FBL Gyro Tuning B.D. Axon Gyro on my T-Rex 700X

[Heliman450]

Hi all, following my successful first hover with my newly built Align T-Rex 700X ( My New T-Rex 700X Build - Page 26), I'm now embarking upon the mystery of tuning my chosen gyro............ a Bavarian Demon Axon. The main reason is that I wanted to experience a different gyro than the one I'd previously used and the B.D. products came highly recommended from a few sources and the Axon specifically by our colleague, Steve (Smoggie).

My first challenge is to make some sense of the instructions. Probably one of the better translations that I've come across but, unfortunately, (to a comparative novice in this hobby) almost complete nonsense. The enclosed instructions are only really a high level guide and the real 'substance' comes from the drop-down information pages in the software. Not really any use when you want to bull-up before opening the software. It's also not so good that you need to connect the unit to the PC before activating the software. So if like in my case, the helicopter doesn't live at home, either the PC (laptop) has to travel to the workshop or the helicopter has to come home onto my dining table. Not very convenient for the family visits over Xmas!

Right, so the thread's open and I've started to decipher the text so back to work.

Bye for now!

 

[Heliman450]

Hi all,

Sorry for a bit of a delay in delivering my output on this challenge. It took me a bit longer than I thought to get to the point where I could publish something here also mixed in with Xmas stuff, too. I took the screen shots from the software and combined them into a PowerPoint file and also included some tables to summarise (and interpret) the B.D. stuff, no easy task I can assure you! I'd appreciate any feedback on the content before I put it into practice at the field. I also needed to delve deeper than before into my Jeti DC-14 instructions to find out how to make most use of its features, one of them being how to programme a slider to be able to make tuning changes to the gyro gain whilst hovering. I must admit to a certain amount of trepidation in using this latest change to my DC-14 capability.

PowerPoint File - View attachment Default Bank Settings.pdf
Word Document - View attachment BD Axon Tuning Tables.pdf

Next job is to address the Horizon Options and finalise my understanding of them.

Bye for now!

 

[Smoggie]

Phil,

I'm surprised having gyro gain assignable to a slider or digital trim wasn't a default option of the Jeti? It's something that is available on most Tx's. I tend to only use it while I'm setting the heli up, once i get to a setting I'm happy with i disable gyro trim adjustment to prevent me accidentally knocking it.

 

[Heliman450]

Phil,

I'm surprised having gyro gain assignable to a slider or digital trim wasn't a default option of the Jeti? It's something that is available on most Tx's. I tend to only use it while I'm setting the heli up, once i get to a setting I'm happy with i disable gyro trim adjustment to prevent me accidentally knocking it.

Hi Steve, Merry Xmas and Happy New Heli Year to come

The Jeti guys seem to pride themselves on pre-programming the least amount of functions as standard leaving it to the user to decide. The instructions even start with a large section telling you how to dismantle it to move all the switches somewhere else

All the proportional controls can be programmed to do something else and they can be programmed as switches, too. It isn't that it's difficult to do, just that it's buried in amongst lots of stuff, that's all. Not sure who thought it was a good idea, but someone thought that switching it on for the first time should be on page 44, connecting the Tx. to a PC comes in at page 140 and connecting it with a USB on page 133. I've found it to be a great device, just not logically explained. I'm working on that one, too.

Cheers again and enjoy Hogmanay.

 

[Heliman450]

Hi all, bad news I'm afraid.................

I've just got back from my latest test and this is the result.

Now the story. So I cleared the snow from the heli pad Went home for lunch, went back to find a group of fellow club members rescuing a plane, which landed in one of the trees backing onto the heli pad the other day. Of course, I had to help them so it took me a bit longer than I thought to get ready for my own test hover to tune-up my BD Axon.

Sorry that there's no video of this, but the bad picture above will have to suffice. So, I spooled up, looking good. Full revs, still looking good, lifted off and a bit of a wag started. Thought "better land that Phil and make an adjustment". Went to set it down (not hard at all) and the right side of the landing gear just snapped and I watched the main rotor rubbing itself on the deck as it slowed down (didn't take long at all). Just to add to the cost, the tail rotor also did its thing on the ground.

First inspection only shows the two sets of rotor blades and the landing gear to be replaced. The teeth are still there on both gearwheels. Now the main question.............

Is it the cold temperature that caused the landing gear to snap? Any thoughts on this much appreciated.

Off for a nice cold beer to drown my sorrows!

 

[Smoggie]

That's a pain! Yes, very cold weather will make plastic go brittle, almost 'glass like' so that it can break under a shock loading. How cold was it? Make sure to double check the torque tube front bevel gears and the small spur gear that drives the bevels, they tend to be the first things to strip on a tail strike.

How bad are the blades?

 

[Heliman450]

That's a pain! Yes, very cold weather will make plastic go brittle, almost 'glass like' so that it can break under a shock loading. How cold was it? Make sure to double check the torque tube front bevel gears and the small spur gear that drives the bevels, they tend to be the first things to strip on a tail strike.

How bad are the blades?

Hi Steve, it didn't really strike the ground, just tipped over in what seemed like slow motion. The main rotor blades took the worst of it but I wouldn't be inclined to use either them or the tail rotor blades again even if I was desperate to save the cash. We had minus 5 deg C overnight but I'd say it had warmed up to about minus 2 by the time I got round to take-off time

I'd agree 100% with your comparison to glass, I couldn't believe it. One more restriction to my next attempt, maybe I should just pack up until spring comes

 

[Smoggie]

I've seen similar breaks in cold weather before but generally only when the component was given a fair 'whack'. I wonder if Align are using some sort of new grade of plastic that's more prone to becoming brittle at lower temperatures? If i can find the landing gear leg that i broke in my crash i might pop it in the freezer and do some testing.

Maybe if the heli had been standing in the snow for a while the landing gear would have chilled down more than normal?

 

[Heliman450]

Since it happened all sorts of things have gone through my mind (after I stopped swearing). In the short time that I've been able to fly it, there has been a tendency for it to lead with the right skid on touchdown. It did that this time, although it came down much gentler than in my video of the first hover a little while back. However, the full weight was on that skid for a fraction of a second. Whilst I was helping the guys to rescue the plane, the heli was waiting patiently on the path leading down to the square so not sitting in the snow at all. That's one reason why I spent the time in the morning to clear about 4 inches away, it was also very powdery so very easy to brush away. I'd guess that it was cooling down for about 30 minutes from leaving the car. The guys were almost finished and I only held the ladder to help out.

I guess my best option when I finish the repairs is to put the training gear on until I'm sure that it will at least hover for a good period. I need to convert my other two batteries and 550 to Supra X connections so that I've got more flight time (hopefully).

 

[Smoggie]

Food for thought:
[video=youtube_share;Q1SwzBGzkrM]https://youtu.be/Q1SwzBGzkrM[/video]

 

[D.O.G.]

Nice presentation Steve . Even with the landing skid frozen, it took a nice couple of whacks before the Skid broke .

 

[Heliman450]

Hi guys, I agree that Steve's test shows something of great interest. Having watched what actually happened, I can say that it wasn't quite a re-run of the real deal. I'm not sure exactly what the as built weight is of the 700X but it must be heavier than Steve's hammer by about 4 times.

I can't say that Align are using a different grade of plastic. I think it's enough to say be careful when the temperature drops as such failures can happen.

Without a strip-down I can't say whether I've got the full list of spares yet, but I've ordered up two sets of blades for both main and tail rotors to give me a pair of spares. The replacement landing gear is peanuts in comparison.

Oh what fun

 

[Smoggie]

The cold certainly had a big effect on the plastic, I could feel that it was less flexible when cold without even hitting it with the hammer. It was still strong when cold, but just not as able to flex in order to absorb impact.
The plastic appears to be the same as other landing gear legs on my other helis, I think possibly it's Acetal (POM). It's not the first time I've seen plastic on landing gear break relatively easily in the cold. Having said that, as D.O.G. pointed out, it did take a fair 'whack' even when cold. I'd be surprised if the part I tested would have failed without at least a 'heavyish' landing, though Phil is right in that a 700 heli is a lot heavier than a hammer!

For anyone wanting to geek out on the cause of the change in properties between the flexible slightly 'rubbery' state at warmer temperature and the stiff but brittle state at low temperature look up 'Glass Transition Temperature'.. It's something that affects all polymers, but at differing temperatures.

Anyway, sorry for the drift off thread topic... me bad

 

[D.O.G.]

I know this is silly but I'll put it out there anyway. Awhile back I purchased unbreakable landing skids for my 450. I don't know the proper name for the skids but I think MSH was the brand. If I remember right, URI had them or mention about them. Their not cheap $19.00 for the 450 skids. I had the same skid forever and. Maybe they make a skid for the 700 or others helis that might have the problem of skids breaking because of weight. Just a thought.

- - - Updated - - -

I just remember the name, "Gorilla landing gear"

 

[Heliman450]

I know this is silly but I'll put it out there anyway. Awhile back I purchased unbreakable landing skids for my 450. I don't know the proper name for the skids but I think MSH was the brand. If I remember right, URI had them or mention about them. Their not cheap $19.00 for the 450 skids. I had the same skid forever and. Maybe they make a skid for the 700 or others helis that might have the problem of skids breaking because of weight. Just a thought.

- - - Updated - - -

I just remember the name, "Gorilla landing gear"

Hi D.O.G., thanks for the tip on the landing gear. I'd be happy with twice the price if there's an option for the bigger helis. Why? The cost of the new parts are over $150 and the new landing gear is only about $7.50 from that! Here's a link to a website showing what looks like a bigger option, but they only mention smaller helis GrandRC Home

Whether they're really so 'indestructible' at the low temperatures will remain a mystery as I don't want to try a live test when I'm paying the bill if they fail (Steve, how about a shock test? )

I have to admit that since getting into the bigger helis, I've always tended towards paranoia when it comes to the landing gear How about this for an upgrade http://shop.align.com.tw/partfinder.php?partlist=4855&partmapping=PART20

 

[Smoggie]

MSH do Gorilla gear for their Protos Max 700: Gorilla Landing Gear - Max V2 [MSH71172, MSH71173] | MSH USA But the fitting is specific to the MSH heli, some butchery would be required to fit an Align. To be honest I doubt the low temperature properties would be much different, the material might be the same stuff for all we know.

I've never found the align gear to be weak under normal use. I'm sure temperature must be an issue in this case, plus I suspect the landing was harder than it appeared.

 

[Heliman450]

MSH do Gorilla gear for their Protos Max 700: Gorilla Landing Gear - Max V2 [MSH71172, MSH71173] | MSH USA But the fitting is specific to the MSH heli, some butchery would be required to fit an Align. To be honest I doubt the low temperature properties would be much different, the material might be the same stuff for all we know.

I've never found the align gear to be weak under normal use. I'm sure temperature must be an issue in this case, plus I suspect the landing was harder than it appeared.

Hi Steve, I might just give this landing gear a chance and order one up. It doesn't look anywhere near as strong as the gear pictured in the 'GrandRC' link that I used below but maybe its strength comes from its flexibility rather than its beefy looks. It also uses only one holding screw per cross-piece. The biggest challenge in the modification seems to come from the front/back sizing with it being a one-piece item unlike the Align four-pieces.

We did get a bit off topic, but I started it and it's my thread anyway

 

[Smoggie]

Phil,

You are spot on, the potential show stopper with the MSH gear would be if the distance between the front an back legs is different to the frame mounting points on the Trex. The chances of it fitting are not great, it would be down to luck if it did fit.

One thing I've seen done to reinforce landing gear is to put a tie wire between the legs at the point they attach to the skids, this stops the legs from splaying out. Potential downside is that it will make the gear more rigid and possibly make frame damage more likely?

 

[Smoggie]

Another option if you really do feel a change of landing gear is necessary is the heavy duty landing gear from a Goblin 700 'KSE'. This has conventional plastic legs and tubular metal skids, but the legs are very beefy: [H0454-S] SAB Landing Skid Set - KYLE STACY EDITION - Goblin 630/700/770/Urukay

The legs would need some modification to fit the Trex but at least the distance between the legs can be adjusted.

 

[Heliman450]

Hi again Steve (like me you're an early riser?),

Problem I see is with the material of construction becoming brittle in the cold weather. I 'geeked-up' on the glass tendency thingey you mentioned earlier and from what I could see if the polymer is losing its springiness with lower temperature then it doesn't really matter how thick you make the section, it will still shatter when impacted too hard with a 700-sized heli or your ball-pein hammer. Getting back to the gyro subject..........

At the moment, my Axon is aligned with the tail boom not the deck. If I use a spare landing gear that doesn't have that angle, does the gyro need to be re-aligned (no pun intended 'Align T-Rex'). On the other hand of course if I decided on a custom winter landing gear together with skis I could do away with clearing the snow on the helipad, too

P.S. Hugo down the road, has the H0454-S skids for 45.90CHF, so based just on price they should almost 6 times stronger!