Introduction: Remove a Servo Controller
Servo motors are great fun when you want to easily interface a geared motor with a micro controller. However, sometimes, you want a nice little geared motor and don't want to be bothered with control circuitry to drive it. At times like this, it is good to know how to remove the controller from inside the servo motor and convert it to direct drive. Follows are instructions for easily removing the control circuit from a continuous rotation servo motor.
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Step 1: Open It Up
Open up the servo by removing the 4 screws fastening it closed.
Once the screws are removed, pry apart the back panel of the motor. You may be tempted to split it in the middle, as this will seem like the natural place to open it up. However, if you split it into two parts as such, it will spill out all the gears and be a mild pain in the neck to put back together.
Step 2: Desolder
Locate the solder terminals for the DC motor. These should be the two largest solder points on the circuit board.
Remove the solder from these with desoldering braid.
Step 3: Pry It Apart
Gently pry the circuit board out of the servo casing once you are sure it is no longer connected to the motor lugs. Be gentle and slowly work it out of the case or it may snap.
It is a good idea to save this circuit board, as it can function later as a small low-power H-bridge circuit for connecting a small motor to a micro controller.
Step 4: Connect New Wires
Connect a red and black wire to the motor.
If there is a marking to indicated one lug is power and one is ground, connect the red one to power (or red to red, as in this case).
Step 5: Case Closed
Close the case back up. Give the shaft of the motor a spin.
It should make the same "wizzing" sound that it made before you did the modification. If it no longer makes the "wizzing" sound, you may need to repair the gear box by realigning the gears.
To control the motor, at this point, now all you need to do is apply power to the motor. To reverse the direction, reverse the wires.
For a similar guide and to learn how to convert servos to be continuous rotation, check out robomaniac's guide here.
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37 Comments
8 years ago on Introduction
if i use dc motor instead of this motor?
it is right to do.
Because when you remove controller from motor it will move continuously and dc motor is also moves continuously.
9 years ago on Introduction
Cool! Looks like there is room to put a new circuit inside too.
9 years ago on Introduction
thanx..admin..i hav got a project 2 present in class...
10 years ago on Introduction
what about getting stuff in nz no online stuff plz
13 years ago on Step 2
Hello Randofo......Can u plz tell me from where v can buy Servo motors....??? I searched them a lot but i did'nt find them
Reply 11 years ago on Introduction
Or Radio Shack.
Reply 12 years ago on Introduction
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/102/Default.aspx
Reply 12 years ago on Step 2
You can buy servo's @ pololu.com (http://www.pololu.com/catalog/category/23).
11 years ago on Introduction
How do you get those awesome photos of your project on a seamless white background?
11 years ago on Introduction
can i use a motor to replace the servo because in uae i can't find it
11 years ago on Introduction
can you get these motors in INDIA ?
13 years ago on Introduction
where do u get this
Reply 13 years ago on Introduction
parallax.com
13 years ago on Introduction
Got bored, had 4 servos laying around, so done this mod to all four of them, zip tied them all together to form a 4 wheeled thing and put a 9 volt battery on there, works perfect! Thanks! Sometime soon im going to pair each side up separately and make the wires longer, so it will be remote control ;)
13 years ago on Introduction
Might as well keep the control board, why throw out working circuitry, only to buy another motor controller like the SN754410NE? You'll use up 2pins per motor instead of one... keep the servo circuitry, cheaper, and saves you pins.
13 years ago on Introduction
What you made is basically transforming a servo into a CC motor with gears, for torque instead of speed.
But why don't you remove the limitation tab on the last gear, to allow continuous rotation? I don't see the point of not doing this.
Reply 13 years ago on Introduction
The project I plan on using this for doesn't require continuous rotation, so I didn't feel necessary to go through that at this point. As well, I am using a parallax servo and they sell two versions of their motor, one of which has continuous rotation already. I figured providing the link at the end to the Instructable that shows you how to do that was enough for now.
Reply 13 years ago on Introduction
OK, so if continuous rotation (which indeed has been very well explained by Robomaniac and many others since long) is not the aim, and the angular command by PWM neither, I still don't understand the very purpose of this mod (i.e. removing the command+feedback circuit and leaving the angular limitation).
How do you know when to stop/reverse the motor? leaving it turned on while the gear is blocked by the tab is not recommended for a too long time. Is there some other sort of feedback loop?
How do you reverse the polarity? I hope, not by powering the motor through digital outputs...
Explaining (a bit) more of your project could help me understand the purpose.
Cheers
Reply 13 years ago on Introduction
i agree; without making it continuous rotation, this servo is now almost useless. if it were continuous, then you could attach the potentiometer to whatever the servo was moving.
one possibility i can think of is that there will be a normally closed switch that would cut power when the servo rotates something over to it, but without the potentiometer you wouldn’t ever know the position, also it would be at full speed and might go straight through the switch.
this just doesn’t seem to have any applications that make sense. i would be very interested to know what the author is using it for.
Reply 13 years ago on Introduction
Perhaps he has a scenario where he needs this to, I dunno, let's say close a gate or something. There's only two states that he needs for this gate - open or closed. If this turns all the way clockwise, it'll be open. Fully counterclockwise and it's closed.
In this scenario, it's simply being used as a geared motor with built-in stops. I could think of tons of uses for something like this.