Follow @eaorobbie tutorial
RC Model for Motion Simulation
http://www.xsimulator.net/community/threads/rc-model-for-motion-simulation.4600/
You can find resources by @eaorobbie to download here:
RC Model Code for Arduino UNO - 2DOF - Expandable 2.0
http://www.xsimulator.net/community/marketplace/rc-model-code-for-arduino-uno-2dof-expandable.89/
Here a debugging step-by-step sequence from @eaorobbie :
http://www.xsimulator.net/community...-to-drive-servo-motors.4822/page-6#post-46606
Dedicated Shields
Driving 16 and more servos with arduino is no problem: 16-channel-pwm-servo-driver from Adafruit