Novatel Smart 6L receiver

The previous Fendt guidance/steering system consisted of two major parts:

• first, an integrated GNSS receiver and navigation controller that received GNSS and correction data, computed the position and used this position to generate steering commands, and
• second, the tractor hardware, steering controller, steering valve, sensors and the display terminal that controlled tractor lateral motion and provided the user interface for operation of the steering system.

The new generation of the Fendt “VarioGuide RTK” guidance/steering system has separated the GNSS receiver and navigation controller and moved the navigation controller to the tractor side of the system.

This means that the corrected GNSS position is now transferred to the tractor instead of the steering commands (Figure 2). This provides a flexible solution for farmers to choose different Fendt-approved GNSS receivers that best meet their needs for use with their VarioGuide system. The NovAtel system used in this test consisted of a NovAtel SMART6-L receiver in combination with two different types of NovAtel correction signals.

The TerraStar-C correction signal provides a centi­meter-level overall system accuracy. The TerraStar-L correction signal provides a decimetre-level system accuracy. Both correction signals are transmitted to the SMART6-L receiver on the tractor via geo­stationary satellites.

The NovAtel SMART6-L is a high performance, cost-effective GNSS-receiver solution. RTK accuracy can be achieved using NTRIP corrections transmitted over a cellular radio link. The receiver can provide RTK accuracy for up to one minute after losing RTK correction signals. The receiver can also bridge RTK outages beyond one minute when falling back to an EGNOS position. The fall back will smoothly and slowly transition between RTK and EGNOS level accuracy.

The NovAtel System provides a special system to react to signal losses: GLIDE is NovAtel’s proprietary filtering method optimized to provide a superior 15-minute (short term) pass-to-pass repeatability. GLIDE works best with SBAS corrections, such as EGNOS, but can also be used autonomously without corrections. The GLIDE filter provides smooth, robust positions making it especially effective when used as a fallback solution during RTK or TerraStar-C correction outages. NovAtel’s STEADYLINE techno­logy reduces position jumps that can occur when a GNSS receiver changes positioning modes. This effect is especially evident when a receiver transitions from a high accuracy RTK position solution to a lower accuracy solution such as PPP (TerraStar), DGPS, SBAS+GLIDE or even autonomous GLIDE™. Smooth transitions are extremely important for precision agricultural steering applications where sudden jumps are disruptive.

In the test, the NovAtel receiver was mounted on a Fendt 828 Vario tractor with 280 kW power according to ECE R24. Further technical data, the measured vehicle geometry, the tyres used, and the settings parameters used for the steering system are summarized in table 2. The steering system’s settings were configured according to the manufacturer’s specifications.

Within the measurement of the performance of the positioning system when RTK corrections are lost and the receiver falls back to the GLIDE solution using STEADYLINE, the system reached the 18-19 cm class of deviations during the one hour run with fall back to GLIDE with EGNOS solution. In a one hour duration test, pass-to-pass errors during a fallback to GLIDE with EGNOS period reached the 10-11 cm class.

The suggested solutions to two predefined problems were determined in order to assess the operating instructions and the help system. Both a description of how an A-B track can be defined and an indication and possible solutions for signal errors like GPS or correction signal losses are available in the user manual. The assessment is, therefore “[+] = Better than the standard”.