Civil Defense Emblem

Mini Thunderbolt

Sirens Main Page

Back to Civil Defense Museum Main

I got the wild-ass idea to build this thing after I built a siren and chopper stator as a "during break and lunch time" manual-lathe-practice project at work. I used a Radioshack 12 volt motor for the chopper motor. After building a single-tone 4 port rotor I had the idea to make a Mini-Thuderbolt out of it. I figured out the scale of the small chopper unit to the real Thunderbolt siren so I could design the rest of the siren from there. The chopper is actually a bit too tall compared to a real Thunderbolt siren but after I had the chopper finished I didn't want to go back and redo it. Here is a description of the progress on the Mini-T so far....

My YouTube Video Mini-Thunderbolt Operating.

Link to my youtube channel.

Chopper, Stator, Upper Bearing And Horn Mount
The size of the Radioshack 12volt motor dictated how large the chopper was going to be. The blower air actually goes through and around the motor and through air holes in the bottom of the stator where the motor mounts. Since these photos were taken the air holes have been enlarged to allow more air to get through. The original aluminum single tone 4-port rotor is in the top 2 photos below. I later made a brass dual-tone chopper (seen in the middle 2 photos below). I added an upper bearing to stabilize the chopper because it was so much heavier than the aluminum chopper. I then ruined the brass chopper by filing the holes into slots. I thought that would allow more air through but all it did was throw the thing way out of balance. I then made another dual-tone chopper out of aluminum which was identical to the brass chopper pictured below. You can just see the holes of the aluminum dual-tone chopper through the stator slot in the lower left photo below.

Stator Air Holes

Original Rotor With Stator And Motor

Brass Dual Tone Rotor With Upper Bearing and Top

Rotor And Top Together

Entire Unit Assembled Before Horn Mounting Boss Installed

Horn Flange Attached To Stator

Rotator, Chopper Housing And Horn

Rotator and chopper housing with chopper assy. removed. The terminal block on the top is a temporary connection for the chopper motor brushes. The wires sticking out of the chopper housing are the wires to the chopper motor. The corner post at the rotator gearbox had to be omitted for the gearbox to fit.

Rotator, Chopper Housing And Horn
Designing the rotator and chopper housing assy. was by far the hardest part of this project. Since I built the thing at 1/6th scale I wanted to keep everything as close to scale as I could. I scaled the rotator box from my real Thunderbolt and then tried to figure out a way to drive the rotator. I found that Tamiya makes a gear box that has a 5000 something to 1 gear ratio resulting in an output shaft speed of about 2 rpm which is perfect for the Thunderbolt horn rotation speed. The Tamiya gearbox was an EXACT fit into the rotator box. It was amost like Tamiya made the gearbox specially for this project. The Tamiya gearbox allowed me to keep the location of the chopper air tube as it passes through the rotator box within .030" of the exact scale location. I only had to cut a few pieces off the plastic frame of the gearbox.
I made a set of pulleys to belt-drive the thing with an o-ring after a coworker suggested that I use o-ring material as a belt. The rotator has a plastic bushing at the top and bottom of the air tube where it goes through the rotator. The upper plastic bushing doubles as the insulator/mounting for the brush collector rings.
I made the horn out of posterboard. I copied scale drawings I did from the real Thunderbolt horn onto posterboard then cut out the pieces. I bent the pieces on the drawing lines to duplicate the bends on the real Thunderbolt horn. I glued a styrene flange on the horn end where it mounts to the chopper stator. In these photos I still have to prime and paint the horn. I made it out of yellow posterboard it's not painted yet. The horn is screwed to the stator boss with 0-80 screws. The horn support is made from styrene angle and mounts to the chopper housing and horn with screws.

Support Mount To Housing

Horn & Support

Blower, Air Pipe & Support
The blower is an electric AIR "smog" pump from a Camaro. It's the closest thing I could find that would fit in the blower box and still have a decent air volume output. It's similar to a vacuum cleaner motor. It's a bit loud but I'll use it until I come across something better that will fit in the blower box. The blower is mounted to an aluminum frame and the PVC air pipe is clamped to the frame. In the photos below the blue stuff is air filter material I wrapped around the blower motor. The air intake is right next to the outlet where the PVC pipe goes into the blower motor. I built the blower frame end where the air pipe clamps on to look like the real Thunderbolt blower frame from the outside. I still have to build the blower box. The blower box in these photos is the temporary cardboard box.


Blower Wiring

Air Pipe Mounting Frame

Blower With Air Filter Removed

My YouTube Video of the Mini-Thunderbolt Parts

Electrical Stuff & Brushes

The Mini-Thunderbolt runs on a 12 volt battery power supply. I built a "Mini-RCM" panel to control it the same way a real Thunderbolt siren is controlled. I use a bank of large capacitors to allow the chopper motor to have a coast-down like the full sized siren. Without the capacitors the chopper motor stops and starts as soon as voltage is switched on or off. With the capacitors in the circuit the chopper coasts-up as the caps charge and coasts-down as the caps discharge when the chopper relay turns off. I use a set of capacitors for the time delay on the Mini-RCM. The time delay is about 7 seconds which keeps the blower and rotator on after the chopper relay disengages just like the real Thunderbolt.

Mini-RCM Control Panel

Brushes & Collector Rings
Before wiring installed.