Topic: Servo centred - not! (Read 10526 times)

SailorGreg · « **on:** February 20, 2015, 05:33:07 pm »

Why is it that when a servo is centred (with a servo tester), it seems impossible to install the arm exactly in line/at 90 degrees to the servo axis? The serrations on every servo I have forces me to offset the arm slightly so there is a little more travel on one side than there is on the other. In the grand scheme of things, I guess this doesn't matter all that much, but it offends my sense of symmetry!

And it would be nice to have the same throw on the rudder each side.

Or am I doing something wrong?

Greg

Umi_Ryuzuki · « **Reply #1 on:** February 20, 2015, 06:01:14 pm »

I think that is why the control rods have the "threaded thingy" on one end or the other.

flashtwo · « **Reply #2 on:** February 20, 2015, 06:03:29 pm »

Hi Greg,

I've had this problem with rudder alignment and it is because there are (if I remember correctly) 22 splines , i.e. 360/22 =16degrees - and that's the best mechanical resolution you can get without adjusting the servo signal.

Ian

inertia · « **Reply #3 on:** February 20, 2015, 06:17:38 pm »

Greg
These things are sent to annoy us. I would recommend an evening either re-arranging your cutlery drawer or watching a boxed set of Bagpuss. You'll feel better..................

Dave M (with sympathy)

Netleyned · « **Reply #4 on:** February 20, 2015, 06:21:51 pm »

Use the misalignment to counteract the paddle wheel effect of the
propeller simples
I see DM has been thrown out of the pub and is back on here

Ned

Martin (Admin) · « **Reply #5 on:** February 20, 2015, 06:32:11 pm »

Accoms servo arms used to ~~efferent~~ different if turned 180o and would also supply two set at with different angles... ah, the good old days.

inertia · « **Reply #6 on:** February 20, 2015, 07:02:09 pm »

Quote from: Martin (Admin) on February 20, 2015, 06:32:11 pm

Accoms servo arms used to efferent if turned 180o and would also supply two set at with different angles... ah, the good old days.

So who's been in the pub???? "Efferent" = fizzy cleaner for dentures?
Bagpuss just has to be better than wall-to-wall Eastenders...............
DM

mrlownotes · « **Reply #7 on:** February 20, 2015, 07:16:53 pm »

Just turn the servo a little bit. Might look a bit skew-wiff but the arm will be perpendicular to the control rod. The travel will be the same both ways. The body position of the servo is only relative to whatever you like.
Simples.

GAZOU · « **Reply #8 on:** February 20, 2015, 08:24:09 pm »

It seems to me that on radios we can adjust the neutral ..............

And possibility of adjusting the trim

Fastfaz · « **Reply #9 on:** February 20, 2015, 08:31:05 pm »

Why not use a connector (tiller arm end) that has a grub screw connector so that you can slide the rod through to align the servo arm and rudder arm parallel. Alternatively cut off a piece of a block connectors remove the nylon and use two pieces of rod side by side loads of adjustment. Hope this helps.
Cheers,
Peter.

malcolmfrary · « **Reply #10 on:** February 21, 2015, 06:30:39 pm »

Most of the 4 way servo arms that I have seen have not had the arms at right angles to each other, so a bit of retrying should wind up with at least one with almost no error. Then again, I have never worried about this very much. Unless the superstructure and hull are perfectly matched and present a symmetrical area fore and aft of the center, whenever a side wind happens, its going to wander off anyway.

plug · « **Reply #11 on:** February 21, 2015, 08:41:57 pm »

Martin, always brings a bit of a wry smile when I hear that expression...... ( ah, the good old days. )......, polio, rickets and the odd dose of the black death, aye they were the good old days alright

regards Jack.

SailorGreg · « **Reply #12 on:** February 21, 2015, 10:51:16 pm »

Thanks for all the comments. I guess the actual answer is some gentle surgery on the servo arm if I get really picky!

Greg

tigertiger · « **Reply #13 on:** February 22, 2015, 03:46:21 am »

Is it important to have the servo centred - not!

Does your TX have a trim button?
If not, the easiest solution has been given twice already, use the threaded adjuster on the push rod. To get the rudder square to the bow in the neutral position.

From my limited experience, I find when sailing that the boat never runs a true line, as so many things can effect the course, and I am constantly adjusting the rudder setting.

inertia · « **Reply #14 on:** February 22, 2015, 11:22:36 am »

I think the problem is that instead of the disc looking like A (with the servo centred using a servo tester), it looks like either B or C. The amount of differential movement introduced would be very small indeed but, if it bothers you or offends your sense of symmetry, just use the trim on the Tx to shift the neutral setting to 'A'. After all, the servo neither knows nor cares whether it's seeing a signal of 1.52mS or 1.49mS at neutral. There may be a corresponding small difference in maximum throw each way but who pushes the Tx stick all the way anyway (unless it's the throttle)?
If it's any consolation it's always annoyed me, too!
Dave M

SailorGreg · « **Reply #15 on:** February 23, 2015, 07:52:37 am »

Yes, it's mostly - well, entirely - just a silly personal desire to have everything neat and tidy. I'm not OCD, honest!

And yes, sometimes I do put the rudder hard over, normally when I realise that I'm heading at another boat or the bank while nattering to a fellow boater or gazing idly into the middle distance.......

Greg

Gazza · « **Reply #16 on:** March 29, 2015, 03:05:14 pm »

If you Buy a computer type TX ( spectrum dx6 ...7 or 8 etc. go into Menu and use the SUB trim

SailorGreg · « **Reply #17 on:** March 29, 2015, 04:08:10 pm »

er...... "buy"? Doesn't that involve spending money?

grasshopper · « **Reply #18 on:** March 29, 2015, 05:02:55 pm »

How many can remember when servos had square output shafts and didn't have the luxury of splines giving you 16' adjustment, it was 90' or nowt....and no such thing as reversing switches so you had to plan your linkages ahead....

In fact, I can remember having to wind up the rubber band for the escapement, then banging that button to get a turn in the required direction.

Eee, these kids nowadays don't know they're born..

ballastanksian · « **Reply #19 on:** April 27, 2015, 10:16:16 pm »

Rubber band? That were luxury. I remember having to tension a sapling against a stone in the hull and hope the rudder post did not fall off when the flour paste got soggy

For idiots like me who also twist the occasional servo cos they are a fidget fingers, you can get llittle electronic center gadgets. I don't know if one would help you adjust the servo to make it neat?

essex2visuvesi · « **Reply #20 on:** April 27, 2015, 10:25:24 pm »

Quote from: ballastanksian on April 27, 2015, 10:16:16 pm

Rubber band? That were luxury. I remember having to tension a sapling against a stone in the hull and hope the rudder post did not fall off when the flour paste got soggy

For idiots like me who also twist the occasional servo cos they are a fidget fingers, you can get llittle electronic center gadgets. I don't know if one would help you adjust the servo to make it neat?

https://www.youtube.com/watch?v=VKHFZBUTA4k

Well someone had to

inertia · « **Reply #21 on:** April 27, 2015, 11:20:28 pm »

Strewth! When that version were first on TV we were livin' in a hole in t'road on t'other side of 'uddersfield, eatin' cold gravel from a sweaty sock and workin' eighty 'ours a day fer an IOU....................

I recognised all four of them straight off. That must make me either very old, very sad - or both.
AND I remember square output shafts on servos AND either Red or Black labels for opposite rotation AND linear output servos ...........you try tellin' 'em that these days!

Yer don't know yer born, you lot.

DM

essex2visuvesi · « **Reply #22 on:** April 27, 2015, 11:30:31 pm »

I remember my uncle used to have on of these bad boys

tsenecal · « **Reply #23 on:** April 28, 2015, 04:05:20 am »

I can remember when the futaba servos were either red label or black label...

RAAArtyGunner · « **Reply #24 on:** April 28, 2015, 08:45:44 am »

Quote from: tsenecal on April 28, 2015, 04:05:20 am

I can remember when the futaba servos were either red label or black label...

Wasn't that Johnnie Walker

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Author Topic: Servo centred - not! (Read 10526 times)

inertia

inertia

plug

inertia

inertia