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Here is Hitec HS-55 sub micro servo. This little devil
(89"x .45"x .94")
has torque 18 oz. in. when powered from 6V and it weights only 0.28 oz.
!
HS-55 is an economy version of HS-50 |
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Just four screws release the whole mystery. On top we
have cover, which hides gears. Then the main part: motor, gears, and
the circuit, then the bottom cover. |
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Let's first remove the gears. Of course it is
important to remember how they were installed! Hopefully this
picture will help. |
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Use a clean surface to temporarily store the gears.
Carefully put the gears in the order they were installed.
Important thing is a servo grease. Handling the gears will remove
most of the grease, which should be replaced. According to Hitec for
servos "use only silicon based servo grease. Using other
type of grease not intended for servo gears may produce gas when used in
sealed cases, which may coat nasty film on the motor brush that could stop
the servo operation." |
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The potentiometer plays very important role in servo's
mechanical construction. It is a shaft for the final gear. Only one screw holds the potentiometer...
Unsolder the potentiometer from the circuit and remove the three
potentiometer wires. |
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The servo position is controlled using a
potentiometer. The role of the potentiometer is to send a feedback
information about the arm position. In our case we won't need this
information. Besides the potentiometer doesn't allow the servo to turn around and it
requires some modification. See the black piece of plastic on the
left side. |
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Using thin soldering gun we melted the plastic and cleaned
everything up. One more thing will prevent the potentiometer from
smooth turning: contacts. They must be removed too. See the
small piece of metal on the right side: this is already bent and pulled up
contact, which must be removed |
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One more thing: the cover has another piece of plastic
limiting the movement. See the left side of the central hole.
It must be removed too... |
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And now the most exciting thing: cheating the circuit!
The potentiometer is approximately 5k ohm. We have to provide two
identical resistors to replace the potentiometer with similar total
value. Luckily this is not very critical thing and as you can
recognize we used 2x 6k8 resistors. |
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Two 0.125W resistors connected together with one of the
contacts are soldered to the circuit. They look gigantic but it is
easier to solder pieces of this size than the ones suitable for
surface mounting. As you can see from the background ruled paper the
circuit size is only 0.4" |
