its a standard servo with some simple modifications
I tore one down and took pictures
ill explain each photo
ok here is a standard futaba digital servo that volunteered for the operation
pretty much any servo will work
first thing you do is remove the 4 screws off the bottom and take the lower and upper half of the servo apart
next you pull the final drive off the top of the servo this might be on tight if it has a bearing race on it just carefull work it back and forth and it will pop off
once you have the drive off you will notice a small tab near the bottom of the drive stem this has to be removed so you get 360 traverse once its removed refit the post to the servo and make sure it rotates freely without catching
once you ensure it rotates freely look at the bottom of the post you will see a small slot inside the gear this bit attaches to a pot inside the servo that stops the servo at certain positions usually this slot is removeable and can be popped out with needle nose pliers if its not removeable you will need to drill it out making sure the pot does not rotate with it replaced
once you get to the point you need to plug the servo in and power up your system the servo will start spinning
use your hand dandy needle nose pliers to turn the pot that is under the final drive gear util the servo stops
NOTE: sometimes the servo is already at true neutral so you dont need to turn anything basically if it stops on its own after a second dont touch anything once it stops move the stick on the remote back and forth and you should see the gears move
at this point put the servo back together and you have a unlimited proportonal servo to use for anything you want
these servo's also make great motors and speed controls for small scale models like the lindberg coastguard tugs plastic kits
my lindberg diesel tug model is powered by a servo and i get 6+ hour runs off the reciever batteries which power everything
hope this helped
PS forum owner if this needs to get moved to a how to section or something please feel free to move it
and apologies if this is in the wrong section