Convert Towerpro MG995 servo to continuous rotation

Do you need some relatively powerful and very cheap servos for continuous rotation? Well, here I will tell you how to go about converting the Towerpro MG995 servo (rumoured to be 10kg/cm Torque) to continuous rotation.

Any constructive advice on the project or on the instructable would be appreciated - this is my first so be gentle :)

Step 1: Items required

To start with, you need some Towerpro MG995 servos to convert.
I purchased 2 with metal gears here http://www.dealextreme.com/p/towerpro-mg995-metal-servo-with-gears-and-parts-10kg-torque-20089

2 each of 2.2 k Ohm resistors per servo motor. (Optionally a 5 k Ohm pot... or even the one in the servo. More about this later)

Then you need a soldering station and solder.
Helping hands help.
Wire cutters.
Small Phillips screwdriver.
Small awl (not pictured in tools photos)
Dremel and cutting disk
Goggles for safety of course.

Some means of testing and driving the servos. I used an arduino perfboard clone, a breadboard and some batteries.

Comments

[Franco0]

Hello, thanks for the instructable, I just want to know how many RPM it arrives, and how much torque it has, approximately, so I can see if it suit my project.

[AgeingHippy]

Hi Franco

I am not sure about the torque, but it certainly delivers enough for my requirements. I used these servos to drive a tracked robot with the tracks printed on my Mendel reprap. These servos deliver enough torque to allow my robot to turn on a carpet, which many builders will tell you is a difficult thing to achieve given the friction created.

The link states they deliver torque up to 10kg. They are cheap so you could simply buy one or two and test them.

As for RPM - I think I get between 40 and 50 rpm.

Regards

[radiogareth]

You can remove the hardened metal pin with a pair of side cutters - not to cut it off, but to grip it and pull like a tooth. Worked for me. On my 10Kg MG towerpro I was able to lift out the pot, leave it in the middle of it's travel and still fit everything back in again. I taped the pin to the pot wires in case I ever need to make a servo out of it again.

Good luck.

Gareth

[AgeingHippy]

Hi Gareth

I did try pulling the retaining pin out with a pair of pliers but just could not manage that. I found it was too tightly rammed in.

Great idea about extracting the pot but not removing it... Much simpler than soldering in the resistors. If I need to do some again I certainly will give that a try.

[radiogareth]

Pliers will slip off, but with care side cutters will grip it enough to lever it out if you use the tip of the clippers as the pivot point, load is pin in middle of jaws, handles for the lever. I think that makes sense :-)

[Gelfling6]

I've done similar to this, with the lower-grade servos, mainly Futabas, for robot projects.. I replaced a pair of constant-rotation servos on a Parallax BOE-BOT frame, with Futaba 3004's, simply by clipping, and filing down the stop-point on the drive gear, and folding the pins for the potentiometers so the post end would poke out the side. (then simply careful twisting the post to center it.) I imagine these, though would hold up a lot stronger, with the metal gears.