Patent Application
20100311306
Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to gravity-driven car racing, specifically an improved electrical timing start switch for race tracks such as used in the popular Pinewood Derby race.
2. Prior Art
Millions of Pinewood Derby races have been run since the inception of the race in 1953, mostly by Cub Scouts and their parents. But the currently available race tracks have a problem in the way electrical car start timers are turned on. Refer to the prior art
Referring again to prior art
The present invention eliminates the imprecise coupling between the mechanical gravity start and a corresponding electrical micro switch-based start signal. The gravity starting trigger mechanism itself is configured as an insulated normally closed contact that will immediately start the race timer when opened. The difference in the time when the start posts allow the car to move and the time such a trigger “switch” activates the timer is then reduced to an extremely short and precise time. This time is that taken for the twisting action of a solid mechanical drop member to propagate from the trigger release point to the starting post /car nose contact point. This delay can be estimated, from the speed of sound in the drop member and post material, to be only 20 millionths of a second for a one lane track.
This application can best be appreciated by referring to the related application Ser. No. 12/321,320 which is now pending. This earlier application also deals with a start gate improvement, but from a mechanical rather than electrical perspective. This earlier application replaces the prior art spring,
Thus, patent application Ser. No. 12/321,320 should be consulted for a full mechanical description of the start gate. Some mechanical details will be reviewed herein as the connection between electrical and mechanical performance is related. The start gate in a holding or cocked state is shown in
Also shown in
An enlarged view of the journal bearing assembly 40 is shown in
It is important for electrical continuity that the metal drop member 33 be rigidly attached mechanically to the metal start post support rod 32 by soldering or welding. In operation, given in more detail later, a slight but purposeful movement of the metal trigger lever 35 in response to the motion arrow of lever 37 will release the drop member 33. Thus the entire rigid pendulum assembly is able to fall and swing under gravity forces as a compound pendulum, in the process releasing the gravity driven cars to gravitational acceleration. Because of the natural smoothness of the pendulum swing at 1 G of acceleration, the cars will begin an unimpeded acceleration of approximately 0.5 G, and without gate slap car jostling, the acceleration onset is well defined.
Back to
As just described, a normally closed switch is thus formed from the trigger lever and drop member contact along with appropriate wiring and select placement of insulation. The enlarged view in
Again, in slow motion, consider the initial twisting torque applied to the pendulum assembly because of its inertia and the force of weight 34 acting over a lever arm distance of about 5 cm to its pivot point. The twisting motion will be propagated first to the left down the drop member to the start post support rod 32, then to the base of start post 22 and then up the post to the point where the start post touches the car nose. The twist motion could have components of both transverse and longitudinal acoustic wave propagation, which in common metals like steel or iron are both approximately 500,000 cm per second. The point where the car nose touches the start post is a distance of about 10 cm through connecting metal to the right tip of member 33. Therefore, the car nose is released to gravitational acceleration approximately 20 millionths of a second after the timer is started, assuming instant electrical communication.
As a first alternative embodiment the side view
A second embodiment includes the addition of a signal inverter 61 in the leads from terminal assembly 41 before they continue to the timer as the wire pair 21. Some of the commercially available timers used in gravity driven model racing may not accept opening of a normally closed contact as a valid input trigger. Such timers require a normally open contact going closed to start the timer. For these, a signal inverter can be used as shown. The signal inverter is a common flip-flop type of electrical device that will give an open output as long as its input is in a normally conducting or closed state. This is usually accomplished by sending a very small bias current through the normally closed input contacts. And, when the inverter input switches to an open non-conducting state, the interruption of its bias current causes the inverter output to immediately flip to a conducting state, just as when a normally open switch closes.
A third embodiment is shown in
The reader can see that the described embodiments of the improved electrical switch will allow a race timer to start substantially closer to the proper moment when gravity acceleration of the car begins. The separation of the drop member from the top of the trigger lever is the gravity turn on switch when car motion begins. This identical separation, then, can also serve as the timer turn on switch. As can be seen from the specification description, for this to be possible unusual attention must be paid to ensuring electrical continuity among the several mechanical parts of the start gate. Also, insulating bushings and washers must be placed at appropriate points to isolate the electrical path.
Prior art start gate builders simply did not care about the fine points of ensuring high precision between gravity acceleration onset and timer start. Most race timers are usually sold separately from the commercial race tracks that incorporate start gates. The levered micro switch became a quick and convenient interface in applying a timer from a large commercial selection to a wide commercial variety of tracks. But this invention, in combination with Ser. No. 12/321,320, can also be easily retrofit into existing commercial tracks.
A few prior art timer starters use a light beam shut off by the car noses. But these use after-the-start motion rather than its onset, also giving a false start time. And, the shape of a car nose may affect how the light beam is interrupted, thus affording an unfair advantage to some cars.
A model pinewood derby car will travel at about 480 cm/sec or about 11 mph if started at a 4 foot elevation. In one millisecond (ms), the distance traveled is 0.48 cm or about 3/16 inch. We have measured prior art type start micro switches and found that the start time errors can show a bias of about 10 ms and a standard deviation of about 4 ms. The bias is the average time delay between the application of gravity acceleration to the car and the timer start electrical signal. The standard deviation is a measure of the random time errors in the timer start signal. On the average the prior art start time is thus delayed by an amount that is equivalent to 1.9 inches car travel at the finish line with a standard deviation of plus or minus ¾ inches. For several cars released simultaneously, they all suffer the same timer start delay relative to gravity force onset, which would not be a factor in which one wins the single heat. But in repeat races of a single car to get a time average to separately compare with single race averages of other competing cars, the random error of plus or minus ¾ inch is indeed a factor in which one wins. And when one is trying to fine tune the performance of a single car through repeat runs, the ¾ inch error is a very significant factor. Also, when one is comparing a simulator theoretical time to an experimental time, the whole 1.9±¾ inches is a factor. In terms of car lengths at the finish of a 7-inch long model car, this error ranges from 16% to 38% of a car length. These errors are substantial, and with the present invention, they can be reduced to only 20 millionths of a second mechanical delay or 0.004 inches at the finish line. The electrical signal delay is of no consequence, as it travels at ⅔ the speed of light in the wiring.
This application is an extension of an already filed related application Ser. No. 12/321,320. In that application, it is shown that prior art builders also did not appreciate the unnecessary variance in race start times caused by using strong springs to open their start gate. And there it is shown that the drop member and trigger lever arrangement used to drop the pendulum assembly can substantially improve the race time repeatability by allowing a smooth controlled start. Thus the previously-filed application and this present application improve respectively the mechanical and electrical precision of the race start. Thus, the pendulum-based start gate can be used to improve timing start even if a prior art micro switch is used. And the use of the drop member and trigger lever separation as a start signal can improve start time accuracy even if the prior art spring activation is used. The best timing start precision, however, is to apply both inventions in combination as in the preferred embodiment here as supported by related application Ser. No. 12/321,320.
While the above invention contains many specificities, these should not be construed as limitations on the scope of any other possible embodiments, but rather as examples of the presently presented embodiments. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the descriptive examples given. For example, the electrical connections may be modified somewhat from those showed in the preferred or alternate embodiments without changing the basic concept of the invention.
This application claims the benefit of patent application Ser. No. 12/321,320 filed Jan. 16, 09 by the present inventor, which is incorporated herein by reference.
