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Old Jan 04, 2010, 06:39 PM
Registered User
mudville
Joined Nov 2002
952 Posts
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micro electromagnetic servo/actuator

Here is my idea for a micro sized servo/actuator with optional feedback.
I think that of these can be built that would match the performance
of the available smallest servos, which at this time is a .65 gram
servo that has 6mm throw with 10 grams of force.

Here is a link to that servo..which is a work or art no doubt ...

http://www.microflierradio.com/Actuators.html

My idea uses no motor, but a couple of magnetic coils, aided
by using iron cores to make the magnetic fields larger for each coil.

The coils push against a pair of magnets to move the arm.

The arm has a magnet on one end which moves across the linear
hall effect sensors in a slide by technique. The hall effect sensors
are really tiny

A couple of centering springs keep it centered so it could be used
without feedback.

It could possibly be modified to use one coil/core/spring/magnet...



The second image is a microcontroller circuit for it that uses
an cpu, hbridge, and 3 hall effect sensors. This is variant of
the other servo/actuator circuit I posted on another project.
the CPU could also be a PIC chip as well...
I posted a schematic for a PIC too, with a lot of slide by sensors..


Here is a link to some pre-wound small coils that are availble...

http://www.microflight.com/Online-Ca...t-Actuator-Kit

The weight of those is .07 grams each and each one comes with two
1.5mm x .5 mm magnets. The ID of the coils is 3 mm
I have a picture of it below.




This link and one of the photos shows some very small springs
used in model trains, but here are used as the centering springs.


http://www.toysperiod.com/kadee-235-...new-p-323.html



The hall effect sensors are approximately 2 x 3 mm
The hbridge is approximately 3 x 3 mm
The cpu is approximately 3 x 3 mm

I will have to weight this stuff to see what it totals out to...

http://www.rcgroups.com/forums/showp...5&postcount=18

http://www.rcgroups.com/forums/showt...mg#post5783302

are both links to stuff with weights of smd chips

Resistor 0402=0.6mg 0603=2.5mg 0805=5.5mg 1206=10mg
Capacitor xxpF/0805=5mg xF/0402=1.4mg xF/0603=6mg 10F/0603=7mg 10


C8051F300 P 0.024gm ... this is a 3x3x1 mm QFN11 part, which is the size of an a3901 bridge.
C8051F336 P 0.041gm ... this ia a 4x4x1 mm QFN20 part. A pic 16f690 is a comparable
PIC chip sizewise..

So as a guestimate,

A a1391 2x3x.75mm hall effect sensor weighs 2/3 * .024 gm*.75 == .012gm
A a3901 3x3x1mm hbridge weighs 1 * .024 gm*.75 == .018 gm
A xxxxx 4x4x1mm cpu weighs 1 * .041 gm == .041 gm
A xxxxx SC70-3 2n3904 transistor weighs 1 * .007 gm == .010 gm
A xxxxx SC70-5 voltage regulator weighs 1 * .007 gm == .010 gm
A xxxxx 0603 .1 uF cap or resistor weighs t 1 * .006 gm == .006 gm

SO lets take a guess here..
A 10mm detection range needs 5 hall effect sensors stacked side by side
5 sensors == .060gm
1 hbridge == .018gm
1 cpu == .041gm
1 xistor == .007gm
1 vreg == .007gm
15 0603 == .090gm
///////////////////////////////
total == .223gm

From this it seems tough the get a controller that will weight less than .223 gams, unless
doing the slide by technique is abandoned or the detection range is changed to 6mm
, saving from 2 to 4 sensors or about 024 to 048 mg
the min weight for a controller would be less than .200 grams in that case.
...Without a pcb...
Maybe the sensors can be epoxied together to become the "structure"
for the servo mechanics
.
.
.
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Last edited by shoutchen; Jan 18, 2010 at 02:27 PM. Reason: spellin, cipherin
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Old Jan 14, 2010, 07:58 PM
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AleG's Avatar
Bangkok
Joined Oct 2007
1,631 Posts
Oops!, wrong thread.

One idea I had some time ago about making lighter servos is to use a single driver circuit for 2 or 3 servos, one microcontroller receiving the commands from the receiver and one H bridge that could be multiplexed (somehow) to drive 2 or 3 motors. That should save some weight...
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Old Sep 05, 2012, 11:24 PM
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nemoskull's Avatar
United States, AZ, Yuma
Joined Sep 2009
2,749 Posts
i know this is real old but...

ive been poking around this for a while, mostly as an alternitive to super small servos. i want coil acts on my HK DSM2 rx.
im looking at an A1301 hall effect, a MCP1640 step up VR, and a small h-bridge. all run by an tiny13 micro controller. im hoping for 1g AUW and can work to a 20 gram plane.....
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