Instructables

Sub-Micro Continuous Rotation Servo Modification

Picture of Sub-Micro Continuous Rotation Servo Modification
The following steps will, despite their manufacturer's best efforts, demonstrate the modification of sub-micro servos for continuous rotation with position feedback. We leveraged this process for a 4 axis positioning system, but it may be useful in your other projects as well. Anyway, our build used the Hitec HS-55 servos, but other servos of similar size should also be modifiable with similar steps.  Note that if another type of servo is used for the aquarium project, the CAD models for the 3D printed parts may need to be changed as well. This was part of a project for the spring 2012 Things That Think class at CU Boulder.

Supplies:
    1 Hitec HS-55 sub-micro servo
    2 2.2K Ohm 1/8 Watt resistors
    Approx. 1 ft 30 AWG wire
    Knife
    Needle-nose pliers
    Soldering equipment 
    Wire cutters, wire strippers
    A lot of patience
 
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Step 1: Remove the Backside Casing

Picture of Remove the Backside Casing
On the back of the servo, remove the four easy to loose screws and the back cover, placing them safely to the side.  Note that these four screws hold on the front cover and gear train and, as such, care should be taken to make sure the front cover does not fall off.

Step 2: Remove the Frontside Casing

Picture of Remove the Frontside Casing
IMAG0336.jpg
Face the front of the servo upward and lift off the front cover to expose the gears.  After noting the arrangement of these small plastic pieces so that they can be re-assembled later, carefully remove the gears with tweezers, setting them in a safe location.  However, be sure to leave in place the brass gear attached to the motor shaft.

Step 3: Remove Upper Physical Stop

Picture of Remove Upper Physical Stop
On the inside of the front cover, at the top between the output hole and the top edge, there is a small plastic peg that prevents the output gear from turning all the way around.  Using diagonal cutters, a knife, sandpaper, or whatever works best for you, cut, scrape, or sand this peg down until it is level with the rim of the output hole.
ssrdi021 month ago

Its like

http://www.instructables.com/id/Servo-Feedback-Hack-free/?ALLSTEPS

. . . so use a similar arduino sketch. I do like this. Its a cheap way to create a controlled pivot.

Ugifer2 years ago
This is a great 'ible and looks like just the 'mod that I was looking for - thanks.

Can I check with you, however: How do you control the servo after the mod? I understand that you can read the 'pot to tell you the position of the shaft, which is great, but how to you make it turn one way or the other and stop when you reach your desired position?

Many thanks.

Ugi