micro electromagnetic servo/actuator - RC Groups
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This thread is privately moderated by shoutchen, who may elect to delete unwanted replies.
Jan 04, 2010, 07:39 PM
Registered User

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 ...


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...


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.


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...



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
Last edited by shoutchen; Jan 18, 2010 at 03:27 PM. Reason: spellin, cipherin
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Jan 14, 2010, 08:58 PM
Registered User
AleG's Avatar
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...
Sep 06, 2012, 12:24 AM
Pilot, Co-pilot, Navagator
nemoskull's Avatar
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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