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Self Exciting Vibration


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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Thu Sep 13, 2012 11:53 am
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My latest clone 450SEV2, built mostly from spares, which I'm using to assess the viability of mounting a Telebee gyro as close as possible to the main shaft. OK it's an odd place to mount a gyro, but it doesn't seem to have suffered lack of authority as yet, but not been able to give it a good workout. Anyway, these Telebee gyros look like a pea on a drum on the back of the frame. This way it's under the canopy.



It had been exhibiting a medium frequency vibration at lift-off, tail wag up n down. Blade tracking was spot-on, so removed the main rotor head for strip-down and inspection, all OK, careful rebuild and balance checks. Refit head and blades and spooled up and the vibration began again.

Set it down and reconnected the battery and spooled up again this time there was glitch, shut down and connected test battery via the UBEC so as omit ESC, testing showed no sign of a glitch. Reconnected flight battery and spooled up again this time the motor hesitated and the pitch and aileron servos reacted as the receiver rebooted flicking the swashplate, and the heli flipped over on its side, luckily no damage.

The source of the problem turned out to be the connector to the UBEC. With only two pins in the male and female the connections were less firm than with three. Fitted new connectors with all three pins good snug fit, zip-tied to the frame and that solved the vibration problem.



It would seem that as the motor spooled up the connector began to vibrate and the intermittent continuity inducing a self exciting vibration.

Good thing it wasn't at any hight when this happened.
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admiral
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Joined: 20 Mar 2009
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Location: Brisbane, Australia

PostPosted: Thu Sep 13, 2012 6:49 pm
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Hi Burgess,

You obviously are very fussy with your builds with the amount of detail you go into, so I'm interested in what you are doing.

I would have thought by moving the Gyro closer to the axis point of the helicopter that you would be desensitizing the gyro by reducing the moment or distance it moves for any movement of the helicopter.

Is this the case or not, I set my helicopter up pretty much as everyone else does because they do, I'm always open to new ideas.
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tombo242
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Joined: 04 Nov 2008
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Thu Sep 13, 2012 8:07 pm
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admiral wrote:
I would have thought by moving the Gyro closer to the axis point of the helicopter that you would be desensitizing the gyro by reducing the moment or distance it moves for any movement of the helicopter.

Is this the case or not, I set my helicopter up pretty much as everyone else does because they do, I'm always open to new ideas.


It's the angle that the gyro moves through not the distance, mounting it as close to the mainshaft as possible makes good sense. (In a fixed wing it goes at/over the CG if possible.) Only problem I can see is that it is too close to the motor. It is recommended with 450 power to have a minimum of 100mm (~4") from the motor and ESC to the gyro. Seems unlikely that it meets this distance and could be subjected to electrical transmission interference. Lot depends on shielding of course.

Tom.
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Fri Sep 14, 2012 12:25 am
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Whilst the aim of this report was to highlight UBEC connection problems as a point to watch out for.

As you find this installation intriguing, I'll post a more detailed account in the Electric RC Helicopter General Discussion forum, as soon as I've written it up.

**************Edit*****************
See Gyro location and Response under General Discussion
*********************************

I feel the need, the need for a nice SUNNY DAY 'Razz' The green, green grass of home only gets that way because it rains and rains and....well you just get wet. When there's a change in the weather, it's usually a change of wind direction. 'Laughing'


Burgess


Last edited by Burgess on Sat Sep 22, 2012 5:47 pm; edited 1 time in total
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tombo242
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Joined: 04 Nov 2008
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Fri Sep 14, 2012 2:13 am
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Maybe you should come here, no rain in the Algarve since April and todays' temp 41ºC on my shade veranda. Standing in the field with the air temp well above blood heat and 90+ humidity does take it out of you.

Tom.
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Burgess
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PostPosted: Fri Sep 14, 2012 4:18 am
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Yeah...but I'm asthmatic now so don't fare well in prolonged heat or high humidity. It dose rain here, but then when the sun does shine this is a wonderful place to be, not too hot and not too cold. 'Wink'
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tombo242
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Fri Sep 14, 2012 4:47 am
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Well I spent some time at RAF Valley, Anglesey (Maes Awyr Môn now), summers were wet and warm, winters were wet and cold. The high spot of my time there was seeing the Northern Lights one winter night - absolutely wonderful.

Not an area I would chose for a beach holiday, but facinating local history if you look for it. I have been back once and the changes in Rhosneigr where I lived at the time had spoiled the old atmosphere of the village. I do not think that I will go back again. Best that the good times remain in memory.

Tom.
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Burgess
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PostPosted: Tue Sep 18, 2012 8:54 pm
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admiral wrote:
...I would have thought by moving the Gyro closer to the axis point of the helicopter that you would be desensitizing the gyro by reducing the moment or distance it moves for any movement of the helicopter....


On page 2 of the Telebee-GR302-AD.1.pdf manual states:-

"1. Find a position at or near the centre of mass of the R/C helicopter where there should be little vibration."

The Align REC-550 gyro is very similar if not identical gyro
It's manual has a similar statement:-

"Find a position at or near the centre of mass (main shaft) of the R/C helicopter. Make sure to avoid source of vibration, to eliminate any vibration from the tail and rotorhead."

------------------------
Tom,
Wet and warm in summer, wet and cold winter...now that sounds more like the beer.

Sun, sea sand and a Sea King from RAF Valley demonstrating excellent control during a rescue just over the road.


Just rescued the two in the foreground from the cliff.
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