Making a Continuous Rotation Servo

NOTE!  There are a couple of different designs of these servos, even from the same vendor.

• The written notes below are for a through-hole style board
• The video covers the non-through-hole syle
• One kind of Potentiometer has rotation stoppers which must be broken off.
• One kind of Potentiometer rotates freely and doesn't need to be modified.
• If you don't need to modify the pot, you don't have to remove the stack of gears.

Continuous rotation servers are popular for cheap robotics projects because a pair of them give you a complete drive train (motor, controller, and gears).  A pair of 9 gram servos (such as the popular HXT900 from hobbyking) should be less than $7 or so.

Start by testing your servo, either with a servo tester or with an arduino sketch that drives the servo back and forth.  There's nothing more discouraging than having bad results, only to find out that it's not your fault because you started with a bad unit!  Likewise, be sure and test your battery voltage.

Servo Anatomy, In Depth

A really great presentation.  He covers the usual PWM stuff (nicely), and then talks about the electronics inside the server, including how the controller works.  It took me a couple of weeks of self-study to get about 75% of the stuff he covers.

There's lots of other interesting stuff on the site as well.

Supplement: Controller magic is courtesy of the Mitsubishi M51660L.  Another great writeup is here.

Servo Extension Arms for 3D Foamies

Great advice from Leadfeather:

• For good 3D you should have at least +- 45 degrees. 
• Cut slits only if you have stiff hinges. If they are already flexible the slits won't help.
• The longer arms are pretty typical, especially for the 5 gram servos.
• Possibly increase the servo travel if your Tx allows. Most computer radios allow you to do this in the "travel adjustment" and also in the "dual rate/expo" set up.
• For me, more throw means I use more expo for nice control response.
• For the HXT 500, Dubro 930 Micro Servo Arm XL
• For the HXT 900, Dubro 932 Micro Servo Arm XL