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HomeAircraftHelicopterHelicopter Main Discussion › My FBL heli acts like it wants to flip over upon takeoff!
08-09-2018 01:26 AM  73 days agoPost 1
OneHoof

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Cold Spring, Kentucky

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I am new to Flybarless helicopters.

Yesterday, my FBL Airstar Mongoose acted like it was going to flip over upon takeoff!

I had test flown it twice previously and it flew okay until the plastic tail rotor control rod broke and I had to do a hovering auto.

(I lost the bind to the transmitter and despite following Mikado’s binding instructions, I could not get it to bind. Finally having to plug in the JR Receiver into a satellite port, using the RX as a satellite. But I finally got it to bind.)

I have heard different things, in regard to using cyclic input/corrections during pickup.

So, I am wondering if is something I am doing wrong, or something is not set right in the Mikado VBar FBL control system.

I ensure I do not touch the cyclic while the FBL system is initializing.

It has plastic skid struts, which flex a lot, and I am wondering if the movement from all of the flexing is causing the FBL unit to make unwanted corrections?

I attempted 3 take offs. The first time it started to roll to the left..., then it started tipping forward and finally it started to tip to the right.

All 3 times I hit throttle hold, and bottomed the collective pitch, just in the nick of time, before the blades hit the ground.

So, now I am scared to fly it, until I figure out what I am doing wrong, or what is set up incorrectly.

Any insight would be greatly appreciated. Thanks!

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08-09-2018 02:02 AM  73 days agoPost 2
utahbob

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St. George Utah

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You should go back to square one..check your bird out mechanically..make sure your v-bar is securely attached..go back through your setup of the v-bar on the computer and make sure everything is right and cautiously try hovering again.if it still acts up I'd suspect the fbl unit.

I do a great decending funnel!

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08-09-2018 02:24 AM  73 days agoPost 3
ICUR1-2

rrElite Veteran

Ottawa, Ontario

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Have you checked the swash to be sure it correct in the right direction.

spending time, paying attention

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08-09-2018 06:35 AM  73 days agoPost 4
heli4fun

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TRUMP, USA

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Yes,i'd make sure the fbl unit is correcting in the right direction.If you tilt the heli from tail in towards the left,the swash should counter act and tilt to the right,for elevator push nose forward and the swash should tilt back and visa versa.
If it's not,than you have to go back to your setup and reposition the fbl unit according to the manual.
On my Vbar Neo,which i have installed at the front of my heli I had the Neo positioned with the servo wires towards the front.When I checked to see if the Neo was correcting in the right direction,the swash plate was tilting in the same direction that i was tilting the heli.I went back to the setup,and noticed that i had installed the Neo incorrectly,the servo wires were to be facing the rear of the heli,after that the swash was tilting/correcting in the right direction.
Also,during spool up "Do not touch the cyclic" until you are off the ground.

Good luck

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08-09-2018 12:41 PM  73 days agoPost 5
Flyin for Jesus

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Troy, IL. 62294

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I have never had any cyclic issues while on the ground. I touch everything all the time. As soon as the blades start spinning, I consider that I'm flying and start doing what I need to do.
With dampers in the head. The disc can lean even though the skids are flat on the ground, all of that I correct while spooling up. Lifts off perfect everytime.

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08-09-2018 12:48 PM  73 days agoPost 6
ICUR1-2

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Ottawa, Ontario

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Flyin for Jesus
I touch everything all the time. As soon as the blades start spinning, I consider that I'm flying and start doing what I need to do.
+1
You can move your sticks as necessary to lift off.

spending time, paying attention

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08-09-2018 02:25 PM  73 days agoPost 7
youngbuck

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Maine

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Ya I've had similar issues so I went to lowes and got two pieces of 1/8 in h round rod steel about 24 inches long, I criss crossed them and put very small woffel balls on the ends. And then ziptied them to my skids. Now yes it does look silly but I'm still in the learning process even though I've been building helis for the past 7 years, I still stink at flying them. And this 6 dollar device has saved my 3,000 dollar heli atleast a handful of times on takeoffs and landings and once u get comfortable, cut the zip ties off and you will be good to go sir!

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08-09-2018 03:15 PM  73 days agoPost 8
Pistol Pete

rrProfessor

Seffner, FL

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Another option is to take off from grass versus concrete as such can potentially increase resonance.

~~Enjoying the hobby one flight at a time~~

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08-09-2018 03:27 PM  73 days agoPost 9
chopper37

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NJ and Long Island

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Just to make sure your on the correct model in the transmitter, I’ve seen it happen

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08-10-2018 02:18 AM  72 days agoPost 10
RM3

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Killeen, Texas - USA

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chopper37
Just to make sure your on the correct model in the transmitter, I’ve seen it happen
yup... done it myself. you learn real quick to check that after spending $200 in repairs on a heli that never left the ground...

showing a preference will only get you into trouble, 90% of everything is crap...

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08-10-2018 06:44 AM  72 days agoPost 11
R.J.

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SF bay area, CA USA

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Since it’s a gasser, make sure you have adequate vibration isolation for the FBL sensor with foam or gel pad.

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08-10-2018 02:08 PM  72 days agoPost 12
cudaboy_71

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sacramento, ca, u.s.

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since it is vbar, you have several tools at your disposal. If you're tethered to a computer, it's a little trickier. If you're NOT on Vcontrol--I suggest getting the bluetooth adapter (there is a DIY option for less than $10) so you can use the software from a safe distance--especially for the vibration tests which require the heli be spooled up.

1. as others have said, verify your sticks move the swash in the correct direction; make sure the FBL unit is compensating in the correct direction (opposite control surface deflection when you physically tip the airframe for both aileron and elevator)

2. go in to the software and there is a bar graph for each of the control surfaces sensors. when you physically tip the aircraft in elevator and aileron directions, the bar graphs should rise and fall according to your P and I values (P is the rising portion of the graph; I is the falling rate of the graph). I've actually had one of the gyro sensors begin to fail slowly, and the bar graph test showed me this...until the day that the aileron sensor failed to respond at all. In that case, it was time for a new sensor.

3. vibrations play hell on the sensors. I've had a bad rear bearing cause an erratic shake in the heli. While the rotor is spooled up (you need blades on--the issue may not be in the motor), open up the live vibration screen. In my experience, any significant vibrations above 50% on the vertical axis need to be addressed. Sometimes it can be masked with different types of mounting pads. Back on the old black vbar sensor days, I used the kyosho zeal tape on nitro to mask normal nitro vibrations. On the newer NEO unit the sensors are better and the stock gray tape has been working fine. In any case, the way to read the vibration log is by RPM on the horizontal axis. The frequency of the vibration is indicative of RPM, that is: If you have a vibration spike in the 13,000-18,000hz range, that's a motor issue (on a nitro); 1,500-2,200hz is main rotor; ~6,000-10,000hz will be tail rotor. Inspect and address issues accordingly.

if it ain't broke, break it.

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08-10-2018 02:31 PM  72 days agoPost 13
Ladymagic

rrKey Veteran

South Korea

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Do all other functions operate correctly after the rebind?

I think your best bet is to go through the setup process one last time. Check your gyro correction direction also...it could simply be reversed.

If that's not your issue, then I would look more to your mechanical setup; something may have been bent or gotten damaged after your forced auto incident...especially if it was a rather rough landing.

Mellisa

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08-10-2018 11:24 PM  71 days agoPost 14
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
/

I don't like vbar just above motor magnet ... Radio frecuency interference are there doing dangerous situations...

Take the main blades off... Start all over... Try to isolate servo by servo...

Run ferrite ring on ciclic servos ...

/

Saludos cordiales,

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08-11-2018 03:12 AM  71 days agoPost 15
OneHoof

rrApprentice

Cold Spring, Kentucky

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Thanks guys! I will check on those things.

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08-11-2018 03:13 AM  71 days agoPost 16
OneHoof

rrApprentice

Cold Spring, Kentucky

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I am also reading that it’s the generally accepted rule now that FBL's don't like being on the ground. "Light on the skids" is something you want to avoid. Let the heli spool up with slight negative to hold it down, then get right up in the air. The ground makes the fbl not know what to do, because if you move the sticks it will sense the input, but not the corresponding roll rates because of the ground.

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08-11-2018 03:15 AM  71 days agoPost 17
OneHoof

rrApprentice

Cold Spring, Kentucky

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I also read that With a FBL system, your input is ordering a rate of rotation around an axis. The control loop then controls the servos to achieve that rate of rotation. If the heli is on the ground, the heli can't rotate at all, so the control loop will try progressively harder to make the heli rotate. At lift-off/light skids, this can mean a very sudden response once the skids gets off the ground since the FBL system is trying to catch up.
This is of course a simplification, and I'm sure that the software in the controllers have some dirty tricks in order to try and mitigate this as much as possible.

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08-11-2018 03:19 AM  71 days agoPost 18
OneHoof

rrApprentice

Cold Spring, Kentucky

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In my research, I also read that FBL units do not like to be on the ground. The head gyro is like a heading hold tail gyro but with decay built in.
Heading hold tries to rigidly keep a direction (in the case of a rotor head a tilt or aileron and elevator) as the heli body attains the requested attitude the swash returns to level. However, this is not the whole story.
The feed forward sets the initial rate of the alteration, then the decay starts to eat it back. Decay is like the drift of a rate mode gyro (just a little slower). In short the FBL unit tries to act like a super accurate flybar, stabilizing you as quick as possible into an attitude, but with some give so if too much resistance it can normalize (like a regular physical flybar).
What does this all mean. for takeoff and landing:
If the heli starts to tip through blade lift, you can (and should) correct, but appropriately. A slight bit of negative collective on spoolup helps prevent lifting on one skid or another and you can see the rotor disk tilt to correct on ground (and prevent the control feedback loop that will cause a blade strike).
Once the rotor has takeoff speed, ideal to get both skids off the ground (no need to rocket it up), but trying to balance on one skid is generally not a good idea (unless you know what you are doing).
Similarly with landing. Negative collective once skid on ground is you friend. I ease to negative to slow rotor blades too (as long as power is off) as once you are on ground you normally want to stop and make heli safe. I usually mini-auto (TH at about 3 feet or less) and gently touch down with no power. This way a lot of blade speed is already gone when I touch down

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08-11-2018 03:29 AM  71 days agoPost 19
OneHoof

rrApprentice

Cold Spring, Kentucky

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Hmmm? I was trying to take off from grass, and in my opinion the plastic skid struts are too flimsy. I prefer the metal skids.

So, I guess it is possible with it sitting on the soft grass, and with the skid struts flexing and moving, the FBL control unit is attempting to correct these perceived movements, but because it is on the ground, it can’t.

I make slow, smooth takeoffs, and once it gets light on the skids, maybe its attempted corrections happen, causing it to want to flip over?

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08-11-2018 03:50 AM  71 days agoPost 20
Flyin for Jesus

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Troy, IL. 62294

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I have 6 helis with the NEO and no matter how rigid or flimsy the skids are, grass or concrete... none of my helis want to tip over.
Maybe shoot a video of what's going on. In the video show the swash correcting for movements. ( Blades not spinning, just hold the heli by hand and tilt it in all directions )

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HomeAircraftHelicopterHelicopter Main Discussion › My FBL heli acts like it wants to flip over upon takeoff!
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