Preliminary Detailed Design
Team Vision for Preliminary Detailed Design PhasePlans for this phase involved a refinement of the system design generated during the previous phase. This involved more detailed design of physical components, including updated CAD models of relevant subsystems and parts. Additionally, simulation was performed in order to understand the effects of temperature change on different potential coupon samples and design materials. Finally, preliminary prototyping was carried out with purchased components. The intention is to demonstrate a working prototype of the maglev concept for the upcoming design review.
Feasibility & Design Prototyping
Prototype Structure DesignA prototype maglev system was constructed using rudimentary sensors (not sensitive enough to measure CTE but enough to measure gross position), an off-the-shelf electromagnet, and a 3D printed frame. Since this is simply a demonstration of the maglev system, 3D printing was used to quickly generate the support structure with no concern as to its thermal/phsyical properties. The demo frame was designed to mimic the adjustable concept selected in the previous phase for the final design.
Prototype maglev system. Components: 3D printed frame, DC Electromagnet, IR sensor, control circuit (shown below)
Electrical DesignThe maglev control circuitry involves a Hall-effect sensor for position sensing, an electromagnet to provide lifting force, a transistor to control current through the magnet, and an Arduino board for programming. The control circuit is shown in schematic form below.
The circuit functions by sensing position via the Hall sensor, which transmits a signal to the Arduino controller. Based on this signal, the Arduino emits a pulse-width-modulated signal to the transistor. When the signal is active, the transistor channel opens, allowing current to flow from the positive supply to ground through the magnet, activating it. When the transistor is off, a diode connected parallel to the magnet protects it from reverse current flow. A test of the Arduino's output capabilities is shown below.
This oscilloscope output shows the input signal on CH1 (yellow) and the output signal on CH2 (blue). The input is a digital signal from an inductive position sensor (unsuitable for the electromagnet controller due to lack of ratiometric output, but easy to use for testing). The output is the pulse-width-modulated signal from the Arduino, specified via a Simulink program.
Using Simulink/Arduino integration we are able to run control systems real time. Below shows the top and sub levels of the current control design. Figure 1 shows the top level architecture where we have our analog input from the IR sensor leading into a conversion box, which can be seen in Figure 2. The conversion box converts the raw sensor data to useful data. From the conversion box the system leads into the controller and following the controller we get to the PWM output. This controller consists of a threshold voltage, if the output from the conversion box is above the threshold the PWM has 100% duty cycle, if it is below the threshold the PWM has 0% duty cycle. The PWM output of the control system then leads to the gate of a MOSFET which turns the electromagnet on or off.
Engineering Analysis & SimulationFour different engineering materials were selected as possible candidates for constructing the test apparatus: Invar 36, Unidirectional T300/5200 Carbon Fiber composite, 6061-T6 Aluminum, and Steel, with generalized properties. Each material was analyzed using a temperature range of 50-100 degrees Fahrenheit, or a temperature change of 50 degrees. It was assumed that, at any point, the sample was at a uniform temperature. The samples have initial dimensions of 8"x1"x.007". An instantaneous coefficient of thermal expansion was used for analysis. The Carbon Fiber sample is unidirectional, with an analysis done for vertical and horizontal fiber alignment. The material properties utilized, and the simulation results are shown below. Material Properties
|Material||Deflection at 100F [in*10^-3]|
|Carbon Fiber (T300/5200, vertical)||6.400|
|Carbon Fiber (T300/5200, horizontal)||0.436|
As expected from using an instantaneous CTE analysis, the deformation of the material is linear with respect to distance along the sample, and change in temperature. From the analysis, Invar 36 would be the most desired material to use for the testing apparatus, as it has the lowest thermal expansion and is isotropic. Carbon Fiber with fibers oriented horizontally would be the next best option, however difficulty may arise in properly orienting the material throughout the apparatus, due to its orthotropic nature. If a more common engineering material needs to be used, then some kind of Steel alloy is preffered. However, expansion of the apparatus will increase by an order of magnitude if Invar or Carbon Fiber cannot be used.
Drawings & Schematics
Screw Clamp Concept
- Simple design with minimal parts
- User friendly design makes loading and securing coupons easy
- Adjustable size and clamping force
- Allows for variety of coupon shapes and sizes
- Coupon may not stay centered (tilt off vertical position)
- More complex manufacturing of arms
Spring Clamp Concept
- Not necessary to adjusting clamping force
- Ease of manufacturing: make base and arms, buy hinges and hardware
- Allows for variety of coupon shapes and sizes
- More complex design
- One arm could apply a greater force than the other
- Loading coupon and closing hinge may prove difficult
Plate Clamp concept
- Ease of manufacturing: simple parts to make
- Possibility of unbalanced clamping force
- Thicker coupons would shift the center of gravity
- Screws may prevent certain coupon shapes from fitting
Bill of Material (BOM)
The total expenditure at the end of the Preliminary Detailed Design phase is $248.95. From a total budget of $4000, the project has $3,751.05 remaining.
Link to the live bill of materials here.
Live document detailing test procedures available here.
Risk assessment changed only slightly from previous design phase. Budget concerns had severity lowered after considering the minimal cost of all materials purchased so far. Additionally, a chamber purchase is not necessary, and therefore no longer a factor in budgeting. As individual system components are finalized, care will be taken to ensure integration with Harris fixturing (item 10).
Risk severity will be updated as more feasibility data is available from prototyping & analysis.
Link to the live document here.
Design Review Materials
The directory containing each team member's individual three-week-plan may be found at /public/Detailed Design Documents/Individual Plans
Plans for next phase
- As individuals, follow through on goals outlined in three-week plans
- As a team, focus on unfinished/in-progress goals laid out for Preliminary Detailed Design phase (shown below).