16 replies to this topic

[gary76]

At a race meeting recently and the position of the lap time transponder was brought up. After a while I convinced my colleagues that the position along the car was irrelevant as far as lap times were concerned but we came to a bit of a pause when race times were brought into the discussion. I would surmise that timing starts at the 'lights out'. Now in the event of a 'dead heat' a car with the transponder mounted at the front of the car will benefit over a car with the transponder mounted at the rear. There must be a simple explanation, is n't there?
I am sure this has been discussed before but I cannot recall.

[Lukin]

Your example is right. For a timed lap it's no different but if its close the guy with the timing device closest to the front has the upper hand.

In our series the x position of the timing reciever is mandated to stop this.

[Andy Donovan]

I'm glad you asked this, as it's something I've often idly wondered myself. I assumed that seeing as it's never mentioned it's not an issue due to it being mandated (as Lukin says it is), or everyone happened to put them in the same place due to packaging issues or something.

[kos]

Transponder position is mandated in the Technical regs:

20.4 Transponders:
All cars must be fitted with a timing transponder supplied by the
officially appointed timekeepers. This transponder must be fitted in
strict accordance with the instructions detailed in the Appendix to
these regulations.

http://www.fia.com/r...REGULATIONS.pdf

[mmmcurry]

When I raced radio controlled cars we had the transponders to time laps. I could not convince some people that for a timed lap it made no difference, however it would matter when its the first past the line.

Also somehow otherwise clever people claimed that the motor brushes would wear out quicker on one side 'cos there was more current on one side, err, how does that one work?

Steve.

[McGuire]

Originally posted by gary76
At a race meeting recently and the position of the lap time transponder was brought up. After a while I convinced my colleagues that the position along the car was irrelevant as far as lap times were concerned but we came to a bit of a pause when race times were brought into the discussion. I would surmise that timing starts at the 'lights out'. Now in the event of a 'dead heat' a car with the transponder mounted at the front of the car will benefit over a car with the transponder mounted at the rear. There must be a simple explanation, is n't there?

Yes, and you pretty much nailed it.

However, by the time this thread is over the issue could be nearly incomprehensible.

[phantom II]

A transponder responds to an incoming radio signal by replying with its own encoded signal. There's some transit time and processing time involved, but that's equal for all competitors. Xponders vary in sophistication, but even NASCAR with the most expensive system, depends on the camera lens to determine the winner. Unlike F1, the leader of each lap gets points and each position at the time of yellow flag drop, etc. is recorded just in case of a red flag to end the race.
In the case of NASCAR, they are all mounted in exactly the same position in each car by regulation.
At club solo I and autocross events, the xponder receiver they use takes too long to process the info and they have no multiple access and signal collision detection like NASCAR has, so in the event of a close finish, the winner can't be determined by this method no matter where the Xponder is mounted in the car.. The receiver is placed in a position where interference of other cars, be it sheet metal or carbon fiber is not a factor. Something not found at club events.
All x ponders are on the same frequency, using the same modulation method. Before a transponder responds, it must listen to make sure that the channel is free, and only then it transmits a brief identifying pulse. Because of it's nondeterministic nature, the system must allow for the possibility of signal collisions and be able to detect same. The alignment of the receiver antenna/s is also crutial.

Originally posted by gary76
At a race meeting recently and the position of the lap time transponder was brought up. After a while I convinced my colleagues that the position along the car was irrelevant as far as lap times were concerned but we came to a bit of a pause when race times were brought into the discussion. I would surmise that timing starts at the 'lights out'. Now in the event of a 'dead heat' a car with the transponder mounted at the front of the car will benefit over a car with the transponder mounted at the rear. There must be a simple explanation, is n't there?
I am sure this has been discussed before but I cannot recall.

[Patrick Sumner]

Originally posted by gary76
At a race meeting recently and the position of the lap time transponder was brought up. After a while I convinced my colleagues that the position along the car was irrelevant as far as lap times were concerned but we came to a bit of a pause when race times were brought into the discussion. I would surmise that timing starts at the 'lights out'. Now in the event of a 'dead heat' a car with the transponder mounted at the front of the car will benefit over a car with the transponder mounted at the rear. There must be a simple explanation, is n't there?
I am sure this has been discussed before but I cannot recall.

I raised this with MST Timing in April 2005 as my tiny brain couldn't work it out. Here's the definitive answer:

"If you are car racing in the UK it does not matter on the positioning of the transponder. - Front or back. Under MSA regulations it is a light beam which triggers the time and this works in conjunction with your transponder. Every passing of your car records the difference between the beam time and the transponder time and records that in a table. If you cross the control line with one or more competitors, we have a very accurate record to show the time when you had crossed the line if another competitor had not been in the way. This software in unique and many people are trying to copy it. You need this when timing cars like the 2CV who cross the line five per time or another example are the Legends.

John Ward
MST sports timing Ltd. "

[gary76]

Thanks Patrick that all begins to make sense, but I bet the argument will still continue in the many clubrooms.

[pUs]

Originally posted by mmmcurry
When I raced radio controlled cars we had the transponders to time laps. I could not convince some people that for a timed lap it made no difference, however it would matter when its the first past the line.

Also somehow otherwise clever people claimed that the motor brushes would wear out quicker on one side 'cos there was more current on one side, err, how does that one work?

Steve.

OT; They do wear quicker on the + side. I don't know the technical explanation for this, but in 12th scale racing it wasn't unusual to see people use different brush springs on the + side.

[mmmcurry]

Originally posted by pUs


OT; They do wear quicker on the + side. I don't know the technical explanation for this, but in 12th scale racing it wasn't unusual to see people use different brush springs on the + side.

Yeah, I noticed it too, but ther expaination given was obviously wrong.

Steve.

[McGuire]

Originally posted by mmmcurry
Also somehow otherwise clever people claimed that the motor brushes would wear out quicker on one side 'cos there was more current on one side, err, how does that one work?

Short story or long?

Short: in a simple DC permanent magnet motor, current flows from brush to commutator on one side and from commutator to brush on the other. On each side we have an anode and a cathode and a potential, so we will be performing some electrodeposition. Brushes of negative polarity deposit material while those of positive polarity remove it.

[mmmcurry]

Originally posted by McGuire


Short story or long?

Short: in a simple DC permanent magnet motor, current flows from brush to commutator on one side and from commutator to brush on the other. On each side we have an anode and a cathode and a potential, so we will be performing some electrodeposition. Brushes of negative polarity deposit material while those of positive polarity remove it.

Thats far better than the garbage I was told about more current on one side of the motor, thanks.

Steve.

[McGuire]

Originally posted by mmmcurry


Thats far better than the garbage I was told about more current on one side of the motor, thanks.

Steve.

Good thing I didn't give you the long version; it's really difficult to believe.

[desmo]

C'mon McG, my credulity could use a check.

[mmmcurry]

Originally posted by McGuire


Good thing I didn't give you the long version; it's really difficult to believe.

Thats got me interested.

Steve.

[McGuire]

Unless it is explained exactly right it reads sort of like Korean fan death.