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Big Lama blade strike? Yes, inevitable!


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St Bosse
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PostPosted: Wed Sep 07, 2011 1:56 am
PostPost subject: Big Lama blade strike? Yes, inevitable!
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Was enjoying my Esky Big Lama in the park, already flying my second battery - late afternoon, light breeze. My finding is that the stick input from indoors to light breeze is from slight touch to quite severe, especially wind up.

Anyway, I was busy with a straight and level crosswind leg about 20m up when suddenly, "clack", blade strike! Sad The Lama came down like a stone and now looks as if a car drove over it. Replacement parts:- body, skids, all blades, chassis, both shafts, top blade holder. Luckily all electronics are still fine. Repair bill +/- $63 (parts) plus some TLC. Definitely now converting to the EXTENDED INNER SHAFT! (Read a lot about it but I now fully agree that it is a MUST!)

There is of course another interesting question about this incident.
1) Did the heli have a bird/bug strike Question - Didn't see anything (three of us were watching the heli)
2) Since co-axials have long shafts, they do tend to swing on the rotors with sudden movement such as a gust of wind. I did observe a couple of sudden pendulum swings while hovering. Could such a sudden jerk on the body have caused the blade strike Question
3) Or did the thermal fuse on one of the stock motors cut out due to overheating which I doubt because the speed was fast resulting in good cooling at that moment, also, moderate throttle. Also the heli was flying straight - no sudden rudder action occurred.

I always like to know why and what happened that caused the incident so as to gain knowledge and learn from the experience.

At this time, the three of us watching still can't figure out what caused the accident.

Any ideas Question


Last edited by St Bosse on Wed Sep 07, 2011 3:35 am; edited 2 times in total
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admiral
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PostPosted: Wed Sep 07, 2011 3:01 am
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Hi St Bosse,

My vote would go for a gust of wind causing it, you gave no control input, you did not see anything strike it, only leaves a mechanical failure or environmental influence. Probably no way to rule machanical failure in or out because of the damaged caused when it hit the ground, but I have noticed random gusts of wind hit my B400 or T450 that can cause the helicopter to suddenly lift several inches, that would probably be enough to cause a blade stike in a co-axial.
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tombo242
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PostPosted: Wed Sep 07, 2011 3:10 am
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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St Bosse wrote:
Since coaxials have long shafts, they do tend to swing on the rotors with sudden movement such as a gust of wind. I did observe a couple of sudden pendulum swings while hovering. Could such a sudden jerk on the body have caused the blade strike Question


I think that this is most likely. I have found that any sudden sharp corrections on the BL can cause a blade strike. I've reduced the Rate on mine to 80% which seems to help a lot, but of course you can't do that with the useless stock Tx. Mine is running with the Spektrum DX6i.

Tom.

Edit "Expo" should have read Rate. (Senior moment , I think!)


Last edited by tombo242 on Thu Sep 08, 2011 9:55 pm; edited 1 time in total
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St Bosse
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PostPosted: Wed Sep 07, 2011 3:21 am
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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tombo242 wrote:
...I've reduced the expo on mine to 80% which seems to help a lot,...


Yes, I agree with you on that. Definitely makes sense. I do that on my fixed wing planes as well.

At this point I am still trying to keep the heli budget low until the bug bites me good and solid. So for now, it'll have to be the stock Tx. Crying or Very sad
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St Bosse
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PostPosted: Wed Sep 07, 2011 3:31 am
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Keith,

I tend to also lean towards the wind issues. I think for now we can call it a "Force Majeure" incident. The wife will buy this excuse when it comes to the sudden rise in heli spares purchases. Wink
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Skyepuncher
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PostPosted: Wed Sep 07, 2011 4:10 am
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I say it was the wind, to. Coax`s don`t like it. I have had smaller
micro-coax`s blade-strike just by hustling around indoors, trying
to do banked turns, etc. The don`t like to be anything other than
level. That`s their nature. They have to fight themselves to move
in any direction. The wind only multiplies that battle. It beat
itself up.
Scott
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platinum
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PostPosted: Wed Sep 07, 2011 5:41 am
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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tombo242 wrote:
......
I think that this is most likely. I have found that any sudden sharp corrections on the BL can cause a blade strike. I've reduced the expo on mine to 80% which seems to help a lot, but of course you can't do that with the useless stock Tx. Mine is running with the Spektrum DX6i.
Tom.

I'v done with Tom's SETTING DUAL RATES (A Tombo production) since Jun 15, 2011.
http://www.electric-rc-helicopter.com/phpbb/viewtopic.php?t=4005&highlight=
Now I still flying my two BL with the stock shafts.
I really agree about the wind and flight characteristics.

platinum
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tombo242
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PostPosted: Thu Sep 08, 2011 7:56 pm
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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tombo242 wrote:
...I've reduced the expo on mine to 80% which seems to help a lot,...
Got to apologise here Folks (senior moment), that should read Rate not Expo. Embarassed

Currently:
For indoor I'm using +10% Expo and 85% Rate on Elevator & Aileron.
For outdoor or exciting indoor -20% Expo and 85% Rate on Elevator & Aileron.
Rudder is always 100% Rate and Inhibited Expo.

Tom.
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St Bosse
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PostPosted: Thu Sep 08, 2011 8:15 pm
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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tombo242 wrote:
...Got to apologise here Folks (senior moment), that should read Rate not Expo. Embarassed

Tom.


No need to apologise Tom Wink, I think we all know what you were trying to say. "Softening" the sticks around centre position is a good idea, thereby minimizing jerky flying.

Unfortunately, we with low or no heli budgets must make do with the stock Tx without those facilities. Confused
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tombo242
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PostPosted: Thu Sep 08, 2011 10:01 pm
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Well one cheap way of doing something similar on the stock gear would be to move your links a little closer to the servo pivots. That would give a similar softening 'expo' effect and reduce the 'rate'.

Of course, you could not switch to the faster functions for outdoor flying with a flick of the switch.

Tom.
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solentlife
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PostPosted: Thu Sep 08, 2011 11:15 pm
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tombo242 wrote:
Well one cheap way of doing something similar on the stock gear would be to move your links a little closer to the servo pivots. That would give a similar softening 'expo' effect and reduce the 'rate'.

Of course, you could not switch to the faster functions for outdoor flying with a flick of the switch.

Tom.


Doing that would only reduce proportionally ALL stick movement as in dual rate ... but would not give any EXPO at all.

Sorry to be nit-picky ... Wink
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St Bosse
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PostPosted: Fri Sep 09, 2011 1:26 am
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solentlife wrote:

Doing that would only reduce proportionally ALL stick movement as in dual rate ... but would not give any EXPO at all.

Sorry to be nit-picky ... Wink


mmmm Confused Not quite. Moving the push rods one or so hole closer to the servo shaft will have the following effect.

Tx = Same stick travel
Servo = Same arm travel
Servo > Swash plate push rod = less travel because of the shorter leverage activity due to the push rod being closer to servo shaft resulting in a smaller dia circle of travel.

Result: Same stick activity = softer jerks on the swash plate.

Of course the disadvantage is like everybody have mentioned, no quick reset to high movement. Sad

My personal opinion: Learn to not be jerky on the box.

My posting is based on the stock Tx that comes with the BL.
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St Bosse
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PostPosted: Fri Sep 09, 2011 1:38 am
PostPost subject: Re: Big Lama blade strike? Yes, inevitable!
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St Bosse wrote:
...3) Or did the thermal fuse on one of the stock motors cut-out due to overheating Question


This possibility as posted in my posting above, first posting, has since been disqualified.

After searching through the forums I came across a posting where the remedy for motor cut-outs was discussed. The trick being to remove the thermal fuse. After closer inspection to my own motors and a subsequent visit to my supplier, we've noticed that the thermal fuses are no longer installed.

Must say I think the whole principle was a bit stupid - saving a motor and killing a heli. Where is the logic? Shocked
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Skyepuncher
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PostPosted: Fri Sep 09, 2011 2:59 am
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I agree w/ Solentlife on the expo deal. Moving in one hole on the
servo arm does not provide expo. Your rate of movement is the
same throughout stick travel, regardless of the diameter if the
arc of the servo arm swing. You would still have to add expo
to lessen servo response around center stick. The only thing
you would be reducing is servo travel, not sensitivity.
It`s not the same animal.
Scott Wink
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platinum
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PostPosted: Fri Sep 09, 2011 11:59 am
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This illustration may help to get the idea. Rolling Eyes



platinum
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Last edited by platinum on Fri Sep 09, 2011 8:30 pm; edited 1 time in total
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