Of all of my recent projects, SUPERNUS, the Sky Globe has received the most attention. Apart from it’s great looks (ahem!) people love the interconnection between the temporal, the electronic and the mechanical aspects of the design.
SUPERNUS, the Sky Globe: showing solar position (elevation 64 deg., azimuth 182 deg. ) close to solar noon on 26 July 2015.
Imagine then my upset, then, when I found that the elevation servo motor had burnt out!
Knowing that I had to replace at least one servo, I decided to change the azimuth servo as well. I had not been content that the azimuth servo only swung 180 degrees and therefore only worked to trace a solar or lunar path from due East (90º) to due West (270º). As of the writing of this article, the sun is setting with an azimuth of >290º (WNW), so the unit was unable to properly trace its position in the sky. I wanted the azimuth servo to have a full 360 degree swing so it could position the sun and moon anywhere in the sky.
However, almost all so-called “360 degree servos” that I found online were, in fact, continuous rotation servos – essentially direction and speed-controlled motors – which could not be controlled to move to an absolute position (e.g. 198 degrees). Despite assurances from the vendors that their “360 degree servos” could be positioned absolutely, they all turned out to be continuous rotation motors, and consequently of no use in this project (Don’t worry, I ended up getting refunded!).
I finally came across a suite of servos referred to as “Digital Sail Winch Servos” that are used by remote control boat builders to hoist or set sails.
SUPERNUS, the Sky Globe: Azimuth servo
These servos are much larger and more powerful that the small 9g ones I had been using, and they come in a variety of configurations. I chose a unit described as “one turn”, two ball bearings (1T 2BB) (see eBay).
It turns out that this would do the trick.