Servo-driven Z-axis for pen

Lifts straight up, perpendicular to surface. Unlike many others servo-driven pen axes which rotate when lifting pen. Roughly 10 mm travel.

Used in the penplotter which was the award given to the winners of Oslo Innovation Award 2016. Successfully printed the diploma live on stage.

Vitamins needed:

* Microservo. SG92R or other with same size head, https://www.adafruit.com/product/169
* Low-friction tape. UHMW PE or Teflon ideal. Kapton can be used as replacement
* 2x M3x30 + M3 hex nut