Rotary Racer - Drivers Manual

Rotary Racer - Drivers Manual

Software Version 14

Car Computer

The Rotary Racer car computer provides the following functions:

  • Measures and logs parameters including: Date and Time, Battery Voltage, Battery Current, Speed, Distance, Motor Temperature, Battery pack number and Battery charge levels.
  • Controls motor power via the PWM Motor Speed controller. The actual motor power algorithm sets the motor power to a value based on throttle position, the motor current and cars speed.
  • Protects motor and speed controller by providing soft start and limiting current.
  • Manages current usage to maximise the power verses battery usage compromise through race.
  • Protects batteries by reducing available current and issuing a warning when overall battery voltage falls below 21 Volts.
  • Controls the cooling fans based on the motor temperature.
  • Display warnings to the driver.
  • Logs all data to a SDCARD for later retrieval.

Car Display

The cars display panel has a two line LCD display, three LED's and 4 push button switches numbered 1 through 4 (Left to right). The display will show several separate pages of information. The modes are as follows:

Mode Description
0 Display: Speed (S), Battery Number (B0, B1), Battery Charge in %, Current (C) and Average Current (CA) since last reset.
1 Display: Average Speed (SA) , Average Current (CA), Peak Speed (SP) and Current at peak speed from last switch on (CP). Useful for checking the cars performance during testing. The Average speed and Average current values are for speeds over 35 Km/H so this eliminates the pre-lap and post-lap slow periods to give readings that would match those in a continuous race better.
2 Display: Voltage (V), Current (C), Temperature (T), and motor speed average setting (MA).
3 Display: Voltage (V), Current (C), Accelerator position (A), Motor Speed setting (M)
4 Set up Average current. The car computer will limit the average current consumption to this value. Normally set to 23 Amps (23.0).
5 Set up the current management algorithm. Normally set to 1.
6 Set up Data Log Frequency. Sets the data logging frequency in seconds. Normally set to 1.

The main items of interest on the display are the current (C) and average current (CA) values. The average current should be around 23 Amps. If it is above 25 Amps the car is unlikely to finish the race as the batteries will be exhausted. If the average current is below 23 Amps we could go faster by changing the Average current setting. The current (C) value will be around the 23 Amps but will go higher during acceleration, up hill and into the wind and lower on slowing down, down hill sections and with the wind.

 The buttons operate as follows:

Mode Button1 Button2 Button3 Button4
0,1,2,3 Turbo     Mode
4,5,6 Turbo  Up Down Mode

If all buttons are pressed together, then the Computer will reset all parameters to initial race start values.
The turbo button will turn off the motor current limiting for 20 seconds. This will give a "Turbo" boost assuming the cars gearing is set appropriately. The turbo button will not be able to be used for 2 minutes after previous use.
If there is a problem, the RED LED will  light and an appropriate message will be flashed on the panel. The main warnings currently available include:

Battery Low The battery voltage is low.  The maximum current has been limited to protect the batteries. Enter pits as soon as possible. If the voltage recovers full power will be restored after 20 seconds or after a reset.
Motor Temp High The motor is too hot. The maximum current has been limited to protect the motor.


The display LED's provide the following information:

Mode Red Yellow Blue
Accelerator off OFF OFF OFF
Accelerator at mid position OFF ON OFF
Accelerator at full position OFF OFF OFF
Warning ON OFF OFF


The twist grip throttle will control the speed of the car. The maximum current to the motor will be limited to 60 Amps, thus when the car starts off the throttle will not provide the actual full power available. This is done to protect the motor, speed controller and batteries.
As the cars speed increases above 35Km/H the maximum motor current available will be reduced until at and above 45Km/hour the motor current will be limited to 23Amps or whatever is set as the Average Current. So in normal racing conditions the Car Computer will regulate the maximum power available to make sure the batteries will last the race.
If the turbo button is pressed the current limiting system will limit the current to 60Amps rather than the Average Current setting for about 20 seconds. This will give a "Turbo" boost assuming the cars gearing is set appropriately.

When racing, ideally the car should be kept at full throttle (No Yellow LED on) for best performance. When having to slow down for sharp corners or the pits try and anticipate slowing down and use a lower throttle setting in advance to slow the car before hand rather than rely on using the brakes. Every use of the brakes effectively uses up power that could have been used to make the car go faster. Drive smoothly and safely being aware of cars both in front and behind you. Always keep an eye on the mirros so that you are aware of what is behind you. Where possible use the inner track as the lap distance will be smaller there but follow a smooth racing line.

Car Computer Settings

At the start of a race the Car Computer should be reset to defaults. This is accomplished by pressing all 4 buttons on the display panel simultaneously.
The modes 4 and 5 allow the Average current and data logging frequency to be set up. The Average current is normally set to 23.0 which is 23 Amps. The  data logging frequency is normally set two 1 second if an SDCARD is being used or set to 8 seconds for a race where two EEPROMS are used for logging data. This ensures that all of the data from a 4 hour race can be stored.


If you hear or see a mechanical failure of the car or if you smell smoke or see fire in the car do the following:

  1. Turn off the power using the battery isolator switch at the right of the driver.
  2. Drive the car off the track and stop as soon as possible.
  3. Get out of the car and wait near the car in a safe place off the track for rescue.


  • The car computer employs SDCARD EEPROM memory to retain critical information during power off. Thus there is no problem turning the power on and off during a race. A reset of the computer is performed on power on and can thus be used to clear some fault conditions and to clear the temparary peak and average values (as shown in mode 1).
  • The computer employs a Watchdog timer. This will reset the car computer if the computer has crashed for some reason.
  • If all buttons are pressed together, then the Computer will reset all parameters to initial race start values. This should be done just prior to a race.