Rubber Bands Drive This Baby Auto Three Miles (Feb, 1933)
Rubber Bands Drive This Baby Auto Three Miles
by DICK COLE
Here’s something distinctly new in the way of midget autos. Powered by a battery of rubber bands from old inner tubes, it will cover a distance of three miles at a surprising clipâ€”and on one winding. Seated at the wheel you’ll be the envy of all the youngsters in town.
Be there the boy with soul so dead, Who to himself has never said: “Gee, I wish I had a baby auto.”
THIS article will make those wishes come true. Here is a nifty looking baby with clutch, two forward speeds and reverse, and Free Wheeling. The design is simple; the materials are cheap; which brings the building of this miniature car within the scope or the average mechanically minded boy’s pocket book.
It is powered with rubber band motors!
Now don’t let skepticism enter your mind until you have listened to reason.
To show the reader how much power can be stored up in the rubber band “motor” of the baby car, I shall illustrate. Suppose you looped three, heavy-duty, 6″ inner tubes of good, live rubber over a solid post, and looped the other ends around the bumper of a light car. Now start the car. The tubes will stretch out about five times their original length and will actually stall the car in low gear.
Now think of the potential energy possessed by those stretched tubes! Think how high they could hurl a rock if made into a giant catapult!
That is the potential power stored in the rubber band motorâ€”only more. When the amount of rubber contained in three inner tubes is cut into narrow strips, the rubber has a greater elastic limit. The purpose of the rubber band motor is to conserve all the available power and deliver it to the wheels of the car in an even flow.
The plan and side view in Figs. 9 and 8 respectively, are not offered to familiarize the builder with the general working principles of the baby car. Here we see the sixteen rubber band motors which contribute their twisting torque through a train ‘ of small gears to a common master gear. This, in turn, operates the pinion gear shaft which communicates the power to a cross-shaft, thence by belt drive to the wheels.
The forward drive is through the right rear wheel only, and two round leather belts running over V pulleys of different sizes provide two speed ratios. Normally the belts are free on the pulleys, but an idler pulley can be brought to bear against either belt. The contact surface of the V pulleys is highly polished so that very little friction is contributed by the slack belt.
The driven pulley floats freely on the back axle, and is fitted with a simple side ratchet device which engages the wheel itself. This provides free wheeling when the rubber band motor is stopped.
This is done by pressing the left pedal. This action snubs a turn of sash-cord in a grooved pulley on the cross drive-shaft. See Fig. 9. Brakes are provided by passing a loop of sash-cord around a grooved pulley bolted to the side of each wheel, and leading the cord to the right pedal.
Each rubber band unit of the motor passes through a hole in the end cross rail of the frame and is fastened to a special clip (Fig. 10). This permits the bands to be stretched while winding, which adds greatly to the capacity of the motor.
Fig. 4 shows the frame of the baby auto. Let it be understood that this must be strong and rigid to resist the twisting torque and pull of the sixteen rubber band motor. It is well to tightly mortise, glue and screw all joints, and, as an extra precaution, cap the joints with angle plates. The middle rails support the transmission unit of the motor, but this is covered in a special detail (Fig. 3).
Front Axle Fig. 6 covers all the details of the front axle and the steering spindles. Carefully selected wood should be used, and an especially hard, knotty piece for the steering spindles. Birds-eye maple is recommended.
The sheet metal plates around the ends of the axle should be secured in place before cutting the notch to receive the steering spindle (See Fig. 6). The cutting can be done on a jig-saw with a metal cutting blade. The size of the wheel axles depends upon the size of the hole in the wheels used.
An old brake-rod with yokes, from an auto wrecking yard, will provide the tie-rods in conjunction with arms made of 5/16″ eyebolts. The steering wheel hook-up is shown in a later detail. The spring suspension method of the front axle is better understood by consulting Fig. 4.
In Fig. 6 we have the rear axle, drive pulleys, free-wheeling and the spring suspension of the midget car. The notations attached to the drawings should make everything obvious. Here we see how four discarded valve springs add support to the Otherwise rather flimsy springs.
The simplicity of the free-wheeling is shown in Fig. 1 and needs no explanation. It is the free wheeling feature which gives the baby auto its wide range of travel. A few impulse turns of the motor, then freewheel, and so on. By this economical means the car has a travel range of over three miles on one winding of the motor.
The sketch shows 12″ rubber-tired coaster wagon or scooter wheels used. These can be obtained from a hardware jobber dealing in toys, etc. They may have to be ordered special and cost about $3.50 a set of four.
In Fig. 3 we have the vital unit of the baby carâ€”the power and transmission assembly. While this may seem rather complicated at first look, it is really very simple. Stock gears are used throughout, and can be bought cheaply from manufacturer’s distributors throughout the country. If you have difficulty obtaining the gears, Modern Mechanix will inform you of your nearest agent.
Of course all the holes must be laid out carefully, and, for safety, it is best to allow about .005″ more than the regular pitch diameter to prevent the possibility of any binding. All the gears are “with hubs,” and it is better to pin them to the shafts than to trust to set screws only.
The location of the motor brake pulleyâ€” or clutch pulley:â€”is shown. It can readily be understood how a length of sash-cord can be led to the clutch pedal, and how it will snub the pulley when the pedal is depressed.
Fig. 9 gives the layout of all the pulleys. Selected white maple will serve for all the pulleys, but it is suggested that fiber or aluminum be used for the idler pulleys. These, of necessity, must be very thin to clear the idle belt.
Note that all the drive pulleys are grooved 60 degrees. Round belts are used for transmission, and after a little wear they will assume narrow, flat sides which will fit perfectly in the V grooves. Positive traction can then be had with very little tension on the belt, and if the grooves are sand-papered very smooth, little friction is offered when the belts; “idle.”
Fig. 9 shows the miscellaneous parts that enter into the complete car. The “gear shift” lever will appeal to boys who want all the do-dads, but if one forward speed only is used, the lever can be eliminated, as the free wheeling arrangement does away with the need of an idler pulley.
Fig. 8 offers a tentative design for the body of the midget car. This design is really a suggestion, only, subject to many variations at the whim of the builder.
The Rubber Bands Now for the all-essential source of powerâ€”the rubber bands. These can be had practically without cost. Visit some tire or vulcanizing shop and buy a quantity of discarded inner tubes. The prevalent market price is 1/2c a pound.
From out of this mass of rubber you are sure to find hopelessly blown out tubes with the rubber still live and active. With sharp, wire-edge scissors, start at the valve stem and split the tube completely around its inner circumferenceâ€”the part next to the tire flap. The tube now appears like a wide rubber belt Now start at some point on the edge and cut a 3/16″ strip around and around the belt. Eventually the wide belt is converted into a long, narrow strip of rubber.
Enough strips must be cut to provide 24 strands for each individual motor. The strands are looped in place without any pulling tension, and are held on their clips with a wrapping of soft wire wound in notches in the horns on the clips.
The motors are wound individually with a wheel drill, as with a model airplane. Be sure the motors are wound in the right direction and the same number of turns to each. Stretch the bands well while winding.
Use Graphite on Bands It is well to treat the rubber bands with rubber lubricantâ€”powdered mica or flake graphite. Under ideal conditions each motor can be wound nearly 2500 turns. The potential energy thus stored up, if used sparingly, in conjunction with the free wheeling, will give the midget car a three-mile range of travel.
A rubber band motored midget car is subject to a wide variety of designs. Perhaps the reader can think up a better design than this. Maybe a friction drive “job” with a wide range of driving ratios might be better.
No doubt more individual motors and a higher gear ratio would increase the travel range of this model. A commendable point of the design presented is that the driving gears are subjected to no end thrust, since the motors pull equally on both ends of the shafts. Keep this in mind when you design a car.
When a boy in any neighborhood builds a rubber band motored midget, his playmates are bound to follow suit. Competitive races are bound to ensue. Who knows but that we may have professional midget races? They race turtles nightly in Hollywood. Why not midget cars?