The tail design started as a series of copper tubes connected by springs. This would allow me to create just about any length of flexible framework to attach foam or hollow tubing. I wanted to be able to add motion to the tail, preferably by using one or more motors. (With all of the other parts, I didn't need something else that would require manual control.) One possibility was to use some sort of gear reduction motor, with a arm that would drive a lever assembly. Then I thought about using a windshield wiper motor, because this had the advantage of being both gear driven, and having a limited motion reciprocating action. A search of the J.C. Whitney web site turned up several small wiper motors, of a design to replace manual wipers on Model T or jeep vehicles. These turned out to be about half the size of what the local auto parts store had in stock, and used less than one amp of 12V power.
Starting with one foot lengths of 1/2" copper tubing, I started to piece several sections together. While a single tube could be used to attach a frame for the wiper motor, a two-tube approach would maintain better support, and prevent the motor from twisting.
A flat spot was ground on the shaft of the wiper motor. A steel bushing (with set screw) was soldered to two steel reinforcing brackets laid end-to-end. A frame to fit around the wiper motor was formed out of 1/4" copper tube, and a steel washer was soldered in place for the wiper shaft to be bolted to.
Instead of using tubes and springs for the entire tail, I attached a long spring removed from the inside of a spring-type shower rod. Two screws hold the long springs into the copper pipe. On the end of the back frame, two hitch pins lock the other ends of the springs into the pipe ends of the frame.
A test was done by running steel picture frame wire from the ends of the steel brackets down to the first copper tube in the tail assembly. When the wiper motor swings the bracket back and forth, the cable pulls the tail back and forth. The springs allow this oscillating motion to carry through the entire length of the tail.
Two brackets soldered end to end, with a steel bushing to attach to the motor shaft.
The wiper motor is held in place by a frame made from 1/4" copper tubing.
The mostly completed tail assembly. The springs attach directly to the shoulder frame. Springs above the motor allow for the whole tail to swing back and forth, but with motion restricted closer to the body.
To add a "twitch" to the end of the tail, I modified a small gear motor. The motor came with a steel frame for mounting, an arm mounted to the gear drive, and a steel rod attached to the arm. The mounting frame was cut off short, then the gear arm bent up, parallel to the gear shaft. A cover for the moving parts was constructed out of brass sheet and a couple sections of tubing. The smaller tube extending from the large pipe is just large enough for a piece of vacuum tubing to be held in place.
The motor frame was then bent back, parallel to the motor, then the pipe shield positioned over the arm and rod. The shield was pop-riveted to the motor frame. A short section of 1/2" copper pipe was then positioned and riveted to the frame. (A stainless steel hose clamp provides some extra holding power, in case the rivets aren't enough.)
Silicon grease was forced into the hose, then the hose slid over the bent steel rod. The grease allows the steel rod to rotate inside the tubing when power is applied to the motor. The tubing rotates very little, but the bent rod will deform the tail back and forth, and even raise it slightly off the ground.
(This is the same technique used with "dancing flowers". The figure remains "stationary", facing one direction, while the rotating rod causes the figure to gyrate or "dance" back and forth.)
The copper tube is fastened to the spring at the end of the tail. Split loom tubing protects the wires from the motor and extends up the center of the spring, then along the outside of any copper tubing sections. Wires from the wiper motor enter the tubing as it passes the upper motor, and extend up to the back frame. These terminate in a 4-prong connector that will be mated to wiring on the back frame.
|The small gear motor with constructed shield.
The shield is riveted to the motor frame, then a copper pipe is riveted and clamped to the frame.
The greased tubing in position over the steel rod.
|Covering the tail
Constructing the tail entirely out of foam would make it too rigid to easily move with the wiper motor. To allow the tail to bend easily, flexible dryer vent and air duct hose was fastened to the spring and tube construction with cable ties. Duct tape was used to smooth the connection between the hoses. Cardboard over a foam core was used at the end where the tail attaches to the body, and another sheet of cardboard was bent over the top, leaving a gap for the wiper motor cables to pass down to the first tail joint (inside the larger hose.)
A thin covering of 1/2" foam was used to cover the tip of the tail, where the small gear motor extended its rubber hose-covered wire. Foam of increasing thickness was glued over the flexible duct to create a support for the fabric scales that will be added in the finishing stage.
The two springs extending from the tail section were trimmed off to about 2" in length, and the last loop was bent up to anchor the tail to the back frame. Holes were drilled in the end of the back frame tubes and spring clips passed through the loop in the spring and prevent it from pulling out of the end of the tubing.
Hitch pins hold the tail securely, and allow it to be quickly connected and disconnected without special tools. The cable for the motors connects to an extension from the control panel fastened to the brace on the back frame.
Flexible hose is fastened to the tail using plastic cable ties. Foam is then glued over the top of the tubing to further shape and create a tapered tail.
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