Rotors

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lllazar
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Re: Rotors

Postby lllazar » March 25th, 2011, 6:59 pm

Well, if you know how to make a good jig, our at least are willing to do some research, it shouldn't be too hard to make those kinds of props. But if this is your first copter, maybe try something a bit less complex, as Chia said. Building experience will help you fix all the mistakes you made on the first one.
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Re: Rotors

Postby chia » March 26th, 2011, 3:09 pm

I think I need to find a better way of attaching the rotors to the wire. Currently I'm just gluing it straight to the side of the rotor at the center spar, with another piece of wood on top to keep it straight. Obviously not the best option, balance- and strength-wise.
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Re: Rotors

Postby lllazar » March 26th, 2011, 5:56 pm

I poke the wire through the two spars and glue the the whole shut. It's not working too well either. I think if i used wood glue for the holes instead of super glue. Titebond is apparently as strong as oak.
2011 Season Events~

Fossils (Regionals ~1st) (State ~6th)
Towers (Regionals ~1st) (State ~3rd)
Helicopter (Regionals -3rd gahhh) (State ~5th)
Wind Power (Regionals ~1st) (State ~3rd TIERED!)

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Re: Rotors

Postby thewinner » March 26th, 2011, 7:00 pm

I do the same thing. I just wish the wire was stiffer, so it wouldn't bend under the force of the rubber band and twist the whole rotor out of alignment.
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Re: Rotors

Postby jander14indoor » March 27th, 2011, 4:31 am

Rotor to wire joint. DON'T depend on a straight wire held with glue, too much glue, not enough strength. With the high torques needed to fly these things, say 2.0 in oz. At the surface of a 0.020 inch wire you have 400 lb of force trying to break things!!!!! Instead, bend over a short L, say 1/8 inch at the end which lies against the wood directly and reacts the torque. Force will drop to something like 16 lb needing almost NO glue. Also, run the wire through the centers of your spars, and sandwich wood on either side, don't put it on the side.

As to wire stiffness, if bending too much, go to the next wire size up and save the weight someplace else.

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Re: Rotors

Postby lucwilder42 » March 28th, 2011, 4:36 pm

Hey Jeff, is there any merit to a three bladed rotor for this event?
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Re: Rotors

Postby chalker7 » March 28th, 2011, 5:37 pm

I'm not Jeff, but I'd like to add my two cents.
There may be some benefit to a tri-bladed design, however I can't know for sure since very few (if any) people have built one.
I saw one 4-bladed design earlier in the year that flew extremely well (in fact, it was probably the most stable SO Helicopter flight I have ever seen), but was significantly overweight so it did not have exceptional duration. So, long story short, 3 or 4 blades could or could not help but you will definitely run into difficulties with weight (particularly with 4 blades) and alignment (with 3 blades). In either case, you should try to build a few and let us know if they work well for you!
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Re: Rotors

Postby illusionist » March 28th, 2011, 5:58 pm

I have also experienced those properties with the 4 blade design. I tried two counter-rotating rotors with 4 blades each, and it was much, much more stable, but duration was cut short. I also had to reduce the pitch of my blades to accommodate the extra drag. The helicopter weighed about 6ish grams, obviously reducing its potential flight times. So with my more experienced building skills now, I might give it another go. However three blades seems like a challenge.
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Re: Rotors

Postby thewinner » March 28th, 2011, 6:56 pm

How exactly would you get all four (or three) rotors to spin? It sounds interesting.
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Re: Rotors

Postby lucwilder42 » March 28th, 2011, 7:00 pm

On a separate note, assuming weight is under control, has anyone had success with three rotors? We have good two blade two rotor standard copters that we're boxing up til state, now I'm goin balls to the walls with new designs
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Re: Rotors

Postby Frogger4907 » March 28th, 2011, 7:29 pm

lucwilder42 wrote:On a separate note, assuming weight is under control, has anyone had success with three rotors? We have good two blade two rotor standard copters that we're boxing up til state, now I'm goin balls to the walls with new designs

It would need more torque to turn, i suppose if u know what your doing you could be successful.
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Re: Rotors

Postby illusionist » March 29th, 2011, 3:49 am

thewinner wrote:How exactly would you get all four (or three) rotors to spin? It sounds interesting.

You just build it the way you build the two blade designs, but instead you just add another set of blades at a right angle.
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Re: Rotors

Postby thewinner » March 29th, 2011, 12:23 pm

Okay, thanks.
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Re: Rotors

Postby Frogger4907 » March 29th, 2011, 1:12 pm

thewinner wrote:Okay, thanks.

Make sure your angles are perfect, it needs to be balanced.
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Re: Rotors

Postby illusionist » March 29th, 2011, 1:35 pm

Yeah, having a jig helps tremendously in making the blades identical. I didn't have one at the time I made it, so I plan on remaking one, but if you happen to beat me to it, please let me know how it works!
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