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Old Dec 08, 2010, 10:57 AM
John Kim is offline
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Magnetic Induction Servo


Mi Servos finally hit the market!

Until now servos have always relied on a potentiometer, however 'Pots'
have always been the root cause of many issues in servos,
from poor accuracy to eventual failure from wear.

Now there is a new type of servo that uses a Magnetic Rotary Encoder
instea of the old-school potentiometer to control servo arm position.

from HobbyKing

http://www.hobbyking.com/hobbyking/s...14828&aff=8620

It is expensive. $30 in China.
Last edited by John Kim; Dec 08, 2010 at 11:08 AM.
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Old Dec 08, 2010, 11:45 AM
onewasp is offline
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We will see if these, there is more than the one manufacturer currently offering "potless" servos---JR for one, though not in the USA, grab hold this time.

Their predecessors by Kraft in 1968 with variable inductance, and another by
F&M at roughly the same time or perhaps a little earlier did not.

Time, as always, will tell.
Old Dec 08, 2010, 12:03 PM
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thread already started.
https://www.rcgroups.com/forums/show....php?t=1351600
The trick is to get them when in stock.
Old Dec 08, 2010, 12:18 PM
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Heathkit used varcaps on their servos. We had problems with them getting out of trim between cool dry days and hot humid days, but I don't know if that was pushrod expansion (Nyrod) or the servos themselves. Maybe I'll play with the old Heathkit and see if I can figure it out. It's been a loooong time!

Andy
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Old Dec 08, 2010, 01:04 PM
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HK's Magnetic Induction Servos - Not an Original Idea


Quote:
Originally Posted by John Kim View Post
Mi Servos finally hit the market!
Until now servos have always relied on a potentiometer, however 'Pots'
have always been the root cause of many issues in servos,
from poor accuracy to eventual failure from wear.Now there is a new type of servo that uses a Magnetic Rotary Encoder instea of the old-school potentiometer to control servo arm position.from HobbyKing
http://www.hobbyking.com/hobbyking/s...14828&aff=8620 It is expensive. $30 in China.
Not a new idea, yet another innovation copied from an existing product by a Chinese manufacturer.
From another group:
Well, the technology is out there. Hitec builds a magnetic encoder servo here:
HS-M7990TH Mega Torque HV Magnetic Encoder Servo
Whether or not this one is quality is to be seen. For the price, I would give it a shot for something small as it is a mini servo. Actually, the specs are pretty darn good if they are to be believed. I'm surprised that they didn't make a larger servo if they were going to use titanium gears. FWIW, I have had mixed results with HobbyKing sourced servos. The performance was good, but QC was sometimes lacking. YMMV."

Futaba 14mz and 12z use encoders not pots. They can go bad - I just had the aileron encoder replaced in my 14m (after 300hrs use...) Still they should offer better life and resolution. __IMAC ARD - Alberta"

Alan T.
Alan's Hobby, Model & RC FAQ Web Links
Old Dec 08, 2010, 01:05 PM
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The old Falcon micro servo has been pot less for years,it use a magnet and Hall effect transistor for feed back:
http://www.falconmodels.uk.com/acata...tion_page.html
Even the Fetmo (.8 gram) has that!
Old Dec 08, 2010, 04:23 PM
John Kim is offline
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This technology was tried many years ago in transmitters to replace the pots used in the control-stick assemblies but for various reasons, it never became mainstream.

Bruce
rcmodelreviews.com

Maybe, pots were economical and it has fairly long life.
My old transmitters never failed because of pots until they became obsolete and discarded.
Last edited by John Kim; Dec 16, 2010 at 11:20 AM.
Old Dec 08, 2010, 05:07 PM
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I built a kit for servos that used a coil with a metal center that moved with servo arm position to very the inductance of the coil. It worked quite well but was quite expensive and somewhat susceptible to the effects of vibration.
Old Dec 15, 2010, 12:19 PM
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The Futaba "encoder" IS A POT! It's just a fancy word for a pot. I replaced the pots in my 12Z. They are $1.23 each from DigiKey. These "encoders" don't last long. Seems like the old AB pots lasted forever but maybe we didn't fly that much back then.

My question has always been: "What happens if the 100 AMP motor wire runs near the servo in your e-model ?"

I may buy one of these and play with it:

http://search.digikey.com/scripts/Dk...me=490-4635-ND

It looks suspiciously like the prototype picture of the Hitec 7990 that was posted.
Last edited by Four Stroker; Dec 15, 2010 at 12:29 PM.
Old Dec 16, 2010, 12:07 AM
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Both of my telescopes use dual optical encoders. This gives them insane resolution and precision pointing every time. There are two IR LED's and two IR receivers that sit in front of the encoder mask and encoder wheel. One of the reasons they use two is to determine the direction the gearbox is running.

Why not just incorporate similar features in servos? ---- Other than price. I know potentiometers are very inexpensive, but a hall effect sensor's envelope is in my opinion too narrow. What about outside magnetic fields as mentioned previously?
Old Dec 16, 2010, 03:12 AM
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Manufacturer specs found elsewhere on net are:
> "zero dead zone" less than 0.001ms dead zone
> "zero error" travel accuracy
> "zero error" centering accuracy
> all-digital circuit processing
> 360 degree output gear (2BB Rotation 1BB)
> Coreless motor
> Copper/Titanium/Aluminum alloy gear tooth(most aluminum's have ti in them naturally)
> O-type rubber ring, for shock, dust, and oil.
> J-Plugs.

- OFFICIAL MI PRODUCTS HERE: http://www.ltair.com/en/productlist.php?intClassID=50
- MORE CHINESE PRICES HERE: http://shop63239329.taobao.com/?sear...&queryType=cat
Last edited by Mikarro; Dec 16, 2010 at 04:11 AM.


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