Blimp envelope payload
Based on our experiments so far the blimp envelope supplied with the blimpduino project has a payload capacity of about 120 grams when fully inflated. The blimpduino board weighs just about 80grams by the time we add in some velcro to hold it to the envelope. The wireless camera we are using has an internal lipo battery but even when pulling it out of its case it still weighs about 70 grams. We are about 30 grams over weight. We need to shave some weight off somewhere or get a larger envelope.
Envelopes that are 52 x 37 inches are commercially available. I believe the blimp envelope supplied with the blimpduino kit is 52 x 27 inches. (Will have to measure it to be sure.)
Another possibility is that the helium we got from the Party City Helium balloon kit is not very pure.
We could also pull the lipo off the camera and run it from the one of the cells on the blimpduino board. The camera only pulls about 30mA so load balancing issues shouldn't be that bad.
What sort of payloads are folks getting out of their envelopes? It seems like the 52 x 27 is the most common size. There are also 66 inch envelopes available commercially, has anyone tried one and can give an idea of the payload?
I have an extra 52x27 envelope and I suppose we could just velcro the two envelopes together to give increase payload, but that would really increase the inertia of the system.
Alternately, maybe I should find a lighter camera?
Ideas folks?
Thanks!
mmason
mtsacflight.blogspot.com
Envelopes that are 52 x 37 inches are commercially available. I believe the blimp envelope supplied with the blimpduino kit is 52 x 27 inches. (Will have to measure it to be sure.)
Another possibility is that the helium we got from the Party City Helium balloon kit is not very pure.
We could also pull the lipo off the camera and run it from the one of the cells on the blimpduino board. The camera only pulls about 30mA so load balancing issues shouldn't be that bad.
What sort of payloads are folks getting out of their envelopes? It seems like the 52 x 27 is the most common size. There are also 66 inch envelopes available commercially, has anyone tried one and can give an idea of the payload?
I have an extra 52x27 envelope and I suppose we could just velcro the two envelopes together to give increase payload, but that would really increase the inertia of the system.
Alternately, maybe I should find a lighter camera?
Ideas folks?
Thanks!
mmason
mtsacflight.blogspot.com
Replies to This Discussion
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ModeratorPermalink Reply by Chris Anderson on -
Before you get a bigger envelope, with the cost (both of the envelope and the helium) and the larger room, you might want to look for a lighter camera. 70 grams is very heavy. Have you considered cameras like this, which weighs about 8 grams?
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Permalink Reply by profmason on -
I had looked at that camera, but it still needs an external power source. I just pulled another camera off the remote turret gun and it only weighs 12 grams, but will need an external supply. It is designed to be run off a 9V. Pulling the board apart I can see that the camera itself runs off 5V (There is an onboard regulator) and the transmitter wants 8V. (Another onboard regulator) Considering I need about 0.5 Volts to keep the regulator in regulation, I will need around 8.7 Volts. This is more then even the two cell peak of the lipo (8.4) Oh this camera pulls a LOT more current then the other one ~200 mA! Ok, so I can run a 11.1 Volt battery into the entire thing. Now can the motors handle the higher voltage? Hmm it seems like the motors are only rated to 4.5V? The servo is probably happy at 7.4 but not at 11! Or is everything run off the regulator? Peering at the schematic, it looks like everything is run from the 4940 5V regulator. In that case, there is no point in dumping extra heat into the regulator, and I should just add a single cell in series to the camera to boost the voltage. I am sorry if this has been covered elsewhere, and please correct me if I am wrong!
I have a bunch of 20 gram cells in the drawer. This might just do it. Thanks for the boost to my thinking!
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ModeratorPermalink Reply by Chris Anderson on -
I'll bet you can power the eyecam from the blimpduino board, which is 5v. Might involve bypassing the internal power regulator. It seems wrong to have two batteries on board when a little electronics can solve the prob.
Do you have enough budget to get one of the eyecams and experiment?
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Permalink Reply by profmason on
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Good point! A little electronics can solve the problem. I just pulled a 5V - 9V buck boost transformer off an old LAN card. I can run this off the regulated output from the board and it should solve the problem nicely.
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ModeratorPermalink Reply by Gary Mortimer on -
Fly it in a deep freeze!
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Permalink Reply by profmason on
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Ok, so after making some measurements, the envelope plus blimpduino board plus the balloon envelope weigh 94 grams. This leaves us with just about 26 grams of payload. (Our RC receiver weighs just about that so the blimp is barely neutral with the RC reciever attached. What ever camera system we use should weigh less then about 26 grams total.
I have ordered the 36" envelope. This should give us an additional 160 grams or so of payload (assuming rho air is 1.2 kg/m3 and rho He is 0.18 kg/m3. Since 27^2 is ~730 and 36^3 is 1300 we should get about 1300/730 = 1.7x the payload. Of course as a practical engineering approximation we should hope for 1.5x since the balloons aren't perfect cylinders.
According to the website, the 27inch holds 5 cubic feet and the 36 inch holds 7 cubic feet. This does not fit with my calculations at all!
We also had better fill the 110 liter helium tank.
Ordered:
http://www.rctoys.com/rc-toys-and-parts/MACH-HLENV-SILVER/RC-PARTS-...
Will report on the new payload when it arrives in a week or so.
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ModeratorPermalink Reply by Chris Anderson on -
I'm confused by these calculations. I've got the same envelope and fully inflated with helium it can lift about 120 grams above and beyond the envelope itself. The blimpduino board with battery weights 80 grams. Our receiver, a standard Futaba R156F, weighs 10 grams. That leaves 30 grams for a camera even if you've got RC onboard as well.
If you're getting less lift, I'd question whether your helium supply is pure. Also, you definitely want a lighter RC receiver--26 grams is a monster!
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Permalink Reply by profmason on
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Thanks for the feedback! I get 79 grams for the blimpduino board with battery, so that matches up. Our total lifting payload is 105 grams when fully inflated. We are seeing about 15 grams less payload capacity then you are, so I think you are right in that we don't have pure helium in the balloon.
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Permalink Reply by Morli on -
What about these spectrum micro receiver weighing only 2 gms ?! that should leave lot of gms for any thing else :)
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ModeratorPermalink Reply by Gary Mortimer on -
Heat the helium up, or make the envelope black and go for some solar gain
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Permalink Reply by profmason on
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Ahh I get it!
Lets the melting point of mylar is 254oC. With some quick tests with my hot air gun, the mylar begins to warp at around 160oC. Lets say we heat the gas up to 150oC.
Hmm, using a naive ideal gas approximation (Isn't helium pretty close to ideal?) PV=nRT. Assuming that we fill the envelope to the same pressure and volume, the amount of gas n is inversely proportional to T. Increasing the temperature of the gas going into the balloon would require less gas, but provide the same buoyant force. Now we usually fill the balloon at 20oC or 293 kelvin, going to 150oC or 423 K. Then the amount of gas going into the balloon would be 293/423 as much. Since the density of helium is 0.4 at 20oC, the density of helium at 423K would then be 293/423 * 0.4 = .27 so we would get about 1.5x the lift. Sounds great!
The only thing that occurs to me is that the temperature of the balloon would drop rapidly after it was heated, as it cooled, the volume of the balloon would decrease and consequently the payload would decrease. Once the balloon reached room temperature, its payload would be less (due to the small displacement) then if we had just filled it with room temperature Helium. I have no clear idea for how rapid this process would be. I suspect that the mylar envelope is a pretty good radiator. Since radiation goes as sT^4, I would expect the process to be pretty quick... But I have no experimental experience with this.... Wouldn't a black envelope(A better radiator?) make this even worse?
OK, I trust what folks have actually tried and done, has anyone played with this?
Meanwhile, I have built a very light camera setup and plugged it into the boarduino board. I am running it off the regulated 5V that is on the programming port. It works great up to about 120 feet. (Plenty for the Gym)
Here are the details:
http://profmason.com/?p=801
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Permalink Reply by Ricardo Colas on -
But how would you go about this? Do you heat the outside of the blimp, or do you come up with some crazy scheme to heat the inside?
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