Performance Evaluation of a Tracking Total Station as a Position Reference forDynamic GNSS Accuracy Testing

The dynamic accuracy of a tracking total station (TTS) was evaluated using a rotary test fixture to determine the viability of using a TTS as a position reference for dynamic global navigation satellite-based system (GNSS) accuracy testing. Tests were performed at angular velocities ranging from 0 to 3.72 rad/s at a radius of 0.635 m. A technique was developed to determine the average latency of the TTS measurement serial data output. TTS measurements were interpolated at a GNSS sampling interval to provide a method for direct comparison between TTS and GNSS position measurements. The estimated latency from the TTS serial data output was shown to be consistently near 0.25 s for all angular velocities and less variable when using a reflector-based machine target versus a prism-based target. Average positional error in the TTS position measurement increased with angular velocity from 3 to 90 mm, partly due to internal filtering which caused the magnitude of the TTS position measurement to decrease under stead-state sinusoidal motion. The standard deviation of error ranged from less than 1 to 20 mm as angular velocity increased. Sight distance from the TTS to the target was shown to have very little effect on accuracy between 4 and 30 m. The TTS was determined to be an adequate benchmark for most dynamic GNSS and vehicle auto-guidance testing but is limited by relatively large position measurement errors at high angular velocities

Nozzle Sensor for In-System Chemical Concentration Monitoring

Chemical concentration is a vital parameter for determining appropriate chemical application. This study describes the design and testing of a sensor that attempted to monitor concentration of chemicals upstream from each nozzle body. The sensor is based on an LED and photodiode pair. Its ability to detect chemical concentration within the main carrier was tested with a 2,4-D formulation, a glyphosate formulation, and a powdered Acid Blue 9 dye. The liquid herbicide formulations of glyphosate and 2,4-D were tested across common application concentrations of 0% to 12.5% by volume. The powdered dye produced a much stronger effect on the sensor and was only tested at the much lower concentrations of 0 to 50 mg L-1. Further tests were conducted in which the dye was mixed with the herbicide formulation before the combined solution was added to the carrier. While this enabled establishment of pre-determined sensor outputs based on given concentrations of the pre-mixed solution, the sensor may have been responding to the predominance of a dye mixed with a herbicide formulation and not directly to the concentration of the herbicide. While the sensor did not appreciably respond to the concentration of the glyphosate formulation, it did respond in a consistent manner to the 2,4-D formulation and the dye. The sensor‘s response to the concentration of these chemicals was a rational (1/x type) relationship, and the R2 values for the rational models describing these relationships were greater than 0.99. With the mixed dye and herbicide formulation, the effects of the dye and the 2,4-D formulation combined independently, and the total sensor output was a multiplication of the percent effect of each alone. The test with the pre-mixed dye and 2,4-D formulation produced the expected 1 V output at a 12.5% by volume concentration of the 2,4-D formulation, proving that dye can be added to a herbicide to produce a desired response from the sensor. Overall, the sensor‘s response was remarkably stable, with a maximum standard deviation of 42.2 mg L-1 of 2,4-D active ingredient for samples taken at a constant chemical concentration. These tests confirmed that the sensor could respond to chemical formulations and dye in a consistent and predictable manner. However, use of the sensor for herbicide monitoring will require sensor calibration for each combination of herbicide and dye mixture, as the light transmittance properties of the tested mixtures were not quantified and the light transmittance properties of formulations and dyes can be arbitrarily changed by manufacturers

Methods for Calculating Relative Cross-Track Error for ASABE/ISO Standard 12188-2 from Discrete Measurements

ASABE/ISO Standard 12188-2 provides test procedures for positioning and guidance systems in agricultural vehicles during straight and level travel. While the standard provides excellent descriptions of test procedures, it does not provide detail on methods to carry out the calculations necessary to calculate relative cross-track error (XTE), which is the primary error statistic used to judge accuracy. Given the travel speed and sampling constraints provided by the standard, the difference between a method based on nearest points or one based on path interpolation could hypothetically be as large as 25 cm. In this project, the standard was used to estimate the guidance accuracy of a relatively low-accuracy vehicle at 1.25 and 0.5 m s-1. At 1.25 m s-1, a basic nearest point calculation overestimated mean XTE by 0.8 cm, or 8.2%. The location sampling density was much higher with a 0.5 m s-1 travel speed, and mean XTE was only overestimated by 0.1 cm with the nearest point method. There are clearly situations where the calculation method will affect results, and the use of the more complicated methods explained in this article are suggested when using this standard

The Global Positioning System

The Global Positioning System (GPS) is quickly becoming part of the fabric of everyday life. Beyond recreational activities such as boating and backpacking, GPS receivers are becoming a very important tool to such industries as agriculture, transportation, and surveying. Very soon, every cell phone will incorporate GPS technology to aid first responders in answering emergency calls

Biodiesel Basics

Biodiesel is a renewable fuel for diesel engines. Biodiesel, defined by ASTM International (D6751), consists of longchain fatty acid alkyl esters and is made from renewable vegetable oils, recycled cooking oils, or animal fats. It can be used at full strength, but it is typically blended with petroleum diesel. A blend of 2 percent biodiesel and 98 percent diesel is referred to as B2. Other typical blends include B5, B10, and B20; pure biodiesel is sometimes referred to as B100. Biodiesel is safer for the environment and produces significantly less air pollution compared to petroleum diesel. Biodiesel can be produced locally and can be integrated into the existing petroleum infrastructure

Scalable Control Architecture for Variable-Rate Turn Compensation

The objective of this study was to determine if a CAN bus could be used to implement variable-rate turn compensation in a manner that is scalable by encoding application rates for an entire implement into a single data message. A variable-rate turn compensation test fixture was developed that used a CAN bus to communicate application rates to 16 individual nodes using a 2-byte data message (80-bit extended identifier CAN messages). The system assumed that the physical structure of an implement was linear and that the control nodes were equally spaced. Application rates for the outer-most nodes were broadcasted and the remaining nodes calculated their application rate using a linear interpolation method. Node locations were determined using a 4-bit binary thumbwheel switch located at each control node, allowing all nodes to run an identical program. Servo-controlled gauges were used to visualize node application rate across the test fixture. A joystick interface was developed to simulate vehicle movements and desired application rates. The system transmitted Bluetooth serial messages at a rate of 20 Hz, which were received by the test fixture and converted to CAN messages before being broadcasted to the control nodes. Two USB to CAN interfaces were connected to the CAN bus to insert additional traffic and measure bandwidth utilization. Due to the minimal amount of bandwidth required (\u3c1%) to transmit variable-rate control messages, the system functioned properly when the CAN bus was heavily loaded with traffic up to 99% of the available bandwidth of 250 kbps. The variable-rate turn compensation test fixture demonstrated that a CAN bus is a suitable protocol for communicating variable-rate data. The scalable encoding technique developed in this study resulted in a single message required to update all nodes, regardless of the number of nodes in the system. The system has broad applicability in future planting, fertilizing, and chemical application systems where deposition points are evenly spaced along an implement

Crop Yield Response to Precision Deep Tillage

Experimental precision deep tillage was applied at three sites in central Kentucky with relatively well-drained silt loam soils in no-till crop production. Fields were divided into 0.4 ha (1 ac) grid cells using DGPS mapping. Assessment of soil compaction by machinery traffic was made using multiple soil cone penetrometer measurements and expressed as cone index (CI). Corn, wheat, and soybean yields were depressed in grid cells with CIavg ≥ 1.5 MPa (218 psi) prior to application of tillage treatments at sites 1 and 3, whereas at site 2, where most of the highest average CI values ranged from 1.44 to 1.49 MPa (209 to 216 psi), the opposite was true. In general, deep tillage resulted in yield improvement in compacted grid cells relative to those receiving no deep tillage; however, differences were significant at the 10% level in only two of six instances. Cells tilled to 40 cm generally had higher yields than cells tilled only to the depth at which CIavg ≥ 1.5 MPa (218 psi) (precision deep tillage) at sites 1 and 3. However, the opposite was true for double-crop soybean subjected to limited rainfall. At site 2, tilled cells had higher yields than non-tilled cells, with precision tillage showing the maximum relative yield

Controller Area Network Based Distributed Control for Autonomous Vehicles

The goal of this project was to evaluate the potential of a controller area network (CAN bus) to be used as the communication network for a distributed control system on an autonomous agricultural vehicle. The prototype system utilized microcontroller-driven nodes to act as control points along a CAN bus. Messages were transferred to the steering, transmission, and hitch control nodes via a task computer. The task computer utilized global positioning system data to generate appropriate control commands. Laboratory and field testing demonstrated that each of the control nodes could function simultaneously over the CAN bus. Results showed that the task computer adequately applied a feedback control model to the system and achieved guidance accuracy levels well within the desired range. Testing also demonstrated the system’s ability to complete normal field operations, such as headland turning and implement control

Biodiesel FAQ

Biodiesel and other alternative fuels continue to gain popularity as petroleum fuel prices rise and we become more concerned about our environment. Introduction of these fuels raises many questions about actually using them in current equipment. The purpose of this factsheet is to address some of the common questions asked by those considering the use of biodiesel in existing diesel equipment