There are a lot of rumors and myths concerning GPS based data logging systems and most people reject it as a useful data source. Some drivers question the lap timing accuracy and reliability. Others claim that the racing line drawings and positioning precision is useless in karting. Actually the most common cause for problems is that they are “holding it wrong” or just using the wrong piece of equipment!
If you are already asking yourself “What do those RaceCloud guys mean by holding it wrong?” we are about to reveal the mystery.
Global Positioning Systems use radio signals to locate your position by sending information from satellites in the sky to your receiver. Obviously as a result the position precision depends on the signal quality, the number of satellites in range, the class of your receiver and hardware architecture. Well, you cannot easily improve the hardware you’ve got but you can influence the other factors.
Unfortunately the strength of the signal you get from the satellites cannot be easily improved either. In fact by the time it reaches your receiver it is extremely weak. However that is not a problem as long as it is clear of other noise and distortion, which actually causes most of the problems. In karting, for example – simply using a spark plug and spark plug boot without an integrated resistance dramatically increases the noise levels and as a result reduces the signal’s quality.
The key to having good reception is the GPS antenna itself. Since positioning relies solely on measuring signal reception time it requires unobstructed view to the signal’s source (direct line of sight from the receiver to the satellite). In other words – the antenna needs a clear view to the sky at all times. Any objects that cover its horizon will reduce the number of satellites in view, the signal quality and strength, and so will generate lower accuracy of the calculated position. Also nearby objects cause signals to “bounce” and degrade receiver performance even further by fooling the electronics into thinking they’ve got your location just right but in fact it is few meters away.
This is what we call the “holding it wrong” factor – finding the right location and mounting the GPS antenna. You are already asking “What could go wrong with this one?”, aren’t you? Well, fair number of things. Have you ever asked yourself why the RaceCloud BUNDLE’s Go-Kart MOTION is dedicated for mounting on the nose and should be there? Simply to be always on top and have the better part of 360* view from the top plane of the module to the sky. This guarantees the best possible visibility to the constellation of satellites in the sky. Remember what we mentioned in the previous paragraph – this is how you improve the GPS signal quality. For example if you place the GPS antenna upside-down, mount any additional equipment obstructing it (camera etc.) or locate it under a metal or other solid objects (like the steering wheel, foiled bodywork or chassis and frame elements) the device will have limited reception or will receive reflected signals – all leading to incorrect location being reported. Furthermore – mounting the antenna on a detail which is moving (steering wheel for example) constantly changes the visible part of the sky and satellites in view. All that put together – you can have 10-13-15 satellites when you are in the pit and still have very poor signal quality on the track or vice versa. In fact on number of occasions we have seen that having 6-7 satellites with very good signal quality gives far better performance than 12 with average strength. Taking a look at the figure bellow you will find a few incorrect locations and mounting of the GPS antenna (in red) and the right way to do it (in green).
The signal received by the GPS contains a very precise time stamp generated by atomic clocks on board the satellites. RaceCloud uses that information to calculate your lap timing to achieve milliseconds precision. If any of the listed above factors have been neglected, you will end up not only with incorrect racing line, but inaccurate lap and sector timing too. It may even miss counting some laps completely, if the interference is so great that the receiver thinks you haven’t crossed the start/finish or split line.
And here comes the good part! If you are holding the right tool in your hands and you are holding it as your manufacturer advised, you will get an awesome positioning accuracy (expect horizontal accuracy of 90 down to 20 centimeters) and lap timing precision within just a few thousands (0.00x) or 1-2 hundredths (0.0x) of a second. Well, this is what you can expect from a RaceCloud… we cannot guarantee that for other data loggers.