The first step for the design of the model, keeping in mind the prototype considerations of the storyline of The Wind Waggon Trek blog, was to configure an eight radial arm bottom support for the sail panels. The material for the arms is akin to red oak wood. Each arm on the prototype will have a ten foot radius when assembled, although each piece is somewhat shorter to provide the central hole for the main mast that will be attached at the center.
Each radial arm is sized to handle the prototype sail panel applied stress. On the model the parts will also be red oak or other hard wood suitable for cutting on the mini-mill. A metal hub will be attached on top that also supports the main mast and another hub on bottom that connects to the support bearings and the main turntable drive shaft below. The other end of the drive shaft will also connect to a bearing hub. Near the ends of the radial arms there are mounting holes for the sail panel bottom bearing.
At the hub end of each radial arm there will be three bolt holes used to attach the arm to the hub. The extreme end of the radial arm will have a bolt hole for a metal braces that connect to the neighbor radial arms. The ring of metal braces form a hoop that keeps the arms at a constant angle to one another. The model parts are scaled 3/4" = 1ft. The prototype radial arms have a 20 ft overall diameter. The model will have a corresponding scaled size of 15" diameter.
The bolts that connect the radial arms to the metal hub will be #2-56. At this point they will thread into a lower hub disc with matching hole positions. The outer end bolt connecting to the metal braces connecting adjacent arms will be #0-80. In addition to the bolts, a pocket for a 0.2" diameter bearing is located at a prototype radius of 9' which scales to 6.75" radius on the model. Those bearings will support the sail panels and permit them to freely swivel. The sail panel shaft diameter will be 0.125" on the model, 2" on the prototype. The bearing will be a metal pocket with 0.01" clearance. The end of the sail panel shaft will be tapered and rounded to provide a vertical support. The sail panel should freely rotate on the metal to metal bearing.
A slightly tapered main mast will mount in the center hole of the hub and connect to the center of an upper hub supporting the top set of radial arms. The mast couples the torque from the upper sail panels to the bottom hubs. The metal hub at the top connects together the eight top wood radial arms that look similar to those on the bottom and have essentially identical functions. Each radial arm at either the top or bottom carries the same lateral load, one half of sail panel wind pressure. The radial arms are strong enough to carry the lateral load. The mast is strong enough to carry the rotational force loading of the top set of radial arms. A shaft from the bottom hub couples the entire torque load of the sail panels down to the power take off pulley. The bottom shaft like the upper main mast is also wood. Both the upper main mast and lower drive shaft are pinned to the metal portion of the hubs to prevent slippage under torque loading.
The turntable will consist of many pieces: (List subject to revision)
Eight lower radial arms
Eight upper radial arms
Eight sail panels
Sixteen sail panel bearings
Sixteen bearing outer housing
Sixteen bearing inner housing
Sixteen radial arm tip brackets
Sixteen radial arm tie rods
Sixteen radial arm tie rod keepers
Sixteen radial arm tie rod keeper bolts
Upper main mast
Lower drive shaft
Upper top hub
Upper bottom hub
Lower top hub
Lower bottom hub and bearing housing
Lower hub bearing
Lower hub housing
Bottom drive shaft upper hub
Bottom drive shaft lower hub and bearing housing
Bottom drive shaft bearing
Bottom drive shaft bearing housing
Bolts for hubs to secure shafts
Bolts for radial arms to secure arms to hubs
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