Helicopters C

bjt4888
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Re: Helicopters C

Postby bjt4888 » February 27th, 2017, 5:53 pm

calgoddard wrote:

"maxxxxx -

A helicopter could have one two-bladed rotor rotatably mounted on a bearing at the upper end of the motor stick, and one single-bladed rotor rigidly connected to the lower end of the motor stick.

As long as the blade of the single-bladed rotor had a correctly oriented pitch opposite to that of the blades of the two-bladed rotor, each rotor would provide lift based on the torque of a wound rubber motor. That rubber motor would have to be connected between a hook on the shaft of the upper rotor and a hook connected to the motor stick near its lower end.

The helicopter configuration described above would be entitled to receive the 25% bonus in Rule 5.a, provided all other provisions of the rules were satisfied. This is not the only helicopter configuration that would be eligible to receive that bonus, but just an example.

Based on a previous answer to an FAQ in a prior season of this event, in order to be entitled to the 25% bonus the single-bladed rotor must be rotatable independent of any other rotor and it must be driven by the rubber band so that it actively generates lift, i.e. it cannot passively rotate due to airflow generated by other rotors.

This is not an official source for rules interpretation."

Cal,

I will second this explanation of a single-bladed rotor. This discussion came up several years ago when middle school had a single bladed rotor bonus. I was judging the event at an invitational and I was give specific guidance to watch for attempts to qualify a single rotor blade attached to a motor stick that had two independently rotating rotors, one on each end of the stick (each with its own shaft and bearing). The single rotor blade attached to the motor stick in this configuration is not being driven by the rubber motor and should not qualify for the bonus.

My statements here are unofficial, of course, but i am thinking of posting a rules clarification.

Brian T.

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Re: Helicopters C

Postby _deltaV » February 28th, 2017, 10:02 am

I just want to add my 2 cents to this bonus discussion. A rotor rigidly attached to the motorstick, rotating independently of any of the other rotors, under ideal conditions, should not qualify for the bonus because we assume that the motorstick doesn't rotate. However, some of the energy of the rubber band is invariably exerted as a torque on the motorstick, causing it to rotate independently of the two rotors. Thus, the rubber band is powering the rotation of the motorstick and that rotation causes any lifting surfaces attached to it to generate lift, however insignificant that rotation may be. If I was a supervisor, I would have to see that the motorstick would not rotate throughout the course of the flight for the bonus not to be earned.
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Re: Helicopters C

Postby andrew lorino » February 28th, 2017, 10:07 am

Regarding 1-blade rotors, some advice:

I decided to use a 1-blade rotor for the bottom for 2 reasons:
1) people were saying that they had stability issues with 2 blades over 2 blades, and I had already completed the top blade frame in 2 blades
2) covering the blades is a PITB, and I'm lazy

You might be wondering, "why did this 'genius' use a 1-blade rotor to increase stability?" Well, my (unproven) hypothesis was that while 2 over 2 would be constantly more stable, any slight push would knock it off center, and away it would go. A 2 over 1 design would be less stable, but in a predictable way. Namely, that I could be fairly sure that if it went off in some direction, that its curved flight path would keep its net direction more upwards, sort of like a football or a spin-stabilized rocket. I have no idea if that makes sense, but i'm putting it in to explain my reasoning. Please correct me if it makes no sense.

Now, on to performance. Because the FFM kit only came with 2 sets of 2 blade center pieces, and the 2 blade center is a logical choice for a single bladed rotor, I could not build a 2 bladed bottom rotor and compare the 2. At first, I tested the helicopter with few winds, and no counterweight. Its turning circle was far too large, so a counterweight was added, only attempting to balance the mass, and not the torque of the rotor. This significantly improved the turning circle. However, the counterweight magically disappeared (fell off) before the competition, and could not be found. But at the higher torque and RPM the helicopter was wound to at the competition, it flew remarkably well, going nearly straight up. Despite my fears that the helicopter would be caught on a ceiling beam because of its inevitable dance across the ceiling, exacerbated by the instability of the design, the helicopter's torque and changing center of thrust allowed it to force its way around obstacles. Overall, the helicopter flew for 34ish seconds, 42ish including the bonus, leading to a 6th place finish at regionals. While this isn't National (or state) grade, it is the best that I have done. Would it have been better with a 2 over 2 design? Maybe. But the point of this is to show that the stability issues of a 2 over 1 design are , IMO, somewhat overblown, and that balancing the mass of the blade or just increasing the RPM will mitigate the problem enough to make a helicopter viable

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Re: Helicopters C

Postby CrypticBuilder23 » March 2nd, 2017, 4:57 am

So I learned that my states event location for helicopters is a gym with a ceiling full of wires and girders. Should I alter the design of my helicopter to minimize the chance of it getting stuck?

At regions, the helicopter got stuck twice so I really don't want a repeat of that :shock:
2015-16:
Regionals/Montgomery/State
Astro: 12 / - / -
WIDI: 12 / - / -
Bridge: 2 / 10 / 1
Wind Power: - / 1 / Cancelled
It's About Time: - / 6 / 8

2016-17:
Regionals/Princeton/State
Towers: 1 / 1 / 1
Helicopters: 4 / 6 / Cancelled
Wind Power: - / 13 / 10
Electric Vehicle: - / - / 7

andrew lorino
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Re: Helicopters C

Postby andrew lorino » March 2nd, 2017, 5:55 am

CrypticBuilder23 wrote:So I learned that my states event location for helicopters is a gym with a ceiling full of wires and girders. Should I alter the design of my helicopter to minimize the chance of it getting stuck?

At regions, the helicopter got stuck twice so I really don't want a repeat of that :shock:


Ouch. A couple of suggestions:

1) Decrease the torque enough (using your preferred method) so it never reaches the ceiling. This is not ideal because you will lose massive amounts of time.

2) Increase the torque enough so that it might be able to power through something that entangles it. This is not ideal because you might break something, and it might not work in the first place.

3) Aim at a clearish spot and pray.

4) Put the balsa disk on the end of a ludicrously long stick at the top of the helicopter. This might enable you to 'top out', but still have the important bits beneath the obstructions. Of course the longer the stick the more likely it is to break off and end the flight.

#1 is the only way that will for-sure work, but it is far from ideal. #4 is something I just thought of right now. Alas, event coordinators seem to be unable to find big enough rooms at most venues with flat ceilings, so there is a random element to the event. And if you aren't already, bring a collapsible pole for 'motivating' the helicopter to get unstuck so you can try again. Good luck at states :)

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Re: Helicopters C

Postby AznPr0d1gy » March 2nd, 2017, 6:13 am

Just build a perfectly balanced helicopter with a free moving stab, even if its not perfectly balanced the upward force should keep it in the same place unless the ceiling itself is slanted. All competitions except MIT and Berkeley that I've gone to so far had rafters, but they're not really an issue.

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Re: Helicopters C

Postby BuildingFriend » March 2nd, 2017, 9:20 am

It would be a good time to switch to a religion and pray. Being atheist at this time would be unfortunate.
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Re: Helicopters C

Postby jander14indoor » March 2nd, 2017, 5:07 pm

Use a dual strategy.
First official flight, be conservative, fly below the rafters, get a sure, OK time.
Second flight, go for it. Bang it into those rafters and hope for a killer time.

For ALL of this, PAY ATTENTION TO THE CEILING! I'm shocked at how many teams I watch launch in what with a little thought is the worst possible place to launch. Low spot, most complicated, etc. Especially helicopters which tend to fly straight up to a pretty predictable spot. You can fly into that clear opening and stay there pretty well.

A comment to event planners.
- Consider lower sites with smooth ceilings. Yes, high ceiling flights are more impressive, but you can still separate good teams from bad without so much risk to the students helicopters.
- Consider taller locations with smaller floor spaces. I've found racquetball/squash courts make very nice places for helicopters. Reasonably tall, smooth ceilings. Very easy to control crowds and the ones with the back wall in glass or a balcony for watching still allow good spectator views.
- A tall entrance lobby can be good if you can control the external doors.

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Re: Helicopters C

Postby chalker » March 9th, 2017, 7:30 pm

For those of you competing in Ohio, I'm soliciting input over in the Ohio thread about potential venues for the state tournament:
viewtopic.php?f=229&t=9708&p=309244#p309244

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Re: Helicopters C

Postby dhdarren » March 17th, 2017, 8:40 pm

Hey all, I'd like to throw out a potential idea regarding rotors, and perhaps get some feedback and unofficial rules interpretation.

Would a rotor that is designed sort of like an Archimedes' Screw work? Basically the rotor takes the shape/form of an archimedes' screw, but it only spirals one time (to go around 360 degrees), thus only making a single spiral. In terms of design, would it be sound to fly? Perhaps more importantly, however, is whether or not it would qualify for the bonus. Since it is one continuous "screw", it could be covered with a single, spiraling piece of mylar, thus being "one lifting surface." Does anybody see any possible parts that would violate the rules that qualify it for the bonus?
Past Seasons
2015:
R | S
Bridge: 1 | 8
AirTraj: 5 | 26
WS: 12 | 9
Scrambler: 6 | 17
DP: 7 | X

2016:
Bridge: 2 | 15
AirTraj: 2 | 6
WS: 3 | 11
DP: 4 | 15
GeoMap: 4 | 25

2017:
Heli: 1 | 1
Hover: 1 | 4
Towers: 2 | 15
DP: 1 | 6
Wind: 2 | 8


2018:
R | S
Heli:
Hover:
Towers:
DP:
Eco:
MV:

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Re: Helicopters C

Postby jander14indoor » March 18th, 2017, 12:08 pm

As usual, unofficial, hard to judge based on words, etc.

An archimedes screw type rotor is a really inefficient way to generate lift.
And one turn over a light of one minute, again, not much lift there.
Finally, how are you powering it?

Overall, I think you'd have a difficult discussion with an ES about whether such a device provided lift to qualify for the bonus.

But again, that is without seeing it in action.

Jeff Anderson
Livonia, MI

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Re: Helicopters C

Postby dhdarren » March 18th, 2017, 12:18 pm

jander14indoor wrote:As usual, unofficial, hard to judge based on words, etc.

An archimedes screw type rotor is a really inefficient way to generate lift.
And one turn over a light of one minute, again, not much lift there.
Finally, how are you powering it?

Overall, I think you'd have a difficult discussion with an ES about whether such a device provided lift to qualify for the bonus.

But again, that is without seeing it in action.

Jeff Anderson
Livonia, MI


I don't know if it would work either, but in terms of powering it, it is no different that a traditional rotor. The "screw" rotor would take the place of the top rotor, and be powered by the rubber motor via a motor hook all the same.
Past Seasons
2015:
R | S
Bridge: 1 | 8
AirTraj: 5 | 26
WS: 12 | 9
Scrambler: 6 | 17
DP: 7 | X

2016:
Bridge: 2 | 15
AirTraj: 2 | 6
WS: 3 | 11
DP: 4 | 15
GeoMap: 4 | 25

2017:
Heli: 1 | 1
Hover: 1 | 4
Towers: 2 | 15
DP: 1 | 6
Wind: 2 | 8


2018:
R | S
Heli:
Hover:
Towers:
DP:
Eco:
MV:

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Re: Helicopters C

Postby kaziscioly » March 18th, 2017, 12:41 pm

Does anyone have a scanned version of the template paper you can use to set up a 4 bladed rotor with the FFM kit? I have the laser cut pieces and such, just not the paper. Any help would be appreciated. Thanks!

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Re: Helicopters C

Postby bernard » March 18th, 2017, 12:48 pm

kaziscioly wrote:Does anyone have a scanned version of the template paper you can use to set up a 4 bladed rotor with the FFM kit? I have the laser cut pieces and such, just not the paper. Any help would be appreciated. Thanks!

Are you looking for the four blade upper or lower or both?
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Re: Helicopters C

Postby kaziscioly » March 18th, 2017, 12:53 pm

bernard wrote:
kaziscioly wrote:Does anyone have a scanned version of the template paper you can use to set up a 4 bladed rotor with the FFM kit? I have the laser cut pieces and such, just not the paper. Any help would be appreciated. Thanks!

Are you looking for the four blade upper or lower or both?


Nevermind, I just got them. Thank you though!


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