Study on the Load Cell Utilization for Dynamic Torque Measurement in 3-Blade Savonius Wind Turbine Design

This paper presents the design and analysis of a Savonius wind turbine. Wind turbines harness wind energy to generate electricity, presenting a renewable and clean alternative to traditional power sources. This savonius wind turbine is a type of wind turbine that can rotate even at relatively low wind speeds, so it is necessary to develop a measuring instrument that has high accuracy and is affordable to evaluate the performance of this turbine. In this research, a load cell with an affordable price with a percentage error of approximately 15%, is used as a dynamic torque measurement tool on wind turbines, this torque parameter can be used as an important performance determinant of the wind turbine in generating power. This research was conducted in the Agricultural Machinery Workshop and Integrated Laboratoryy, University of Sumatera Utara, Medan from March to August 2022. The research is performed in several phases, which are 3D design, simulation, schematic design, prototype making, collecting actual data, analyzing actual data, and simulation data. The simulation results are compared with the actual data from the loadcell that has been tested, from the results of the comparison the accuracy value and deviation value of the instrument will be obtained.


Introduction
Indonesia is located in the tropics area and is passed by the monsoon in each season, so the utilization of wind energy has very potential to be developed and applied.Wind speed in Indonesia generally varies between 3 m/s to 10 m/s [1].Measurement results from BMKG show that the average wind speed measurement in North Sumatra is 5 m/s.The utilization of wind energy is done by using wind turbines as a means of converting wind kinetic energy into electrical energy, this energy conversion is done by a generator connected to a wind turbine [2].
Wind turbines are generally divided into 2 types, namely horizontal axis and vertical axis wind turbines, horizontal axis wind turbines require high wind flow speeds and are in the same direction as the turbine, while vertical wind turbines can be used with high or low-speed variations and can be used from various wind source directions [3].
Vertical axis wind turbines (VAWTs) are categorized based on the force propelling the rotor movement, distinguishing between the Savonius turbine, which relies on drag, and the Darrieus turbine, which operates on lift [4].The Savonius turbine offers benefits such as effective operation in low-speed conditions and reliable self-starting capabilities.Widely employed for wind energy generation, the Savonius turbine has also found diverse applications in hydrokinetic and offshore energy production [5].The characteristics of the Savonius wind turbine are the type of wind turbine that can rotate even at relatively low wind speeds, so it is necessary to develop a measuring instrument that has high accuracy and is affordable to evaluate the performance of this turbine [6].
One of the important parameters that can be used to determine the power in this Savonius wind turbine is torque.Torque values can be divided into static torque and dynamic torque.Dynamic torque is the torque produced by the system that rotates.In this study, measurements were made on the dynamic torque of the Savonius wind turbine [7] [8].
Several studies on Savonius-type vertical wind turbines have resulted in shape variations of the blade which affects the output power [9].A convex blade surface will have a smaller surface drag coefficient compared to a convex blade surface; thus, the concave surface side will provide greater drag when given wind flow so that the rotor can rotate optimally [10].Savonius model with three blades has the best performance at a high tip speed ratio.The highest tip speed ratio is 0.555 for a wind speed of 7 m/s [11].
Therefore, research on Savonius vertical wind turbines on the effect of output power for the North Sumatra region, especially in agricultural areas, needs to be carried out to determine the most optimal shape and number of blades to use [12].The research was conducted to test the loadcell used as a dynamic torque measuring device, determine the type of blade and the number of blades that can produce maximum output power, and data on the effect of wind speed and blade type [13].

Study location and materials
This research was conducted in the Agricultural Machinery Workshop and Integrated Laboratory, University of Sumatera Utara, Medan from March 10th, 2023, to August 20th, 2023.
The materials used in this research are an aluminum sheet, AC generator, bearing, 16" fan, power bank, and a single laptop.The instruments used for measurement purposes are anemometer, tachometer, multimeter, loadcell, data logger, and Arduino.A few programs used for analysis, circuit, and program testing, and modeling are Solidworks 2018, Proteus 8.15, and Ansys Fluent 2021 R1.

Procedures
This research is performed in several phases, which are 3D design, simulation, schematic design, prototype making, collecting actual data, analyzing actual data, and simulation data.3-dimensional modeling is done in the Solidworks application to determine the overview and strength of the material to be used, simulation and rotational dynamics analysis is done in Ansys using Ansys Fluent with several types of wind speed treatment.

3D design.
This 3D design is carried out based on the theoretical power calculation of the wind turbine to determine the wind catchment area (blade).

Simulation.
After the 3D design has been completed, the design will be tested against several types of wind speeds based on actual environmental conditions.This analysis will be conducted using CFD (computational fluid dynamics) method.This simulation will produce torque data which can then be used as material for analysis.

Schematic design.
Some electronic components used in this research have a high level of sensitivity, with the use of microprocessors, electronic simulation is needed to ensure that there are no obstacles in the process of designing electronic components.This simulation is done using the proteus application with firmware coding which after success will be uploaded to the Arduino board to be assembled.
3 2.2.4.Prototype construction.This Savonius wind turbine prototype is made with predetermined materials, and the electronic components that have been prepared will be installed as sensors for testing torque data on wind turbines.

Instrument testing.
The data received from the load cell will be stored in the SD card for the next data analysis process.This test will be carried out on several types of wind speed conditions and will go through 3 repetition processes to ensure data accuracy.

Data analysis.
In this process, a comparison is made between the simulation results and the actual data from the loadcell that has been tested, from the results of the comparison the accuracy value and error value of the instrument will be obtained.In this research, the main material used in the Savonius wind turbine manufacturing process is aluminum with a 2 mm thickness.The shaft uses hollow iron material with a diameter of 4 mm which functions as a blade support, the bearing that is used has a diameter of 3.5 cm.Static simulation to test the loading on the wind turbine frame can be seen in Figure 6.In the static simulation results it can be seen that with 3-blade loading (15 kg), the frame on the wind turbine is still in a good level of stress resistance.

Figure 6. Structural stress analysis of Savonius wind turbine
After the design and analysis of the Savonius wind turbine structure, the process of making the Savonius wind turbine using the specified material is carried out.The electronic circuit is made in proteus for electronic simulation, after completing the design and assembly process, the Arduino and loadcell are installed to be connected to the Savonius wind turbine.In the research conducted, the anemometer will be used to measure the wind speed during the test, the loadcell will be placed perpendicular to the bottom of the wind turbine shaft which will rotate simultaneously, and the loadcell will measure the resistance force of the water placed in the bucket.Every time it rotates, force on the load cell will occur due to the resistance force from the water that holds the load cell to move.This resistance force will be converted into a torque value.The movement of the loadcell on the Savonius wind turbine shaft can be seen in Figure when the turbine rotates, the loadcell will rotate to collide with the water that has been provided at the bottom of the wind turbine.Every movement of the wind turbine will apply pressure by water to the loadcell, this data will be saved to the SD card.

Results and Discussions
Based on the design drawings that have been prepared, the blade size and frame are adjusted to be able to receive the maximum wind force to be converted into kinetic energy in the generator.The process of making this Savonius wind turbine was carried out for 2 months and made adjustments according to several experiments that have been passed.Some improvements were made to maximize the performance of this Savonius wind turbine.Some important components of this Savonius wind turbine are the blade, the center shaft of the turbine, the gear with a ratio of 1:10.95,bearings to facilitate the rotation of this wind turbine, the lower frame as a blade support, and a generator to generate electricity.Important components in the tests carried out are loadcell and Arduino uno as sensor processors and torque readers.
From the results of the Ansys simulation carried out, simulation data is obtained which can be compared with the actual data collected.Based on simulation data with a 5 m/s windspeed set, this turbine moves at an average speed of 60 rpm.In Figure 9, it can also be seen the wind flow and wind speed after hitting the Savonius wind turbine.In this simulation, the Savonius wind turbine gets an average torque value of about 0.07298 Nm, with a power average of about 12.032 watts.Based on the image of the simulation results, we can see that the incoming wind speed (inlet) at 5 m/s collides with the wind turbine which causes the wind turbine to move in a circular motion.On the back side of the wind turbine (outlet) this wind speed drops which results in almost no wind on the back of the wind turbine that is hit by the wind.This could be caused by the Savonius blade area capturing the force exerted by the wind to rotate optimally.The highest power from the results of the simulation experiments carried out is around 24.535 watts at 73 rpm.Calculation of torque and power in this simulation using the equation Torque = Moment of inertia x angular acceleration.From Table 2 we can determine that wind speed significantly affects the rotational speed of the turbine, with a speed of 3 m/s, this turbine rotates with an average of 44.6 rpm, and the highest rotation speed is obtained at a wind speed of 7 m/s, which is 74.3 rpm.The higher the wind speed received by the wind turbine, the faster the rotation of the wind turbine will be.This torque data is obtained from the Arduino microprocessor which processes the signal from the hx711 loadcell and is stored in the SD card so that it can be viewed in Excel format.The equation used in determining the torque value in Arduino is torque = F x d, with F = m x g and d = the length of the arm connected to the load cell.

Data comparison
After obtaining data from the simulation results and actual data from Arduino, we compare the data to determine the accuracy of the simulation that has been performed.

Figure 11. RPM and Torque comparison
From the graphs that have been generated, the rpm graph shows results that have similarities between the data from the simulation results and the actual data tested.The deviation rate in the rpm test results is 0.8%, 1.16%, and 0.89%, respectively.However, in the torque data comparison graph, a higher deviation is found, respectively 16.45%, 13.52%, and 14.50%.This can be caused by an anomaly in the loadcell sensor used, the loadcell sensor is very sensitive to vibration when it placed in water [6].The vibration that causes this anomaly can be minimized by using a larger plate on the back of the loadcell to protect the loadcell from the waves of water that form when the turbine rotates rapidly.The wind turbine's capacity to yield 12.032 watts under a wind speed of 5 m/s attests to its efficacy in converting kinetic energy into electrical power.This outcome underscores the system's commendable efficiency in harnessing renewable resources.Furthermore, the turbine's operation is characterized by a notable absence of emissions, aligning with ecological imperatives and positioning it as an environmentally benign alternative within the broader spectrum of energy solutions.

Conclusions
Based on the power data we have obtained, this Savonius wind turbine is suitable for small-scale use.With the power measurements that have been made, we found that the use of batteries is necessary to maximize the potential of this wind turbine, considering that there is not always enough wind speed to rotate the turbine for 24 hours every day.With this research, it was found that the loadcell with an affordable price with a percentage error of approximately 15%, can be used as a dynamic torque measurement tool on wind turbines, this torque parameter can be used as a performance determinant of wind turbines in generating power.In conclusion, the demonstrated power generation efficiency of the wind turbine, coupled with its low environmental impact during operation, substantiates its potential as a sustainable energy solution.

Figure 4 . Top view Figure 5 .
Figure 4. Top view Figure 5. Front view

Table 1 .
Dimensions A view of the design is given in Figures2, 3, 4, and 5.These drawings are from multiple views such as isometric, top, side, and front.

Table 2 .
CFD simulation data

Table 3 .
Actual rotational speed based on windspeed

Table 4 .
Actual torque of Savonius wind turbine