No announcement yet.

Lap Counting: Dead Strips, Light Bridges, Other

  • Filter
  • Time
  • Show
Clear All
new posts

  • Lap Counting: Dead Strips, Light Bridges, Other

    Cool. SCI is back!

    So now we need to get some controversy going! Wake things up a bit!

    When it comes to lap counting I'm firmly in the camp of using dead strips for triggering. Yes, it is neanderthal technology. Nothing wrong with that! Sometimes the best way to solve a problem is a hearty whack to the head with a big old club. Dead strips have been with us since the very beginning, and they are still doing yeoman's service, thank you. Almost all the tracks I have raced on have used dead strips. If the car is in the slot, they work.

    The downsides of dead strips? Well, they are kinda -- dead. If you stop there you won't get going again without a push. Solution: Don't stop there.

    And your car has to coast across them. It can do that. Dead strips are only a few inches long. Put them on a long straight, you won't know they are there.

    If you are truly obsessive about it you can provide some power on a dead strip. It has been done, and it does work. Useful? Eh...

    Light bridges seem to be the most common alternative to dead strips. Upside? No power interruptions. Downside? More complicated. Still, done right, absolutely reliable. It's that 'done right' that can be an issue.

    Other options? Microswitches. Reed switches. Proximity switches. Something else?

    Right. Now I'm going to step back and await the incoming. Enjoy the show!

    Ed Bianchi

  • #2
    Anything can be made to work. Conversely some can screw anything up. Personally I prefer optical sensors (a.k.a. light bridge).


    • #3
      I like what Maddman said.
      HO RacePro, you sure do like controversy. We already had this discussion on another forum not a light year away from here - maybe 2 states.

      For my part
      - Dead strips aren't much use if you are using plastic track. Not many people have the tools to create them by cutting track sections up
      - Dead strips really do need buffer zones - and those buffer zones need sufficient gap to avoid arcing of longer braids
      - Dead strips require protection hardware components if you wish to run your track in both directions.
      - Dead strips cannot be quite as "plug and play" for the non technical track builder - and believe me, that is about 95% of them from my 13 years experience supplying track hardware.

      That said:
      - The absence of an overhead gantry is very useful - the "in-slot" photo sensor systems do not work very well, particularly at high speeds or when you have guides which are not fully opaque to IR 870/940nm wavelengths.
      - The dead strip means portable tracks can be set up more quickly. (I have a 6 module portable 90% built, it will use mono-directional dead strips)

      Light bridges are not however "more complicated" - really can't figure out where you get that idea from.
      Setting up a dead strip with buffer zones and bi-direction switching is actually more complicated

      LED light bridge system is simply a case of drilling a hole in each slot to underneath, poking a photosensor on a pre-made lead up the hole and taping it in place.
      When you have repeated that for each lane, you place the light bridge above them and plug it's supply into a power source.
      As I say, 95% of track builders struggle with wiring issues, not woodwork issues, so since a photo sensor system can be supplied ready to use, I think most people see them as easier to set up, and a solution without problems.


      • #4
        I've used both dead strips and light bridge/photo cells successfully. A few years back I converted both my tracks to the light bridge/photocell set-up and have not looked back.



        • #5
          Reed Switches mounted at the track surface with the blades flat to the plane of the track., Worked for years even with T-Jets.


          • #6
            HO RacePro does want to have a bit of fun. Have to remember that some of his choices are biased toward the type of track he builds. HO RacePro builds routed tracks using braid instead of rail and prefers cars with guide flags instead of guide pins. I enjoy this type of discussion as we can all learn something.

            My first response was rather short and sweet. I thought it was time to elaborate so here we go. Over the last 50 years I have worked with every possible way to count laps. These include Dead strips, Reed Switches, Optical Sensors, Cameras and Micro-switches. It also includes systems using relay driven impluse counters to the early "Digital/Analog" systems to today's truly digital PC based race management systems. All were made to work but . . .

            Dead strips are a very reliable system. As some have mentioned if you stop on then your car is not moving without a push. There are some arguments about having the dead strip wired to help the car across the lap counter or to try and stop the car when it hits the dead strip. Either way can be made to work.

            Problems that I have had with dead strips is the gap between conventional powered rails and the dead strip. An insufficient gap can cause the dead strip to short out. Another problem I have had with dead strips is pickup bounce. If the transition between gap and dead strip rail is abrupt, the pickup can lift off of the track. This caused failures in one event as the cars worked fine in slow speed testing. At race speeds the lapcounter missed as many laps as it counted. If the minimum lap time was set sufficiently low my guess is that the system would have double counted as well. Some of the early relay based dead strip systems would double count if the car bounced over the dead strip. If you are tying a dead strip into a PC based race management system you may need a special interface to make it work. Dead strips were the way to go at the beginning of time. They remain the default method for 1/24th. HO has for the most part moved away from dead strip systems.

            Reed switches were the logical replacement for dead strips as they were smaller, could be actuated by the cars motor magnets and did not require a dead strip. With magnets becoming stronger and being located closer to the rails, reed switches gained popularity. Unfortunately, it’s becoming more and more difficult to find a suitable reed switch as they are obsolete. Problems are finding a suitably sensitive reed switch and aligning the reed switch with the rail. I have seen reed switch systems fail rather spectacularly with in-line magnet cars. Mostly these failures resulted from false counts in adjacent lanes. This included a HOPRA nationals where the main had to be stopped, the reeds replaced and tweaked before the system was declared reliable and the race restarted. Note that the failure was detected in the fifth out of six segments and about 80% of the race had to be rerun. This resulted in a different winner. Getting a reed switch system to work over the range of cars from T-jets to NEO including Gravity would require an amazing amount of work and testing. I wonder if a closed can M-20 gravity car motor has enough stray magnetic field to trigger a reed switch located 1/8” from the motor?

            I won’t spend too much time on Micro-switches and cameras except to say they can be made to work. Micro-switches might require guide flags to operate at their best and might not be the best thing for HO cars unless you like cars with slide guides.

            This leaves optical sensors. Personally, these are my favorite. Some of the early optical sensor systems suffered from update time issues. This was for the most part resolved with the PC based race management systems. I installed Trakmate for DOS with optical sensors in the late 1990s for my first track's last big race. The system worked perfectly through testing and equally well for the event. I have at least 20 years experience with PC based systems that use optical sensor and for the most part they work perfectly. There were problems with the second-generation Trakmate cards that were eliminated by installing the cards in a Faraday cage. It appears that static electricity could cause the cards to reset. Installing the card in a grounded steel enclosure cured the problem. This problem was addressed by changes in later generations of the Trakmate card. I was a tester for Trakmate and Slottrak and identified many issues that were successfully resolved. This included multiple 24 hour tests and 50,000+ lap tests using test rigs to simulate cars crossing the light beam. The current generation of software/hardware is excellent. I will not comment on RC or Visaue as I have never tested their hardware.

            There are 1/24 and 1/32 installations that install both the emitter and sensor in the track and use the car’s guide flag to break the beam. Failures have resulted from guide flags that let too much light through. Painting the flag or replacing the flag with one made from a more opaque plastic seems to have resolve these issues. These sensors probably wouldn't work with guide pins as the beam is larger than the pin and the pin would never completely block the optical path.

            A major problem with optical sensors was matching up the emitters and receivers. You want to get them both on the same wavelength. The Radio Shack LED emitters operated at a wavelength of 950 nanometers. The Trakmate sensors operated at 850 nanometers. They were far enough off that they had a hard time working together unless you ran the LEDs at their maximum rated current. They did not live long if you did this. Once I found 850 nanometer LEDs I could build a light bridge that operated reliably with the LEDs drawing only 20% of their maximum rated current. Those light bridges lasted many times longer than the ones using the RS LEDs.

            The major issues with any lapcounter system are sensitivity, update time and reset time. If you get these right then just about anything can be made to work. I have seen all kinds of lap counter systems fail as result of sensitivity, update time and reset time issues. No system should just be used in a race immediately after it is installed. The installed system needs to be thoroughly tested to verify it is accurate and reliable. My test for an optical system is to attach a 3/8” wide wing to the front of a superstock car. The wing reaches into the adjacent lanes and is long enough to trigger their light sensors. The car is then driven as fast as possible for say 20 laps at a time. All the lanes tested need to have the same lap totals. I do something similar for a dead strip. With a dead strip I cover at least half of the dead strip with tape. I might first test the strip with the front half covered and again with the back half covered. I might also cover the middel of the dead strip to test for double counts. More 20 lap heats are run comparing hand counted laps with the system's display. They need to match. This test gives a safety factor of two and provides assurance that the system will count accurately. Like the optical sensor test a dead strip that has passed this test has never failed during a race.

            Can’t really do much to test reed switches, mirco-switches or cameras except to run laps and compare hand counts with the system counts. Unfortunately, these tests only show that it worked when you tested it. These tests do not provide any safety factor. History has demonstrated time and time again that a system that reliably counts laps with cars that cross the lap counter section at 20 feet per second does not guarantee that it will reliably count laps if the cars speed increases to 21 feet per second. A test that includes a safety factor assures success.

            That’s my two cents.


            • #7
              Yes, SlotsNZ, I do enjoy controversy! Done politely, I find it entertaining. Also, occasionally, enlightening.

              Anyway, how else can we keep conversations going on forums about little toy cars that we've been all wrapped up in since the 1960's?


              My first lap counter was the electro-mechanical gizzy made by Aurora way back then. It was designed for two lanes and used relays and ratchet wheels to count up to 99 laps. It used a variation of the dead strip to trigger same. It came with a 9-inch straight that was electrically isolated from the rest of the track. The power rails on the track were powered, with the lap counter relay in series. When a car crossed the track it completed the circuit, receiving the same current that operated the lap counter's relay.

              In theory that powered both the car and the lap counter. In practice there wasn't much power for either. The car was slow and the lap counter unreliable.

              So I added a 6-volt power supply to the circuit, in series. Originally I used a lantern battery. Later a transformer.

              When I built my 4-lane routed track, back in 1968, I added a second lap counter. A big investment! But hey, they worked. And my 'dead strip' wasn't really dead. With the added power the cars would cross it with alacrity.

              My two existing tracks, built back in the 1990's, use a venerable TrikTrax Mini-4 lap counter with an unpowered dead strip. It uses a wall-wart power supply and 5 wires to the dead strip. Bone simple and as reliable as sunrise. If I recall the TrikTrax cost something like US$300 -- a huge amount of money for me at the time -- but worth every centavo. I expect it will still be working like a trooper when I'm pushing up daisies. I need to leave it to someone in my will.

              There would be worse things in the world if someone would reverse-engineer one and restart production. The world needs simple and utterly reliable solutions!

              Ed Bianchi


              • #8
                Originally posted by HO RacePro View Post
                Solution: Don't stop there.
                What about track calls?


                • #9
                  My first lap counter was made from two Aurora impulse lap counters. They were tacky at best. However I made them work just fine. They were replaced after a few years with restable impulse counters. Unfortunately reset-able impulse counters are becoming hard to find. Hence the move to PC based systems.

                  Track calls have nothing to do with lap-counters. When a track call comes you turn the track power off. Lap counter power stays on. If you coast across the counter you get your lap.


                  • #10
                    Along with the TrikTrax counter Ed uses a GrayLab timer that is plugged into a remote controlled AC outlet. At the start of a heat the power to the timer is turned off and the timer is reset. The counter is zeroed and the remote's on button is pushed to start the timer. The track power relay is plugged into the timer so the track power comes on. For track calls the off button on the remote is pushed, that shuts off the timer and the track power relay. At the end of a heat the timer shuts off the relay and the track power goes off. You have to remember to hit the remote off button or the cars will start up as soon as the timer is reset. Some of the remote controlled outlets have an on and an off button, but the are also some that only have a single button.
                    If you are running a race with lane rotations you need to use a scoring sheet to keep track of each racer's total laps.
                    My own track used a similar system before I switched to Trackmate. I also have a TrikTrax counter and a GrayLab timer, but the remote controlled AC outlets were not available years ago, so I built my own track call system with red and green buttons mounted in boxes on extension cords. The buttons would normally be operated by a race director, but if there were not enough people one box could be located between driver stations 1 and 2 while the other one was between stations 3 and 4. The boxes with the buttons were connected to a control box with relays that switch the track power relays and also control two sets of red and green lights mounted at the back of the track.


                    • #11
                      Originally posted by Maddman View Post
                      Track calls have nothing to do with lap-counters. When a track call comes you turn the track power off. Lap counter power stays on. If you coast across the counter you get your lap.
                      But if you come to rest in the dead bit when the power comes on you won't move.

                      Not a massive deal if the DS is near race control and they spot you, but for sure a 'con' when it comes to comparing counting methods.


                      • #12
                        I was going to add that if you get stuck in the counter a marshal would push you though before power was turned back on. Guess I forgot about those who would need to have that explained to them.


                        • #13
                          I've never had an issue with a car's pickups shorting across the gap from the track to the dead strip. In fact I have set up dead strips mechanically parallel to power conductors, with maybe a 1/32nd inch gap, so that my Slide Guide pickup wires contact both at once. My TrikTrax and other counters -- including cheap ten-dollar eBay counters -- don't seem to mind the extraneous power connection. I assume they have a high enough input impedance that any 'short circuit' current is limited to milliamps at most. All their circuitry is looking for is a contact lasting long enough to time out their debounce setting.

                          I have seen polarity be an issue if you run the track in reverse. A nuisance, yes, but if you really want to run the track backwards it can be addressed with appropriate switchgear .

                          I can't speak for PC hardware. Proper design should prevent issues. But (I know my prejudice is showing!) in the PC world proper design can't be assumed.

                          The slotcar environment is really messy electrically. You have huge inductive loops -- the power conductors. A long pair of power conductors can have significant capacitance as well. Power supplies that are pulsing at high frequencies can put out radio frequency interference. Slot car motors have commutators that produce electrical spikes and sparks tens of thousands of times per second. Pickup systems arc and spark with gay abandon. All this going on with currents that can be tens of amps -- significant power.

                          Hey, I'm not even an electrical engineer, and all the havoc cited above makes me want to crawl into a Faraday cage and close the door!

                          Is it a wonder we're still having issues with our electronics and PC's?

                          Ed Bianchi


                          • #14
                            Originally posted by Maddman View Post
                            I was going to add that if you get stuck in the counter a marshal would push you though before power was turned back on. Guess I forgot about those who would need to have that explained to them.
                            As long as one is nearby, and paying attention. I have seen people lose finals when they are not. Bear in mind on the UK BigTracks marshals can be a long way away

                            Not a massive deal, but one of the reasons I don't use dead strips.
                            Last edited by NicoRosberg.; 02-04-2020, 11:53 PM.


                            • #15
                              Originally posted by HO RacePro View Post

                              I can't speak for PC hardware. Proper design should prevent issues. But (I know my prejudice is showing!) in the PC world proper design can't be assumed.

                              Ed Bianchi
                              Beggar me Ed - if you haven't become familiar with setting up systems with PCs, your experience of options is so limited, you cannot possibly provide an unbiased overview.
                              The problem then arises when people assume that your experience is rounded and advice is fully balanced.

                              Maddman has taken the time to provide a good overview and pros and cons of the issues

                              New people trying to learn what options are best for them may be misled.
                              I think your enjoyment of controversy via a thread like this is a bit mischevious.

                              I hope you consider your effect on others.

                              Last edited by SlotsNZ; 02-04-2020, 04:21 PM.