Rotors

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Re: Rotors

Post by jander14indoor » October 28th, 2010, 12:16 pm

franklinknights wrote:how do i make the robot assembkly? im thinking about using paper cups for rotor shape and got design to cut them but idk how to make rest of assembly
If you are making the rotor blades from the cups, this is just a variation on method 2 in the post just above yours, check that links. Scale up the spar size of course, use your cup blades instead of the molded balsa ones, thicker wire, say 0.020 inch diameter.

Unless of course I've comletely misunderstood your question, if so rephrase and I'll try again.

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Re: Rotors

Post by SFCMS » October 29th, 2010, 11:52 am

OK, so I am not quite understanding what everyone is saying so I have to ask this...

If you make your own propeller, can you buy a thrust bearing from a store and use it, or do you have to make your own?

And my second question: This is especially to jander14indoor, since you seem very good at this-

Would the helicopter still be able to fly if both rotors were fixed (I don't know if I'm using the correct term, but I'm talking about the prop attached to a motor...), instead of having one "free" and one "fixed"? In other words, there would be two seperate motors, each half the length of the entire helicopter, and one motor would go with one prop... I hope that makes sense... :oops:

PLEASE HELP ME! :?

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Re: Rotors

Post by jander14indoor » October 29th, 2010, 7:13 pm

Remembering my caveat, anything I say is my opinion, yada, yada... And I'll ask, do you have a copy of the rules? Because if not, GET THEM! Can't emphasize it enough, to be successful in SO, you MUST read the rules for yourself!!

OK, off soapbox, sort of.
SFCMS wrote:<SNIP>If you make your own propeller, can you buy a thrust bearing from a store and use it, or do you have to make your own? <SNIP>
The rules para 2.e says: "Competitors must construct the rotors themselves. Commercially available rotors or propellers must not be used in whole or part. Rotor thrust bearings may be commercially available items." Seems pretty clear, you HAVE to make your rotor/propeller, (the word 'must' is used) you have a CHOICE about the bearing make it or buy it (word 'may' is used) up to you.
SFCMS wrote:<SNIP>This is especially to jander14indoor, since you seem very good at this- <SNIP>
I wish... more like capable, good is a whole 'nother level, just been mentoring Wright Stuff a while and have SOME knowledge of aeronautics. I actually DON'T know what the nationals winning design will look like. I have a guess, but only minimal experience and minimal theory to justify it. So I'm keeping my mind open. There are some absolutes I know, beyond that, there's a WHOLE lot of room for surprises.
SFCMS wrote:<SNIP>Would the helicopter still be able to fly if both rotors were fixed (I don't know if I'm using the correct term, but I'm talking about the prop attached to a motor...), instead of having one "free" and one "fixed"? In other words, there would be two seperate motors, each half the length of the entire helicopter, and one motor would go with one prop... I hope that makes sense... :oops:

PLEASE HELP ME! :?
Kind of makes sense, pictures or drawing would help.
Anyway, the rules seem to allow for multiple motors (para 2.f) and don't say how you use them. I'd phrase what you are trying to say differently. I'd say you have two 'free' rotors, each individually powered.
Some approaches would work, some wouldn't. What are you going to anchor the other end of the rubber band to? How are the rotors spinning? With two, you almost HAVE to have them counter-rotating, or the thing will spin funny, not creating power/lift.
If you just have one motor stick with rotors top and bottom and the ends anchored to the stick, and counter-rotating, you really have the same dual rotor design we've been talking about, think about it or a while and you'll see.
I did see one last year at nationals that had two rotors with half motors each. Each pointed up, and had its own motor stick. They were side by side and had a frame in-between. Think a Chinook copter like this: http://en.wikipedia.org/wiki/File:CH-47_2.jpg Not very successful because it weighed too much for all that connecting structure. Stability was questionable for what little flight time it had, could probably resolve that.

Hope that helps

Jeff Anderson
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Re: Rotors

Post by illusionist » October 30th, 2010, 7:03 am

I am currently using an Ikara prop hanger (such as the one found here: http://www.aeroracers.com/images/accessories/KI-95.JPG) in order to attach my rotors. The hanger and the washer/bead are the only two things I am using from the Ikara prop. I think the hanger is too heavy... What are my other options for attaching the rotors? I know that there are the pig tail prop hangers...
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Re: Rotors

Post by SFCMS » October 30th, 2010, 2:04 pm

Yes, the each motor would be half the length of the motor stick. And in the middle of the stick, there would be two hooks (a small distance apart) anchoring the other end of each motor... Are you a coach? Do you still think this kind of design would be successful? And if so, what kind a rotor design would gift the most lift? Right now I was just thinking about using the basic rectangular design, but I am sure there are much better designs... And yes I do have the rules, its just that I didn't really understand their wording of certain sections... I am very appreciative of all your help! :D

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Re: Rotors

Post by jander14indoor » October 30th, 2010, 9:06 pm

SFCMS wrote:Yes, the each motor would be half the length of the motor stick. And in the middle of the stick, there would be two hooks (a small distance apart) anchoring the other end of each motor... Are you a coach? Do you still think this kind of design would be successful? And if so, what kind a rotor design would gift the most lift? Right now I was just thinking about using the basic rectangular design, but I am sure there are much better designs... And yes I do have the rules, its just that I didn't really understand their wording of certain sections... I am very appreciative of all your help! :D
Like most, I'm many things. Mentor, event supervisor, state director, etc. As such I don't coach any individual team, appearance of conflict of interest if not in fact. I do however run workshops, and answer questions on forums like this because I HATE timing the race to the floor. Students can't learn (or not much and probably the wrong lesson) unless their device is basically working (flying in this case).

So, will your idea work, implemented properly, yes. Work well, again, if you do your part, probably. Best approach, if I even knew what that was, I wouldn't say, would defeat the point. But in this case I DON'T know. Maybe after a few years of watching what you students come up with!!

As to best rotor design, you need to consider two factor. Maximum lift and minimum drag. I suspect, but only suspect, little data, and only enough theory to be dangerous, that a helical pitch distribution rotor with the individual blades that are elliptically shaped outline and efficient airfoil will be best, but exactly what that design looks like, haven't seen it yet.

Now, lets talk about what successful is. First level, build a copter that really flies. Leaves your hand, raises at least say 10 feet or more and flies say 20 to 30 seconds. Frankly that will do pretty well at most regionals this year. To win, you probably need to get it to fly a minute or better (except at the most competitive regionals). At states, that would also do well, might win some states. At the more competitive tournaments, expect to need to do two minutes or better to win. At nationals, two minutes will get a good placing, but you'll PROBABLY need two and a half or three minutes to win this year.

I saw a nothing special two rotor, counter-rotating design win the national trial last year with about a two minute flight. It was well built and well flown mind you, but no secrets that I could see. So, focus on getting a copter built, nothing too fancy to start and get experience with real flying. Then start modifying.

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Re: Rotors

Post by SFCMS » October 31st, 2010, 10:48 am

Ok thanks, and what would would be a good length for the motor stick to start off with? Thanks for being so much help!
Last edited by SFCMS on November 1st, 2010, 12:56 pm, edited 1 time in total.

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Re: Rotors

Post by jander14indoor » October 31st, 2010, 6:38 pm

I'm assuming you mean the motor stick? If so, 8-12 inches is fine.

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Re: Rotors

Post by new horizon » November 3rd, 2010, 6:46 pm

I kind of feel dumb for asking this, but I can't find it in the forums!
Are both rotors, fixed and free the same thing? I understand one spins clockwise and one spins counterclockwise, but when you carve the props there is no difference correct?
And also, is the fixed prop or the free prop the clockwise one?

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Re: Rotors

Post by smartkid222 » November 3rd, 2010, 7:19 pm

The free rotor is the one that is attached to the motor and spins. The fixed motor is attached (glued) to the motor stick. Basically, if you would up the rubber motor and then just held onto the motor stick, the free rotor would spin and the fixed would not. The fixed is fixed on the motor stick. In actual flight they both spin in different directions because the motor stick is spinning with the fixed motor.
Which one is counterclockwise or clockwise is your choice as long as they are opposite.
When you carve them one is a right handed rotor one is a left handed rotor.
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