Posted by D. Seeley on September 1, 2008 at 6:28pm
Hello DIY Drones community. I am posting here in the hopes of interesting many of you in a project and soliciting expert advice.Our design firm has been asked to create a spectacular experience in a large indoor dome structure as a permanent installation. The budget is too small to consider large built structures, so we have turned our creative minds towards inflatable objects.Our current research direction is a fleet of autonomous blimps that behave as an emergent system. The overall creative goal would be to evoke creatures in a menagerie or aviary. They might be brightly colored, have abstract shapes, and would have a range of personalities. We are not so much interested in showcasing mini airships, but rather employing them in service to a larger creative goal.We propose these specs:- 2-8' in diameter- able to fly a 100' distance 10 times per hour- live in a dome 120' wide and 120' tall with no wind currents- must stay at least 12' above the ground at all times- locative system or good sensor package to achieve the aboveThis is a permanent installation. It's clear to us that some maintenance and "airship wrangling" will be necessary to keep the fleet working, we need a better idea of just how much work is involved. Our primary questions are these:- How much and how often is attention required to maintain neutral buoyancy?- How often will helium recharges be necessary?- How long do the bladders last in weeks or months?- How long might a battery pack last given the above flight mission?- Is it realistic to guarantee that the ships will never go below 12'?- Is it realistic to design automated docking and inductive charging?... And a thousand other questions that will immediately be raised by this informed group.We are serious about this idea and want to see it happen. We're committed to the learning and research that would be necessary to achieve it. Any input you can offer is greatly appreciated.Many Thanks,Damon SeeleyElectrolandhttp://electroland.net
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1. Safety Guarantee. The ships can be certainly be guarenteed to be 100% safe for humans under all conditions. They should use large slow and soft propellers (which could be decorative as well) - or enclosed propellers.
You can largely guarantee fall-outs will not occur, if you have a safety ballast held closed by a constant current (ie solenoid) and a watchdog circuit which is fed by a positive assurance of altitude (ie proximity/barometer or beacons). In any failure mode including power or cpu failure, as well as a low altitude signal, the craft would rise to the ceiling and be noticed.
2. If lighting is good or substantially natural, you may be able to use lightweight solar panels for power. Blimps use far less power than planes. In addition, you can lower power requirements with a fully active helium system. There are compressed air systems used in RC planes for landing gear. These valves, tanks, and their servos could be re-purposed to adjust the helium for active control or neutral density.
There is an interesting technology for extended service vehicles which involves slight changes in buoyancy - combined with small wings to convert buoyancy-driven vertical movement into forward momentum. Such an approach can yield very long service times, slow speeds etc ... A very small pump can recompress a small bit of helium which will change the buoyancy enough to create motion. One nice additional effect is the inexplicable and invisible means of motivation. On that note, I would encourage the use of natural movement to create motion ie. large inflatable wings or fins that move.
One last thought, if you can impact the building airflow, you might be able to create a slow swirling pattern. If you have warmer air rising and spinning, the room would have a bowl-like isothermal profile, and would tend to keep even inert inflatables in the main area of the space. It is worth noting that similar schemes have been used to house certain jellyfish which are so delicate that they break when they collide with a standard aquarium glass. Creating a swirl might be as simple as directional grills on the A/C system, or a few large fans on the perimeter.
For detecting 12 feet, I would throw out differential barometer. If you include a barometer on one of the beacons at say 16 feet, and encode the pressure reading into the beacon signal, then each airship would know when its pressure dropped below the 16 foot pressure mark. It might be accurate enough for your purposes. Another option might be a scanning laser placed at 12 feet or so, a sensor on the lower portion of each airship would sense the laser as it approached the laser line.
I wonder if another material would decrease helium leakage. Is the leaking primarily because of a valve interface or due to micro holes in the materials?
Sounds like batteries are going to be a major issue. I like the idea of super-sizing the fleet and limiting the numbers in operation at once. I bet we can realize economy of scale in manufacturing that would make this feasible.
We use 66" polyurethane bladders with YARB, and helium top-off time is similar to what Chris suggests at 48hours.
Our battery pack is 800mAh. The motors easily draw 100mA each, and our processor draws another 70mA. We use Wifi, which is a hog at close to 200mA, but Zigbee should work well for this application.
The easiest approach might be to have the blimps return to a docking station and have someone manually swap battery packs. For inductive charging, you need *really* close range. In one of our customers' installations, www.bpexplorer.com.au, the customer has 15 total robots with 5 in operation at any given time.
You are going to need a beacon system. For 100 ft range, fixed ultrasonic transmitters that are sequenced probably will give best results. This is the approach used by one of our customers (MIT Space Systems) on the SPHERES project for the International Space Station. You might use 8 beacons spaced approx 100 milliseconds apart, but the beacons will have to be synchronized.
If you're using mylar envelopes like ours, you'll probably need to top off the helium at least once every 48 hours. But the envelopes can last for months if not years.
If you're using 52" envelopes like ours, the biggest battery you can hold is about 300mah, which will last about an hour with good power management. I've got no idea how to do automated docking and inductive charging with a blimp--those are really hard problems. It might be easier to have a robotic hook that can grab a wire loop that the blimps trail beneath them, and then somehow charge via that wire.
Staying 12' above the ground is also a bit tricky, since that's beyond the range of our ultrasonic sensors. Maybe laser rangefinding?
Replies
You can largely guarantee fall-outs will not occur, if you have a safety ballast held closed by a constant current (ie solenoid) and a watchdog circuit which is fed by a positive assurance of altitude (ie proximity/barometer or beacons). In any failure mode including power or cpu failure, as well as a low altitude signal, the craft would rise to the ceiling and be noticed.
2. If lighting is good or substantially natural, you may be able to use lightweight solar panels for power. Blimps use far less power than planes. In addition, you can lower power requirements with a fully active helium system. There are compressed air systems used in RC planes for landing gear. These valves, tanks, and their servos could be re-purposed to adjust the helium for active control or neutral density.
There is an interesting technology for extended service vehicles which involves slight changes in buoyancy - combined with small wings to convert buoyancy-driven vertical movement into forward momentum. Such an approach can yield very long service times, slow speeds etc ... A very small pump can recompress a small bit of helium which will change the buoyancy enough to create motion. One nice additional effect is the inexplicable and invisible means of motivation. On that note, I would encourage the use of natural movement to create motion ie. large inflatable wings or fins that move.
One last thought, if you can impact the building airflow, you might be able to create a slow swirling pattern. If you have warmer air rising and spinning, the room would have a bowl-like isothermal profile, and would tend to keep even inert inflatables in the main area of the space. It is worth noting that similar schemes have been used to house certain jellyfish which are so delicate that they break when they collide with a standard aquarium glass. Creating a swirl might be as simple as directional grills on the A/C system, or a few large fans on the perimeter.
For detecting 12 feet, I would throw out differential barometer. If you include a barometer on one of the beacons at say 16 feet, and encode the pressure reading into the beacon signal, then each airship would know when its pressure dropped below the 16 foot pressure mark. It might be accurate enough for your purposes. Another option might be a scanning laser placed at 12 feet or so, a sensor on the lower portion of each airship would sense the laser as it approached the laser line.
I wonder if another material would decrease helium leakage. Is the leaking primarily because of a valve interface or due to micro holes in the materials?
Sounds like batteries are going to be a major issue. I like the idea of super-sizing the fleet and limiting the numbers in operation at once. I bet we can realize economy of scale in manufacturing that would make this feasible.
Our battery pack is 800mAh. The motors easily draw 100mA each, and our processor draws another 70mA. We use Wifi, which is a hog at close to 200mA, but Zigbee should work well for this application.
The easiest approach might be to have the blimps return to a docking station and have someone manually swap battery packs. For inductive charging, you need *really* close range. In one of our customers' installations, www.bpexplorer.com.au, the customer has 15 total robots with 5 in operation at any given time.
You are going to need a beacon system. For 100 ft range, fixed ultrasonic transmitters that are sequenced probably will give best results. This is the approach used by one of our customers (MIT Space Systems) on the SPHERES project for the International Space Station. You might use 8 beacons spaced approx 100 milliseconds apart, but the beacons will have to be synchronized.
If you're using 52" envelopes like ours, the biggest battery you can hold is about 300mah, which will last about an hour with good power management. I've got no idea how to do automated docking and inductive charging with a blimp--those are really hard problems. It might be easier to have a robotic hook that can grab a wire loop that the blimps trail beneath them, and then somehow charge via that wire.
Staying 12' above the ground is also a bit tricky, since that's beyond the range of our ultrasonic sensors. Maybe laser rangefinding?