U Stepper Robot Arm Rev4 - Open Loop Control Mod

## Credits

This Design is based on the awesome Robot Arm Rev 4 from the guys at uStepper. You may find the original work, as well as extensive documentation including the kinematics here:
https://github.com/uStepper/Robot-Arm-Rev-4/tree/master


## Background

As uStepper is focussed on closed loop servo controllers their design does not require any endstops. This makes the phyisical design and programming much easier while not requiring a homing procedure during startup. As a bonus you may detect motor slip and other fault conditions with closed loop controllers like the ones from uStepper. On the other hand this type of controller drives the component costs and adds some complexity to the electronics.

In order to compare a closed loop control with an open loop control based on a practical example I re-designed the uStepper Rev 4 arm to integrate optical end stops and a bracket to hold an interface board for hooking the arm up to a CNC controller.
On the board you may fin