Rotor Egg Drop B

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Re: Rotor Egg Drop B

Post by InfiniCuber » October 27th, 2012, 8:58 am

e_sully wrote:Be very careful with laminated rotors that they are not arched, or at least have a solid bottom. A curved rotor will act like a parachute and can get you DQ'd.
I agree, but make sure that it spins and it will be ok.
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Re: Rotor Egg Drop B

Post by jander14indoor » October 28th, 2012, 5:37 am

e_sully wrote:Be very careful with laminated rotors that they are not arched, or at least have a solid bottom. A curved rotor will act like a parachute and can get you DQ'd.
That's the second time I've heard that, but I still don't understand it. Nothing in the rules about a curved bottom.

MANY airfoil shapes have curved bottoms but certainly don't act as a parachute. The key would seem to be rotary movement, NOT shape. A flat plat that doesn't rotate acts the same as a parachute.

Where is this statement coming from?

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Re: Rotor Egg Drop B

Post by Skink » October 28th, 2012, 8:43 am

I suspect it's conjecture. At this time, the defintion of 'parachute' is open to interpretation, but I'd expect an Official Clarification on the matter sooner rather than later.

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Re: Rotor Egg Drop B

Post by sofan » November 5th, 2012, 6:52 pm

How many rotors should i use if i really really really want to win?

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Re: Rotor Egg Drop B

Post by Aletheia » November 5th, 2012, 7:48 pm

Do keep in mind, that, nevertheless how many rotors you use, the entire contraption is to fit inside a 51 by 51 by 51 cm cube. Basically, 20 inches.
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Re: Rotor Egg Drop B

Post by chalker7 » November 5th, 2012, 8:40 pm

sofan wrote:How many rotors should i use if i really really really want to win?
I don't think anyone has figured that out yet. The best bet is for you to build a few of them with different numbers of rotors and do some comparison tests.
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Re: Rotor Egg Drop B

Post by sofan » November 7th, 2012, 5:53 am

chalker7 wrote:
sofan wrote:How many rotors should i use if i really really really want to win?
I don't think anyone has figured that out yet. The best bet is for you to build a few of them with different numbers of rotors and do some comparison tests.
Thanks
New school year! New scioly season! Another year to do something great!

2013 galveston regionals:
rotor: 3rd
pic: 2nd(Texas event)
overall:3rd
2013 state:
rotor:4th
overall: 12th :I

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Re: Rotor Egg Drop B

Post by jander14indoor » November 8th, 2012, 8:25 am

sofan, I see you are struggling with where to start. Unfortunately this event is new so there aren't 'canned' answers available. BUT, that's not to say there arent' places to start.

I'll assume you read my general statements at the head of this string and are still lost. Let me see if I can give you a simple place to start and maybe a plan of attack to advance.

Spend some time looing at this years and last years discussions on helicopter duration and this years helicopter wiki. Aerodynamically VERY similar events. See how they construct a rotor. Many pictures, examples and plans.

Now, scale the rotor up to a size that fits the 50 cm box for this event. Make ONE rotor. Don't worry too much how wide to seperate the tips, or how tall to make it to start. But if you want a place to start, as a purely arbitrary start, try 8 cm tip seperation and 2 cm height between spars. Make the spars 50 cm long. Glue a short stick (5 cm or so) below the rotor along the center axis. Suspend the egg below the rotor with a fine string that will let the rotor spin. Drop and measure time to descend vs height. Several times each. Now go back and vary the rotor design parameters to see what slows the egg more. Wider tips? More height seperation of spars? Longer spars?

Once you know how to make a good, simple rotor, try additional variations. Try four blades instead of two, better or worse? Try two rotors, counter rotating like helicopter duration, but not rubber powered. Try different blade shapes.

Oh, in all of this STAY AWARE OF WEIGHT! You can't compare two designs unless they weigh the same or weight will swamp the effect of the aerodynamics.

Once you've started, if you get stuck on a specific item, ask here. This forum is MUCH better at answering specific, focused questions on things you've tried than broad things like how do I get started.

Jeff Anderson
Livonia, MI

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Re: Rotor Egg Drop B

Post by sofan » November 8th, 2012, 2:31 pm

jander14indoor wrote:sofan, I see you are struggling with where to start. Unfortunately this event is new so there aren't 'canned' answers available. BUT, that's not to say there arent' places to start.

I'll assume you read my general statements at the head of this string and are still lost. Let me see if I can give you a simple place to start and maybe a plan of attack to advance.

Spend some time looing at this years and last years discussions on helicopter duration and this years helicopter wiki. Aerodynamically VERY similar events. See how they construct a rotor. Many pictures, examples and plans.

Now, scale the rotor up to a size that fits the 50 cm box for this event. Make ONE rotor. Don't worry too much how wide to seperate the tips, or how tall to make it to start. But if you want a place to start, as a purely arbitrary start, try 8 cm tip seperation and 2 cm height between spars. Make the spars 50 cm long. Glue a short stick (5 cm or so) below the rotor along the center axis. Suspend the egg below the rotor with a fine string that will let the rotor spin. Drop and measure time to descend vs height. Several times each. Now go back and vary the rotor design parameters to see what slows the egg more. Wider tips? More height seperation of spars? Longer spars?

Once you know how to make a good, simple rotor, try additional variations. Try four blades instead of two, better or worse? Try two rotors, counter rotating like helicopter duration, but not rubber powered. Try different blade shapes.

Oh, in all of this STAY AWARE OF WEIGHT! You can't compare two designs unless they weigh the same or weight will swamp the effect of the aerodynamics.

Once you've started, if you get stuck on a specific item, ask here. This forum is MUCH better at answering specific, focused questions on things you've tried than broad things like how do I get started.

Jeff Anderson
Livonia, MI
Thanks now i need wood and i can be ready for the first invitational.
New school year! New scioly season! Another year to do something great!

2013 galveston regionals:
rotor: 3rd
pic: 2nd(Texas event)
overall:3rd
2013 state:
rotor:4th
overall: 12th :I

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Re: Rotor Egg Drop B

Post by JimY » November 9th, 2012, 7:07 pm

I've finally learned that the egg is to sit in a paper cup that is mounted or suspended from the bottom of the device, rather than just hanging out in space. Hanging out in space was in the Indiana rules last season as well as the draft rules for this season. The event supervisors for this season may have dodged a bullet with the cup. Story: our high school got stuck in Tier 3 at the state meet last season, and in dead last place. :( Reason: the event supervisors at state judged us to violate one of the construction rules on placement of the egg. The curious part is that we used the exact same design regarding placement of the egg at the regional, and both of our teams ended up in Tier 1. So yes, the same device with the draft rules could be judged differently, depending on who runs it. This is far less likely to be the case with the paper cup. The rules for the trial event stated that the egg had to be mounted or suspended from the bottom of the device such that the egg (inside a bag) is the first thing to contact the floor. One of the devices at state had the egg hanging out the bottom of a hollow tube, and therefore had no bottom to mount or suspend the egg from. The egg broke, so by the rules, it should have gotten placed in tier 4. Since we ended up in last place, the hollow tube device did not get stuck with the same construction violation as us, even though it should have. Bad memories on a trial event run amuck! So for the national folks that are monitoring this post, if the rules for next season are changed such that cups are no longer used, please do not incorporate the phase "mounted or suspended from the bottom of the device such that". This clearly does not allow hollow tube designs for holding the egg, since they have no bottoms. Rather, say "The egg must be attached to the device such that the egg in the bag is the first thing that contacts the floor." This is so much easier to decipher for students, coaches, and especially judges. I mulled over this particular section of the trial event rules last season for longer than I care to admit. The kicker is that the regional was judged by college professors and state was judged by college students. I'm hoping that with this story told, I can finally let go of it....

To address the rotor question posed, we tried both 6 and 8 rotor designs last season. The 6 was better than the 8. Most likely because it was lighter. The difference in times, however, was very small. The 6 rotor design weighed about 65 grams, and the 8 rotor was about 80. So, both were much heavier than I would guess the best teams will be this year by at least a factor of 2. We used construction foam for the blades, shaped into airfoils. SO, while they could not weigh the same, the lighter one was a bit better than the heavier one. If we were doing this event this season, I'd be pushing the students to use rotors made of balsa and mylar.

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