Calibration – Spreader Systems

In this article we will break down some of the key considerations for the process of calibrating spreader systems in agricultural drones.

Introduction

Spreader systems enjoy marginally less regulation than spray systems as the product to be distributed is often not as controlled as liquid pesticide. However, calibrating your system correctly is still fundamental to ensuring accurate application rates, efficient use of product, and optimal coverage.

In this article we will break down some of the key considerations in the process of calibrating spreader systems.

When to Calibrate

Calibrating your spreader system may be required in a number of different circumstances. These are normally detailed in the manufacturer documentation, but some of the key reasons are:

1. Product Type: Changing between products of varying grain/pellet size may require a recalibration.
2. Equipment Changes: Following repair or after changing the size or specification of key components (e.g. auger plates).
3. Deviation: When any anomaly or difference between expected and actual system performance is noticed.

Understand the RPA and Spreader Specifications

Payload Capacity

Knowing the maximum payload capacity and maximum take-off weight (MTOW) of your drone can help you to prevent overloading. Unlike spray systems, where liquid weight is relatively standard across all products, there can be a large difference in weights of various granular or pellet type products. It is therefore possible to exceed the MTOW of your system if filling the hopper to 100% with a heavy product.

Spreader Type

There are a number of different spreader types in use today in drone agriculture:

• Centrifugal
• Pneumatic
• Rotary

Each have very different mechanisms and offer different spread patterns.

Ensure that the spreader systems you are using is not only compatible with your aircraft, but is also suitable for the intended product and application.

Preparation

Unlike spray system calibration, which is always performed using water, spreader calibration will use the intended product. Therefore, make sure that operators have access to appropriate personal protective equipment (PPE) to carry out the task:

• Long-sleeve pants and shirt
• Gloves
• Protective Eyewear

Plan to calibrate your system in a flat, dry, open area. Preferably choose somewhere that is free from obstacles and sheltered from the wind.

Depending on your system, it may be necessary to raise the aircraft off the ground so that a collection vessel can be placed beneath the spreader. It may also be necessary to remove spreader discs to prevent product being ejected over too large an area.

If a software system is to be used during the calibration process. Make sure that the correct procedure is selected and follow on-screen prompts to prepare the aircraft for calibration.

Determining Application Rate

The application rate defines the actual amount of product we need to apply to a given area to achieve a successful outcome. This rate is usually specified on the product label and has been calculated to give the best performance and most cost effective application. It is rarely beneficial to change this rate under normal circumstances.

Measuring the Output Rate

Prepare the RPA for calibration as required by the manufacturer guidelines (e.g. raised off floor, remove spreader disks). Fill the spreader with the material to be used.

Collect Material and Measure Volume/Weight

Run the system over set period of time (e.g. 1 minute) and collect the material ejected in a strong container.

Measure the total volume or weight of the material collected and divide by the collection time to get the output rate per minute.

EXAMPLE:

5kg collected over 30 seconds = 5 / 0.5(mins) = 10kg/min

Adjust Settings

If the output rate is not within the desired range, adjust the spreader settings (e.g. opening size, auger size, disc speed) and repeat the measurement until the correct rate is achieved.

Field Testing and Adjustment

The final step in the calibration process is to perform field testing.

Test Flights

Conduct test flights over a known area to verify the application rate and coverage. Have a set field planned to ensure the test can be repeated and try to ensure similar environmental conditions for each test (particularly wind speed).

Collect Data

Use onboard sensors and ground-based measurement tools to collect data on spread distribution and coverage. Ensure material is being spread uniformly by visually inspecting the spread pattern and measuring the distribution across the swath.

Adjust Settings

Based on your test results, adjust the drone’s speed, height, and spreader settings to fine-tune the application.

Record Keeping and Documentation

Detailed records must be maintained when performing manual calibration of spreader systems. Keep notes of current calibration settings, test results, and adjustments made.

This information is not only useful for future calibration and troubleshooting problems, but may also be used to ensure compliance with local regulations and industry standards.

Equipment Maintenance

Maintenance is essential for spreader system efficiency and performance. Regular inspection of spray assemblies is mandatory to ensure optimum system performance.

Be sure to follow manufacturer maintenance guidelines where available.

Remember that all maintenance, whether routine or on-condition, must be documented within the RPA Technical Log in accordance with CASR Part 101 regulations.

Software Updates

Most modern agricultural RPA use software applications to calibrate spreader systems for optimum performance. Operators should follow the manufacturer operator manual on the procedures to calibrate the systems prior to use.

Conclusion

Calibrating spreader systems for RPA involves precise measurement, adjustment, and verification to ensure efficient and effective material application. This improves operational efficiency while minimising waste and environmental impact.