If you are having a race meeting amongst friends at home then it would be diplomatic to have something up to the job but still not critical because the sheep stations are only little ones.
If you are running club events with points and/or prizes then you have little choice!! You can not afford to have a system that even drops one lap in a thousand. The person who has lost the lap will know it and your life will be misery from then on!!
So what's the solution?
My first question would be, do you want the sensors/program to be 100% reliable? 90% reliable, 70% reliable or almost useless. You think I'm joking don't you! trust me whem I say I have seen just about all of it now!!
Starting from the bottom I rate the little 'U' shaped emitter collector/units used primarily in 'Hall effect' devices as probably the worst choice. They work well but are not 100% and will aggravate a race meeting by not recording the odd speeding model with a shallow guide or anything with a blue (Scalextric) guide. SCX cars too are prone to missing laps with this little device, don't ask me why, I'm only interested in things that work!!
Next up are lane sensors mounted in the track surface beside a slot. A good system but some Red cars, especially F1's may not record odd laps as the models are IR transparent and will allow the IR part of the illumination to pass right through the body and not record a lap' . Also, some of the new Classic F1's are that narrow that on a warm day or in bright room lighting there will be enough light bleed past the side of the body to not record a passing car. True!
IR emitting LED's. again not my first love. They don't have a long range. LED's set to allow trucks to pass underneath may well be too high for the sensor. One solution is to reduce the value of the accompanying resistor. This will increase the LED's emission intensity but this will move the IR LED reliability into the doubtful zone!
Next up is the sensor in the slot. this can have its reliability impaired by mounting it too deep and allowing a build up of detritus over the sensor with a consequential loss of recording ability.
Lastly there is the dead strip. Probably one of the most reliable systems but they are just that, a dead strip. They need to be considerably longer than the length of the model braids if operating on a computer of less that 400 processor speed. In the wrong place you can experience brief model stall, especially at starts. The dead strip needs to be accompanied by extra electronics to transfer the high/low signal to the low voltage terminals of the computer. If any stray or ambient voltage makes its way to the parallel port you run the risk of burning out your mother board. So a type of opto couple system or similar will be needed in conjunction with a dead strip. So what can we do.
First pitfall is the computer processor speed. I recommend at least a 400mhz processor and 250 meg of ram for the average race management program. If this is the case, ALL other programs will need to be removed from the computer! It is my experience that a lot of race management systems are run on old upgraded computers. When a computer boots up it will initiate a whole plethora of programs which will run in the background just waiting to be called upon, these programs take up ram and procesor speed before you have even started. Microsoft programs are notorious for this. Programs like Office and Internet explorer take a chunk of anything you leave laying about, leaving the poor old race manager to wait in the queue for access! Better still, if you are using an old box, format the hard drive and re install windows basics only.
Next, if you are using an old box and the program has the function to let you put custom sounds in for different track events either
a. Don't use any custom sounds
b. Make sure the custom sounds are the smallest files possible. ie edit them on a sound editor like the microsoft sound recorder which comes with most versions of windows. Keep them below 50 kb and save them as 8 bit sound.
Why, when the program triggers the sound to play, the computer will prioritise it and if it's too big, someone passing through the lap counters will not record the lap as the processor is too busy!! True!!
Another pitfall is the loss or non recording of a lap if two or more cars pass over the sensors together. Again caused by a slow processor or too much running in the background!
Another pitfall is the non recording of a lap because the model has not broken the beam for a sufficient period due to extraneous infra red in the area of the sensors. In Queensland in the summer we can run most lap counter systems situated in a bright room or shed in the garden without lights or IR emitters because there is so much ambient IR. Especially in metal sheds!!
Another pitfall is , as mentioned before, not enough model mass to cover the sensor for long enough.
Scenario: The sensors are fitted near or at the beginning of a straight. It goes that if this is the beginning then there must be a curve prior to it. Open wheeler models taking the last corner before the straight can sometimes get sideways at the beginning of a straight allowing only part of the front suspension to pass over the sensors!! Not enough.
Tracks with 'in slot' sensors can get a dust build up on the sensor!! This sensor is mounted too low!! Push the sensor up through the slot base and run a model over it to set its height. Have the sensor protruding from the bottom of the slot if you have space!
My preferred mounting.
1. Always use as big a component that you can find for the sensor. 5.00 mm dia or better,
2. When mounting in the bottom of a slot (my preferred position) make sure it is proud of the bottom of the slot to deter dust build up above it.
3. Carefully enlarge the area of track directly above the sensor to seven or eight mm to allow more light in.
4. In wood or black plastic, paint the area around the sensor hole wit silver or aluminium paint to enhance its light collecting abilities.
5. Use incandescent bulbs directly above each sensor. LES or MES types. The brighter the better! IR emitters have a short range and a very narrow beam width, sometimes as little as ten degrees and, as you can't see them working, it can be frustrating trying to determine if they are emitting!! (apparently, a digital camera focused on the light will show its beam but I have never tried this!)
6. Finally, don't mount the lap timer lights anywhere a driver can reach. There may be a deslot and if near a driver, they are always tempted to reach over and marshall their own model. This is when wayward hands pass under lap timing gantries to reclaim their model and as a consequence, laps can be added to other drivers tallies if the false trip time in the program (if it has one)isn't set correctly. But worse still, the scramble for the model may see the light gantry dislodged, bringing the race event to a premature close!!
So there are a few pointers to start with, I will add that these are based on experience in real competition and not the meanderings of someone who hasn't actually been 'OUT THERE'
If you have any words of wisdom that could be added to this please do not hesitate to post a reply. There is too much myth involved with lap timing and it must be dispelled.