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Flap Servo Set Up

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G-JIMG18/06/2018 12:18:01
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74 forum posts
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Although I've built, and flown, many models in the past, the current build is the first with Flaps.

I'm using torque tubes connected to a single Servo arm, so movement of the arm moves both Flaps in unison.

What's the best way to set the Servo?

1. Set the Servo against the stops in the Flaps Up position and have all the drive available for deployment.

2. Set the Servo so it's nearly against the stops in the Flaps Up position so there's 'room for adjustment'.

Or, doesn't it matter?

Jim G

Don Fry18/06/2018 12:49:14
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3724 forum posts
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2. Does the job.

You might consider using one servo for each flap, so when you set up the system you have a precise adjustment facility available for each servo.

Geoff Peacock18/06/2018 12:54:49
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209 forum posts
68 photos

On plugging the servo into the flap channel on my Sanwa rx, the servo immediately goes to full extent of travel in one direct, giving full travel the other way. Yours might do this. You may have to reverse travel direction at the tx.

Biggles' Elder Brother - Moderator18/06/2018 13:07:56
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Flaps are always a bit of a headache to set up, they very rarely in my experience need full servo throw - often considerably less.

The way I often do it is this:

1. Set the servos to centre with a servo checker and place the arm on tilted towards the flap by about 30 degrees. Set the flap linkage so that servo centre is flaps up - flush with the wing.

2. Set up your Tx with a very small servo movement - 10-20%

3. Disconnect the linkages - that way if the servo is going the wrong way it won't strain the hinges.

4. Try that out, make any servo reversals necessary.

5. Start a trial and error process increasing the percentage throw until you get the settings you want.

Now you might be thinking "What a waste of servo movement and control resolution - he's only using half the throw" Well yes, that's true, but in my defence I would cite the following - firstly, you usually only need about half the throw on a flap anyway so it doesn't really matter where the half comes from; secondly, its easy to align; thirdly deploying flaps is not a high resolution activity - they are "off", "half-on" or "all-on" just three descrete positions, you don't need high resolution for that!

Hope this helps a bit

BEB

Edited By Biggles' Elder Brother - Moderator on 18/06/2018 13:09:05

Simon Chaddock18/06/2018 13:14:22
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5405 forum posts
2824 photos

Setting the servo against the flap up stops could be a problem as when switched on as the servo can travel to full (110%) deflection which would mean the servo could be 'stalled' against the flap stops..

Rather safer to just rely on the flap servo travel (it can be adjusted from the transmitter) to set the flap limits, both up and down.

A 'stalled' servo will always sooner or later lead to trouble.wink 2

G-JIMG18/06/2018 14:38:04
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74 forum posts
9 photos

Thanks guys, all useful stuff.

I'll set it up as BEB suggests and take it from there.

Jim G

G-JIMG18/06/2018 14:43:47
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74 forum posts
9 photos

Just had a thought ...........................

I've never used Flaps before, is it usual to mix in Elevator? If so, how much as a starting point?

Jim G

Denis Watkins18/06/2018 14:48:28
3728 forum posts
177 photos

I doubt you can premix Jim, without flying it first, you may go the wrong way

Get your speed way down, then deploy the flaps, usually the model then settles to a nice landing speed

Of course if it balloons up, consider some down

But often ballooning comes with traveling too fast with them down

Biggles' Elder Brother - Moderator18/06/2018 14:50:42
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15748 forum posts
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I usually start without any elevator mixed in, not all models need it, especially if you can slow the flap deployment so they don't just snap down!

Try no elevator compensation, at safe height, see what happens. Remember to try at different thottle settings too, often throttling back a bit, then bringing in the flaps helps. Often people put the flaps down with the model going too fast. If it does balloon a bit on you land, put in 5% elevator mix and try again. See what that's like etc.

BEB

Biggles' Elder Brother - Moderator18/06/2018 14:51:34
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15748 forum posts
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Denis and I on the same wavelength!

BEB

G-JIMG18/06/2018 15:37:19
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74 forum posts
9 photos

Many thanks.

Jim G

Geoff Peacock18/06/2018 16:15:34
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209 forum posts
68 photos
Posted by Biggles' Elder Brother - Moderator on 18/06/2018 13:07:56:

Flaps are always a bit of a headache to set up, they very rarely in my experience need full servo throw - often considerably less.

The way I often do it is this:

1. Set the servos to centre with a servo checker and place the arm on tilted towards the flap by about 30 degrees. Set the flap linkage so that servo centre is flaps up - flush with the wing.

2. Set up your Tx with a very small servo movement - 10-20%

3. Disconnect the linkages - that way if the servo is going the wrong way it won't strain the hinges.

4. Try that out, make any servo reversals necessary.

5. Start a trial and error process increasing the percentage throw until you get the settings you want.

Now you might be thinking "What a waste of servo movement and control resolution - he's only using half the throw" Well yes, that's true, but in my defence I would cite the following - firstly, you usually only need about half the throw on a flap anyway so it doesn't really matter where the half comes from; secondly, its easy to align; thirdly deploying flaps is not a high resolution activity - they are "off", "half-on" or "all-on" just three descrete positions, you don't need high resolution for that!

Hope this helps a bit

BEB

Edited By Biggles' Elder Brother - Moderator on 18/06/2018 13:09:05

Perhaps this might help:
my DH Beaver uses 15 deg down for take-off and 45 deg down for landing - set up just as the full size aircraft. I achieved the 'full flap down' (45 deg) by setting the servo and flap horns by trial and error. I also use a servo slow in the circuit - very realistic.

High wing models are apparently the ones which most need a little down elevator mixing in, although mine has none (possibly helped by the servo slow), but as BEB and Dennis say, they're all different, so you'll most likely have to 'suck it and see". Hope this helps.

Don Fry18/06/2018 16:38:29
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3724 forum posts
42 photos

BEB has a point about being a pain to set up. I have in the past done an off plane mockup, to get the geometry sorted before committing to the wing itself.

robert chamberlain26/01/2019 03:06:53
117 forum posts

Is there a device to slow down the flap extend/retract time to make it more realistic ? I can not do this from my transmitter. Bob C in Kansas

Broken Prop26/01/2019 06:23:17
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590 forum posts
1 photos

Hi Bob

Model Radio Workshop in the UK do a nice servo slow. Go to www.modelradioworkshop.co.uk

Pete

Don Fry26/01/2019 07:39:57
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3724 forum posts
42 photos

Hobby king do one as well, SKU TSSR-3

John Duncker26/01/2019 14:18:28
79 forum posts
7 photos

If you are setting up flaps on a larger faster model and are using 2 or more servos then you do want to over spec the servos used and digital is my preferred servo type.You also want to think about the 'mechanical advantage' you can gain by using the full travel of a servo.

Having one side of a flap command blow back while the other is fully deployed is a BAAAAD thing to have happen.

Not so likely on a slow high winger but a REAL possibility on a 20 lb Starfighter.

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