Tunnels are becoming more and more popular as Halloween attractions. tunnels come in varying sizes and designs. The basic concept is a large tube with luminescent paint that rotates as one walks through. Generally there is an opening at each end, a raised walking plank from end to end, and hand rails. Black lights are typically mounted below the walking plank. Our finished tunnel had a 10' diameter tube that was 12' in length.
The key concerns when we built our tunnel were safety, achieving the desired effect, costs, ease of construction, and long-term storage.
This instructable will delve into the mechanics and drive line and not the finished product.
Step 1: Vortex tunnel designs
The vortex tunnel tube is usually built with a series of hoops covered with cloth or plastic. Hoops can be constructed of metal, wood, or plastic. Metal is the strongest and most reliable but steel is heavy and aluminum expensive. Wood is easy to work but can warp in damp weather. Plastic PVC is inexpensive but quite flexible. The lining can be plastic or cloth. Some builders call for fire proofing the cloth. What ever you use has to be dark, and able to take the glowing paint.
We found two primary types of drives. One method uses a series of (say 12") bicycle wheels near the ground that the hoops run in. This has the advantage of a more forgiving design, and also that the inside of the tube at the top is visually unimpaired. It has the disadvantage of having more moving parts. A variation on this uses two smaller capstans at the bottom.
A second method uses a single (3") capstan at the top of the vortex tube which not only holds the tube in place but drives it. The capstan is held between bearings on each end of a 12" pipe. This has the advantage of a single moving part - the capstan and less noise, fewer alignment problems. A disadvantage of the capstan approach is that the tolerances are smaller; the tube must be straight and balanced. Also, all of the weight winds up at about 11' off the ground and so a larger supporting structure is needed. A final disadvantage of the capstan approach is that the 3" tube is visible by the viewer. However it if is painted black it is not noticeable. There are also capstan designs with supporting bearings in the center.
With any of the designs pay a lot of attention to keeping the spinning parts balanced. Even adding the five rubber couplings - the additional ten hose clamps added a noticeable vibration - and so we moved them to be 90 degrees apart. And then I added a piece of 3/8" circular plates on each and as a thrust washer - and that added to imbalance and vibration.
Walkway / Plank
We found that the plank needed to be about 12" off the ground. Ours was constructed of plywood and joist hangers. We originally designed a tube that was 20' long but the limiting factor was the strength of the plank. In the end we wound up with a 13' plank and 12' tube which is more than adequate.