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Stand/Powertrain Overview
Stand/Powertrain Overview
Our stand consists of 3 main components: a steel tube, welded flat bars for support, and pillow blocks for transmission mounting. The steel tube serves as the main vertical support, providing the structural rigidity necessary to keep the turbine stable and long enough that the blades can spin without ground interference. The transmission has a belt pulley system with a reduction of 1:2, which was implemented to increase the RPM delivered to the gear pump. The belt and pulleys were sized based on the torque requirements and the desired rotational speed of the gear pump, ensuring efficient power transfer from the turbine to the pump. Following the belt pulley system, a gear ratio increase of 1:4 increases the rotational velocity to meet the pump's operational requirements.
Stand
Stand
Tube
The steel tube is 36 inches long and 3 inches in diameter. As stated above, this is the main support of the turbine. This long length was chosen for a number of reasons. Firstly, we had not defined how long our wind blades would be and wanted to accommodate varying lengths. We knew that the blades were limited by what we could print on the printer and set a rough estimate of 24 inches or under for our blade lengths. Buying 36 inches of tube allowed for some variability. We could size the tube to whatever blade length we chose. The tube also has two pass-throughs—a fixed, centered hole and a slot. The hole is for the turbine to pass through, and keeping this position fixed made sense in terms of keeping the blade mount structurally sound and, for the most part, immovable. The slot was a design choice made for 2 different reasons. Firstly, we needed a way of tensioning our belt, and we chose not to use a belt tensioner because it would add a lot of new parts to the assembly. This was unnecessary complexity, and the slot was a much easier solution, as we could just change the shaft position to whatever belt tension felt right. Secondly, we were choosing between a lot of different gear ratios, which introduced different diameter gears and, in turn, shifted shaft positions. The slot was made long enough to accommodate a range of different gear sizes.
PillowBlocks and Shafts
The pillowblocks are 3D-printed parts that act as the mounting points for our shaft. They have a 3 inch diameter hole, which allows them to slide up and down the tube and stay fixed from a clamping collar-based feature. Allowing the pillow blocks to be variable positions was important for our design process, as we had a lot of unknowns and needed to design a structure that would still work despite uncertainty of the component being attached to it. The shafts used were .25 in diameter, and this was due to already having.5 in OD and .25 in ID bearings on hand. We needed to verify that these shafts and bearings would spin smoothly, and performed calculations to understand that the bearings could support the intended loads.
Belt-Pulley System
Belt-Pulley System
Our belt system acts as one half of our powertrain along with the gears. We chose to use a belt pulley system to transfer motion mainly because of the visual aesthetic we were going for with our final piece. We wanted the fountain to be underneath the wind blades, and the belt was the best way to create that distance between the turbine shaft output and the pump input. The pulleys are 24 and 12 teeth, and our reduction is 2:1, meaning we have double the amount of RPM generated by the blades at the output shaft of the pulley.
Gear Reduction
Gear Reduction
The gear reduction acts as the second half of our powertrain. The gears have a 4:1 ratio, making the total transmission ration 8:1 for an ideal output speed of at least 800 rpm in the pump's gears. Having two gears on the outside of the stand instead of a gear train allows for a sleeker design and lets us make less gears, which are difficult to manufacture using Olin's facilities.
Gear Analysis
Gear Analysis
A static FEA study was conducted on the gears to ensure they would not fail due to stress. The study looked at the stress in the teeth with one 40 tooth gear driven at 0.54Nm of torque and the 10 tooth driven gear with. The study showed that the ABS gears would not fail from being driven by the pulleys and blades.
Function Code
Function Code
Example Inputs/Outputs
Example Inputs/Outputs
Powertrain Efficiency Calculations
Powertrain Efficiency Calculations
The script begins with user-defined input parameters, including the turbine's RPM, the target RPM for the pump, pulley and gear ratios, power and torque output from the turbine, belt type, and a time step. The belt type is particularly important because it determines the slippage factor, which determines efficiency losses in the pulley system. For example, a timing belt has minimal slippage, while a V-belt introduces slightly greater losses. These parameters form the foundation for simulating the powertrain's performance. The simulation is over 10-seconds, with results captured at regular intervals defined by the time step. We used a time array is created to iterate through each time step, allowing calculations to be performed repeatedly and consistently throughout the duration of the simulation.
After that, the RPM at each stage—the pulley system, gear system, and pump—is calculated based on the input RPM from the turbine. Slippage in the belt reduces the RPM as power is transferred to the pulley system, and further reductions occur through the gear ratio before reaching the pump. At the same time, we also calculated power and torque values to understand the system's energy transfer. Power losses are modeled using the slippage factor, which reduces available power as it moves from the turbine to the pulley, through the gear system, and finally to the pump. Torque was then found at each stage based on the relationship between power and rotational speed, using Torque=Power/(2𝜋⋅RPM/60).
Efficiency is calculated at each stage as the ratio of power output to power input. The outputs are the time-based results for RPM, power, torque, and efficiency at each stage.We defined the main transfer stages as: from the turbine to the pulley system, from the pulley to the gear system, and from the gear system to the pump.
Given that we had a lot of unknowns between different components, the efficiency script was a way to get predictions out of the most essential metrics when sizing/designing another part.
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