Rotor Egg Drop B

[VulpesFox]

Couldn't find a forum for coaches, so post here I will! I'm coaching a team (two actually) for Rotor Egg Drop, and I need to know what a good, competitive time is. Does anyone have any examples?

[jander14indoor]

No seperate coaches forum on this site. This site is about open exchange between students, coaches, event supervisors, mentors.

As to good times, check last years discussions, I think national winning times were listed. Since limited time to prepare and limited competition to force improvement I doubt they are the best possible, but they are a starting point.

Jeff Anderson
Livonia, MI

[rotoreggdropums]

Can you use rubber bands as part of your machine? Thanks.

[jander14indoor]

Keep in mind this is not the place for clarifications, any answer you hear is pure opinion, not official, etc no matter who makes the statement.

The rule says: "No energy-producing mechanism of any type may be used to power the rotor(s) to slow the descent of the device." and "No other shock absorbing or cushioning materials may be used either inside (including trapped air) orou tside the bag or cup to protect the egg before the cup contacts the floor."

As long as the rubber band isn't doing those things its probably legal.

BUT, rubber bands are commonly used to power rotors. As a coach I'd ask you to consider what advantage they give vs the risk of an event supervisor thinking it provides power and being place in tier 3 or 4.

Jeff Anderson
Livonia, MI

[qiqishi]

Heyyyyyyyy my friend and I are building an egg drop. We were wondering what a good flight time at regionals, state, and national level is. Thxxx

[jander14indoor]

Heyyyyyyyy my friend and I are building an egg drop. We were wondering what a good flight time at regionals, state, and national level is. Thxxx

Check back up this chain about three note above your question.

Jeff Anderson
Livonia, MI

[hogger]

I would like to discuss the design with the experts (Jeff and the rest) to get a better idea on how to attack this event.

Here are what I assume to be true for this event (correct me if I'm wrong):
- It is better to have more rotor surface for airfoil for lift, provided that the extra area does not add too much weight.
- Given we have basically a cube space for building all the airfoil surface, we should build multiple rotors, maybe as much as we could to fit into the volume.

So if those are somewhat correct, we should build as many rotors as we can that can fit within the volume and as many blade area as we could on a rotating plane of each rotor. Does this make sense? If so, I can see building a stack of rotors, maybe 5 or 6 or even more. Half of them should spin in one direction opposite of the other half to counter balance the spin and for steady flight.

Then I thought, those large rotors are probably slow to turn and get started. Maybe instead, we should build some smaller rotors (shorter blades) to help with the beginning of the flight to slow it down and then the longer bigger blades can come into play in a bigger way once they get going. So, the set of smaller blades should have higher pitch and then another set of longer and larger blades with lower pitch.

These ideas are good, bad, or totally missing the point?

[jander14indoor]

While all the things you say are directionally correct, as you mention, there is a point of diminishing returns that due to newness of the event no one can give you specific answers on.

Perhaps more important, in engineering (and life in general) I've mostly learned (the hard way, ie by failing, and I still repeat the mistake on occasion) that it is dangerous to start a new endeavor with too complicated a plan. Complicated things rarely work on the first try and its very hard to sort out why.

Instead of starting out with everything, including the kitchen sink, I suggest you start with much simpler designs and add elements once they are perfected.

Start with a single rotor, two blades, see how it behaves. Make changes to area and pitch and see result. Now try three or four blades, how much is gained by each blade. Does adding a blade change the ideal area/pitch of individual blades? At what point does it NOT pay to add another blade?

Now try two rotors, counter rotating. Use the basic design you've proven with one rotor as the base. See if there is a new optimum point when two rotors are used and again, is it worth it?

Then try three, four, whatever until they just don't pay and backoff.

Try the mix idea AFTER you've proven the basic idea.

I'm not saying don't do complicated things. What I'm saying is make sure you have a SOLID foundation in the basics first.

And if you run out of time by the day of the tournament, you'll still be in good shape. A simpler designe operating at 90% will beat that complex design that's capable of wonders, but is only operating at 10%.

Jeff Anderson
Livonia, MI

[hogger]

I hear what you are saying. Even if we can't do all the pie in the sky things, at least we can discuss the merit of certain ideas? It might lead to some simple things you can do to test out some of the possibilities...

[jander14indoor]

Hey, if you haven't figured it out yet, I'll discuss ANYTHING, and I'm VERY free with my opinions!! I do try to make it clear when I'm talking beginning vs advanced stuff. And I lean towards beginning stuff on this event because it is so new.

And you do seem to have the point as I hope I made clear.

OPINION only on your suggestions. Backed up only by experience, reasonably sound theory, and very limited data. Good solid data with specifics an overturn any of these.
I suspect 2 bladed rotors are pretty darn good, 3 or 4 bladed rotors are about optimal 5 and more difficult to build with little net gain.
I suspect that two rotors is better than one, but not much net benefit from adding a third or fourth.
IF you keep everything light, I suspect large, low pitch rotors will start up plenty fast for a long drop, I'm suspicious about short drops.
I'm not seeing how a couple of smaller, faster to spin up rotors helps the big rotors to spin up. I'd suspect the just slow the drop quickly and leave less force to spin up the big ones. But this is really getting speculative because I'm seeing one thing from your description and may be way off base, as well as no data.

Jeff Anderson
Livonia, MI