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Picture of Tower Pro SG 90 Micro Servo Hack
Hi there! This instructable contains the comprehensive instructions of how you can hack a tower pro SG 90 micro servo for continuous rotation. 

Why?

Micro servos can be used as robot wheels and are more convenient for such applications. This is due to the fact that micro servos have a certain figure that helps you attach it to a robot chassis or what not. PLUS: It has that cute but not irritating sound that makes it really nice to be used on cute but reliable robots.

Micro servos usually have a maximum rotation of 180 degrees and a dc motor on the other hand has continuous rotation.

REMINDER:

Before proceeding to this tutorial, make sure you have extra money because you might do this wrong if you're doing it for the first time. But nevertheless, since I am going to guide you to this process, I just wish you good luck and I hope you're money gets spent for a cause.

I am also not held responsible for whatever happens to your servo and it is really hard to put everything back the way it is once you've done this hack. (Yeah, I've tried it out and luckily I got the servo back to normal)

ALSO, TAKE A SNAPSHOT OF YOUR SERVO AFTER EVERY STEP. In this way, you can go back to step one any time. 
 
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Step 1: Materials

Picture of Materials
All you need for this project are the following:

Shear cutter or Hobby drill
Soldering iron
Soldering lead
Stranded or solid wire
Precision screwdriver
And of course, a micro servo

However, I understand that some people don't have a micro servo and might want to buy one.
Here are my store suggestions:

In North America,
- Sparkfun through shipping
- Radioshack

In the Philippines,
- eGizmo, Taft for almost P200

Step 2: Open it!

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Opening the servo is the first step in doing this hack. Use your precision screwdriver and take note, BE CAREFUL AND DON'T FORCE THE SCREWDRIVER. This is a common mistake for first timers because sometimes the screw won't budge and the screw gets busted and you can no longer open it at all (except by force). Be sure to use the exact if not almost the most accurate screwdriver for the screws. 

Also, make sure you keep the removed screws because you will put it back later. 

Step 3: Familiarize

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Next, you must familiarize yourself with the servo's body and everything else. It's because there is always a possibility you will fail thus you can put it back any time.

See the photo for the parts you must take note of.

Make sure you DON'T remove the motor and remove only the PCB with the capacitor later on.

Step 4: Open it again

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What I mean is remove the next layer until you see the white gears and make sure you TAKE A PHOTO again since you will put it back after removing a part from one of the gears.

Now, I want you to take the gear I will indicate through the photo above. BE CAREFUL and don't remove the other gears. Just in case you removed them, put them back and use the photo as your reference. 

Step 5: Cut the protection

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After getting the gear, you will see the protection "thing" of the servo. This is the part responsible for the 180 degree rotation capability of your servo. You have to cut this out using either a shear cutter or melting it through a soldering gun (I don't recommend the gun though). I mentioned the gun since sometimes the shear cutter can't cut the whole thing and it's hard to cut the leftovers at this point.

WARNING: Melting plastic is harmful to one's health. Proceed with using the gun wearing at least a mask so you won't inhale the melted plastic.

Step 6: Put it all back

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Return the gear in place. 

Yeah, but wait, you're not done.

Proceed to the next step! 

Step 7: Time to cut some wireeesss

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You now have to cut and remove the small pcb on the other layer of your servo. Make sure you don't remove the potentiometer and remove only the wire connections. 

After that, solder your desired wires to the two pins/terminals of your the small motor. In my case, I use either a stranded wire or cut female connector depending on where I will connect it right after. For your convenience, use a red and black wire for the two leads so it won't be hard to determine which is reverse or forward.

But a small tip, apply tinning on your wires so it will stick easier. Place also a few tin on your motor leads. This will help you a lot with soldering.

Lastly, you might want to add holes on the cover of your servo. In this way, you can insert the wires on the holes because sometimes the wire is too thick it won't fit through the original opening of the servo case.

Step 8: Testing time

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Put everything back by screwing the servo back to its original state. To test the servo, apply at least 5V voltage and don't go beyond this voltage first because testing it on a high voltage might break the motor if you assembled it back wrong. Just in case this happened, go back to step one (yeah seriously) and check out what might be wrong.

TROUBLESHOOTING

Why is my servo not moving at all and it makes a clicking sound? 
- Your gears might not be placed correctly and firmly. Open it again and don't apply any voltage until you get it running continuously.

WTH? Why is this motor really noisy?
- Yeah, your motor will really have that crispy sound. Nevertheless, you will get surprised on how much torque it has.

I accidentally removed the potentiometer, what should i do?
- Put it back since your motor might not run properly without it even though it has no connection to the circuit at all. It acts like a bearing so please, put it back.

I can't put back my servo and you wasted my money!
- Sorry, I just told you I'm not reliable for what might happen to your servo. Peace man.

How many servos have you done this with already?
- I've done almost 10. I have 3 robots that uses them and it's very stable. It's not like other people say that servo gears get worn out after a certain period of time.


Step 9: Congratulations!

You have finished the tutorial and I hope you've learned something new.

Thank you and please follow my other tutorials especially about Arduino, robotics, motors, etc.

If you have some queries and suggestions, just insert a comment below and please also visit my blog at:
http://iloverobots11.tumblr.com

Keep on tinkering!

- D
pocholox817 days ago
awesome, another maker from the ph! nice to meet you, dude hahaha dude you're from around Taft?