Clockwork Coop Version 1 Mechanics Second Try

After several failures using DC motors, I wanted explore other options to open, close, and secure the door.  I decided to investigate a stepper motor and lead screw mechanism.  The door would open and close exactly as before, but the new setup had several advantages.

1)  The door was lowered under power so there was less chance of it getting stuck

2)  The door could be "locked" at any location simply by stopping the motor.  This meant the mechanics was simpler

3)  The stepper motor I chose had more power than my DC motor and could raise and lower the door faster.

I used a pair of A4988 driver chips under full-step mode to run the stepper motors.  Initially I just used two pins for each chip, but I realized the motors were drawing a lot of unnecessary power this way.  I decided to use the enable line on the chips to reduce power consumption but this would require 6 total pins (when I only had 5 available).  However, since I wasn't using the serial port for anything, I could re-purpose the TX line (D1) as one of the 6 pins.

I quickly realized an installation and maintenance problem needed to be solved.  How can the door be easily attached to or detached from the lead screw?  Additionally, there's a requirement to easily disengage the door from electronic control in the case of a power outage.  How do I make this easy?

The lead screw setup works by spinning a long threaded rod that has a nut attached to it.  The nut is trapped by a bracket that prevents it from spinning.  This converts the spinning motion of the rod into the linear motion of the trapped nut.  So, I designed a bracket that traps the nut and attaches to the door.  The bracket was made out of two parts.  One part attached to the door and allowed the threaded rod and nut to fully pass into it.  The second part snapped into the first in such a way that the threaded rod was held firmly against the bracket.  This fully captured the rod and nut while being easy to disengage.  I'm very pleased with this setup and it made installation a breeze.  I still need to design a latch to hold the door open if it is disengaged during a power outage.  In that situation, I can open and close the outer doors manually until power is restored and the door can be re-engaged.