Overview

Advanced systems – exceptional accuracy

All RT3000 family products incorporate two distinct and complementary sensor systems – a six-axis Inertial Measurement Unit (IMU) and a survey grade GPS receiver – to provide a level of confidence never before available to the vehicle testing engineer. Measurements acquired by three micro machined, navigation grade Servo (force feedback) Accelerometers and three solid state angular rate sensors are used in conjunction with GPS signals and advanced Kalman filtering to provide bias-free and scale-factor-free measurements.

The RT3000 family uses GPS to determine position and velocity (as well as heading on models equipped with dual-antenna functionality). The Kalman filter at the heart of the system also uses GPS signals to prevent the Inertial Navigation System from drifting, as well as to predict and correct any errors that may occur. This important feature separates the RT3000 family from conventional vertical reference units (VRU's) or stabilized platforms, which tend to drift and lose accuracy over time.

Unlike most GPS-only devices, the velocity output is free from jumps and glitches. This is because measurement values from the system's Inertial Navigation Systems are derived from the accelerometers and gyros. The GPS (when available and suitably accurate) is only used through the Kalman filtering process to update the inertial measurements and maintain accuracy. Even then, the corrections made by the Kalman filter are smoothed to ensure there are no jumps in the output.

The outputs of the Inertial Measurement Unit (IMU) are integrated in a WGS-84 strap down navigator – making the system immune to effects of earth rotation, transport rate and Coriolis accelerations. The strap down navigator also provides real-time outputs, while the GPS receiver and the Kalman filter enable very low latency measurements.

Working in concert, the components function to provide a wide range of exceptionally reliable angular and position based measurements. For example, by combining heading and velocity, vehicle slip angle or yaw angle can be determined with unprecedented ease and accuracy.

Available configurations

Each of the RT3000 family products uses the same inertial platform and processing engine, but incorporates either Real-Time Kinematic (RTK) GPS, or standard differential GPS (DGPS) to optimize price/performance ratios demanded by a wide range of user-specific applications. RTK systems use L1 (civilian) and/or L2 (military) signals. Products are also available with single-antenna or dual-antenna configurations. Dual-antenna configurations offer the added advantage of providing highly accurate heading data, even at standstill or under low-dynamic conditions. All models are equipped with high-performance, carrier-phase tracking GPS receivers to ensure maximum performance. For adaptability to changing demands, all products are easily upgraded.

The L1/L2 RTK and L1 RTK GPS can be supplied with their own base stations, normally an RT-Base. Data is transmitted from the base station to the vehicle via radio modems. Post-measurement processing software is available as an option, which allows real-time stand-alone data quality in the vehicle and later high-precision results by post-processing with the data from a base-station receiver. For real-time monitoring of data output, a user-supplied laptop computer running Windows is recommended. Outputs can also be sent directly to other equipment, for example into multi-beam echo sounders and data acquisition systems.

Superior accuracy

RT3000 family provides superior accuracy and performance compared to distributed systems of accelerometers, gyros and GPS. By combining these individual systems in one box and processing the data using high-power microcomputers we deliver performance that vastly exceeds the accuracy that can be obtained from individual sensors.

Position accuracy to 2cm

RT3000 provides position accuracy to 2cm under dynamic conditions, enabling high accurate in the following applications:

– drift measurement
– driving-line measurements for racing applications
– steering robot operation
– survey for simulators, for example for inside/outside track measurements, height profile, road camber, etc.
– survey for non-automotive applications, such as aerial photography, marine multi-beam echo sounders, rail survey and land survey where GPS alone is less than acceptable.

Like most survey L1/L2 GPS receivers the static positioning accuracy is better than 2cm, but under dynamic conditions GPS-only receivers degrade their positioning accuracy.

Heading accuracy to 0.1°

The RT3000 family can maintain a heading accuracy of 0.1°, even when stationary, using a variety of techniques. These include Advanced Slip, Heading Lock and Dual-Antenna GPS. This means:

– the ability wait at standstill while examining data (literally for hours) – with no degradation in accuracy and no need to restart the system
– accurate heading/slip angle measurement on low-friction surfaces such as ice, as well as in low acceleration applications such as drift tests and highway testing

Pitch and Roll accuracy to 0.03°

The RT3000 family is continuously corrected using GPS. The Kalman filter provides a fast, 33Hz update to the inertial solutions and the GPS is run at 10Hz (it could run this faster, but 10Hz is about the limit of useful information from the GPS, after this the measurements become too correlated). These fast update rates enable the RT3000 to compute exceptionally accurate orientation measurements.

Speed accuracy to 0.05km/h

Few, if any systems can match the real speed accuracy of the RT3000 family. The L1/L2 RTK models of the RT3000 optimally combine the precision GPS positions with the integrated accelerometer measurements to give very precise measurements of velocity and speed. To accomplish this, the 33Hz Kalman filter works to blend all the available measurements and apply them to give very precise outputs.

Fast, low-latency processing

Every RT3000 family product offers exceptionally low calculation latency, output signals are transmitted a mere 3.9ms after measurements have been made. Combined with a standard 100Hz update rate, this means a significantly better performance than GPS-only systems. The bandwidth of the RT3000 is also wider than GPS, which is limited to about 5Hz due to the way the tracking-loop works. (This is why 20Hz GPS is already faster than the useable limit – 100Hz is computed, but offers little advantage).

RS232, CAN bus or Ethernet interfaces are used to output real-time data, and all measurements are synchronized to GPS time, to allow easy comparisons between multiple test vehicles and/or systems. Optionally analogue or RS422 interfaces can be used.

Full data logging capability

RT3000 family provides full data logging capabilities, with 500 MB internal memory as standard. Logged data can be downloaded quickly via a standard Ethernet connection.

Real-time QNX operating system

Internal to the RT3000 family lies the powerful QNX real-time operating system. Additional software enables real-time monitoring of test data, system configuration and control of download and data logging functions. There is no need to wait during or until the end of tests, the driver or operator can view the results quickly either during or directly after the test. Accurate real-time aids like speed, or cross-track error can be provided.

Quality Control

Quality control is an important factor for most applications. The Kalman filter constantly computes estimates of how accurate each of the outputs are; these are available as Status message outputs.

– Position accuracy
– Velocity accuracy
– Heading, pitch and roll accuracy
– Angular rate bias accuracy
– Angular rate scale factor accuracy
– Accelerometer bias accuracy
– GPS position accuracy
– GPS angle accuracy

Plus many more.

Extended Kalman filtering

An extended 24-state Kalman filter operating at 33 Hz constantly corrects measured quantities and prevents integrated quantities such as roll, pitch, heading, velocity and position from drifting while the GPS is locked-on. As a result, pre-test calibration and post-test data correction are not required.

The 33Hz Kalman filter is one of the fastest Kalman filters currently used for navigation systems. It enables the RT3000 to extract very small levels of motion and use them to correct quantities like Heading, Bias and Scale factor. By running the Kalman filter slower, these small bits of motion do not all the Kalman filter to make as accurate corrections to the outputs.

Parallel tracking of up to 12 satellites

The GPS receiver used in the RT3000 family can track up to 12 satellites on each antenna. Extra circuitry is provided for tracking WAAS/EGNOS satellites and for OmniSTAR corrections. With 12 tracking channels the products get the most from the GPS satellites that are available.

Aerospace technology for automotive applications

Using technology developed for military aircraft, the RT3000 family effectively extends the range and scope of dynamic vehicle testing. Rugged though it excellent design and construction, the compact RT3000 family products are more than capable of withstanding the harsh conditions inherent to automotive road testing and racing applications.

Equipped with a powerful, floating-point DSP that enables 3D anti-aliasing filters to constantly correct the system's inertial sensors, the RT3000 works accurately, even when subjected to high vibration rates and magnitudes. Ride and handling, drive train, tire development and chassis engineering are just a few of the many automotive testing applications that can be refined and simplified using the RT3000.

Steady-state measurements

The RT3000 family perform steady-state measurements including slip angle, lateral acceleration and roll angle accurately and confidently. All products are able to measure slip angle using advanced algorithms to differentiate between heading and course over ground, even when using a single GPS antenna. The products can measure the slip angle at or near the vehicle centre of gravity, and using additional measurements, can compute slip angle at other points on the vehicle (such as at the tyres) without physically repositioning the unit. The bandwidth of the slip angle measurement is as wide as all others and the phase distortion in the 0-10Hz band is negligible.

High-transient measurements

The RT3000 family accurately capture measurements with high transients, such as "J" tests or flick tests. Input conditions and the resultant output motion of the vehicle can be factored-in to acquired measurements to assure maximum accuracy.

Steering measurements

Transfer-function measurement of steering angle to lateral acceleration or yaw rate can be accomplished accurately using the system with a steering wheel angle sensor (not supplied).

Vehicle simulation

For reliable aerodynamics and chassis set-up, vehicle simulation software for race tuning relies heavily on the precise measurement of driving lines. Accurate driving line data from the RT3000 family enables vehicle simulation software to be used with much more confidence.

Position measurements

Precision position measurements give test engineers the confidence of knowing that each test is performed under identical, controlled conditions. The approach between successive tests, the trajectory through the test and the state at the end of the test can be continuously monitored to ensure the test process is measuring actual vehicle dynamics, rather than reactions to differing input stimuli.

Acceleration and brake testing

Acceleration and braking can be measured to centimetre precision with the RT3000 family. Braking line is output automatically using position information. Additionally, pitch and roll data can be used to factor gravity out of acceleration results by rotating acceleration outputs to either level frame or body frame.

Driver training

Accurate driving line comparisons are essential to both racing and vehicle testing applications. The RT3000 family offers many outstanding advantages over conventional systems. Driving line comparisons can be made between both individual tests and selected laps. Whether training drivers for a particular test, a new circuit, a new race car set-up or for different vehicles, the RT3000 family provide exceptionally accurate and detailed information that can help to reduce training time and improve driver performance.

Precision timing of vehicle location between any two points on the circuit can be determined without setting up timing gates in advance. Instead, racing lap times can be determined, to 50ms typically, using position data. Driver times around specific sections of the track can also be used to pinpoint where vital time is lost or gained.

Data can also be viewed by actual distance along the track. There is no skew due to wheel slip. Similarly, on a surveyed track, there is no skew due to lap-to-lap differences in driving lines. Therefore, the ideal driving line can be used as a reference distance and all other measurements can be mapped onto the distance along this ideal line. Whether viewing data from additional sensors or from the outputs of the RT3000 family product, the position of this data will be accurate at every point in the lap.

Track surveys can be performed quickly and affordably using the RT3000 family. By comparison, conventional theodolite, laser or GPS techniques are costly and time consuming. By using the RT3000 family a quick, accurate track survey can be obtained by driving along the inside and outside of the track and using the vehicle trajectory to indicate the track boundaries.

Vehicle monitoring

The RT3000 family can track the position of test vehicles, show vehicles or loan vehicles in real-time and log acquired data for record-keeping purposes.

Endurance testing or road-load testing of vehicles, where a driver is hired to drive a particular route, can also benefit from the tracking and dynamic measurement capabilities of the products. Both the route and conditions along the route can be monitored to ensure that the vehicle was subjected to the correct conditions during endurance testing.

Loan vehicles are often used for applications that the owner is not aware of. Tracking and logging systems can be used by the owner to ensure that the vehicle is not left in places where theft is likely, or driven in a manner that is unsafe.