Hack a TowerPro Micro Servo to Spin 360 / Continuous Rotation

Hey guys! Since I've got my servos, I've had two that I set aside for hacking. So, coming to my favorite website for help, I was sorely disappointed when I couldn't seem to find any instructables on how to mod a micro servo. After viewing a few, I went to my workbench and got to work. I was very surprised when I opened up my micro servo and found it to be slightly different then the bigger servos. So, I decided I would make a guide on how to hack into your servo! So what are we waiting for? Lets get started. 
But then you ask, doesn't this defeat the whole purpose of a servo? Well, no. We just utilize the gearbox, so that we can use this motor as a drive motor for a robot. So now, let's really get started!

Step 1: Ingredients:

Ingredients needed: (no, not food ingredients unfortunately)

• Rotary tool or a utility knife
• Very small screwdriver (phillips)
• Soldering pencil* and solder
• Wire snips
• Needle noes pliers
• 2x 2.2k resistors
• Helping Hands (AKA 3rd hand) BTW check out this awesome instructable on making helping hands. Thanks rstraugh!
  
  &
   
• 10 minutes

Comments

[fenix8k]

xD i sugest u to try to get some smd components the resistors are veeeeeeeeeeeery cheap :P i buy a "kit" 100 of all values from 0 to 100kohm 25$ us dolars they are like 5k resistors :P

[Enjoying Electronics]

Okay, once I get some money :D

[fenix8k]

nice work but i can suggest u to use SMD resistors :P i do the same to a copy of this servo and i add a second pivot and almost i can t close it :P with smd resistors (1208) that part would be tiny :P

[Enjoying Electronics]

Yeah, that is a good idea, the only problem is I don't have any SMD anything!

[Gelfling6]

I've done similar with Futaba S3004's, but simple scraping down the travel stop, and feeding the POT shaft out through the side of the case for trimming. (and "Z"-bending the connections, so it would sit at that new position.) Though, the simple "T"-bridge with fixed resistors works, it's still good to have a little trim capability..

[AndyGadget]

I've found an alternative way of doing the pot mod is for this type of servo is to drill out the final drive gear so it spins freely on the shaft and then epoxy the pot travel at half way. This is sometimes a better way for small servos where getting the resistors in is problematical.

[Enjoying Electronics]

Ok, so your saying not to change the resistor at all? Just turn it all the way to 5K then epoxy?

[AndyGadget]

 
Yep - I used a homebrew servo tester set at 1.5ms and tweaked the pot to mid way until the motor was stationary, then added a small drop of epoxy left and right of the slider contact point. 

I came up with the idea after failing to fit resistors into a TowerPro 5g servo. 
Some types are amenable to rounding out the final drive gear hole, some aren't.

[Enjoying Electronics]

Yeah it seems like every servo I get is just a little different from the next. Homemade Servo Tester? Have an instructable on it I can see?

[AndyGadget]

My servo tester is an incredibly little useful piece of kit which I really am going to have to make into an Instructable. It's based on a little development unit I made up for the Picaxe 08m microcontroller.

It's got potentiometer and push button switch on the inputs, LED, beeper and 3-pin servo connector on the outputs.  One mode allows you to set max and min endpoints for the servo travel and then sweeps between them to let you see servo speed.  The other mode gives 20 steps each side of the midpoint to test response of modified servos.

[Enjoying Electronics]

That sounds awesome! I'll be waiting for it!

[e13jimenez]

The whole point of a servo is that the unit knows its position precisely. The 5k pot was the sensing device that tells the arduino how far the motor has spun thats why there's three wires (power ground and signal). By removing it pot from the equation its now just a little motor in a gearbox. The 'servo' now has no clue what its angular position is. Idk how cheap these things are, but I wouldn't recommend running this hack unless you're really in a pinch. You can't use the servo library with this.

[AndyGadget]

 
Further to what Electricloser says, this method has the advantage that you can control the speed of the motor by using the standard servo control signal.  Mid-point (nominally 150) is stationary.  Less than that and the servo will drive in one direction; greater than that it will turn in the other. 
The greater the difference between the control signal and the mid-point value, the faster the motor will run because of the acceleration gradient set by the control circuitry.
Different manufacturers / models will give a differing number of speed steps and from my experience, digital servos give a greater number than analogue ones.  (The best I've had was about 15 each way.)
I'm not familiar with the Arduino servo library but as long as you can set the pulse-width from it, you can control the speed of servos modified in this way.

[Enjoying Electronics]

Well the whole point of this instructable is to have a strong motor that spins endlessly. Yeah, the servo library doesn't work, but, that not what it's for. What this whole thing is for is like for driving the wheels of a smaller robot. Just look around, and you will see tons of smaller-sized robots that use these hacked servos for a drive motor. All the built-in gears eliminates the need for having to buy a extra gearbox. The servo when spinning endlessly makes for a pretty strong drive motor.

[Gelfling6]

Actually, the servo library does still work.. The arduino based robot I made awhile back, used the stock servo library, and controlled 3 servos. (assigned as servo1, servo2, and servo3 off pins 8, 9, & 10. then simply attaching them as servos.. You can then control them as percentages of how fast you want them to spin, in each direction.. ( map(val, -100, 100, 0, 179) for -100% (full backward) to 100% (Full forward) )..

[Enjoying Electronics]

Well, thanks! I don't even know what the servo library is =). And yes, I didn't use the percentages when I was testing this.

[Gelfling6]

For those not familiar, look under File -> Examples -> Servo -> Knob .. the code would be similar to this example, but assigning the -100 to 100 mapping to the full backward (0) to full stop (89) to full forward. (179).. Now, granted, -100 to +100, is a pretty wide range. Usually steps of 10 each direction is reasonable. as long as 0 means stop..
The raw code of the servo library (the included Servo.h), does about the same, mapping the 0 to 179 to the ###-Hz pulse out to the servo. (If you've ever tinkered with the Parallax Basic Stamp, their code directly pulses the driving pin from the MCU out to the servo at the exact #-Hz)..

I've converted Futaba S3004's to continuous rotation, because the cheaper Futba servos Parallax uses for their BOE-Bot, had managed to wear out the motor (the Electric motor inside) bearings. Nothing makes you cringe worse, than hearing a servo motor sqealing. ARGH!

[Robobeard]

Hi, I've bee trying to find instructions on how to do this and yours is the best so far. I'm just wondering if you can add a video of the resistors been soldered into place. If it's not too much to ask, I'm new at this and only have the pair of servos so i don't want to botch this up.

[Enjoying Electronics]

Hey robobeard!
Yes, when soldering to the tiny circuit board, you want to be very careful and not to overheat the board or even worse burn the ICs.
I was intending to put up a video, but my soldering gun wasn't really cooperating at the time. Since I'm doing this to one more of my servos, I'll go ahead and record my soldering. I'll put it in step 3.

I also want to give you the links to my favorite instructables on soldering.
Noahw and his amazing instructable http://www.instructables.com/id/How-to-solder/

&

if you're still having trouble, check out this instructable by curiousinventor
http://www.instructables.com/id/How-to-Solder-Videos%3a-Why-is-soldering-difficult-s/

Hope this helps!

~electricloser

[matt.e.jenkins]

Thanks for this. I have two of the same servos and was looking for instructions on how to do just this to make a toy robot for my son.

[Enjoying Electronics]

Happy I could help! What kind of robot?

[matt.e.jenkins]

Just a simple cheap one made with an Arduino and spare parts laying around. With IR LED wall detection or LDR light following. I always seem to have side projects going on.

[Enjoying Electronics]

Thats cool. I've always wanted to make a simple "robot", but I just don't seem to have the skills needed! Haha, have fun with your project!