Buzz Bomb Bob - RC Groups
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Jul 30, 2017, 03:12 PM
Go small or go home
ruzam's Avatar
Discussion

Buzz Bomb Bob


It's taken a number of years from spark in my brain cells to a realized blimp, with many unsuccessful build attempts along the way, but I'm proud to present Buzz Bomb Bob. This is a micro-aerobatic blimp constructed from heat seal balloon foil. It features a through envelope carbon fiber tube to support the control paddles, internally mounted electronics, custom PPM controller and reversible ESCs, stability tail ring and a 'hidy' pouch for holding the flight battery. Both the paddles and tail ring are detachable for repair, or testing different designs. The blimp was decorated with the local roller derby club colors and logo, which is where it just finished a successful evening of entertaining the crowd.

After decorating it has a lifting capacity of one 750ma battery (and not one gram more!) which will easily fly 15-25 minutes depending on throttle management. The decorated envelope (not including paddles and tail ring) came in at 85 grams total weight. Helium contributes 148 grams to the lift.

An ATTiny24 micro-controller connects directly to the receiver PPM output, mixes throttle and rudder (tank steer) and drives a Pololu H-Bridge motor driver to provide dual reversible ESC for the drive motors (one drive motor on each paddle). The micro-controller also mixes elevator and aileron to control the paddle servos. It flies like a typical airplane (sort of) and doesn't require any kind of special programming on the transmitter side. I plan to have many blimps in the air at a time and I can't afford to start fitting myself out with custom radios. The micro-controller and motor driver are built inside the envelope. Partly to avoid the risk of something electrical contacting the metal foil, partly to let the motor driver heat dissipate safely into the helium (instead of melting the envelope) and mostly to reduce the number of wires getting punched in and out of the envelope. It's a clean design and I don't have to worry about snagging wires. The ATTiny code takes care of initializing the ESC by requiring the stick be moved to full forward and full backward then center before it initializes. The code then uses those endpoints to ensure full throttle resolution (255 steps in either direction). The ATTiny also monitors the battery voltage and starts a cycle of pulsing the motors when the battery drops.

The entire envelope is decorated with fat tip Sharpie pens. Paint was far too heavy and never bonded with the foil surface (I'm still sweeping up black paint flecks from my previous attempt). The Sharpie goes on great and doesn't flake off. However, it doesn't 100% bond and does 'rub' off during handling. Pays to wear black.

Paddles are made with black tray foam. 1.7gram servos were modified with resistors to get 180 travel. The stress of the paddle is supported by two nylon bushings on the CF tube cross arm. The servo simply attaches to the CF with a screw through a modified servo arm so the servo rotates around the CF axis. The drive motors came from quad copter spare parts. These particular parts were from a model that contained a 90 crown gear in the arm which not only boosts the drive power (and prop size) but allows the motor to sit flush with the servo housing. Everything is mostly just tied together with thread and CA's together. The motor arm housing was cut down to just the gear casing support. The drive motors pivot with the paddle so thrust is directed with the paddle (180 degrees, full up and full down). Because the gears and the envelope amplification, the motors are super loud (IMO), but as it turns out, they were no match for the arena sound equipment and the blimp could be considered silent regardless. I honestly don't know if there is any benefit to the paddle surface itself. I believe the motor thrust does all the work and the paddle would probably work just as well without the extra surface area. Since it's detachable, it's easy to experiment with

Enjoy!

Buzz Bomb Paddles (0 min 14 sec)

Buzz Bomb Dancing 4 (0 min 30 sec)

Buzz Bomb Dancing 3 (0 min 14 sec)
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Jul 30, 2017, 08:18 PM
Registered User
coriolan's Avatar
Very clever idea
Jul 31, 2017, 08:02 AM
Melbourne, Australia
Very impressive - and great manoeuvrability!

How did you handle bringing the wires out of the foil and keeping things gas tight?
Jul 31, 2017, 10:48 AM
Go small or go home
ruzam's Avatar
The wires exit through thin ply disks.

I sandwich the foil between two disks with a small bit of hot glue then iron the disks flat squishing out as much glue as possible. This bonds them really well. Then I drill the smallest holes I can that will fit the wires. The wires are single strand coated wire so there's no seepage within the wire itself. After threading the wires through the holes I CA them in place, then use baking powder and CA to fill any remaining gaps and re-inforce them so the wires will never come loose.

That alone would probably be enough to seal them, but I have a product called 'hi-float' for latex balloons designed to seal in helium. The stuff really does work. It's a water soluble liquid rubber. For it's intended application, you squeeze a bit into a latex balloon, squish it around to coat the interior walls, then inflate the balloon. A latex balloon treated with hi float will hold helium for days, if not weeks, where as an untreated balloon will be on the floor by morning.

I spread the hi-float on the interior ply disk making sure to get coverage over all the exit points then let it dry a couple of days. It has a large water content, so once dry it doesn't weigh much at all and it takes on a rubbery plastic texture. Once it's dry it won't stick to itself either, but it's quite tacky until it does and prone to sticking to itself and lifting off.

I also wrap the CF rod with hi-float soaked tissue internally to prevent Helium from finding it's way through the fibers. The CF rod is a hollow 3mm tube so even a micro crack would be an easy exit.

I'd use hi-float on interior seams as leak insurance, but I've learned that my balloon foil is water sensitive. The mylar layer and the heat seal layer appear to be bonded with a water soluble glue. Putting hi float on an exposed seam causes the layers to de-laminate and separate, exactly what you don't want.

This blimp will easily last several days with only a tiny top up to get the pressure back. I don't know where the leakage is lost. It will hold regular air without loss. Could be seams, could be exit points, could be through the foil itself (the metallized layer is pretty delicate and easily rubbed off). I suspect the most leakage happens through the fill valve.
Last edited by ruzam; Aug 01, 2017 at 10:37 AM. Reason: typos...
Aug 01, 2017, 03:06 AM
Melbourne, Australia
That's brilliant - and thanks for the info! I've tried hi-float myself as a way of sealing foil balloons, but without much luck - if what you say about the bonding layer applies to my foil (and no reason why it wouldn't!) that would explain a lot. Also, nice trick with baking soda and CA - must try that :-).

While we're here, what's the story of the 'skirt' at the back of the airship? I didn't quite get what that was for?

It looks awesome by they way; nice build and very impressive watching you spin it!!
Aug 01, 2017, 10:35 AM
Go small or go home
ruzam's Avatar
The skirt is for stability. Without it the blimp just whips around and there's no control at all. It acts like tail fins, only less obvious.

Initially the skirt was a solid foam ring. I intended it to appear like a proper back end to the blimp so it would look more like a bullet and less like a sausage bag. But my calculations were a little off and it came out larger than I planned, and too heavy. So I cut the circles out of it to drop weight and got it just under the weight limit. It's attached with three small foam pylons at the front of the ring that have (very small) magnets in them. It locks in well, yet is still removable. The back of the ring is supported with thread spokes to maintain the shape. As it turns out, the thread spokes were also very useful for holding a black tissue disk against the back of the blimp, hiding the filler valve (a foil balloon filler valve).

I'm currently re-working the skirt into a lighter, slightly smaller version that will cut me a little slack in the lift and help with the overall balance. I may try to cover the ring with black tissue to return it to my original idea of a solid ring. The over-weight ring is the only thing I can fault this blimp with.

Once I get the revised ring built and tested, I'm going to play with an idea of an alternate four fin 'bomb style' tail more in keeping with the overall theme. I'm not convinced it's possible without over doing the weight again, but since it's attached with magnets, it doesn't cost me anything to try.
Aug 07, 2017, 11:54 PM
Build and rebuild
Brainstorm's Avatar
Quote:
Originally Posted by ruzam
It's taken a number of years from spark in my brain cells to a realized blimp, with many unsuccessful build attempts along the way, but I'm proud to present Buzz Bomb Bob. This is a micro-aerobatic blimp constructed from heat seal balloon foil. It features a through envelope carbon fiber tube to support the control paddles, internally mounted electronics, custom PPM controller and reversible ESCs, stability tail ring and a 'hidy' pouch for holding the flight battery.
Brilliant design and brilliant execution, Ruzam! I like the concept of the "paddles." They provide incredible aerobatic maneuverability. And the differential thrust works very effectively. The ring-shaped empennage seems to work wonders as well. Kudos!

Quote:
Originally Posted by ruzam
That alone would probably be enough to seal them, but I have a product called 'hi-float' for latex balloons designed to seal in helium. The stuff really does work.
I've been a helium-head since I was a kid. But I had never heard of "hi-float" until now. Will have to look it up and get up to speed.
Aug 28, 2017, 08:24 AM
Fuzzy Member
lupy's Avatar
Very cool results! Do you have a link to the balloon material? Finding a big enough balloon to work with has been a problem
Aug 29, 2017, 01:34 AM
Go small or go home
ruzam's Avatar
I purchased my balloon foil from American Science and Surplus They don't ship to Canada, so I had a relative order it for me through the US.

It's not the best foil material, but so far it's the only material I've had to work with. It's pre-printed for mass producing small foil balloons. So it's heavier with paint than it needs to be and you have to construct the envelope shiny side in if you don't want 'happy birthday' logos everywhere. Even without the paint I suspect there are lighter thinner foils that could be had. Some day I'll get my hands on better quality foil.

Rubbing alcohol will take off the paint, if you're careful to soak it. The metallised finish is very delicate and easily rubbed off. All the more reason to put it to the inside of the envelope. I kind of prefer the matte silver finish anyway.

The foil is made of two layers. A strong (non stretchable) PET layer which gets the metallised coating on one side bonded to a soft polyethylene layer which provides the heat sealable side. The bond between the two layers isn't that great and easily separated by contact with water, ammonia, or just about anything else you might use to strip the painted logos with. I also find it rather finicky about heat sealing. Not enough heat and it bonds just well enough to blow out when inflated. Too much heat and the layers separate. I'm still learning the dos and don'ts of working with this material.
Sep 13, 2017, 11:27 PM
Go small or go home
ruzam's Avatar
Buzz got trimmed down with a new 'skirt' and some paddle adjustments that knocked off just enough weight to slip in a micro FPV camera (5.7grams). The video is not spectacular. I'm not entirely sure where the problem lies. It might be the cheap camera, it might be the cheap receiver, it might be the cheap video recorder or it might be because the transmitting antenna is jammed up next to a huge metallized sphere. Actually, I think the camera might have a transmitting power setting that's set too low. None the less it was a huge amount of fun!

Buzz Bomb Bob Heating up the House (1 min 6 sec)


Buzz Bomb Bob - Let's Ride! (7 min 31 sec)
Sep 23, 2017, 03:18 PM
Registered User
May you go into more detail on how you sealed the balloon foil? I am having trouble with the same foil you are...
Sep 26, 2017, 04:20 PM
Go small or go home
ruzam's Avatar
I'll try to post some pictures later after work.

I make my seams by butting the gores then joining them with a thin strip over top of the butt. I don't know if it's any stronger/easier/leaky but it's just the way I do it. I don't have a seam edge to fold in or trim off or pretend doesn't exist.

Anyway, I've had problems getting a good seam weld. I think the material has some kind of release agent on it from the manufacturing. I've found that isopropyl alcohol (rubbing alcohol) helps clean the surface. You can really tell where the surface has been cleaned well when it comes time to mark it up with sharpie pen. On cleaned surfaces the ink just glides on and dries shiny with a reasonable bond. On un-cleaned surfaces the ink clogs, drags and dries dull and rubs off more easily (nothing I've found yet could be considered 'permanent' colour). So before I weld seams I rub the contact areas with an alcohol soaked paper towel to clean them. I don't spend a lot of time with it, just a quick wipe. The alcohol dries in seconds.

Second it seems to take a combination of heat 'and' pressure. You've really got to push that seam together. Maybe that's an indication that I'm not using enough heat? My goring tool has a cloth braid ribbon glued flat. So where the foil seam is made, there's a criss-cross pattern of threads embossed into the seam. I feel the ribbon gives the ironing surface a little give so a flat iron on a flat gore tool doesn't result in some parts of the seam getting more pressure than others. Also because the thread pattern is raised, it forces the embossed parts of the seam to get extra heat and pressure so even if all conditions aren't perfect you can still get a mostly good bonded seam. Before starting an envelope I load up the gore edge (the cloth ribbon) with a light dusting of contact cement so the foil will stick to it on it's own. Then I line up the foil edges on the gore tool, rub down the alcohol, line up the thin strip of (reversed) foil on top, tack it every couple of inches with the hot iron (quickly touch the iron edge to 'spot weld' the seam strip in place). Finally I put parchment paper of the seam and run the iron over that. Parchment paper lets you push down on the iron hard and drag it without catching/melting the foil. As I get better I use a hotter iron temperature and quicker action on the seam.

Finally, I have a rubber stamp pad roller that I use to run over the seam with as quickly as I can after the iron. While the seam is still hot I press with as much pressure as I can. It embosses the cloth pattern into the seam and the rubber roller cools the foil as it goes. The more heat and pressure you use, the more embossing the seam gets. I think it's easier to see you've succeeded by the texture of the embossing. More often than not, my iron automatically shuts off when I'm not paying attention. I'll run the whole seam, press it with the stamp roller and remove the parchment paper only to find very little embossing and the seam edges lifting away. Better to find those seams up front than to finish the whole blimp and find seams pulling away when you go to fill it.

So ya, clean the seam surface with alcohol, then heat and pressure. You'll just have to feel it out for yourself from there until you know just how much of each to use.

I've had to make a number of electronic repairs to this blimp, and the electronics are inside the envelope. So every fix has required slicing an opening into the envelope and patching it after. It's like surgery. Start by cleaning the foil to be cut open with alcohol, then use a very sharp exacto blade to slice a clean opening in the foil. The foil has a nasty tendency to rip once it's got a start, so I verrrry carefully stick scotch tape to the inside of the cut at each end. The tape reinforces the cut start/end so it doesn't spread. It's probably harder to get the tape lined up and stuck down cleanly from that backside than any other part of the repair, but it's worth the extra time. To seal the cut when I'm done I flatten the foil over a silicon rubber baking sheet. It has just enough squishy give. You have to repair the seam over the back side foil, so the back side foil is stretched out smooth over the silicon sheet. Then a piece of parchment paper slightly bigger than the cut (all my blimps have a left over parchment paper piece inside from the construction process) is lined up behind the cut, then the final layer of foil with the repair cut is lined up on top of that and a foil 'patch' big enough to cover the cut is placed over that. I iron the 'patch' through a second parchment paper sheet to protect the foil, then stamp roller it for pressure while it's still hot. It's much easier and faster than I make it sound. I was nervous about slicing up sealed envelope, but as long as you're careful and keep things flat and laid out smooth, a patch will iron on and become virtually invisible. Because the patch is ironed on flat, the result is also flat and you really have no way to know if the seam is solid just by looking at it. If you didn't use enough heat you may have just ironed a patch flat without actually bonding it over the foil you're trying to repair! The heat seal side of the foil will change from 'frosty' silver to 'clear' on silver when it gets enough heat to melt. So I look for the edges of the seam having a clear look different from un-heated foil.
Oct 08, 2017, 10:25 PM
Fuzzy Member
lupy's Avatar
Thanks for the tips. I bought some of the material from American sci and surplus. It's a little thinner than the material I scavenged from jumbo balloons. It also doesn't stick together quite as well,but has the huge advantage of being a nice long piece. I have been building 4 gore blimps with seams on the outside. I don't think I have the patience to do it the way you describe, though I see the seam should be stronger your way. I will try your idea of using alcohol to enhance the bond.


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