I know there are a lot of methods for doing this but I was unhappy with the other methods. Servos have 4 basic parts motor, gear train, controller board, and poteniometer(pot). The two things we need to modify are the gear train and the pot. What I will do different is by using a different pot that allows for adjustment in case your servo doesn't spin the same speed in either direction or needs to match speeds with another servo. The pot im using is a 5k Ohm, 10% tolerance, 25 Turn trough hole trim pot from Digikey. I'm also assuming that you know the basics on how a servo motor work and if not see the pdf below.