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Unbalanced elevator and aileron pitch


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sbobby
Extreme 3D
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Joined: 07 Nov 2009
Posts: 115
Location: Melbourne, Australia

PostPosted: Sun Aug 25, 2013 5:38 am
PostPost subject: Unbalanced elevator and aileron pitch
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I have a HK450 V2 (clone from TRex 450 V2). Its aileron pitch is unbalanced +5 -7 and elevator is +8 -5.
Need some expert advice on what causes the unbalance and to get rid of them.
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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: Sun Aug 25, 2013 4:20 pm
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Hi Sbobby,

This is called 'interaction'. All servos of the same make and pattern are very slightly different in their response to input. Level swash at mid-stick is only the start. After completing the midstick zeroing you then need to check for level swash at high and low stick. The collective is rarely completely level throughout its travel and must be for a stable hover. Any slight tilt (called an interaction) will cause the heli to drift in that direction.

Once the head is level throughout its travel we start on your problem:
These differeing values must be levelled out with the "Programmable Mix" settings.
DX6i 'Adjust List' #9 & #10 or whatever your Tx has.
(It is only necessary to set one of the blades for each mix and do not let the flybar move while making these adjustments.)

Set Blades @ 90º to the fuse (flybar in line with fuse and level).
Set Mix 1 to always ON, and now mix Elevator with Elevator,
on the Rate Down (hold the stick full forward) increase the value
until you have -7º.
Now hold the stick hard back and adjust the Rate Up until you have +7º.

Main blades in line with the fuse (flybar @ 90º to fuse and level).
Select Mix 2 and set that to ON, and mix Aileron with Aileron.
Holding the stick hard to one side then the other adjust the mix
until you have -7º and +7º in aileron.

These settings will over ride the limits set in the "Travel Adjust" for the cyclic only
and will have no effect on the collective pitch settings.

Tom.
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sbobby
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Joined: 07 Nov 2009
Posts: 115
Location: Melbourne, Australia

PostPosted: Tue Aug 27, 2013 12:49 pm
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Thanks tombo. It's brilliant ideas to use mixing aileron with aileron and elevator with elevator.
I can understand mixing between throttle and rudder but mixing with themselves, I am not sure. Just wondering whether the stick response curve under the mixing (themselves) is still linear or not.
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Tue Aug 27, 2013 7:36 pm
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Why not program in the mixing settings and then take pitch angle readings for each pitch-curve percentage-point, and generate a graph from a spreadsheet. Also, a spreadsheet with data from readings taken for Pitch, Throttle, Volts, Amps, and watts, makes a good tool for fine tuning an electric heli.

Burgess
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tombo242
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Tue Aug 27, 2013 11:20 pm
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Hi Sbobby,

As you are setting the values to counter interaction the servos should give a more linear response than without this mixing. However, I must admit that I have never checked for linear response. It does fly better though and that was all I was ever interested in.

Just one point that I left out, you must view the heli from the left (port) side when setting the elevator and nose in towards you for aileron. Otherwise the +ve & -ve values will appear reversed.

Burgess, that's a great idea, very handy for future reference.

Tom.
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Burgess
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Location: Wales

PostPosted: Mon Sep 09, 2013 12:41 am
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The extent of any interaction, in the first instance, depends on servo response resolution.

Test by using one cyclic channel this provides some degree of control, and any variables will then be confined to the servos.
Set the sub-trim to zero and both end point travel adjustments to 100%
Now using the sub-trim, count the number of clicks needed for the servo output arm to move above and then below the centre position. Do likewise for all three cyclic servos. Ideally all three should be identical, if there is any miss-match, use the two servos with closest matching responses for Aileron and Pitch, that way deflections to port or starboard should centre. With the response of each servo now known, test the reaction with the other two cyclic channels, and if needs be match servos to channels. With a bit of luck they will move in unison.
OK, so it takes time...well these days I don't have to be anywhere in a rush.


Analog servos tend to exhibit more disparity of movement than digital servos doo.
Some time back the spec for Hextronik HXT900 servos changed and they began exhibiting more cogging than previously, consequently excessive interaction.
I tried a set of Hobbyking HKSCM9-6 Singlechip Digital Micro Servos
Spec.
Torque: 1.4kg @ 4.8v, 1.6kg @ 6v
Weight: 10g
Speed: 0.09/60deg @ 4.8v, 0.07/60deg @ 6v
Voltage: 4.8v~6v
Plug: JR
At a Hobbyking price of AU3.26 = GBP1.97 they're great value, especially when funds are limited.

The difference was amassing very smooth and little or no interaction. I'm using Flasher T6EH-M 2.4ghz 6channel radio gear, it does not have the channel mixing function like the Spectrum DX6i; consequently the need for matching servo responses is more critical.

Here's the end point adjustment settings for my three T-rex 450SEV2s

Aileron.....105/ 105%
Elevator...105/ 105%
Pitch........105/ 105%

Aileron.....102/ 102%
Elevator... 97/ 97%
Pitch........102/ 102%

Aileron.....100/ 100%
Elevator...100/ 95%
Pitch........100/ 102%


Burgess
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mariamunir
Charging
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Joined: 08 Jan 2015
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PostPosted: Thu Jan 08, 2015 4:40 pm
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Someone mentioned this before. i think it is spot on.
RC heli is the most difficult to fly well. Then RC airplane. Then RC cars/trucks?




_____________
Princy
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Shaun96
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Joined: 07 Jan 2015
Posts: 29
Location: San Fransisco

PostPosted: Fri Jan 09, 2015 1:50 pm
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mariamunir wrote:
Someone mentioned this before. i think it is spot on.
RC heli is the most difficult to fly well. Then RC airplane. Then RC cars/trucks?




_____________
Princy


rc helis and rc planes are difficult coz landings and take offs are involved, while in rc car/truck are easy coz they remain on ground
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