Designs

[chalker7]

What is the definition of "Chinook-style helicopter"? I mean, how will Event Supervisors determine if it is a chinook-style copter? Will it just be common sense, or are there certain guidelines?

I'm thinking something like this.

Which has been done before.

How does the single rubber power both of the rotors on that helicopter? I've been trying to visualize some sort of transmission for a tandem-rotor helicopter, but I just can't seem to.

That helicopter was entered at nationals two years ago when it was a trial event. The mechanism they used was very innovative, but not particularly effective.
Going through the center and sticking beneath each rotor there is a central drive shaft made of a solid wood (balsa or otherwise) dowel. The team then took a single strand of rubber and wrapped it around each shaft, counter-rotating the rotors and stretching the rubber as they went. When they released the device, the rubber contracted and the rotors turned. It worked, but just barely and for only a few seconds. I suspect there are various optimizations that could make it a little better, but I doubt that is an especially competitive plan.

[illusionist]

Wow, kudos to them for being so creative. I would have not thought about using rubber power like that.

[illusionist]

So I used some spare parts from last year, and threw together a tandem heli. It consisted of a rectangular body, using the two vertical sides as motorsticks. I'm guessing it weighed something around 8g. I used a couple 3/16 rubber bands, one for each rotor. First flight was 2 seconds. Second one was looking like it would be 10, but one rotor broke (it was in the basement for a year). As far as balance though, I didn't wind fully, so I'm not sure how torque will play out. However, left-right balance and front-back seemed to be alright. Flight did look a little shaky. And winding was a real pain... I managed to do it with only two people, but it was a little gross. So based on this 15-min attempt, I can say that with some careful building, I should be able to get around 15 seconds easily.

[thedoctor]

Hmm...even with that 3x bonus it's probably more beneficial for an experienced builder to go with a co-axle design. Do you think it was the significant weight that was the problem?

[chia]

I was doodling in physics class and came up with an awkward little tandem design which is probably inefficient, but I may try building one within the month. It looks cute on paper, but maybe it only works in theory. I'll post more about it when I actually build it.

[danyalukin]

While not very stable, it would be most efficient to use two rubber bands, one for each rotor.

[chia]

While not very stable, it would be most efficient to use two rubber bands, one for each rotor.

Mine uses two, since I haven't been able to come up with a way to power both rotors with one.

[illusionist]

I am also using two. The power will vary, so a torque meter will be EXTREMELY helpful. But I see more benefits with the tandem rotor design, than the coaxial one.

[Frogger4907]

What is the definition of "Chinook-style helicopter"? I mean, how will Event Supervisors determine if it is a chinook-style copter? Will it just be common sense, or are there certain guidelines?

I'm thinking something like this.

Which has been done before.

Chinook-style helicopter would be where the axis of the two rotors are separated by at least the radius of a rotor.

[Bob8372]

Does it still count as a non-coaxial copter if one rotor is vertical i.e. do both rotors have to be horizontal for the 3x score?