PAVAS – TSD Run Mode

This menu is entered from the Run TSD for selected stage menu. The TSD menu uses a Null Guidance Technique ((c) JCI 2018). This method uses low and high frequency tones to guide the driver to the desired average speed. To familiarize the driver with the frequencies used for the under speed low over speed high speed tones, they are played for two seconds at the start of the menu. They can be bypassed by pressing any key.

The next part of the menu is to select a stage. PAVAS can stored the parameters for up to 64 stages and it remembers the last stage selected and returns to that stage. The stage number is edited in the standard way of using the Up/Down buttons and the Left/Right buttons to select the digit. Once the stage number is correct, the operator presses the Select button.

PAVAS now displays the stage number and a Manual prompt on the top line and a rotating display on the second line. The rotating display changes every two seconds and shows the TSD Stage Speed, TSD stage distance, TSD stage time and finally the prompt to press Select to start. To review a parameter, the left and right button can be used to change the display. If this is done, then the display pauses on the selected parameter for six seconds before the automatic rotate recommences.

An alternative to starting the stage by manually pressing the Select button, is the Launch mode. This is designed to be engaged when the vehicle has reached the start line for the event. The Launch mode is activated by pressing the Up button. As soon as the vehicle moves, the stage data is commenced. In the case of a false start, the stage can be aborted in the first 500 meters by pressing to the Up/Down buttons. During this time, AAA is displayed in the upper row. The procedure is further discussed in the TSD Launch Mode page

Once the stage has started, Null Guidance tones commence and the top line of the displays shows the actual speed and prompt arrows. The second line is a rotating display that shows TSD Stage Distance, the Average Speed to date, the Stage Distance remaining and the Stage Time Remaining. The parameters displayed rotate every two seconds. These displays can be manually selected with the Left/Right buttons. Once selected, the persistence of the displayed parameter will increase to six seconds.

To aid the navigator, three arrows are displayed in the top row with the current speed. Up arrows indicates the speed should be increased. Down arrows indicate the speed should be decreased. At large diversions from the designated average speed up, to three arrows are displayed. As the diversion decreases, less arrows are displayed. In the case of overspeed the minimum number of arrows is one. In the case of under-speed the display will move from one arrow to three small rectangles. This indicates that the average speed in in the dead zone. Note this display is not for the driver but is to be used by the navigator.

The other feature of note is the ability to log the distance in reverse. This is described in PAVAS TSD Reversing

To understand the next section, it is useful to consider some mathematics. The time measurements are derived from the MCU clock circuit and are accurate to about one millisecond. The distance measurements are derived from the wheel pulses and have a resolution of approximately one meter depending the on the wheel diameter. So after a short distance of one hundred meters the accuracy is only one part in a 100 or about 1%. Due to the simple computation performed, this would also be the accuracy of the average speed reading. As the distance increases the accuracy of the average speed does as well, so that at one kilometer, the accuracy would be about 0.1 %. Now required accuracy of TSD average speed is typically about 0.1 kph. So to be useful PAVAS needs to be able to guide the driver to a speed accuracy of better than this.

The solution is an adaptive dead zone. At the half way point through a stage, PAVAS adjusts the dead zone parameters so it is reduced from 1 kph wide to 0.2 kph. The arrow displays correspond to the new dead zone value. The average speed format changes and is now displayed to 1/100 kph. This is intended for the navigator rather than the driver.

Finally, it is worth considering some mathematics again. Towards the end of a stage the distance traveled and the time taken are now relatively large values and, hopefully, the average speed is close to the desired speed. Since incremental distances and time periods are small with respect to the accumulated distance and time, there is less need to control the speed closely. This effect is called Average Speed Sensitivity (ASS). So to trim up the average speed, large speed excursions are possible and since PAVAS displays the average speed to 0.01 kph and is calculating the average continuously, it is possible for the navigator to provide guidance to get the average speed close to the ideal value at the end of the stage. The second point is that the digit in the second decimal place will be changing slowly and so it can be easily visually tracked. This effect can be tested in the TSD Demonstration mode. At the start of a TSD stage, ASS is high and falls dramatically near the end of the stage.