Setting up a 550-700-800 single rotor for AP

[R_Lefebvre]

Well, so much for that. Spent all day testing, and during one iteration it started shaking so bad I lost it and crashed.

[onlocation]

Usually a major vibration like that isn't caused by some minor problems with runout or tolerances. If you had a vibration big enough to cause a crash it was probably a harmonics issue with your frame design or blades that were not equally tightened.

[nightflyr]

Just my observation here...
I have run both TT and belt drive tails assemblies.....
Any vibration issues can be mechanically corrected with little effort.

My thought of using a DDT wasn't to cure any vibration issue , but to be able to have proper tail authority when running HS below 850 RPM.
Very tough to hold a solid tail on a 800, 900 or 1000 class at that low of a HS

[R_Lefebvre]

Originally Posted by onlocation

Usually a major vibration like that isn't caused by some minor problems with runout or tolerances. If you had a vibration big enough to cause a crash it was probably a harmonics issue with your frame design or blades that were not equally tightened.

The shake wasn't so bad as to cause a crash by itself. But it confused the gyros and they made it tip over. But it was bad enough...

I'm sure the main shaft slop was the cause, because it got drastically worse when I freed up the main shaft (it had been glued into the bearings).

But, you may be right anyway. I'd be wondering if I was having this much trouble because I stretched a 550-600 to a 700, and then using Spinblade Asymmetrics. Those blades are VERY heavy, probably almost twice the weight of sport 600's. 50% more anyway. So maybe it's just too much. Turns out I have all the parts to rebuild it as a 600, so I think that's what I'm going to do.

I'm starting to have misgivings about the whole "stretch" thing. Maybe you can get away with it if everything is PERFECT. But with the design that Align uses (ie: sloppy) it might be hard to do it successfully.

For sure it's *possible*, I flew this thing a fair amount. Even a single 25 minute flight. But it has an RPM range where it just doesn't work. (right about 1800). I flew it a number of times at 12-1400. It still vibrates, too much for video, but you wouldn't notice anything was wrong otherwise. But at 1800, it gets bad. At 1900 it gets bad again.

[pc3associate]

Sorry to hear that Rob.

As far as shafts and bearings go- we had success with 550 and 600 stretches. We added third bearing blocks (used 600 nitro main shaft with a 10 mm shaft collar) and using RC-TEK bearing blocks everything was fine setting up. Had a 550 stretched to 800 for a while no problem.

[R_Lefebvre]

Ok, well then, it must be the sloppy shaft. This was the variable I was playing with all day long trying to solve the problem, and it got drastically worse when I freed up the shaft. I use the Heli Option one-piece bearing block system. Both bearings in a single block with thrust bearings. It's nice because you can take the entire shaft and support system out as one piece. (also nice because of the frame stiffness it creates) This allows the ability to clamp the entire assembly in a vice and use a dial indicator on it. This is how I found out that when I glued in the main shaft (to get rid of the slop) I glued it with a 5 thou runout. It seems to be nearly impossible to glue it in dead straight.

I had spent the rest of the day checking the setup of the entire head with a main shaft mounted in a lathe, and a dial indicator. The shafts are bang-on. The head seemed to be straight within 1/2 thou.I even mounted up the grips and measured the position of the blade grip bolts. This is somewhat pointless as the dampers allow so much movement.

Anyway, main shaft and head are straight when measured in a lathe head. But measured in the bearing blocks, I had 5 thou rounout with the shaft glued in, and then some ungodly number like 50 thou of rock when I removed the glue.

I believe that the two-bearing system could work if the shaft wasn't 0.10mm undersize. But it's friggen hopeless as it is.

Using 3 bearings and remove the free play... though I'm not sure if it just masks the issue. I don't really see how it can allow precise alignment of the shaft. The BEST solution has got to be a properly sized main shaft.

When I did the DD Tail, I used high quality hardened and ground industrial 5mm shafting. I had no problem at all getting it into the bearings. Just slips right in like it should. The only problem I had is the fit of the pitch slider is tight. This, again, is due to poor manufacturing tolerance and/or design of the original parts. I had to hone out the bore of the pitch slider. It became very obvious when I did this that the issue is the bore gets deformed (pinched in) when you tighten the bushing into the yoke thread. It's just a poor design, which Align solve by, again, using an undersized shaft.

My only fear with using a true 10mm shaft for the main shaft, is how it will fit in the swash plate spherical bearing.

As for adding a 3rd bearing block... This seems to be tricky. Most of the shafts available now don't have the added length below the OWB anymore. Used to be you could use the 600e shaft. But now they are too tall for the 3G FBL system, and DFC is even worse (not that I'd ever use that POS).

The only solution I can see here is to do something like what KDE is doing for the 700 DFC 3rd bearing system. A little stub shaft that you stuff in the bottom of the main shaft to give you the extra length required.

But this isn't really the ideal mechanical solution.

Any other ideas I'm all ears.

[R_Lefebvre]

Originally Posted by nightflyr

Just my observation here...
I have run both TT and belt drive tails assemblies.....
Any vibration issues can be mechanically corrected with little effort.

My thought of using a DDT wasn't to cure any vibration issue , but to be able to have proper tail authority when running HS below 850 RPM.
Very tough to hold a solid tail on a 800, 900 or 1000 class at that low of a HS

Wow, now that's low! I tried 1000 and it was very slow and didn't fly so great. It flew, but you had to be careful because you don't have a lot of reserve power.

It may be possible to cure most of the vibration problems with a mechanically driven tail, but I can't see how you'd totally eliminate all of them.

A belt is always going to flap. No way to completely get rid of that. I think TT's need more bearings to eliminate shaft whip. That single bearing just isn't enough. That's a LONG shaft.

And then I don't see how any amount of mechanical setup is going to get rid of all the problems. Align's shafts seem reasonably straight. But the gears are still not round, especially the auto-rotation gear. And every straight-cut gear mesh is a source of vibration, even if the gear was perfect.

If there's any tricks I'm missing, I'm all ears. That's what this thread is for.

Besides all that, the benefit of the DD Tail is you you eliminate the need to futz with any of that mechanical setup. It's just gone. Set up your ESC governor, and you're good to go. There's just one shaft, and a couple bearings. No belts to tighten or worry about static. No gears to get stripped out. No non-adjustable meshes to worry about. It's just simple.

But mainly I'm biased as my day job mostly involves rebuilding old industrial machines by removing all the line shafts and change-gears and replacing that mess with variable speed motors. More reliable, and much better operational flexibility.

[nightflyr]

Wow, now that's low! I tried 1000 and it was very slow and didn't fly so great. It flew, but you had to be careful because you don't have a lot of reserve power.

I've flown with lower HS never much of a problem..except for the tail holding.
But a quick fix for that was to craft up a stacked tail assembly, then later on crafting a set of 170mm tail blades








It may be possible to cure most of the vibration problems with a mechanically driven tail, but I can't see how you'd totally eliminate all of them.

If you always have an issue with vibration using stock hardware, perhaps it time to look at a different solution...
I found off the shelf components had a lot to be desired.. So if they don't work the way you want...
Make it yourself...
Hand craft all my TT for my fleet out of stainless steel, way stronger and spin truer than any off the shelf part.



A belt is always going to flap. No way to completely get rid of that...

I don't have any issues when running a belt driven tail, proper tension and lubrication are key factors
Also having a well designed boom block enhances the performance..





I think TT's need more bearings to eliminate shaft whip. That single bearing just isn't enough. That's a LONG shaft.

On a 600 all I've ever used was a single, 700 install 2 bearings.
On my longest torque tubes, 44 inches I'll run 3 for the raised tail 4

And then I don't see how any amount of mechanical setup is going to get rid of all the problems. Align's shafts seem reasonably straight.

"Reasonably straight" is not enough when it comes to this aspect of the hobby, got to shoot for the gold standard.

But the gears are still not round, especially the auto-rotation gear. And every straight-cut gear mesh is a source of vibration, even if the gear was perfect.

Ahhhhh there in lies another trick or 2..
To start with. I have a stock pile of the original FAD MOD 1 gears I purchased just before he closed down production.
Great pity, I have yet to find a better composite gear that will out perform those FAD MOD 1 gears.

A second option....

All metal gears...







Metal M0.8 Torque Tube Front Drive Gear Set/34T
Out of stock $45.95 $45.95
If there's any tricks I'm missing, I'm all ears. That's what this thread is for.

Not sure that there are any tricks.. more to the point of experimenting and experience.
Or perhaps having a knack for it.. I really don't know..This part of it is very natural for me.
I really don't put a whole lot of thought into, I just build the way I think it should be and go from there.

Besides all that, the benefit of the DD Tail is you you eliminate the need to futz with any of that mechanical setup. It's just gone. Set up your ESC governor, and you're good to go. There's just one shaft, and a couple bearings. No belts to tighten or worry about static. No gears to get stripped out. No non-adjustable meshes to worry about. It's just simple.

As I stated your reason(s) for a DDT where way different than mine....
I really do not care for the tail mounted motor layout for a few reasons..
1) Possible damage from debris kicking up into an exposed motor.
2) Having that much weight in wire ( I assume you run your wiring down the boom )
3) Possibly inducing vibration from the wiring shaking with in the boom..

I envisioned a different approach where it would solve a low tail RPM issue, and use the existing hardware to simplify the mechanics as much as possible.


But mainly I'm biased as my day job mostly involves rebuilding old industrial machines by removing all the line shafts and change-gears and replacing that mess with variable speed motors. More reliable, and much better operational flexibility.

Nothing wrong in that... But you need to be open to other solutions that may provide a more viable answer.

In the end, you experiment and try to adapt what hopefully will work in your specific requirement(s)

Sometimes you you get it right, and sometime you get an epic fail.
Experience is what you will always gain.

And when it all comes together the way you plan ..it works like a charm..

GOPR0 Clean Raw Footage (6 min 33 sec)

[onlocation]

Originally Posted by R_Lefebvre

The shake wasn't so bad as to cause a crash by itself. But it confused the gyros and they made it tip over. But it was bad enough...

What FBL gyro? Did you have any type of auto leveling function turned on? Did you give it any stick inputs while it was on the ground?

FBL gyros, especially on tall flexible a/p setups, do not like to be light on the skids. Combined that with any type of ground resonance and you will have major problems. It's best to get head speed up with 0 pitch, then pop if off the ground with no cyclic input before it's flying. Don't let it skate around or get light on the skids, and don't take off with auto level turned on.

If you are spooling up and notice a major wobble due to ground resonance, you only have a few seconds to decide to hit throttle hold or try and get it off the ground. Ground resonance could be caused by having your blades too loose or having too soft of dampeners for the weight of your blades. Long flexible landing gear tend to make it worse.

I've had half a dozen different 700-800 A/P configurations over the last several years, mainly Trex and Logo based. The Trex can be smooth but it takes a lot of setup and a bit of luck, the belt drive seems to be a little more consistent. The main benefit of the belt drive is less moving parts. For example the Logo drive system only uses 4 bearings, while the Trex system uses 12 or more. It's also significantly lighter of an airframe allowing a heavier payload for a given disc size. It's not without it's own problems though. With belt drive, belt tension is critical to remove belt slap and vibrations. The problem is the tension can change often, even during flight, as the temperature of the tail boom and belt change.

Regarding tolerances like the undersized shafts, in some cases it is actually a design feature to allow thermal expansion rates of different materials. For example you'll find play in the brass bushing on your tail slider, but play is needed so it doesn't bind at lower temperatures when the metal shrinks. This is the same reason your tail shaft or belt tension must be readjusted often, because the shaft/belt doesn't expand or contract at the same rate as the tail boom. This is also a reason carbon is preferred over aluminum for tail boom material, because it expands and contracts a smaller amount.

But the tolerance between certain parts should be minimized, for example the tail hub on the tail shaft should be a solid fit. I fill any gap with green locktite and once it's dry I balance the entire assembly on the dubro prop balance.

For main blade balance a Koll blade balance and .01 gram scale are the preferred tools. Span-wise and lengthwise balance are critical for these heavy blades to insure even tracking.

And if anyone is interested in a ready to fly 700-800 setup there is a nearly new, we have one for sale here.

[Goldenhour]

Onlocation is right about the blade balancing. I have a set of 620 Rotortek symmetrical blades I've used for a couple years. Per suggestions from a pro here I bought all the blade balancing gear and a video by "Ray" on blade balancing. One blade was off 2 grams in chordwise balance from its mate. Both blades were off in spanwise balance between them. Both blades, however, were within a tenth of a gram in weight between them as they came out of the box. The chordwise balance I rechecked three times to be sure. It was off that much. Rotortek are suppose to be one of the "don't need to balance them" type blades.
I think for having fun you never need to worry about balance that much but when we are sweatin it out with the vibes it does.

[R_Lefebvre]

What FBL gyro? Did you have any type of auto leveling function turned on? Did you give it any stick inputs while it was on the ground?

It was Arducopter. Yes, auto-leveling. I didn't touch the sticks when it was on the ground, not that that was matter, we can handle that just fine. You can push it over at least 15° and hold it there with the blades scraping the ground if you want.

I took it up, saw it was shaking as it had before, but it got really bad. The skids were a blur. (Dubro large plastic airplane legs with PVC tube runners). I immediately started trying to bring it down, but do it softly. It lost tail control, spun around and in it went. The vibes were so bad that for all I know, the APM might have come off it's mountings, or the servo wires came off. I don't know. The vibes were CRAZY bad.

This was obviously a very bad situation. In hindsight, I never should have attempted to fly it with the shaft that loose. Though... that is how it comes by design. There must be some kind of interaction with some other part that I cannot find, like the chordwise balance, or I don't know. All the other parts on the head were very straight.

These were Spinblades which are supposed to be very good. I balanced them to 0.02g. But can't do the chord.

These mechanics flew well as a 600, using 600 Spinblades. But has never flown right on 700, with either the 700 Spinblades, or another set of cheap 700 blades I have.

In the meantime, I'm getting flawless video with a multirotor.

[R_Lefebvre]

So here's my results from my H8 Multirotor. This makes it really hard to keep slogging along with the helicopters.



I can fly up to 60 km/h so far with virtually perfect stability, never any shaking. And that's with the lens hood installed even. Keep forget to take it off, but it doesn't seem to matter.

No Post Stab of course, just optical stabilization.

[salience]

Originally Posted by stmpngrnd

Ok...just to be totally clear. You guys are using TREX 600 tail cases right?

Here's one I built from a 600 case for an unstretched 600. I opted for replacing the port-side Align plate with an easily made CF plate, eliminated the "4th" bearing, used a collar and spacer on the shaft to retain the stb-side bearing and prevent motor case from drifting to port if by chance it decided to do so under load (you don't have a circlip on the shaft next to the motor - DON'T cut one or your shaft will promptly snap there). The motor is a Turnigy Aerodrive SK3 - 4240-530kv - definitely oversize. All 4 mounting bolts/holes used, and tail case cross bolt conveniently fits in a standard cutout in the motor case. The shaft is the longer Align 450 mainshaft - the one that conveniently comes with a collar and is 3 to a pack for bargain price. Main motor is on 8S but I'll use a third battery - 4S - for the tail and electronics. To be APM-controlled - all electronics et al. inside with 4S LiPos supported on rails along the sides - 3rd 4S on the bottom deck at the front.

This has not been flown yet - I'm a very slow hobbyist - just getting started on this one, but I have set up same deal on a 450 and the entire setup is incredibly smooth and silent at all rpms - a very slight resonance and jello on the ground while spinning up, but essentially perfect video in air with a small CMOS tube-style camera mounted totally solid underneath the forward landing gear - no vibe-absorbing material at all. Formerly I had a TT setup in this, and could never get anything but very jello-y video even though it didn't seem to vibrate much. After a couple of crashes - my fault (actually one was a tail spinout caused by a defective ESC or tail motor or both, replaced now with an SK3 and YEP 18A ESC, perfect!) - on rebuild I no longer even take much trouble with precise balancing or anything else except slapping it back together and getting airborne. Nothing seems to matter.

Just started testing a 500 with the same setup. Also very smooth. I also suspect vibration problems in the largest machines, especially when they are very rpm-specific - result from some kind of resonance, where perhaps a small and otherwise unimportant vibe in the head (which you are never going to eliminate entirely), resonates with another vibe or flexibility in the frame or tail (especially with that heavy motor out there), and you get get a Tacoma Narrows Bridge effect - a slight energy input at the right (wrong) frequency gets the thing swinging, wagging, shaking, and collapsing.

[NexxuSix]

Subscribed...

I have a Trex 500, DFC, TT, Trex 600 landing gear, with Naza-H + gps. I'm looking at putting a Tarot gimbal and GoPro Hero 3 on board...

I'm struggling a bit with CG issues at the moment. I want to add the gimbal and camera to the front of the heli, and had thoughts of strapping a 6000mAh battery to the bottom of the heli using a second bottom plate as a battery tray of sorts. I will most definitely need to add foam tubing to the gear to get the heli up high enough for the underslung battery.

I have experimented with home brew extended landing gear, but no matter what material I've chosen, I get a really wicked resonating hum in the landing gear to the point where it shook a side mounted Midland 720HD camera out of it's clip! So, right now I'm a little leery about using oversized landing gear to put a camera under the heli... I think I'd rather use an underslung battery to adjust my CG.

Thoughts?

[pc3associate]

Yes Rob multi rotors are much less complex to get flying smooth. But IMHO, they each have their place for AP. We use multis now for any slow close in shots, structures, etc. Any wide open longer sweeping shots are done with the single rotors. Also anything around high value structures or in populated areas are shot with multi spinning xoar wooden props (in the event of a failure a multi swinging wooden props will result in minimum damage compared to 700-800 size carbon blades. Necessary? Probably not as the only failures we have ever had wr were able to auto to a safe landing. But the peace of mind is nice flying a multi setup with wooden props.

Going from single rotor to multi rotor is easy, going from multi to single is a huge learning curve.

[R_Lefebvre]

Just started testing a 500 with the same setup. Also very smooth. I also suspect vibration problems in the largest machines, especially when they are very rpm-specific - result from some kind of resonance, where perhaps a small and otherwise unimportant vibe in the head (which you are never going to eliminate entirely), resonates with another vibe or flexibility in the frame or tail (especially with that heavy motor out there), and you get get a Tacoma Narrows Bridge effect - a slight energy input at the right (wrong) frequency gets the thing swinging, wagging, shaking, and collapsing.

I have experimented with home brew extended landing gear, but no matter what material I've chosen, I get a really wicked resonating hum in the landing gear to the point where it shook a side mounted Midland 720HD camera out of it's clip! So, right now I'm a little leery about using oversized landing gear to put a camera under the heli... I think I'd rather use an underslung battery to adjust my CG.

I think both of these comments are relevant to the problems I'm having. There must have been something about the frame or landing gear that was making the problem worse. Because it just doesn't make sense that I had as bad of a problem as I did, after doing as much measuring and balancing as I did on the rotor system.

Maybe it was the chord-wise balance. I wish I could get that blade balancing video, but it's not available anymore.

But that's not enough, because then nobody would be flying with these blades. So I wonder if it was just lighting up the landing gear, right at their resonant frequency. They were a blur. But the rest of the frame and the rotor disk, you couldn't see vibration at all, looked fine. It was just the landing gear.

And ground resonance was fine. Just a little wobble on spool up, not much or I would have shut it down. But as soon as I lifted off, the landing gear just lit up.

I had been using pool noodles on the runners. But suspecting the mass of them was exacerbating the problem, I pulled the noodles off. Whatever the natural frequency of the gear was, removing mass would make it even higher frequency. So, maybe the wrong thing to do.

[NexxuSix]

Originally Posted by R_Lefebvre

But that's not enough, because then nobody would be flying with these blades. So I wonder if it was just lighting up the landing gear, right at their resonant frequency. They were a blur. But the rest of the frame and the rotor disk, you couldn't see anything. It was just the landing gear.

And ground resonance was fine. Just a little wobble on spool up, not much or I would have shut it down. But as soon as I lifted off, the landing gear just lit up.

Rob, you describe exactly what I was seeing on my setup as well. Everything was fine until takeoff, then a few seconds into being airborne and my landing gear was a blurred, humming apparatus that was gonna take my heli out with it if I didn't land quickly... When my camera fell off and was dangling on the lanyard, the CG shifted violently. So now I'm trying to land a heli that's humming with resonance, and off balance as well!

[R_Lefebvre]

Originally Posted by pc3associate

Yes Rob multi rotors are much less complex to get flying smooth. But IMHO, they each have their place for AP. We use multis now for any slow close in shots, structures, etc. Any wide open longer sweeping shots are done with the single rotors. Also anything around high value structures or in populated areas are shot with multi spinning xoar wooden props (in the event of a failure a multi swinging wooden props will result in minimum damage compared to 700-800 size carbon blades. Necessary? Probably not as the only failures we have ever had wr were able to auto to a safe landing. But the peace of mind is nice flying a multi setup with wooden props.

Going from single rotor to multi rotor is easy, going from multi to single is a huge learning curve.

Just so it's clear... I'm not going from multi to heli. I started with heli. And I'm the lead developer adapting the arducopter program to work on helis.

I only got started with multis begrudgingly. But with results like I got yesterday... man. I never thought a multi could fly that fast with perfectly stable footage.

Helis have been a constant struggle. Early on I was using Hobby King parts. Kind of a necessary evil due to the rate I was writing off helicopters while developing the program. But at some point the software got mature enough that the mechanics were holding me back, so I went upscale. Everything was fine with this heli as a 600, but stretching it to 700 has been a disaster and a whole lot of wasted time and effort. Now I'm wondering how much of it was just the darn landing gear.

[salience]

Helis have been challenging for me too - a diving accident many years ago left my right hand - especially the thumb - quite insensitive. No chance of controlling a swash with that thumb! So I'm in mode 3 Tx, and have some special tricks for the right stick... Finally I'm starting to get the hang of it all. So for AP, you see my interest in APM's automation to protect my more expensive equipment.

Rob: Speaking of APM, and vibration, I'm just about to mount mine in the 600 and am debating vibration isolation. I've got a slab of Sorbothane left over from deciding not to use it with cameras, as I mentioned. The stuff might be good for APM I thought because you could easily have a piece the sie of the APM box, no wagging possible, and the stuff should be very good at higher vibe frequencies. Your opinion?

[R_Lefebvre]

I haven't used sorbothane, and have heard mixed things about it. Can't recommend it.

The best vibration damping I have seen is what I concocted on Saturday for my F450.



This works exceptionally well on this quad, but I am pretty sure it's far too soft for a helicopter. Probably ok if everything is perfect, but if you get a main rotor shake, it'll light up. These are 100g dampers from Foxtech.

On my big heli, I used these little bulb dampers I found somewhere, they're smaller, but stiffer. Work well enough.

Heli's actually seem easier for vibration damping than multirotors, as far as APM is concerned. As long as your bearings aren't too bad, and nothing is visibly shaking, it's fine. On my little 450 heli, I use nothing more complicated than those little blue grommets you see there. And it's perfect.