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RC blimp for Aerial Video

#1
Hey all, I have been asked by my church if I could do dome aerial video work for them at an up coming event. They first asked if my airplane would be able to fly in a 800 person arena. I said it could, but it would end up hitting a wall and fall onto people. I did mention to them that I have a multi rotor that might work, but I now think it would be to risky. If an engine went on it or if anything happened to it, it would not end well.

I am now thinking on building a rc blimp to carrie my GoPro and FPV gear. I have looked at some commercial rc blimps you can rent or buy, but they are up there in the price range.

I have found some formulas and numbers on how many liters of helium it takes to pick up so many grams (1 gram per liter)

I am now trying to figure out how the programming would go on my Spektrum DX7?

I am thinking 4 motors, two for forward/backward movement, one on the tale for turning, and one on the bottom for elevation control.

How would you set the motors up on your radio? I'm almost thinking I would set it up like a helicopter on my transmitter? I would be able to use the pitch curves to make the motors go forward and reverse.

Any suggestions/advice would be helping me out a lot.

Thanks,

Maxwell
 

earthsciteach

Moderator
Moderator
#2
I've thought a bit about this idea, myself. Didn't know the 1 g/l rule - good stuff!

I think I know what you are getting at, but don't know how to make it happen. How many channels can you control esc's from? I think you could program the throttle from 50%(centered) to 100% to be the forward driving motors. Then from 50% to 0% to be the rear driving motors. 50% stick would be 0 voltage to both sets of motors. So, 0% stick would be 100% reverse. 100% stick would be 100% forward. I'm sure someone can program this, but not me!



Perhaps you could reverse a given motor with some kind of switch that diverts power from one leg of the 3 motors leads to another. The switch control voltage would come from the rx. There probably is a device out there capable of doing that, but I'm not an electronics guy. Someone much more knowledgeable than me might be able to help you out.

Another option (theoretically, anyway) would be variable pitch props. But, I don't know if they make such a thing in such a small size. Maybe modify a cp heli rotor assembly???

Cool stuff! Let us know if you figure it out!
 
#5
That would work! but can I get it before the 27th?

Now I have been trying to figure out how big the balloon would need to be?

Most blimps that can carry GoPros and some other gear seem to be 10-18ft long and about 6ft wide. I have found a formula that gives you the amount of liters in a balloon:

4/3 x pi x r x r x r

an example for a 30cm balloon:

4/3 x pi x 15 x 15 x 15 = 14,137 cubic centimeters = 14 liters

so it should be able to pick up 14 grams including the weight of the balloon.

Does that sound right to you guys? Here is the link to the website I got that info from:

http://science.howstuffworks.com/science-vs-myth/everyday-myths/question185.htm
 

earthsciteach

Moderator
Moderator
#6
Well....

If you are filling a "bladder," then that should be close enough. If you are filling a latex balloon in which the pressure of the helium causes inflation by stretching the skin of the balloon, then it might be a bit off. That's because the helium must overcome the tension caused by the elasticity of the latex. Its like stretching a rubber band, but in three dimensions. So, the helium is under more than atmospheric pressure. Its subject to atmospheric pressure+the pressure used to expand the latex of the balloon. Therefore, the weight of the helium is greater than an equal volume of helium subject to only atmospheric pressure.

Ok, so that's the egghead response. In reality, you can inflate the number of balloons you deem necessary to overcome the weight of the structure, systems and payload then add more until you get neutral buoyancy.

Another solution is to make a cylindrical bladder and inflate with helium. By bladder, I mean some "not stretchy" material. The volume of a cylinder = pi*r^2*length.
 

earthsciteach

Moderator
Moderator
#7
OH - Thurmond... I picked up on your little not-so-subliminal message. So, my question for you is, what is the minimum diameter tube you would use? I hear 1/4"OD is too small. What about 3/8" OD, 1/4" ID? Or, should I just stop being a cheapskate and go with 1/2" ID or greater? :cool:
 

Tritium

Amateur Extra Class K5TWM
#11
Airships must be neutral flotation. Neither rise or fall at full load. The gas lift just offsets the weight of the craft and payload.

For Hydrogen, 1 gallon of water provides 4707 liters of hydrogen which will offset 12.42 lbs of weight at standard temperature and pressure.

Teach, clean out your PM inbox, it is full, and by the way Hydrogen lifts 1.2gr /liter @stp.

Thurmond
 
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lobstermash

Propaganda machine
Mentor
#12
Right on there, Thurmond. It's tricky getting the buoyancy just right. Most just overdo it and tether the thing, so it goes in slow, wide circles according to how your power system propels it.
 

Tritium

Amateur Extra Class K5TWM
#16
Tritium- are you saying that I might be able to use hydrogen instead of helium? And that I cam make it myself?
Watch a video of the Hindenburg first. Then Remember the statements below:
Yes by electrolysis of H2O but remember it is explosive and flammable.
Keep in mind that I am experienced in working with hydrogen and in a very isolated area.
Helium is completely safe (other than being an asphyxiate).

Also you are planning to fly over a crowd so the rule would be Helium ONLY for your situation!

Thurmond
 
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earthsciteach

Moderator
Moderator
#17
You also make hydrogen gas with zinc and hydrochloric acid. A small handful of zinc and 100 ml of HCl will produce quite a bit of gas. It's easy to collect it in a balloon, too.

But, Thurmond pointed out the one small hitch-it is EXTREMELY flammable. But, on a good note, the only product of combustion is water!