fly micros you are going to have a very tough time of it until you get into web/mailorder. The micro gear is just not in enough demand for hobby shops to cary much, if any of it. Web/mailorder is quite easy and fast, even across continents. Honestly, your are spinning your wheels if you refuse to use it.

In general, larger, slower turning props are more efficient, so for a given size motor you can get more thrust by gearing. Epilot's BUMP is a good example of direct drive. Here you have a light plane with large motor, so you can trade some efficiency for the simplicty of DD. If you need to get the most from your motor, gearing, with the correct prop, is the way to go.

Dave
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Old Nov 19, 2005, 11:20 AM
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Toronto,ON
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Agreed. Eventually I'll have to start ordering things from the internet. Tiny Li-Po's are especially difficult to find.

But for just starting out I'm trying to get as much done simply and cheaply as possible. I'm even powering my motors with a tiny watch type battery right now ($1) to test prop designs. I need some way to test thrust right now. Guessing by the amount of air blowing in my face doesn't seem all that accurate.
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Old Nov 19, 2005, 12:33 PM
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USA, FL, Fort Lauderdale
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Quote:
Originally Posted by ToJo
I'm even powering my motors with a tiny watch type battery right now ($1) to test prop designs. I need some way to test thrust right now. Guessing by the amount of air blowing in my face doesn't seem all that accurate.
If you are just testing thrust on the bench, do not use small batteries. They have very limited current output and you are likely not getting anywhere near the voltage you are aiming for. If you have a decent voltmeter, hook it up to the motor terminals during your tests. Make sure your cells are delivering the same voltage your eventual flight pack will, for example about 3.7 volts for a single Lipoly. If you don't have a voltmeter, use large cells, like a "D" size alk. for 1.5 volts or a 500 mah or so nicad for 1.2 volts. Also make sure your props are balanced, an unbalanced prop can rob a lot of power. A music wire shaft resting on two parallell razorblades that have been glued to a block of wood to hold them about an inch apart is a good, cheap balancer. The blades have to be perfectly level, both to each other and the table.

Dave
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Old Nov 21, 2005, 09:52 AM
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Toronto,ON
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New version. This one actually looks pretty good and spins very well.
I think it's a bit small at just under 5cm though.
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Old Nov 21, 2005, 05:06 PM
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riverside, CA
Joined Feb 2003
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check out this page for carving props. I've made a few that worked pretty good from this design. had my micro BL banchee hovering on one a while back. http://www.marcee.org/Articles/Helic...ropellers.html
I havn't made any in a while, but i'll attach a picture of my p-nut equipped with one. They come out pretty good if you follow the directions right.
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Old Nov 21, 2005, 05:29 PM
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Toronto,ON
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Is the prop glued right onto the shaft?
I glued mine onto the motor shaft but now I'm wishing I would've somehow mounted it in a way that it could be removed without being destroyed.

That website doesn't mention much about different prop sizes and configurations. Right now I'm deciding whether to build a wider and longer prop. I think I'll have to do some reading about this stuff.

Or just order some carbon fiber cloth and take a mold from a proven prop.
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Old Nov 22, 2005, 01:00 AM
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riverside, CA
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I believe that sight explains how you would go about changing their formula to adapt to your needed prop size. After reading it a few times, you'll pick it up. It's really an easy method, which can produce any size prop.

The prop on my banchee is on a prop adaptor. This is no problem to remove. The prop on the smaller P-nut plane was glued to a carbon fiber shaft. I land this plane in the grass, but i have crashed it once or twice. All that happens is I break a prop and a carbon prop shaft, then i replace them. I don't crash too often as this is one of my favorite planes.. but when i do i can fix it and carve another prop in about 20 minutes while the battery charges, and be up and flying again in no time.

It takes a bit of figuring out, but you can use the carvprop page to make any size prop. As a matter of fact, i havn't made one in a while and i think i'll do one for my new 3 gram indoor plane i'm making. I'll post a picture when i get it done. Play around with that formula dude! it's not too heavy after you read it a few times and take each step one at a time. you'll be amazed all the different props you can cut up.


casey
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Old Nov 22, 2005, 01:03 AM
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riverside, CA
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Quote:
Originally Posted by ToJo
Or just order some carbon fiber cloth and take a mold from a proven prop.
an easy solution for this might be the fiber glass cloth at your local auto parts store. They call it bondo, it's for fixing dented or rusty car bodies. if the woven fiberglass is thin enough, or you can thin it out, I know the stuff is cheap and pliable. I made a whole motorcycle fairing out of the cloth and a few containers of bondo. I imagine it would make some good props

as the website carvprop states...
"Whenever I feel the need for something inspirational I pull out my old copy "Airplane Design" by K.D. Woods open it to the cahpter on wing desing and read, "Anything that looks like a wing will perform almost as well as the best wing". (Fred) Weick has reached the same conclusion regarding propellers."

I kindof use this rule for making ribs in my airfoils
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Old Nov 22, 2005, 02:59 AM
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riverside, CA
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I just finished the prop for my living room sprite. the plane was .9 grams so i figured i'd shoot for .1 gram for a prop and even things up to 1 gram.
That carvprop page works great if you have the patients to sit there and actually carve the prop. it may take a while but the end result looks quite nice. Almost like those little props that come with the Gasparin C02 motors. At any rate, i have the finished 2"x4 prop i wanted at the start. all you do is use the formulas with your own measurements instead of using thier measurements. Just swap over the formula
casey
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Old Nov 22, 2005, 03:03 AM
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riverside, CA
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more pictures
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Old Nov 22, 2005, 12:38 PM
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Toronto,ON
Joined Jan 2002
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Looks good. I wish I had a way to test thrust.

Even with a mediocre prop I figure a 6mm motor should be able to get something under 2 grams to hover.
Am I wrong? I read some of these little motors with different props are putting out over 10g thrust. I'm not using any gearing....but still....2g isn't much to ask.
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Old Nov 22, 2005, 04:57 PM
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riverside, CA
Joined Feb 2003
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seems like i had better luck on this plane with the 4x6mm motor over the 6x10mm motor. the extra weight was bringing me down bigtime. the tiny lil 4x6mm 10 ohm pager motor could probably hover something.. I had one hovering itself on a prop last night before i put it into that plane. but for a hovering plane, I'd use gearing to swing a bigger prop, so you can punch the torque coming out of the hover. I'm not sure how well ungeared small motors do, but i know you can pull 2 grams of thrust for sure on the 4x6mm motor with a 2" prop running direct drive. I still have alot to learn about gear ratios and props myself. I'd be interested in picking up any books that have to do with plane propulsion system design.

BTW:
if you havea small scale and a clamp you can test thrust no problem.
clamp the motor, facing upwards in the clamp, then set the clamp on the scale. Now turn the scale on, and it should set to 0grams. plug a battery to the motor and spin up the prop. the scale should start reading below 0, as if you were lifting weight off of the scale with the motor. the negative reading is your thrust output. I'm pretty sure this is somewhat accurate. anyone feel free to correct me if i'm wrong though!
casey
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Old Nov 23, 2005, 11:04 AM
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bmutlugil's Avatar
Turkey
Joined May 2002
2,178 Posts
Hi,

I have developed a simple jig to duplicate standard propellers in balsa. I had posted about this before.

http://www.rcgroups.com/forums/showthread.php?t=57411

In principle you prepare a carving jig using a standard propeller, substitute a balsa blank and carve the lower sides of the blades. You shape the upper sides of the blades by eye and hand coordination

Regards,

Bulent
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