Drag race Christmas tree
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From: pimpom on 19 Nov 2009 14:33 pimpom wrote: > PeterD wrote: >> On Thu, 19 Nov 2009 12:14:37 +0530, "pimpom" >> <pimpom(a)invalid.com> >> wrote: >> > > There's still an important gap in my understanding of how it > all > works. The sources I've read say that the prestaging and > staging > points are detected with two beams of light, 7 inches apart, > near > the starting line. Fine, I guess I can use laser pointers and > photosensors coupled with the countdown circuit. The gap is > that > none of the sources say how a foul start (before the green GO > light comes on) is detected. No mention of a third beam. > > Since the staging detector beam is already cut off by the > vehicle's front wheel before the countdown begins, I don't see > how that can be used. Detecting the instant the front wheel > /leaves/ the beam seems unsuitable as variations in the size > and > design of the wheel will introduce a factor of uncertainty. Can > you or anyone else provide some enlightenment? Puzzle solved (I think). Although I have not seen a specific statement to the effect, I've come across some indication that the time a racer leaves the starting line /is/ taken as the moment the front wheel leaves the staging marker beam, thereby no longer blocking it. I also read that the beam is placed about an inch above ground. At that height, the wheel of a car or bike would be roughly a foot wide. From a standing start, the time taken for a part of that foot-wide section to cross the beam will be an appreciable fraction of a second. As a point of academic interest, that's quite significant when reaction and elapsed times are measured to within a millisecond.
From: Rich Grise on 19 Nov 2009 15:09 On Thu, 19 Nov 2009 21:24:53 +0530, pimpom wrote: > > Again, that question was mainly to get a feel of how it's usualy done. I'm > not so hot with programming and a computer-controlled option will still > involve designing and building the external hardware like sensors, power > supplies, lamps support structure, lamp drivers, etc. Given the limited > amount of time available, I think I'll stick to a purely hardware > approach. > > I've been thinking of using a crystal oscillator-counter with a 2 Hz > output - probably a 4060 - and good old 4017 decade counter, latched at > the 4th pulse. > > There's still an important gap in my understanding of how it all works. > The sources I've read say that the prestaging and staging points are > detected with two beams of light, 7 inches apart, near the starting line. > Fine, I guess I can use laser pointers and photosensors coupled with the > countdown circuit. The gap is that none of the sources say how a foul > start (before the green GO light comes on) is detected. No mention of a > third beam. You don't need precision timing for the Xmas-tree, just so it's consistent from light to light, so the driver has a sort of countdown. As far as staging beams, the vehicls stops at the first beam, with some kind of "ready" indicator. If the vehicle interrupts the second beam befor the tree goes green, then it's a foul. Is there some kind of structure between the two lanes at start? That way you could have two "foul" beams, so you could tell which one fouled. So, press the "ready" button, the red light at the top of the tree comes on, and if the contestants are "staged", you're ready to go Maybe put some kind of interlock, so you can't start until both vehicles are "staged". Operator presses "Go" button, the tree counts down, and as soon as the green comes on, send a "start" signal to the timer at the end of the track. I don't know how you'd arrange for two "finish line" beams without something between the lanes, but when somebody wins, who cares what the loser's time was? ;-) Good Luck! Rich
From: JeffM on 19 Nov 2009 21:45 Rich Grise wrote: >As far as staging beams, the [vehicle] stops at the first beam, >with some kind of "ready" indicator. >If the vehicle interrupts the second beam >[before] the tree goes green, then it's a foul. Close but no cigar. Interrupting the first beam lights the Pre-Staged light. Interrupting the second beam lights the Staged light. When both cars are staged, the Starter initiates the tree. Uninterrupting the first beam before the green light lights the Foul light. A handicap can also be dialed into one side of the tree. I've seen a 19-second car run against a 14-second car in bracket racing.
From: pimpom on 20 Nov 2009 00:43 JeffM wrote: > Rich Grise wrote: >> As far as staging beams, the [vehicle] stops at the first >> beam, >> with some kind of "ready" indicator. >> If the vehicle interrupts the second beam >> [before] the tree goes green, then it's a foul. > > Close but no cigar. > Interrupting the first beam lights the Pre-Staged light. > Interrupting the second beam lights the Staged light. > When both cars are staged, the Starter initiates the tree. > Uninterrupting the first beam before the green light > lights the Foul light. > According to what I've learned these past few days, even *that* is still not quite correct. Going past the first beam before the start (called "deep staging") is usually allowed, but it carries the risk of also going past the second beam and being disqualified.
From: Frank Buss on 23 Nov 2009 02:16
pimpom wrote: > Commercial units are out of the > question for now. This is not just due to cost, but also because > we don't have easy access to the services and facilities you take > for granted in more advanced places. If you have a parcel service like UPS, I think Digikey will deliver parts, but other shops can deliver full systems, too, if there are no export restrictions to your place. > I can't even ride a bike and what I know about what's needed is > what I've gleaned from the internet over the past 24 hours. None > of the organisers know all the details either. The event is to > take place about 3 weeks from now, so I told them that I'll do > some investigations but can't promise anything at such short > notice. 3 weeks is not much time for building a professional system. The low-cost solution: Some switches, some lamps and a human operator (someone sitting beside the start line and switching the switches while watching for false starts :-) -- Frank Buss, fb(a)frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de |