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Servos that swing both ways!

An idle observation...

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The Wright Stuff20/08/2018 13:09:02
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Here's an unexpected find. I bought a Hobbyking powered glider with flaps, with each wing having two (presumably low cost) micro servos pre-installed. Two sets of Y-leads were supplied with the ARTF, one for ailerons and one for flaps. Upon closer inspection, both flap and aileron servos were mounted as mirror images of the corresponding servo in the other wing.

My heart sank at this point, since I was intending to use it with a mere 6 channel radio.

However, when I went ahead and plugged it all together, joy of joys, it all worked perfectly and in the correct sense.

Conclusion: the servos must have been installed as 'left' and 'right' handed versions. I wonder how it is economical to do this with cheap and cheerful servos, when the mainstream suppliers (e.g. HiTec) don't offer this (programmable servos excepted).

One could (cynically) say that it is a ruse to get the customer to buy 7 or 8 channel radio sets... ...hmmm!

Nigel R20/08/2018 13:30:30
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Probably quite feasible for HK to order a thousand 'lefties' in one go.

It's definitely DIYable on something you can get a soldering iron to.

http://www.glide.net.au/on-the-wing4/ServoReversing.pdf

Obviously the "easy" answer is lots of channels and a fancy TX...

Peter Miller20/08/2018 13:39:57
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In the old days (80s) sets came with four servos.one reversed.

Percy Verance20/08/2018 13:44:51
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Yes Peter, and if you needed more *reversed* servos you had to buy them. No servo reversing (or anything else fancy) on transmitters back then.......

Percy Verance20/08/2018 13:44:53
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Yes Peter, and if you needed more *reversed* servos you had to buy them. No servo reversing (or anything else fancy) on transmitters back then.......

My Flight LInk set had some little reversing widgets you could plug in between the servo and receiver, but these did move the servo neutral slightly.

Edited By Percy Verance on 20/08/2018 13:46:23

The Wright Stuff20/08/2018 13:52:51
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Posted by Peter Miller on 20/08/2018 13:39:57:

In the old days (80s) sets came with four servos.one reversed.

In a very slightly geeky kind of way: that's fascinating.

Edited By The Wright Stuff on 20/08/2018 13:58:50

Peter Christy20/08/2018 14:28:27
1018 forum posts
Posted by The Wright Stuff on 20/08/2018 13:52:51:
Posted by Peter Miller on 20/08/2018 13:39:57:

In the old days (80s) sets came with four servos.one reversed.

In a very slightly geeky kind of way: that's fascinating.

Edited By The Wright Stuff on 20/08/2018 13:58:50

Even better: The servos on my Bonner Digimite (c.1966) had linear outputs and were completely symmetrical. If you wanted to reverse a channel, you simply turned the servo through 180 degrees....!

Each servo was connected to the receiver by 7 wires, and was the size of a packet of 20 cigarettes! The receiver was the size of two ciggie packets strapped together! All up flying weight, along with the 7-cell NiCad to power it was around 2lbs!

And yes, it did have a failsafe!

--

Pete

 

Edited By Peter Christy on 20/08/2018 14:29:24

Edited By Peter Christy on 20/08/2018 14:30:00

Martin Harris20/08/2018 15:01:16
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Posted by The Wright Stuff on 20/08/2018 13:09:02:

Conclusion: the servos must have been installed as 'left' and 'right' handed versions. I wonder how it is economical to do this with cheap and cheerful servos, when the mainstream suppliers (e.g. HiTec) don't offer this (programmable servos excepted).

Might there be an electronic reverser installed in the aileron wiring? These would probably only cost the manufacturer a few pence yuan...

Percy Verance20/08/2018 17:03:36
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That was one of the advantages of linear servos. I bought several Multiplex ones prior to them being phased out. So useful at times..... they have the advantage of producing a completely direct push/pull, with no arc like rotary servos.

p1000065.jpg

p1000066.jpg

The brass screw in the case top could be used to centre the output arms if necessary.......

I can't for the life of me fathom why they stopped producing these. I have a Futaba example too......

Edited By Percy Verance on 20/08/2018 17:07:34

Tom Sharp 220/08/2018 17:31:21
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Skyleader used to sell them under their own name and under the Fleet name. You could remove the push/pull ratchet and use them with ordinary output arms.

Gordon Whitehead 120/08/2018 18:20:16
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I had the Fleet version. I swapped the linear outputs for rotary, not realising that there were no end stops and the rotary output arms could go a full 360 degrees. So if (or in the case of my Fleet radio, when) you lost the signal, the servo would rotate right round until pulled up by the pushrod. This happened one day at height with my lovely HB 61 powered Mick Reeves Fournier, when the servos all went to one end, the elevator being stuck on down. Naturally the plane was a write-off.

If one does wish to use a rotary output on this type of servo, the safe thing to do is cut off the lugs from the linear output racks so that they don't interfere with the output arms, and re-install the racks to act as end-stops. Then if the Rx loses the signal briefly, at least the servos have a chance of returning to normal service when the signal is resumed.

Gordon

Percy Verance20/08/2018 19:11:40
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SRC1's they were Tom. The servo top cases were user interchangeable, so you could use either output. You had to be wary of wear on the splines if you used the rotary outputs though. Once the little splined cone on the end of the output shaft had worn a bit, the servo output discs didn't grip the spines too well and could, with higher flight loads, slip round a bit.......

I still have a few SRC1's lying around........these came with my Skyleader Clubman. The Courier set I bought later - early 80's- had rotary output servos.

 

Edited By Percy Verance on 20/08/2018 19:15:37

Biggles' Elder Brother - Moderator20/08/2018 20:17:35
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More manufacturers are doing this now - Flightline do it in some of their models for example. Whether is a dedicated servo or some trickery in their "blue box" I don't know. Everything is done on Y-leads then.

BEB

BackinBlack20/08/2018 20:47:57
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Referring to the OP, the servos being mounted "mirror image" is quite standard and produces opposing movement for the same input signal via Y -lead. No trick servos here.

MaL20/08/2018 21:35:56
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Posted by BackinBlack on 20/08/2018 20:47:57:

Referring to the OP, the servos being mounted "mirror image" is quite standard and produces opposing movement for the same input signal via Y -lead. No trick servos here.

That is true for the ailerons..but not the flaps...

Biggles' Elder Brother - Moderator20/08/2018 21:39:40
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That works for the ailerons yes - just the arm on the other way round. But not for the flaps. If they are mounted mirror image (and nothing else is done) they won't work - or at least they will work, but as ailerons!

BEB

The Wright Stuff21/08/2018 08:20:43
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Exactly MaL, BEB. I could cope with the ailerons being on different channels, but I specifically wanted to Y-lead the flaps. In fact, with 6 channels, I have the option for both flaps and spoilerons, but that's in the future...

One assumes that it was cheaper to make the wing pockets mirror images and spend more on custom servos, than spend more on the wings and use the same servos. The laws of economics at work!

I can't seen any evidence of a servo reversal widget, but I did note that the 'odd one out' servo has a white signal wire instead of a yellow one... ...like I said, just an idle observation, really...

gangster21/08/2018 08:25:59
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Having come from the era of Futaba and sky leader (and others) supplying both direction servos I was a long time getting out of the habit. Transmitters had reversing switches but not dedicated memories. I saw too many people change models and forget to change the switch. I used reversed servos to ensure the aeleron and ele were the same on every model. This could easily be achieved without surgery to servos which became harder on later servos. Simply Futaba was the opposite sense to Samwa or Hitec so select accordingly. I kept that habit right into the model memory era only stopping recently

It may also be possible that the widgets that plug in line to reverse may still be available

Biggles' Elder Brother - Moderator21/08/2018 08:42:07
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Yes, you can still get servo-reversers. Sonmetimes they are the only practcal solution.

A friend of mine recently had this issue. He had two elevator servos in the tail of his Sbach, one of which was reversed. Easy with modern radio of course, just put the servos on two channels.

He wanted to test a new gyro he had bought - problem,...only one elevator channel on the gyro! The soltution he employed was to have just one elevator channel, use a Y-lead but put a servo reverser in one leg of the lead.

BEB

Martin Harris21/08/2018 10:35:00
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I don't think there's a convention on servo direction - Hitec ones often (always?) work in the opposite direction to Futaba for example. Perhaps the answer was as simple as a large batch of wings being produced with wrong handed mountings and it being cheaper to drop in alternative servos than remanufacture the wings or servo mounting plates?

A friend did once spend time and effort correcting an "error" on a Kyosho FW190's flap servo mounting, carefully removing and re-applying the printed covering after "correcting" the non-mirrored mount. He was rather upset when he burned out a flap servo which was valiantly trying to pull the flap into the wing as its Y leaded partner deployed. We pointed out the error of his ways and he elected to use a reverser rather than disturb the now neatly mirror imaged wing. This was fine until the day he reversed the servos connected to the Y lead incorporating the reverser and both of them tried to operate in the reverse direction, burning both out!

A one off of course - except that a couple of months later, a very experienced modeller (of advancing years) happened to mention the "stupid error" that Kyosho had made and proudly described how he'd just reversed the mounting on his example of the 190 which he was in the process of assembling.

Edited By Martin Harris on 21/08/2018 10:42:58

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