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May 08, 2019, 09:27 PM
Melbourne, Australia
Thread OP
Discussion

Outdoor footage of my squid ship...


Hi Folks,

I realise I never posted video of my last hollow airship - here's a short film of the 'mark 19' which is, it must be admitted, a rather odd looking experiment of an air ship... there turned out to be a bunch of problems; the eight tails didn't work as well as I had hoped, there was a lot of problems with roll, and it lost its ballast half way through the flight... but hey, we managed to fly it back home rather than retrieve it from a tree, so definitely a win, and I learnt a lot!

The footage was actually shot last year; I'm working on the Mark 20 at the moment, but life keeps getting in the way...

cheers,

- Chris

mk19 second flight (1 min 21 sec)
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May 08, 2019, 10:03 PM
Registered User
That's fun!
May 09, 2019, 01:50 AM
Go small or go home
ruzam's Avatar
Dang those cockatoos!

This is fantastic!

What the heck am I looking at???? Looks like you've got a ducted prop through the center? How do you control it?
May 09, 2019, 02:54 AM
Melbourne, Australia
Thread OP
Ducted prop in the centre, and steering fans between pairs of rear 'tentacles' :-).

it looked good on paper, but it needs fins to stabilise it; it's way too twitchy, both with roll and direction... I'm very pleased with the degree of control though; at the end I was able to fly her straight down, despite having lost the balast.
May 09, 2019, 11:37 AM
Go small or go home
ruzam's Avatar
Reminds me of the sentinels from the Matrix. You should throw some red LEDs in the tunnel just for effect

It also looks like a nightmare to seal and leak proof. Bravo.

Gutsy move flight testing it outdoors. I live on the prairies so there's no such thing as a wind free day, and even if there were, the solar heating expansion would probably do my blimps in. I find everything about blimps is twitchy. The lack of opposing forces (lift and gravity) is just screwy. I see you're dealing with the classic 'spin out'. Tail Ring! Just saying

What are you using for roll control? Contra rotating props? Do you have any more pictures? This build is amazing.
May 09, 2019, 05:38 PM
Melbourne, Australia
Thread OP
Hmm... I guess they do look a bit like the sentinels - I can't see that being good for publicity!

And yes, sealing it was a drama - I never really got it quite right, it would get a little bit floppy after about 30 minutes, but even after ten minutes it would no longer be tight - which meant that the rear tentacles wouldn't stay in position. When the motor started up the tentacles would bunch up from the pressure loss...

I would love to use contra rotating props, but I don't have the weight - one of the problems with the design is it calls for a very large internal prop, and I'm struggling to get a prop / motor combination light enough. I'm trying to use a very gentle 'slow fly' prop, but even so the motor is under size for it. Contra rotating is definitely the way to go; because the prop is shrouded you wouldn't get a lot of the noise problems even if the design scaled up.

So at the moment there's no real roll control at all; as you can see it spins like a top when the main motor starts! There's a small amount of balast, but among the many, many things I learnt from this design was that I'm going to need to add tail fins to stabilise both roll and forward flight...

I don't have a whole heap of photos, but here's a shot of the core and steering fan electronics, as well as a banner-style photo I might use on a website :-).
May 09, 2019, 05:40 PM
Melbourne, Australia
Thread OP
(P.S. I never quite wrapped my head around your tail ring idea - I could see how it could stabilise forward flight, but how does it help with roll control?)
May 09, 2019, 07:41 PM
Go small or go home
ruzam's Avatar
Oh, ya, a tail ring would do nothing for the roll. Sky cam rocks back and forth like a ship on heavy seas. I guess that's what you get when you suspend a heavy weight under what is essentially a frictionless air bearing.

Looks like your using at least a 2S (or 3S?) power source. Any coaxial helicopter would have a dual motor, contra rotating, gyro stabilized circuit control board. I have a parts bin full of mxc2s, but those are pretty small (1S). Shouldn't be too hard to find a cheap larger coax heli in your power range. You could use the props and mechanics as is, or substitute them, but the board gyro would completely take care of your roll issues.

4 directional motors? Is that so you don't need a reversible ESC or some other design decision?
May 09, 2019, 09:09 PM
Melbourne, Australia
Thread OP
Coax helicopter blades is an interesting idea, and would suit the low speed airflow really well - thanks for that, I'll look into it! (I might have a very elderly helicopter model lying around actually...).

Yes, using a 2S power source, and a tiny 1S for the rear fans. I use lightweight pairs for a number of reasons; partially symmetry, partially redundancy, but also I had a lot of trouble with making them reversible - finding lightweight reversible ESCs was hard (I'm using car ones), and the little props I use are asymmetrical - they work much better in one direction than the other. So I use them in matched pairs...

There's a lot of things here which I wish I knew more about. I'm paying a lot of weight for ESCs for example, but I think if I was slightly smarter I could reprogram a quad controller to run all four of them at a fraction of the weight. I'd love to use symmetrical props for the fans, but don't know where I can get small ones and making my own seems impractical, so I simply used some small quad props I had lying around.

What I would really like to do is get the steering fans quiet - the main fan is slow and ducted and pretty quiet, but even though they're in little foam shrouds, the steering fans are really loud and buzzy. A previous model (the mark 12) used fins and a rudder, but that has the traditional airship problem of it needing to be going forward to steer. I really like the freedom of movement the fans give because they let you spin the airship in place, or even theoretically back it up...

It a really interesting design, but the practicalities of building it are frustrating!
May 10, 2019, 01:17 AM
Go small or go home
ruzam's Avatar
It's like reading through my own problems check list. Heavy ESCs, non-symetrical props, loud fans.

The non-symetrical props are really getting to be a problem. I started out with small direct drive micro quad motors and props which are fairly simple and not overly optimized for single direction blowing. But I'm working my way up through larger props and geared motor drives and it's very clear that the props are far more efficient at moving air in one direction. I don't have time to get picky and I've picked up so many different types of quad props over the last couple of years that I'll probably live with my selection of commercial prop offerings for the near future, but there's going to come a time when I'm just going to have to bite the bullet and start rolling my own 'rotation neutral' props. For the weight savings if nothing else. Most quad parts are ridiculously over built and heavy for blimp purposes.

I'd like to go brushless, but as you've found, reversible ESCs are difficult to find. Especially if you want it light and cheap. Many ESCs are programmable and can be flashed with reversible firmware. That's probably the smartest solution. A four ESC quad board re-programmed might be the ticket, but that's another rabbit hole of skills I need to pick up first. I'm really happy with my custom designed four motor brushed controller I've built. I make a point of attaching all my motors with plugs and removable mounts so they can be easily replaced for repairs and experimenting. I came across an interesting datasheet for a single chip brushless driver that had everything you'd need in a driver (including one pin reversing control). But the current limit was too low (appears to be designed as a computer fan driver). If I could find a similar type of motor driver chip with a higher current rating, that would be the end of my brushed motor designs.

I don't know that there's any answer to the noise. A tight envelope is perfect noise amplifier no matter how quiet you get the motors. It's like an old style gramophone speaker. Some serious noise isolation will be required in the mounts and that will lead to more weight. When I fly at events, there's always loud background noise and the blimp motor noise becomes insignificant. Maybe it's not even worth fighting. A small single chip audio playback with a peizo speaker stuck to the envelope might be enough to drown out the buzz of the motors with something more interesting.

I've moved away from servos as well. I used micro servos to vector the motor thrust as well as the paddle. So it was just as effective whether the blimp was moving or not. But the micro servos I'm using don't handle the stress very well. Plus I had to modify the servo to get a larger 180 rotation out of it, which was finicky work. Switching to pure motor drivers simplifies the whole setup.

You've done really well with your design. I'm impressed you've been able to pull it off as well as you have.
May 11, 2019, 05:28 PM
Melbourne, Australia
Thread OP
It's nice to know I'm not alone :-).

Reversible lightweight ESCs are rare, but you can get them; I've been using the "HobbyKing Brushless Car ESC 10A w/ Reverse" https://hobbyking.com/en_us/hobbykin...w-reverse.html - they weigh about 10g each, which is pretty light but using four of them adds a lot of weight :-(. I tried messing around with running two motors off the one ESC, which is something that shouldn't work but apparently kinda does if everything is identical, but I wasn't able to get it to work for my steering fans (perhaps because of the prop asymmetry problem).

I love your phrase "rabbit hole of skills" - that is so true! Maybe we should stick a 'help wanted' ad over in the quadcopter forums :-).

As for the noise, I don't think it's the airbag amplifying it that's the problem, because they're just as noisy and buzzy on the test bench - it seems to just be a function of small quadcopter props? There's another skill rabbit hole - the temptation to try to carve one's own props - if they were large I'd be tempted to give it a crack using the 'laminated profiles and then sand' method, but I can't figure out how to do small ones. I considered trying to 3D print them (e.g. https://www.instructables.com/id/3D-Printed-Propellers/) but the results seem a bit rougher than commercial ones, *and* I don't know enough about props to design a quiet one (I gather most of the noise is from the tips, and a blunter tip is noisier). I think maybe small props are just noisy! But then I look at the ones in a computer, and they're fairly quiet - but a lot of blades and a lot heavier. (Hmm... I wonder if I could use a computer fan with some of the blades removed?)
May 11, 2019, 05:30 PM
Forward ever, backward never!
Brainstorm's Avatar
Quote:
Originally Posted by pegacat
...hey, we managed to fly it back home rather than retrieve it from a tree, so definitely a win, and I learnt a lot!
Very cool project, Chris!

I've been following your posts here on RCG, and I have to admit that it flies a lot better than I expected, esp. after losing its ballast. I wonder if you could reprogram a quadcopter flight controller to allow directional control regardless of roll orientation. Then you wouldn't need to bother with ballast at all.

As for counter-rotating props, have you seen the ultralight setups used in F3P indoor pattern competition? Specifically, the Dualsky Typhoon XM2203TY offers a fairly inexpensive, off-the-shelf option. Not nearly as light as the high end custom/DIY setups from Europe, but very affordable. In addition, Aloft Hobbies in California recently received new stock. This after months, if not years, of lacking availability. I'm tempted to buy one, simply to have it in my shop in case of future need.
May 11, 2019, 05:37 PM
Forward ever, backward never!
Brainstorm's Avatar
Quote:
Originally Posted by pegacat
Reversible lightweight ESCs are rare, but you can get them; I've been using the "HobbyKing Brushless Car ESC 10A w/ Reverse" https://hobbyking.com/en_us/hobbykin...w-reverse.html - they weigh about 10g each, which is pretty light but using four of them adds a lot of weight :-(.
...
I love your phrase "rabbit hole of skills" - that is so true! Maybe we should stick a 'help wanted' ad over in the quadcopter forums :-).
Chris: You should definitely look into the 4-in-1 ESC boards available for quadcopters! It is mind boggling how small and light they have become. Looks for options in 20x20mm mounting format, and even smaller 16x16mm mounting size, on Chinese websites like Banggood.

Current versions of BLHeli ESC firmware support reliable and fast motor reversal. Look for Youtube video from Zoe FPV, and check out the Tweaky quad thread, where users Ian444 and Markus Gritsch have been building and successfully flying 3D micro quads with reversing motors.

Cheers,
-Roland
May 12, 2019, 11:17 PM
Melbourne, Australia
Thread OP
Oooh... how about that! (scurries off and orders a Dualsky Typhoon with money he doesn't have...). Thanks for the tip, that looks like an intriguing piece of kit :-).

Now... down the quadcopter rabbit hole... I had a look at the quad thread you recommended, and it seems to be full of deeply scary and talented individuals that are custom programming their boards and are a level above where I'm at! *However*, in the course of exploring that hole... and I think it's more like a wombat hole really... I came across the fact that some quad ESC's don't have full controllers on board? And some still use PWM?

So am I right in thinking that something like this gadget - which as Roland points out is just stupidly light - could be wired up with two pairs of PWM inputs to run two pairs of steering fans?

https://www.cheapdrones.com.au/20x20...ot-dshot-4-1g/

... a nice thing about the airship design is that the fans aren't run continuously, so it's possible to skimp a bit on the ESCs, as they usually won't run super-hot. But if I could use something like the linked unit it would save a significant amount of weight (particularly important on the tail of the airship, as balancing out the tail can be tricky...)

I'm a bit out of my depth here, but if I understand the spec of the board correctly (see attached) it takes 4 PWM input lines off a common ground - and since I want to run pairs I should be able to just do a common linkage to two of the inputs?

That would be so sweet - and if true would also make me feel a bit foolish given the amount of time, money and stuffing around I've done wiring up looms for four independent ESCs...!

thanks so much for the pointers,

- Chris
May 13, 2019, 02:24 AM
Go small or go home
ruzam's Avatar
I believe you've got the gist of it. Here's another even lower amp/weight board from Banggood's offerings https://www.banggood.com/16x16mm-Tee...r_warehouse=CN This one works as low as 1S (my sweet spot).

Pretty much all these boards run BLheli, and are both programmable with the existing firmware, and flashable with different firmware. The potential to convert these to full reversible ESCs is there. If you know the steps...


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