MidTBot Hot-Swap Pen Holder

These parts modify the excellent mid T bot by Bart Dring.

Video here: https://www.youtube.com/watch?v=JLPwHxBBrQM

Features:

1. Head Block has been modified to position the servo slightly back more, giving more surface contact on the pivoting pen arm above.

2. Head block "ears" which hold the timing belt have been strengthened and redesign to allow higher Z-lift for the pen

3. Pivoting pen base is now modular and magnetic to support interchangeable pens.

4. Magnetic modular pen ring now snaps in and out of your mid-t-bot quickly and easily

5. a channel has been created to route the servo wire up and out of the way of the Y-Stop

Print a pen-ring holder for each pen you plan to keep in your collection and install 6mm x 3mm magnets on both the receiver and each pen holder.