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HelicopterFlybarless Rotor Head SystemsV-Bar › Whipping Tail, even after much troubleshooting
12-20-2013 10:43 AM  3 years agoPost 21
Richardmid1

rrProfessor

Leeds, England

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Imagine my struggles with the prior 23T!
Actually the original 700E counter tail gear was 24T so 4.33 ratio which is even worse!

Don't use less pitch than maximum on an Align heli! Sure some other helis have ridiculous tail pitch throws if you go to the limits on the slider but not Aligns, you need to use as much as you can get.

As far as E vs. N tail holding the power delivery is very different, the E has much more torque and instantanious power trying to throw the tail around all over the place, the N is much more gentle on the tail plus those 50 extra rpm translate to an extra 236 rpm on the tail.

Im almost certain if you ran 1950 and the 21T tail gear your whipping problems will be gone.

60% of the time, it works every time!

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12-20-2013 09:00 PM  3 years agoPost 22
Sam2b

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Seattle, WA

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Test Flight 1

Yesterday I experimented with ~20% less tail blade pitch endpoints than before, and so far no whipping (knock on wood)! Thank you, Clarence.

Changes implemented:
  • servo horn linkage in to 15mm (from 17mm).
  • vbar tail defaults.
  • 80 tail common gain (down from 100).
  • 100,100 tail end points. (down from 120,120)
  • Auto trim hover for 60 seconds. (actually corrected with small left rudder input! Apparently had too much right thrust)
  • Optimizer hover with several left & right pirouettes. (result 48,41)
  • Disable optimizer.
  • Test fly with my wacky routine, trying to stress the tail.
  • same 22T torque tube gear (4.727:1 Ratio)
  • same 105mm blades.
  • same 1900 RPM head speed.
.
Would you believe (knock on wood) that one flight had no whipping or blow out? I was shocked to see. Clarence recommended this because he suspected the tail blades were actually stalling. The theory, at least, seems to show good signs so far with just one test flight. I tried to be more aggressive with each subsequent maneuver, but so far felt/looked pretty consistent how I would expect it to be, and no whipping or blow out. Now I'm getting excited.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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12-31-2013 03:16 AM  3 years agoPost 23
Sam2b

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Seattle, WA

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Update

I've reproduced the whip today. Please see the original thread below for details and pictures.

Original thread: http://www.vstabi.info/forum/read.php?26,107841

The maneuver performed is this within ~1 seconds.
1) Clockwise backwards inverted fast speed.
2) Sudden left rudder input (rotating counter clockwise)
3) Result: the left rudder input causes the tail to stick (or hesitate), and then whips left (counter clockwise).

As you will read in the original thread, the only thing I'm left to think is too much torque compensation, however I'm using the default values. I'm tempted to cut the values in half, or use a value of zero just to see what happens during this maneuver, and then test throughout other maneuvers and flights.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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12-31-2013 03:50 AM  3 years agoPost 24
knightofcarnage

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chicago

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I wondering if the motor you are using is dropping the RPMS too much under load.

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12-31-2013 03:52 AM  3 years agoPost 25
Sam2b

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Seattle, WA

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Thanks for the idea. I need to have someone finally video what I'm doing in the sky. I can tell you it's not bogging much at all, and the gov & motor powers through well, it seems. I know the bogging sound and I rarely do that to this machine. (the power line "bug zapper" video is probably the epitome of bogging! LOL)

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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01-01-2014 01:24 PM  3 years agoPost 26
Ronald Thomas

rrMaster

Gainesville, Fl, USA

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Any chance the tail servo is crapping out? The 251 is bulletproof usually so I wouldn't expect that but maybe a swap to see???

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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01-01-2014 07:43 PM  3 years agoPost 27
knightofcarnage

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chicago

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sam2b what head are you using on the 700E?

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01-02-2014 01:11 AM  3 years agoPost 28
Sam2b

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Seattle, WA

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Demonstration Video picture-in-picture

Thanks guys, I love these thoughts and suggestions.
  • Other than this exclusive issue, the tail servo is not exhibiting any other abnormalities. It performs well in all other maneuvers.
  • I'm using the Align 3G head (V1) with the taller shaft (not DFC). However I am using the DFC frames, and a 3rd bearing block. What is significant about the head in this situation?
Yesterday I made this video to demonstrate my actual whipping issue. Read the text description of the YouTube video for the time positions of interest. Then, please read my next post below with results after Rainer's suggestions, as well as two additional changes after this video.

Remember: this video had the following configuration:
  • 1900 head speed
  • 22T tail gear, 4.727:1 ratio
  • 115mm tail blades
  • zero Collective Dynamic on the gov
  • 100 left limit, 120 right limit
  • 100 common gain tail
  • 3 degrees of right thrust at servo center
  • 75 i gain
  • Precomp collective/cyclic 22/9, then 11/4, then 0/0.
  • CG not correct, tail heavy
Demonstration of the whipping problem:

Watch at YouTube

Disregard when I say "it seems normal to me." No, it's whipping all over. Almost every time you hear a large sudden bog in the motor, it is because of a whip as the gyro is trying to catch it with a sudden full right thrust.

The two videos are synchronized very closely ± 0.25 second (if at all). This video served to be awesomely educational in general, but very applicable to my problem. Finally I can stop scratching my head wondering what the heck is going on in the sky! I will be assembling more test flights like this for further tests and study.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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01-02-2014 01:13 AM  3 years agoPost 29
Sam2b

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Seattle, WA

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Today (after the video above) I had one more test flight with Rainer's two suggested changes:
1) Max physical limits for left/right pitch slider. (Bank#2)
2) Removed the long bolts (counter weights), and replaced with the stock short bolts on the tail grips.
3) Fixed the CG from being tail heavy.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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01-02-2014 11:05 AM  3 years agoPost 30
Richardmid1

rrProfessor

Leeds, England

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First time ive seen a tail pitch slider cam! Nice work!

Im not sure about whipping, it is obviously very hard to see in a video.

At 2:04 you said it whipped but you were coming quite fast and the motor loaded up quite a bit at the same time so any heli would whip under those circumstances.

What governor are you using? It certainly seems to be loading up quite a bit especially for a lowish HS like that. How much head room does the governor have?

60% of the time, it works every time!

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01-06-2014 12:38 AM  3 years agoPost 31
Sam2brrElite Veteran - Seattle, WA - My Posts: All  Forum  Topic

Final Result and Conclusion

Since I've done the following, the tail has greatly improved performance and feels very good while flying. The clicking is a broken tooth on my main gear, but I didn't have a spare, so I flew anyway. The previous test flights' whipping actually broke it.

Watch at YouTube

Results: Now I have confidence my tail will be where I put it and where I expect it to be in many fast speed maneuvers. However, while greatly improved, the optimal choice is to not input full left-rudder while traveling fast speed. I found if less/slower left-rudder is input, the gyro can do a better job keeping the rate of pirouette. In my own words, in high speed maneuvers, giving left-rudder is a self-induced blow out. That said, don't stop pursuing an optimal hardware setup, and do so by experimenting. I know first-hand what works and what does not work for my issue, and in the process I found what hardware setup works best (at least for me, and good chance for other pilots too). The proof is test during demanding maneuvers in flight, and tweak until it performs that way you want it to perform and the way you expect it to perform. My experimentation these last 2 weeks have taught me it is possible with diligence and patience.

Here's the combination that works for my heli and my flight style:
  • moved the ball in 10mm on the tail lever (but left the servo horn 15mm)
  • re-installed the counter weights on the grips (long 37mm bolts)
  • Vbar pitch slider physical limits: 90/112
  • Tail common gain 60, p gain 85, i gain 75
  • 115mm tail blades, 22T tail gear 4.727:1 ratio
  • 1900 RPM head speed 9.583:1 ratio (20% motor head room)
  • Futaba BLS251 @ 5v regulated (very consistent voltage with zero dips as per the VoltMagic device at over 1,000 samples per second)
  • CG adjusted from being tail heavy.
.

Note: yes, the 10mm adjustment is extreme, and may sound ridiculous. But it puts the vbar limit values within normal value range while enabling maximum physical limits for the pitch slider. The 10mm adjustment also has essentially sped up the servo in the process, but the mechanical disadvantage is not experienced because of the counter weights installed. I've also taken the time to balance parts to 0.01g of the tail grips, blades, bolts, nuts, and washers. The bolts also have the same length as well as the same weight.

This is a little more aggressive flight with the same configuration.

Watch at YouTube

Perhaps you have ideas or comments, all of which are welcome. For now I'm finally satisfied with the performance.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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08-17-2014 09:55 PM  3 years agoPost 32
Sam2b

rrElite Veteran

Seattle, WA

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battery placement and layout

Another thought and factor: battery placement and layout.

Some airframes have 2 6s packs lateral-parallel layout; more of a block of mass. That layout puts its placement further ahead of the CG, thus distributing more mass towards the nose.
Examples: Gaui 700 and XXtreme 700/800.

Similarly, some heli's have vertical-parallel stack layout with the 2 6s packs, one underneath the other; the same mass distribution on the x axis and z axis as the lateral-parallel layout.
Examples: Raptor G4, JR something.

More curious:
Other airframes have the 2 6s packs in series layout. Now this layout is more interesting to me because more mass is under CG (a good thing?), and less mass ahead of CG.
Examples: Trex 700e, many others.

So, that all said, my thoughts are the parallel layouts described above should have a worse advantage with pirouette whipping, etc. BUT, to its credit, it sure seems not to have a problem (both Gaui and Xxtreme) when I see very aggressive high-speed flight with left-rudder input. (I tend to have a nack for noticing these characteristics.)

Experience:
I've also flown a Gaui 700 and performed EXACTLY as I would expect: no whipping and just felt super locked with consistent pirouette with my typical routine flight, and with all that I could throw at it. So impressive, and made me start thinking of all the factors.

My correlation is compared to a nitro 700 size heli. I realize the overall weight is ~1.5 pounds lighter (680 grams), but [I would think] the mass distribution is also a factor too. My former 700n had a lower tail ratio rpm and was flawless in tail consistency (with Spartan tail gyro and JR tail servo, 5v). I had total confidence in the tail, and it would not could not whip or blow out even in very windy conditions, sea level, and excessive collective and cyclic. It was quite a feeling, and no exaggeration; I tested it in this way so I could rave as I do.

-->So then, given the same tail box and hardware setup and gyro:
1) Is it a matter of a heavier heli?
2) Is it a matter of different mass distribution?
3) Is it a matter of more power/torque surging to the rotors?
4) Is it a matter of tail ratios?
5) "Chinese" counter weights on the grips? (truly balanced to counter the wind force)
6) Other?

I'm thinking its more of #2. I wish I could thorough study the physics, laws, and formulas, and just test this with a controlled experiment. I really wonder if any of these points have been carefully considered when 3D heli designers create their airframes. (I hate to admit the reality that some tail gyros are truly better.)

Thanks for reading. I would love to hear your detailed in-depth responses on such an interesting topic! I don't hear anyone else really digging into this. Thanks.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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08-17-2014 11:38 PM  3 years agoPost 33
AWittleWabbit

rrElite Veteran

O.C., CA

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I thought I'd add some.

6) Profile area and distribution of.
7) Position of tail rotor to main rotor.
8) Actual tail rotor disc area and pitch range.
9) Main to tail gear ratio.
10) Would a high polar moment of inertia

I have but more but I need my caffeine for the day first.

It would be interesting to see line drawings of all the helis drawn on top of one another.

Great topic Sam.

Heli-itis sufferer.

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08-18-2014 01:38 AM  3 years agoPost 34
BobOD

rrElite Veteran

New York- USA

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At one point you mention that the whip happened during an aerobatic auto with no power. Have you been able to confirm this? This is a pretty important detail so you want to be absolutely certain.

You posted a flight log on the vstabi site. Do all your logs look anything like that. I wouldn't conclude anything with all the warnings going on there.

Team POP Secret

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08-18-2014 07:33 AM  3 years agoPost 35
Sam2b

rrElite Veteran

Seattle, WA

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@Bob
whip happened during an aerobatic auto with no power. Have you been able to confirm this?
Hi, Bob. No, I cannot confirm this because it has only happened once. I say the tail pirouette "whipped" during the aerobatic auto (low inverted auto roll/piro stuff) because the tail suddenly shot faster than usual with the usual given amount of left rudder. The even more odd part is, while not under power, there's virtually no torque to counter, so that can't be a factor (my strong guess).

If I had money to throw at this heli (aka: money pit), I would get a new tail servo, quite honestly. The servo seems fine on the work bench, and otherwise it holds the tail well without blowouts on normal 3D stuff and with speed. Further more, I'd like to even try another gyro for kicks and grins. I can swear I have the tail mechanical setup correct according to the several Vbar requirements. Me scratcha me heada.

I just cannot allocate time to fly like I used to for thoroughly working through these trials one by one, logging the performance, and trying other adjustments, and flying some more.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

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HelicopterFlybarless Rotor Head SystemsV-Bar › Whipping Tail, even after much troubleshooting
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