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Aug 08, 2018, 10:32 AM
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The maiden and flight testing

Sorry, no pictures here. I can't even post video taken with the GoPro. In a tragic rookie mistake I accidentally deleted the videos. I HAD the videos, I watched the videos, and now I have no videos.

So here's what I learned...

While I still suspect less than pure helium, SkyCam did not have enough lift to become completely neutral. But given the 4 vertical thrusters, it was flyable.

I'm tempted to blame my Helium supplier for the shortage of lift. I've rechecked my refill invoice, and their gas offerings and I should have been using 99.99% pure. However SkyCam did not achieve positive lift. Very close, but still heavy. I've re-checked my numbers. My lift calculations are off by about 5%. I live at an altitude of approx 600m and the density of air here is less by approx 5%. I haven't done the math, but I believe the error checks out. So for future reference I'll be using a reduced helium lift in my next blimp design (maybe 0.95g/liter).

For SkyCam this means I couldn't use any ballast to balance it out. And since I came out lighter than design on the tail, it was just a little bit nose heavy. This made forward flight awkward. The heavy mass hanging under the blimp wants to stay stationary, so any forward thrust causes the blimp to nose over, compounded by the already downward angle caused by the blimp imbalance. In order to fly forward I used a combination of forward thrust and vertical thrust and flew it at a bit of a nose down angle.

My options at this point are to make the blimp even lighter (which boils down to the motor pods and camera mount) or use a lighter camera system (which I have, fortunately). I've already been trimming back the motor pods and at best I think I may be able to shave off 2g total. Sadly, what I don't have is excess lift that can be put to use with logos. The whole point was to be able to slap some sign-age on the side. I will re-design the camera mount to allow the main support stick to adjust forward and back. If I can tilt the camera mount back I can solve my balance problem without resorting to more ballast. A new lighter tail ring would let me squeeze more grams out of it. At the very least I can get to the point where the blimp is positively buoyant with the GoPro. Playing with the numbers in my spread sheet, if I increase the diameter from 55cm to 57cm I can increase the payload to 25g which would put me back on track (without having to re-design the tail ring). In theory I suppose, I might even be able to cut out the top seam and splice in a 7cm wide panel (and extend the spars, etc, etc). Hard to say if that would be easier than just building new. I'll hold on to that idea as a last resort. The worst part is I have no spare lift now, so every time I fly I'm going to have to completely empty and re-fill the envelope. No topping up between flying days. But enough about that.

The vertical thrust is excellent. I love being able to lift it straight up and down, no questions asked. The motor controller is set up to use channel 5 to switch the rear motor pod operation from all motors thrusting the same direction (vertical thrust), to front and motors working in opposite directions (horizontal tilt). I can say now with confidence that the ability to switch was of no value. Never did I have a need to alter the tilt of the blimp and attempting to use that control only resulted in a camera video bobbing up and down. So future note, skip this option . Likewise, the vertical thrusters are linked to the aileron channel so the blimp can be tilted side to side. Again, this was un-used functionality.

Overall the forward thrust and control was great. Turning was quick and agile. The heavy mass under the blimp is a problem and all controls needed a very light touch. In fact this blimp could really benefit from a good amount of expo on the controls.

The motor pods are far enough away from the camera that they don't drown out the audio. Over all, it's a quiet blimp. But as a camera platform there are some problems. First of all, what I've got here is essentially a pendulum on a frictionless air bearing. The camera is ALWAYS swinging side to side. If the blimp was neutrally buoyant I could have waited for it to settle out, but I had to constantly give it some up thrust to maintain altitude and that just gets it swinging again. For the most part this video won't be anything more than a novelty without running it through image stabilization software. Secondly, I can't use the camera WiFi to feed video back to the phone app. It interferes with the receiver and significantly cuts down on range. When the receiver loses signal it goes into fail safe and sets the throttle to zero, which happens to be the full reverse setting. These small receivers don't have much in the way of fail safe options. Third, the event building I was flying in has air ducts blasting everywhere. So it's not easy to find a dead zone to settle into. But when it worked it was fantastic!

With my original weight calculations, I had expected to attach a cheap FPV camera to the side of the GoPro housing so I could get a live feed of the camera view in a set of goggles. I believe this is the way to go, but it's looking difficult now (SkyCam2!).

The biggest source of camera jitter is the side to side swinging. It's like trying to shoot video from a boat in rough seas. I'm convinced I can assemble a board with a gyro and micro processor to plug between the receiver and the motor controller to intercept the aileron channel and provide active stabilization. This alone might be enough to clean up the video and make it usable without needing any extra processing. I figure a stabilization board would add less than a gram to the weight and I've already got the components to test out something. So I may end up using that aileron channel after all. Hard to say yet if the forward tilting could also use stabilization.

One more thing of note. The motor controllers are programmed to pulse the motor power when the battery gets low. On my other (smaller) blimps this is very noticeable, even from the other side of a stadium. So I always know when it's time to bring the blimp in for a battery change. SkyCam on the other hand is big, the motor thrust comparatively small and for the most part I'm not booting around the arena at top speed with it. Just about every time I completely missed the pulsing motor indicators and ran the batteries down to the "second" cutoff that shut down all power. There were some hairy blimp recovery moments. On the videos later I could faintly hear the motors pulsing in the background. So I'm going to have to add more visual clues that this is happening. Maybe a bright white LED.
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Aug 08, 2018, 07:14 PM
Melbourne, Australia
*grump* - rcgroups ate the last two responses :-/.

Build looks brilliant Ruzam, and thanks so much for the detailed notes - I learn something everytime I read through your posts!

That's a marvellous picture of the final product flying, and I'm now suffering from severe stadium envy; I wish I had a space like that to fly in!

I'm still fascinated by the stabiliser ring - how did you come up with the idea, and how do you find it works? I can see that it might help the craft turn faster, as you don't have a large fin sail surface to slow things down?

I'm also curious as to performance; I guess you're prioritising duration over speed, but how fast does she go, and how long does she fly for?

Looking forward to seeing a video!!


- Chris
Aug 09, 2018, 01:29 AM
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Kind words pegacat, thanks!

All good questions! I wish I had answers for them The lack of lift took me by surprise really threw me off. I kind of lost focus of the important details after that. The 2 hours of sleep the night before may have played a roll

I couldn't get her "up to speed" so to speak as it was badly balanced. The faster it goes the more it wanted to dig into the ground. But I didn't have any trouble getting it around the arena. I'm not normally so lucky to fly in such a large space. That was really a one off. Usually my head room is much less and I'm flying blimps just close enough to make people feel they have to duck . The ring did it's job. No major problems keeping it on course. It's nearly impossible to fly straight backwards, but just like backing up the car, it probably just takes more practice. This is a different shape than I've been flying (cone tail). I might have to put together a dummy weight and see how it behaves without the ring. On my smaller blimps the ring is a necessary piece of equipment. But it's always good to see how much it helps. For example, may be I only need a band a few cm wide. Or maybe a wider ring would work better. I've got room to experiment now.

I was mostly just trying to keep it in one place for steady video. So not using much power at all. The vertical thrusters needed constant tweaking to keep it in the air. If I could have gotten it closer to neutral, it wouldn't have needed any power at all. Initially I was start/starting the video recordings under control of the phone app and wifi. But after I shut that off, the process became start the cam, launch, retrieve, stop the cam (usually after the batteries had completely cut off). From the video length I could have probably told you exactly how long I got out of the flight (if I hadn't deleted the videos). Not that I was going for duration, but it was more than enough time for good long clips. I'm using two 1S 650ma batteries in parallel. One of those batteries would have been considered a normal size for a quad using the motors I'm using. So you can imagine, if the motors aren't running full time how much more duration that amounts to.

I have some small video clips from my phone, but honestly the blimp isn't doing anything special, so they're boring as crap. I did spend some flight time just working the controls and aileron attempting to roll it over completely. That GoPro is a serious boat anchor! I believe I got it to go over, but not before rocking it side to side to wind it up. The steering is also sensitive. But again, with the video camera those are all manoeuvres that just don't fly. My next opportunity to fly is Aug 25 so I'll be sure to put it through the paces AND capture video of it.

I've unpacked my RunCam split 2 and powered it up to start getting a feel for how it works and what the connections are. The video quality looks great and it's less than half the weight of the GoPro. I've also got a video transmitter to go with it So far the only problem is that the RunCam doesn't come with it's own battery and it needs 5v. So either I've got to boost the 1S voltage to 5V, find a pad on the camera down stream of the built in voltage regulator where I can directly drive it from 1S, or I'm going to have to include a additional 2S battery with the camera (there goes the weight savings). Since the RunCam camera is separate from the board there will be much less weight hanging off the end of the camera boom. That alone 'should' result in a little less rocking.

I've only managed to find 2g to strip from the motor pods (so like 0.5g per pod). Unless I can find a way to remove a few more grams from the camera mount, this blimp just isn't going to realistically carry the GoPro. At my altitude anyway... Anyone living at sea level want to buy a turn key camera blimp? haha. So now I'm focused on creating a new camera mount for the RunCam to see what kind of final weight I can come up with. I'm really excited to use my goggles to monitor the field of view next time I get it in the air. Might even be able to figure out the OSD inputs and get battery voltage displayed. That would be sweet!
Aug 09, 2018, 04:53 AM
Melbourne, Australia
Hi Ruzam,

apologies; my reply was a little bit out of sequence :-).

I also live at 600m, and find I get 0.9 - 0.95g lift per litre, so your helium supplier may be blameless! I *have* noticed that air pressure and temperature make a significant difference; I get much better flights first thing in the morning when the air is cold and dense than I do in the afternoon - it may be worth having another shot with different weather conditions? Another option (which I've never tried!) would be to warm it up somehow before the flight; making it 14 degrees C warmer should give you 5% extra lift... not sure how to do that though, maybe a nice electric blanket :-)!)

As a final thought, I still reckon you could take some weight out of the go-pro case; maybe drill a few holes?

Good luck!
Last edited by pegacat; Aug 10, 2018 at 04:46 AM.
Aug 09, 2018, 11:09 AM
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I've also noticed that air pressure and temperature makes a big impact. In my early blimp days it was disappointing to get a blimp all set up and tested at home, only to find that by the time I got it transported to the flying gym it no longer floated. Now I try to build in enough extra payload capacity to allow for changes. Or at least I thought I was. I should have designed for 0.9g lift. Heck, I even expected the actual lift to be closer to 1.06! To be sure I won't be making that mistake in the future.

That GoPro is a tough nut to crack. The Hero 4 is a sealed case. Unlike the other GoPros, the camera 'IS' the water proof housing. Without the right tools, attempting to get it out of the case might even destroy it. The clamp housing that holds it with the attachment point however may have room for improvement. The articulated adjustment joints are over built for my purpose. I've trimmed them down already, but I thought I had more lift when I put together the camera mount. Just the twist knob alone is 3-4g.

As always, now that the blimp construction is complete I regret every single drop of glue that wasn't absolutely necessary.
Aug 13, 2018, 01:36 AM
Registered User
ruzam, this is very impressive stuff. Congratulations!

I have been looking into building something similar for a while too, and have ordered a small portion from Fluffy.

How much material did you have to use to make that? Also, how long was the entire building process? The more I look at it, the more impressive this is and I am hoping I can do something of similar size in a couple weeks!!
Aug 13, 2018, 12:22 PM
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Hey darksejong, a couple of weeks is very doable. I have poor time management skills. If you know what you're doing and just get down to it, this entire blimp could have been built in less than a week I'm sure. It does help that I've done this a few times now. It's slow going when you're figuring things out for the first time.

The absolute minimum fluffy foil needed for this blimp is 2.5m of a roll (2.8yds?). That's assuming you can cut the nose gores from the excess trimmed from the tail cone (fluffy foil being 110cm wide). 3yds would be a safe starting point. Depending on what you have planned you may not need to go as big.
Aug 14, 2018, 06:54 PM
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Hey ruzam,

Awesome thank you! I think I may have purchased a sufficient amount then.

By the way, how did you get such a nice finish around the inflation valve? Still trying to figure out where I should leave the "last opening" after putting everything together using a gore tool.

This is really a lot of information to digest, hopefully I can get something similar!

Thanks again!
Aug 14, 2018, 09:33 PM
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Fill Valve

I should have spent more time documenting the fill valve. I don't know if words will be enough here.

I cut a fill valve from an ordinary foil balloon. Usually I leave enough of the old balloon as a base for the valve to attach to the envelope. If you've made your envelope heat side in as I've done here, then you've got a problem with attaching the valve to the outside of the envelope. The trick is to use another piece of foil on the base of the valve as a patch so you can reverse the side with the heat seal and join it from the inside to the envelope.

On the purple blimp, the tail of the envelope was sealed with a large reverse side circle, so there was already a large heat seal surface exposed. It was pretty simple to cut a slit for the fill valve stem, slide it in place, then seal the valve directly to the envelope. To make it less obvious I ironed another disk of purple foil directly over the back end. The purple 'cover disk' serves no functional purpose, just gets rid of that big silver circle on the back.

With SkyCam I knew I wasn't going to have much space to work with the valve. I wanted it discretely tucked under the tail ring, out of sight. So I cut the valve base very straight and narrow so there was no more than 3-4mm of free flap around the base. Next I cut a piece of patch foil to iron the valve base to. The patch foil lets me reverse the heat seal side so it can be attached to the inside of the envelope. A slit in the patch foil for the valve stem, then iron (carefully) around the valve base on to the patch foil. Finally I cut a slit in the envelope large enough for the valve itself, and inserted it from the inside. Now with the reversed patch foil, I can seal the seam to the envelope. I just saddled it up to the side of the gore tool and did one side at a time, then the ends.

It's trickier than it sounds (more pictures really are needed here). The inner valve stem is nothing more than a flap of thin flexible plastic that is EASILY damaged by heat. More than once I've got the iron too close to the valve stem and ruined the valve. I'm extremely careful to fold the stem out of the way of the iron, allow for some clearance and protect it with parchment paper and maybe a layer of paper towel too just in case. The valve works as well as it does because it's perfectly flat and un-blemished so the air pressure locks it up tight. If you nick it with the iron, even if you've taken precautions to prevent welding it together by temporarily inserting a strip of parchment paper through the stem, you've deformed the valve stem and it no longer wants to stick flat together.

A couple more notes about the fill valve. It's going to take a lot of abuse. More so than any other part of the envelope, and it's no stronger then regular foil. I reinforce the valve with packing tape (both sides). While I'm at it I mark the fill entrance with sharpie first (before tape) so I can easily find it. There's a couple flaps in that fill hole and they don't all go to the valve stem. Now that I've got it marked I know exactly where to insert the inflater. Every time. I mark it before taping because the sharpie will just rub off and then you're back to guessing which plastic cut end starts the fill hole. With the tape protecting the sharpie marking, it's there for life.

Also, my fill valve donors have a half moon heat crimp right at the very end of the fill valve. I believe it's to keep the tip flat so the pressure can do it's thing to force it sealed. But that crimp and the end prevents you from sliding a straw all the way to the end of the valve stem for deflation. If the straw can't make it through the valve stem and out the other side, then there will always be a small bit of valve stem blocking the exit. And to make things worse, if you force the straw to the end of the stem, it'll pull and deform the tip, making it "not flat" again and prone to leaks. So I carefully cut that crimp off the end of the valve stem. It doesn't appear to be necessary. Btw I use paper straws for deflating so there are no sharp plastic edges to catch and stretch the valve stem. Sorry I don't have more pictures this time. Next blimp...
Aug 15, 2018, 12:11 AM
Registered User
Hello ruzam,

I think I understand how you did it much better now. Thank you so much for an awesome explanation!

I think I have a pretty comfortable understanding of the process aside from the production of the gore tool from an excel sheet I found online.

Again, thanks for the super fast responses! I should document by build too.
Aug 15, 2018, 09:11 AM
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Absolutely! Share your build! I like seeing what other people are doing. The whole process is still very much trial by fire and there are no doubt better/easier ways to do many things in this build. Pegcat probably has more good suggestions on filler valves.
Aug 28, 2018, 11:26 PM
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Trimming the fat

Where do you go from a blimp that's too heavy? Not very far.

After trimming, scraping and picking at the motor pods I only managed to trim off 2.65g, total. Not much more I can do there, other than rebuild them with smaller motors.

I also created a new camera mount. The new mount is adjustable and allows the camera to be tilted for and aft to help trim the balance. The new mount also allows me to mount my alternate SplitCam camera. It's a sweet mount coming in a 6.9g, just a wee bit more than the old mount at 5g. So now my pod savings have been reduced to 0.75g. Oh well, at least I'm still ahead.

I trimmed more plastic off the GoPro 'cage' and reduced it from 13.15g to 9.05g. So back in the green by 4.1g or 4.85g total. Now we've got a flying payload again. The GoPro cage is still a beast. I could try to trim more off, but it feels like a lot of risky work for what might amount to maybe another gram or two at most. Same could be said for the rest of the mounting connectors. I know it will fly with the GoPro now, and there's no reason to work any harder at it.

The exciting bit, is the new RunCam Split camera. With the new mount, I can mount the new camera, and the board it comes with, and a video transmitter, and a separate battery just for the camera/transmitter combo. And the best part is the new rig, battery, camera mount and all comes in at only 58.75g! The GoPro alone weighs over 72g. With mount it totalled 96.4g. By switching to the RunCam I've knocked 37.65g off my flying weight!

Not only am I back to using ballast to balance the load, but now I'm back to having some useful payload to spare for a logo. To celebrate I added "SkyCam" lettering (just under a gram).

I'm very happy with the quality of the RunCam. It can record at 1080P 60fps and seems to be doing well in my event lighting conditions. The camera board requires a 5v source. This is provided by a small 5v step up regulator. The video transmitter on the other hand runs directly off a 1S battery source. In testing I managed to record 20 minutes of constant video off a single battery before it cut out. I 'could' connect to the blimp batteries and save the weight of the extra battery. But I don't want to risk having the camera run down the battery and kill the motors.

Both the RunCam board and the transmitter run hot. I mean really hot. After a minute of power on, the video transmitter gets so hot you can burn your fingers on just about every part of it. The video transmitter will actually stop working if it doesn't get some air flow on it. I guess that's not as much of a concern on a quadcopter. The camera board gets almost as hot. Neither board is safe close to blimp foil, so they are mounted to the camera mount suspended away from the foil. It's pretty much required to make all the wires reach anyway. Both the transmitter and camera board have poorly designed regulators that are responsible for most of the heat. For example the transmitter boosts the 1S battery voltage to 5 volts quite efficiently, then drops the voltage to 3.3v with a linear regulator that just burns away excess voltage as heat. But it does the job. I can disconnect the transmitter and leave it off the blimp entirely, but that's not very practical either. The video signal feeds a set of fpv goggles. My blimp helper watches the video and directs me up/down/left/right to keep the video framed. I have some idea of where the video is from the blimp attitude, but not well enough to capture the subject reliably. This is still an R&D process.
Aug 29, 2018, 12:02 AM
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Flight Testing

Finally! Some flight video!

Now that I've got the camera weight issues sorted out, I had a chance to put SkyCam through the paces. I've learned new things. Some that surprise me, some that I should have know better.

First I'll say that these events (roller derby) are murder on blimps. They have 4 huge floor fans set up to blow across the track. It's like trying to navigate a toilet bowl in mid flush. My smaller blimps are more manoeuvrable and seem to be able to handle it better. SkyCam on the other hand is a bit of a whale and the goal is to keep it smooth and steady. So this location is a challenge.

There seems to be enough power, but the tail ring is not working out as well as I hoped. On my smaller blimps, the tail ring stabilizes the blimp 100%. But on SkyCam I'm still running into problems at speed. When it gets going at a good clip, steering becomes erratic and prone to blowing out. It's not totally out of control, but not locked in like it should be. Maybe a bigger tail ring is the answer, or a different design all together.

Rotating on the spot works great, but it's far too sensitive. In fact I think the blimp over all would behave nicer if I reduced the size of the forward thrusters (not to mention a little more weight loss). I just don't need that much power. It's very easy to over steer. I want this blimp to be less demanding on the pilot.

Starting forward flight must be done slowly and carefully. It still suffers from the mass of weight hanging off the belly. To much to fast just causes a nose over. Before with the GoPro, most of the video rocking was side to side. Now with the lighter camera, most of the video rocking seems to be front to back. When it starts rocking it can continue that way without some kind of correction from the vertical thrusters. I still wonder if a gyro and active stabilization is worth investigating. Fortunately, good camera footage also requires slow and smooth motion. So most of these nasty tendencies are avoided. But I'd still like to be able to just dart to a new position on demand.

Vertical thrust is great. Takes off vertical very much like a quad. Quite surprising for the size. Down thrust is slower. The quad props are designed to maximize lifting force, not downward force. There's no problem at all adjusting the altitude. For the most part, I think the fore and aft pods are positioned more or less equally for the surface area. But one thing I didn't count on is the CG. The mass is far forward closer to the front pods. Just like the camera weight impacts the forward thrust it also affects the vertical thrust. Small, quick vertical motion causes the blimp to tilt. I should have designed the camera mount to sit mid way between the pods.

For these videos I was intentionally trying to fly the blimp faster and more acrobatically. For most of the evening it was simply sitting in one place pointed at the track as best as I could. Sometimes floating around the building on the air currents.

SkyCam Flight Testing (0 min 56 sec)

SkyCam testing 2 (0 min 50 sec)

SkyCam Testing 3 (0 min 30 sec)
Last edited by ruzam; Aug 29, 2018 at 12:21 PM. Reason: typo
Aug 29, 2018, 12:09 AM
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For comparison, here's a more controllable blimp at the same event. Well, barely more controllable

Flying Purple People Eater (1 min 1 sec)
Aug 31, 2018, 10:25 AM
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And finally! The fruits of me effort

Derby (5 min 48 sec)

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