SRM sometimes misses passing cars
17/01/2009 15:38 Filed in: Error message
Sometimes, SRM can miss a car when passing a timing sensor. This can have numerous reasons, but most of the time a hardware error is the cause. In general, there are a few things you need to pay attention to when you are going to place your sensors:
- place them on a slow piece of your track
- check that a cornering car going wide can not trigger the sensor of his neighbour
- check your cable from the sensors to the PC. This cable is often highly sensitive to electric fields and may not be close to current transformers, track power cables or the metal conductors of your track. Try to keep is as far away from electrical stuff as possible.
What if SRM misses cars and other software does not, using the same sensors?
This is possible if you have a slower PC on which you run the timing software and more cars pass simultaniously. Due to the complexity of SRM’s timing loop, it takes an amount of time to run through it. This is the routine, very much simplified:
TIMING LOOP
car detected on sensor1? Then go to DETECTION
car detected on sensor2? Then go to DETECTION
car detected on sensor3? Then go to DETECTION
car detected on sensor4? Then go to DETECTION
car detected on sensor5? Then go to DETECTION
car detected on sensor6? Then go to DETECTION
car detected on sensor7? Then go to DETECTION
car detected on sensor8? Then go to DETECTION
DETECTION
1. calculate passed time since last detection
2. is this a fastest laptime? Then store it
3. calculate speed
4. is this a fastest speed? Then store it
5. calculate difference with leader
6. put info on screen in big letters
The Timing Loop is running constantly. When a car passes, the Detection loop is activated for that car. Only one Detection loop can run at a time, so if 3 cars pass simultaniously, the Detection loop has to be triggered 3 times during the time window that the 3 cars are still on the sensor (because if the 3rd car is off the sensor when the Detection loop is completed for the 2nd car, the 3rd car is NOT detected anymore!).
On a slower PC (e.g. a 386), let’s assume that the Detection loop takes 0.004 seconds to complete. In this time, a fast slot car can travel 10mm. If your trigger is a slot mounted trigger detecting guides, you can miss the second and will shurely miss the third car here! If you have a track mounted light sensor with an overhead light source, you will have the full length of the car to detect and you will catch the 2nd and 3rd car too.
On a fast computer (a Pentium machine or better), you won’t have this problem, because the detection loop takes much less than 0,001 second to complete. Other, less complex programs like Trakmate will not have this problem too, because they have a much shorter Detection loop. This is because they do not have as many steps in the detection loop (e.g. only steps 1 and 2).
- place them on a slow piece of your track
- check that a cornering car going wide can not trigger the sensor of his neighbour
- check your cable from the sensors to the PC. This cable is often highly sensitive to electric fields and may not be close to current transformers, track power cables or the metal conductors of your track. Try to keep is as far away from electrical stuff as possible.
What if SRM misses cars and other software does not, using the same sensors?
This is possible if you have a slower PC on which you run the timing software and more cars pass simultaniously. Due to the complexity of SRM’s timing loop, it takes an amount of time to run through it. This is the routine, very much simplified:
TIMING LOOP
car detected on sensor1? Then go to DETECTION
car detected on sensor2? Then go to DETECTION
car detected on sensor3? Then go to DETECTION
car detected on sensor4? Then go to DETECTION
car detected on sensor5? Then go to DETECTION
car detected on sensor6? Then go to DETECTION
car detected on sensor7? Then go to DETECTION
car detected on sensor8? Then go to DETECTION
DETECTION
1. calculate passed time since last detection
2. is this a fastest laptime? Then store it
3. calculate speed
4. is this a fastest speed? Then store it
5. calculate difference with leader
6. put info on screen in big letters
The Timing Loop is running constantly. When a car passes, the Detection loop is activated for that car. Only one Detection loop can run at a time, so if 3 cars pass simultaniously, the Detection loop has to be triggered 3 times during the time window that the 3 cars are still on the sensor (because if the 3rd car is off the sensor when the Detection loop is completed for the 2nd car, the 3rd car is NOT detected anymore!).
On a slower PC (e.g. a 386), let’s assume that the Detection loop takes 0.004 seconds to complete. In this time, a fast slot car can travel 10mm. If your trigger is a slot mounted trigger detecting guides, you can miss the second and will shurely miss the third car here! If you have a track mounted light sensor with an overhead light source, you will have the full length of the car to detect and you will catch the 2nd and 3rd car too.
On a fast computer (a Pentium machine or better), you won’t have this problem, because the detection loop takes much less than 0,001 second to complete. Other, less complex programs like Trakmate will not have this problem too, because they have a much shorter Detection loop. This is because they do not have as many steps in the detection loop (e.g. only steps 1 and 2).