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 servo motor.

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. 

Comments

[mistu99]

can i use a motor to replace the servo because in uae i can't find it

[aravindskumar10]

can you get these motors in INDIA ?

[neoseeker]

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

[randofo]

http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/102/Default.aspx

[Mr.Robotica]

You can buy servo's @ pololu.com (http://www.pololu.com/catalog/category/23).

[cheese7710]

where do u get this

[randofo]

parallax.com

[Danny_Payne]

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 ;)

[amando96]

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.

[laxap]

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.

[randofo]

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.

[laxap]

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

[randofo]

Here is one use http://www.instructables.com/id/Simple-Bots-Walker/

[thinkdunson]

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.

[1up]

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.

[thinkdunson]

but you have no way of knowing the position. and if you do actually hit the stops, you can damage the gears. for your example, it would be much better to have the control circuit still in place. i can think of tons of uses too, but each one would be much better with either the circuit in place, or with it converted to continuous rotation and the potentiometer attached to the object being moved.

[laxap]

I don't know if hitting the stop could really damage the gears, but it would turn the motor into a heating (with no heat sink)...

Now, I see the simple bots family growing:
Wobbler, Walker, ...

Should also be OK for a Most Useless Machine.

[hintss]

it seems he wants to use it without a microcontroller. you know, for ANALOG stuff?

[laxap]

I meant: DC motor

[alcurb]

Great photography. Very easy on the eyes. What did you use, a light box? If so, what kind, a DIY box or a commercial one?

[randofo]

Thanks. I shot it on a white photo backdrop with natural light from a skylight. It was probably about 5 or 6pm, so the light wasn't too direct. I then just fixed the levels in Photoshop.

[alcurb]

No kidding? More instructables should be shot the way you did it. Good work.

[TheGimpAddict]

How fast would the servo spin after removing the controller? I think this would be perfect for a project I'm working on because I really don't want to use any kind of microcontroller. Thanks

[AndyGadget]

Randofo's instructions only remove the controller - As he mentions in the last line, other mods are needed to give full continuous rotation. 
As is, removing the servo board will only allow 270 degrees or so of movement before the servo hits the endstops and the motor stalls.
The speed will be very slightly faster than the normal end-to-end speed of the servo.

[Schmidtn]

It depends on how big your battery is. 9v will spin faster than 3v (two AAs), will spin faster than 1.5v(one AA), etc. It's pretty fun to plug batteries into hacked servos and it's purdy dang easy to use a DPDT switch as a microcontroller free H bridge.

[AndyGadget]

Ha! - Yes. I was assuming you'd use the same voltage as for the original servo, but as you say, you can now run the motor on any (sensible) voltage you like.

[wingzeroj2m]

i can't believe i've never thought of this. nice simple instructable. gj

[AndyGadget]

You could also mention that some of the smaller servos don't have the lugs; they connect to the motor via a pair of wires. These are easier as the circuit board is floating and can be carefully lifted without desoldering anything.

[bijikenyot]

nice to see your big hand 90% of the image.. hihi :D :D just kidding...

[Schmidtn]

Very nice 'Ible and I feel your pain about snapping those little boards in half, done it plenty of times myself. Only thing I'd add is to knot the red and black hookup wires inside the case in step 4 so that if they're pulled it wont put stress in the mechanical connection/solder between the wires and motor terminals. Beautiful pictures by the way!

[randofo]

That's a good point! I should to that with the ones I made and add that to project.