AH-6Z Littlebird Night-Ops build project

[pgkevet]

I stumbled on this a while back: Pamper your tools in a cosy drawer space!

you could plaigerise part of the principle for your transport box...?

[Zeeflyboy]

hah that's cool.

Certainly worth a think.

[scallybert]

[...] Heavily, heavily inspired by the blade 700 setup,

Outrage G5 - honest..!

[Zeeflyboy]

hmm, fair one... I saw the arrangement on the Blade though so I still say inspired by them, who were inspired in their turn by outrage

It's now an Outrage/B700 (basic cyclic idea), TDR (basic anti rotation idea), and Banshee (dual belt drive) inspired remix then

While my batteries are charging for another couple of test flights this afternoon, I've just been doing some work on the project i've now dubbed AH-6 Xtreme for my work folder


Couple of improvements over the current frame so far:


- Tail servo moved in from the tail boom to the frame to help CG.
- Middle bearing block accepts a large angular contact bearing (accepts high radial and thrust loads in one).
- Improved servo geometry, also with no linkages or levers - all direct to swash.
- Ace One IMU mount moved inwards closer to the CG, better for accelerometer accuracy and also helps with overall CG.


I am planning to use a dual belt drive system with compound gearing. I should be able to achieve around 14:1 on the motor to main rotor and then 5:1 on main rotor to tail - this will give more tail authority even with the low main rotor RPM... an improvement over the current 12.5:1 and 4.5:1 of the current setup. I keep reading how smooth the dual belt setups are too so should hopefully keep vibrations low.


I can't design the drive system until I have pulleys and belts in hand though, so now work stops for a while









good view of beefcake 10x26x8mm angular bearing:

[Zeeflyboy]

So, just got back from two more test flights, second one without the training gear


I've got the cyclic behaving fairly nicely in manual, but the tail I can't quite get right, either too loose or too bouncy. I think I have a mechanical gain issue there so I need to get/modify a shorter servo arm there methinks.


I had a very quick flick into Atti a couple of times but it quickly started a rapid drift backwards and left - will need to recheck my swash is level.


However, another 20 minutes of airtime and it's still in one piece!

[trexamanic]

Thats great news.
When i watched your vid, it looked like the swash was acting a little twitchy like the fbl controller was a bit off.
I am a complete novice but thought i saw that.
Well done on the flights and goodluck

[Zeeflyboy]

yeah it was, gains and flybar weight have been reduced by about 10% and it seems to have mostly smoothed it out. The new mechanics will use 16mm servo arms rather than 18mm, so i'll gain a little more resolution on the inputs - will probably have to tweak the gains back up a little after the swap.

[Zeeflyboy]

hmmmm... mixed bag.


Flew another two flights, I have manual mode flying ok-ish, and the tail is better after shortening the servo arm - I think it could stand to go another 2mm shorter or so to get it just perfect. In order to have it not constantly drift to the left and back I had to trim my swash out of level.

I also played around with Atti and GPS atti, including switching between manual and atti/gps atti in flight.

That's where the mixed bag comes in - it didn't crash (yay!) and switch over was smooth between modes. The issue is that upon selecting Atti the helicopter starts a strong drift left and slightly backwards, even with the swash trimmed to fly level in manual mode. humph.

So anyway, on to testing GPS atti and it holds pretty decently in the hover after an initial bump to the left due to having to pass through atti to get there. Weird one though - push forwards and the heli drives about 20-30 degrees left of track rather than straight ahead. And yes I calibrated the compass, twice. The DJI ace one wiki says that if it tracks to the side, then you should rotate the compass. Thing is that's a big offset and where I am is near to 0 degrees declination. I've never had to twist my Naza pucks.

Sigh... I really feel like a product this expensive should be a bit more straight forward. I need to do some reading up on my problems and see if I can find someone experienced with the Ace One.

[Gazzer1uk]

Harder than programming an Airbus to fly it seems!!!! I nkow what you mean in terms of knowledge, these things suddenly make sense and you are all over them, but until that point, its a bit of a dark art. The more complex systems are best managed by simpler green button controls, but no one seems to have got there yet. I am using BeastX and am a beginner with them, suddenly things make sense but up to that point, its mystical!

I would think by the time you have done your "Extreme" work and design and have proven its flight ability, there may be a kitting opportunity.... the thing you are showing here is the mother of inventions, in that your need is inspiring you do to great things, and using the latest technology to deliver. That ought mean you could speak with someone say "Quick UK" when finished to produce and sell kits with you taking a royalty fee to fund more exploits or pay back your investment. Double edged sword though, but given you out be able to hand over a load of electronic files and a build thread, and teh relative cost of production is low, so life could be interesting. Just a thought...... I think from what I have seen so far, I'd be likely to buy one lol!

Good to see a few more posts coming and the ship flying, I should talk mind since destroying my Trex 600 I have nearly rebuilt it (hence the BeastX issue) but not made myself go and fly the 700.... though for my birthday I have now got a Vario Lynx taking up space in the dining room!!!!

Laters,

Gaz

[HeliMonkey]

Z, just out of interest did you end up buying in Horsham (that area anyway) as its 10 mins from me and I'd love to be able to see the AH-6Z fly when its all finished, it will really make a change from everything cool and heli related being in the midlands or up north! That's if you would be up for it of course. Also if you are down this way, have you had any luck finding a club in the area yet?

Cheers

Jack

[Zeeflyboy]

Harder than programming an Airbus to fly it seems!!!! I nkow what you mean in terms of knowledge, these things suddenly make sense and you are all over them, but until that point, its a bit of a dark art. The more complex systems are best managed by simpler green button controls, but no one seems to have got there yet. I am using BeastX and am a beginner with them, suddenly things make sense but up to that point, its mystical!

Hah yeah. The more I look at Pixhawk the more I'm tempted to give that a try - now that is an advanced system. They are starting to take advantage of the new hardware since leaving APM behind and doing some very exciting advanced stuff like enhanced kalman filters and adding to the autonomous stuff with things like waypoint splines. Certainly not a big green button type system but it's completely open - if you have an issue like I do here with the Ace One, you have the tools to figure out why.

I would think by the time you have done your "Extreme" work and design and have proven its flight ability, there may be a kitting opportunity.... the thing you are showing here is the mother of inventions, in that your need is inspiring you do to great things, and using the latest technology to deliver. That ought mean you could speak with someone say "Quick UK" when finished to produce and sell kits with you taking a royalty fee to fund more exploits or pay back your investment. Double edged sword though, but given you out be able to hand over a load of electronic files and a build thread, and teh relative cost of production is low, so life could be interesting. Just a thought...... I think from what I have seen so far, I'd be likely to buy one lol!

You mean just the mechanics? Hadn't really considered it but I think the market is a bit too small for this kind of thing to make it viable.

I have now got a Vario Lynx taking up space in the dining room!!!!

I'd be out on my ear for that I think lol. Thankfully the new house has a shed and a garage

Z, just out of interest did you end up buying in Horsham (that area anyway) as its 10 mins from me and I'd love to be able to see the AH-6Z fly when its all finished, it will really make a change from everything cool and heli related being in the midlands or up north! That's if you would be up for it of course. Also if you are down this way, have you had any luck finding a club in the area yet?

Cheers

Jack

Yes I did mate. Someone did recommend a club that wasn't too far away, I forget the name of it now but I made initial contact with them. From what I understand there is a bit of a waiting list, but I was going to go visit them once I've moved back with all my kit...

I just heard back from the DJI expert I tried to contact (chris bergen), he gave me a phone number to call him on but he's in the US so will have to find a mutually suitable time to speak. Perhaps he will be able to solve my problems

[Zeeflyboy]

Okay, scally is going to like this one.

Mr Bergen suggests my problem may be due to swash timing. I had set this at negative 40 degrees so that with a digital pitch guage on the blade grip over the tail book there was the minimum amount of movement when moving elevator, effectively giving the mechanics a 90 degree phasing. He suggests that while this is a good place to start, it may need adjusting to suit this particular bird.

it would explain that behaviour I mentioned at the first flight last week with the circular oscillations (as though stirring the cyclic in a clockwise circle). Normally if the gains are too high you would expect oscillation in axis, but if the FBL aileron correction is actually say 80% aileron and 20% elevator, (and vice versa) then you could see how this may result in a feedback loop that would provide that funny behaviour. As it went away when I lowered the gains I didn't really give it too much thought at the time. However, that makes sense and would also mean I'm probably running gains too low to mask this problem, which would also explain why the helicopter is feelings bit loose and generally meh in manual mode.

so, he has suggested I re-level my swash again and then start adjusting the phasing angle instead.

[Delarado]

yep I was thinking phasing too, since you have that mega bastard funny multi bladed head on it

good luck with the adjustments. I reckon once you get it to move straight forward in atti mode (Rather than off to the left) youll be able to start increasing the gain again and getting the whole heli feeling more locked in.

[Zeeflyboy]

Fingers crossed thats the root of all the issues...

Right so this is my plan, any flaws?


There is a slider that allows you to adjust phase angle electronically... At the moment it's at negative 40 degrees in order to give a mechanically 90 degree phased head.

My plan is simple, I'm just going to increase the gains right up to the point that the oscillation just starts again. I will then change the phasing to negative 37 degrees and see... If the problem gets worse, then I will try negative 43, if the problem reduces but is still there I'll try negative 35 etc etc. I am guessing it should be a positive change as it is likely cause by the blade lagging, causing the centre of lift to be behind the grip, hence why I will start with moving to negative 37. Once the oscillation goes away (if it does lol) I'll increase the gains until it comes back and continue fine tuning phase angle. Once I get the gains high enough that it starts bouncing on axis but not oscillating, I'll know I've found my phasing angle and then dial the gains down enough to stop the bounce.... Then I'll try atti mode again and see if my problems persist.


That's my theory anyway. I'm just glad I built this training gear because intentionally forcing the heli to oscillate would get my knickers in a twist otherwise.

[Delarado]

can't you just put it in the mode where it veers off to the left instead of going straight forward?

then you don't have to deal with oscillations, you just change the phase angle until it goes straight forward rather than off to the left a bit.

Cant you calculate it though? Is it always 90 degrees phasing, swash ball versus the blade itself?