Engineering Design

Concept Comparison

Throughout the project and leading into decisions made in Phase III of the project, the primary needs and specifications of the design remained largely unchanged. The designed apparatus must provide a solution to the height and angle adjustments of the plate and allow for the integration of a pressure sensor into the impingement plate. Several options were considered initially, the best of which was eventually compared to more options that were thought of later. As seen in the concept selection charts below, the selection criteria remains the same even as new concepts are generated.

The concept selection chart for Phase I shows four different concepts in comparison. The first concept was the design used by the previous design team to solve this problem. The following three concepts were generated by the current design team's efforts. Each was evaluated using the same criteria to determine feasibility, effectiveness, and whether the concepts were worth advancing to the next design stages. After this comparison, concept B using linear actuators was chosen as the best candidate to continue forward with. However, this selection is being reevaluated as new constraints have been considered and the linear actuator method of height adjustment may not fit within the size constraints of the available test section. Entering Phase III, a new concept was considered where the plate's movement would be controlled by a stepper motor rather than entirely by linear actuators. The comparison of this new concept to both the linear actuators and to the previous year's design is shown in the concept selection chart for Phase III.

Concept Selection Criteria - Phase I.

Concept Selection Criteria - Phase III.

A concept comparison was also done specifically to determine the method of angle adjustment for the design, as this is a separate issue from determining the method of height variation. As shown in the angle adjustment concept selection chart, the best option was the "gym" method. This methods employs a pin-and-hole design where the angle can be set manually by changing which hole a pin is placed into on the design. This part of the design was first pictured in Design Concept 1 previously.

Concept Selection Criteria - Angle Adjustment.

Component Selection

After assessing the force exerted by the flow from the nozzle onto the plate, as shown in the Technical Analysis, components needed to be selected that could withstand this force. Because the plate and other primary structural components would be salvaged from the previous team’s design, which was proven to stand up to testing in the tunnel, the choices to be made primarily pertained to the sensing and actuation subsystems. The pressure sensor provided to the team was a model 106B52 ICP Pressure Sensor from PCB Piezotronics. According to the listed specifications from the distributor, the maximum pressure for this model is 345 kPa which is well above the predicted 174 Pa exerted onto the plate by the team’s technical analysis. The resolution of the sensor is .13 Pa, so this sensor was deemed viable for the purposes of this experiment.

ICP Pressure Sensor.

The components for the actuation subsystem needed to be able to withstand the anticipated force of the flow from the nozzle as well as the weight of the impingement plate and other components above it. Originally, the team intended to use one or multiple stepper motors to adjust the impingement plate vertically. This type of motor was selected based on their low cost, but it was determined that the original motor would not be strong enough to lift the plate assembly and withstand the load. The team turned to using a heavy duty linear actuator salvaged from the ABS Makerspace. The maximum load of this particular actuator is 1000N with a 4” stroke which is ideal for the range of heights that the team intends to experiment with. It was decided that based on technical analysis, the team would initially move forward in designing with this actuator in mind for the alpha prototype.

Linear Actuator with Potentiometer.

Before purchasing the above linear actuator, another version was purchased for evaluation and testing. This 1.5A integrated linear actuator stepper motor is pictured to the right. The above actuator was chosen because of its overall strength and lifting capabilities, but as discussed later, the stepper motor was eventually deemed superior due to its smaller size and better fit within the available shock tunnel space. For the electromechanical system to work without physical interference, a new part needed to be designed to allow the impingement plate to translate up and down the stepper motor's lead screw. This new part is further discussed in reference to the beta prototype phase of the project.

Stepper Motor.