Introduction: Halloween Attraction (tech Shop)
Couldn't have done this without tech shop!
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.
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Vortex Tunnel Designs
There are three or four different designs to choose from generally from these two styles. We chose the capstan approach: a long pipe with bearings on both ends that supports the tube.
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.
Step 2: Side View -
here is a sketch of the side view. the tube frame is 14' long to accommodate a 12' tube. I used 3.5" conduit attached with unistrut to create the a frames. the tunnel fabric is shown inside (above) the outside frame has to be pretty stiff - and i suggest using 3/8" ply as sheer (lower).
Step 3: End View
the end view shows the oval path of the tunnel fabric (above). the plank is not shown, but is 12" from the ground. The capstan drive is 12' center to ground. Motor is shown with reduction pulley on capstan. A frame constructed with unistrut, and ~ 5' height.
Top view (lower) shows 14' frame with 12' tunnel, and a porch to be used as an entry way.
Step 4: Drive Line
Your shooting for a tunnel speed of 5-10 RPM. In the case of a set of (6-8) multiple small bicycle wheels generally one of the set is driven by a small motor. In our case we chose the capstan design. AC Motors generally are 1740 RPM or 3600 RPM. 3600 RPM motors are cheaper but are noiseir and require twice the gear reduction.
To hedge our bets I used a step cone pulley for the motor which had four pitches from 1" to 4". I found these already attached to the used motors.
On the capstan end of things we wound up with a 14" dia pulley. Zinc pulleys like this are priced between $50 and $70 new. I found mine on sale at Graingers. Motor shaft was 5/8" and the capstan shaft was 1".
Step 5: Used 3/4 HP Motor
This motor weighs almost 70 pounds. It's a vintage U frame brush motor, 1740 RPM and includes the stepped pulley. I would think that 1/2HP modern motor (T56 Frame, etc) would weigh in at half this and be adequate. Stick with the lower speed motors. Try what you have around. Some vortex tunnels have been powered with electric drills!
This is a 120VAC single phase. When buying motors stick with single phase, as three phase is for industrial only. If you see a capacitors can on the motor it is single phase. Read the label. A three phase motor cannot be operated on single phase. Single phase motors require two conductors. Three phase motors require three.
You are probably looking for a single phase 120VAC motor.
Step 6: Drive Line Worksheet (excel)
attached is the excel spreadsheet with some other data like weight.
Step 7: Vortex Tunnel Layout
this sketch shows the motor as well
Step 8: Building the Capstan
we used schedule 20 pipe which is 3.5" OD. Home Depot sells rubber couplers which slide over and form a traction area to drive the rings in the tunnel.
Step 9: Motor Controls
We have not talked about motor controls. Each end of the tunnel should have emergency kill switch. If you are clever, the kill switch will also turn on some work lights.
If possible find a motor starter (two pole relay) and use this for starting and stopping the motor. I found specific purpose 30 amp air conditioner relays for about $10 each. These are usually 24V coils, but you can order them 120V as well. If you don't know what you are doing, bring in a friendly electrician.
My suggestion is to mount a handy box with a 120V plug so that the motor can be physically unplugged when mucking with the pulleys, etc. The starter (relay) turns on and off the receptical. The other side of the relay is wired opposite of this and turns on the work (safety) lights when the tunnel isn't working.
Find a metal enclosure and mount the relay in it. Run a power cord from the metal box to an AC outlet.
Step 10: Building the Capstan
I spent a lot of time thinking about how to do this. I wound up with 3.5" schedule 20 steel pipe that I found used. I made certain that the pipe was very straight.
The first thing we needed to do was to cut a slot in the 1" shaft for the .25" keyway. This was done on a mil, but if you can order the shaft with the keyway cut you will save some time.
We then created a dwg and cut the shaft plates on the plasma cutter at tech shop. For our purposes this worked alright. It's fast. But the accuracy of the plasma cutter leaves something to be desired.
The main concern was that the 1" shaft would be true to the 3.5" pipe. Two identical plates fit inside the 3.5" pipe. Note that the pipe has a seam, and so we ground the finished plate flat in one spot. In the final version we left about 12" inside the pipe with 6" extending for the bearings and drives.
attached is the cad file in dwg format. it's two circles. note that we cut it to .75" on the plasma and then drilled it out to 1". This whole operation should have been done on a mill - but we were having fun playing with the plasma cutter.
One issue with the plasma cutter is that the edges become hardened. Difficult to trim with a bandsaw, and even on the lathe it took more time than I would have suspected to bring back into tolerance.
Step 12: Finished End Plates From Plasma Cutter
here are the finished end plates.
Step 13: Machining the Plates
We used an enco lathe to turn the plates and enlarge the .75" center to 1.0" press fit. Again - use a milling machine - not a plasma cutter.
Step 14: Plates Pressed Onto Shafts
we pressed the plates onto the shaft. note the keyed slot. on this shaft we will put a 14" pulley (A belt size).
Step 15: 14" Pulley on Shaft
14" with 1" ID pulley on shaft. Die cast pulley, single grove A-sized belts.
Step 16: 3 Degree Misalignment Bearings
I'm using bearings that can be mis-aligned by 3 degrees (mcmaster) 1" ID. We figured max 300 RPM and the total weight of the capstan with the vortex tunnel at less than 400 pounds.
Step 17: Finished Capstan
we first welded the plates to the shaft, then pressed them into the 3.5" pipe (think hammer) and then welded the outer plate to the shaft. A dial caliper on the end showed about .01 run-out.
Step 18: Building the a Frames
This could have been done much easier, but i wanted something that could be taken apart and stored, easily re-assembled for many years. I used a right triangle, and took special effort to weld nuts on the inside plate so that it could be disassembled. I found welding nuts at fastenal.
All bolts are 1/2-13 thread with an allen socket head.
Step 19: Completed a Frame
Here is the completed a frame. I left one length of the unistrut run wild in case I needed additional support.
Step 20: Detail of Welded Nuts
here is a detail of the section
Step 21: Final Assembly
It's a bit difficult to see all that is going on. The two frames sit atop the house. They are connected with 4" electrical conduit. I used the standard straps to attach the conduit. I also added diagonal supports (X frame). At the end of the pipes are thrust washers - cut at the same time as the plates. They are about 10" diameter.
The only issue with this was the thrust washers and the rubber couplings (look below the right hand window and you will see a stainless hose clamp that is holding the rubber section in place) threw the capstan a bit off balance. But at 300 RPM it is tolerable - and we'll chalk it up to a special effect. It runs smooth and quiet.
Oh - and it was a bear to raise this thing from the ground atop of the walls.