UI Marching Band Mobility Platform

It is the goal of the University of Idaho Mechanical Engineering Department to design and fabricate a "Band Mobility Platform" (BMP) for the University of Idaho Marching Band as a continuation of the "Band-Beesten" legacy. The BMP will be an electrically-driven, remote-controlled stage that enables a variety of otherwise stationary performers to perform with a stunning light show in coordination with the marching band.

=Problem Definition=

Deliverables
Small Scale Model to Demonstrate Project Feasibility Full Scale Prototype Modeling of Finished Design Experimental Results/Design Validation
 * Primitive Circuitry and Motor Control Algorithms
 * Laser Cut Wooden Frame and Bolt and Spring-Bolt Suspension System
 * Refined Circuitry, Motor Control Algorithms, and Recharging System
 * Aluminum Frame with Independent Suspension System and Variable/Modular Wheel Positioning
 * Fully Function Performance Activated Lighting Arrangement
 * 3-D Model of the Frame and Suspension System
 * Structural Analysis of the Frame and Suspension System
 * Circuit Analysis on the Power-Control System
 * Translational and Rotational Speed
 * Stability Under Static and Dynamic Loads
 * Battery Duty and Recharge Cycle Periods

Specifications
Functional Requirements Mechanical Requirements Electrical Requirements Software Requirements Environmental Requirements Cost Requirements
 * Motion shall be controlled via remote control by a pilot not located on the platform.
 * The lights of the BMP shall be controlled by the musician located on the on the BMP via regular playing of the applicable instrument which activates shock activated piezoelectric sensors.
 * The design shall be able to support,translate,and rotate a load of 1500 lbs.
 * The stage shall not exceed a length 9 ft nor a width of 7 ft.
 * The total system shall weigh no more than 500lbs.
 * The design shall have a universal mounting system to accommodate a drum set, piano, and a txalaparta.
 * The system shall have a life cycle of years with no component failures.
 * The platform shall translate at a marching pace of 160 steps per minute with a stride of 23 in.
 * The wheels shall remain in contact with the Kibbie Dome field terrain and support equal loading at all times.
 * During operation the voltage shall remain at 24V. The total amps constantly consumed by the system should not exceed 30 amps.
 * The PCS shall be designed with a capacity to operate the entire BMP for a minimum of 15 minutes on a single charge.
 * The software shall be capable of receiving RC input signals from a maximum distance of 70 yards and input signals from the instrument-mounted sensors. The software shall be capable of distributing power from the battery bank to the PCS, motors, and lights as received by the RO and performer.
 * The RO shall utilize a standard radio controller with joy sticks for controlling the left-right and forward-reverse translational movements of the BMP. The performers will control the lights via the drum set and/or the piano.
 * The Product is expected to have full operational capabilities in environments with ambient temperatures of 32F to 100F.
 * The PCS shall comply with the UL 1642 standard for lithium batteries.
 * Cost to build a POC prototype shall not exceed $1400.

=Design Considerations=

Final Conceptual Design
'''Modular Variable Wheel Quantity and Offset with Independent Suspension '''

=Project Learning=

Frame and Suspension
Asymmetric Double Wishbone The first design iteration was an asymmetric double wishbone frame with three points of contact between the frames and the ground, even load distribution would be assured via flexing of the frames. The most notable problem with this design was the asymmetric frame and wheel positioning would prevent smooth forward and reverse translation. The second most notable problem with this design was that the frame would have to be fine tuned for a very specific stiffness to act as both a suspension and safe support structure.

Six Wheeled Symmetric Double Wishbone The second design was the same concept as the previous design double frame except the wheel placement was symmetric which would allow for unbiased translational movement. This design better meets the customer requirements as translational movement is a higher priority than rotational movement. However, the problem of the complex frame still persists.

Six Wheeled Single Frame Independent Suspension The third design was to eliminate the double wishbone frame for a single frame with independent suspension to reduce the cost the design and the complexity of the development. The single frame independent suspension design allows for the same even load distribution as before but with design better for manufacturablity, for the much of the suspension is able to be purchased off the shelf.

Four Wheels Variable Offset Next we reduced the number of wheels to 4 to further reduce costs, complexity, and weight. This creates a greater challenge for designing for both translational and rotational movement while maintaining stability. Several wheel configurations were considered including perimeter centered perimeter parallel, corner positioned perimeter parallel, corner positioned 45 deg. offset, and corner positioned 90 deg. offset. Ultimately, it was decided to use corner positioned wheels with variable offset.

Four/Six Wheels Variable Offset Lastly, it was discovered that reducing the number of wheels to 4 would place too much force on the wheels under full intended capacity. To solve this problem, it was decided that the wheels would be modular with variable positioning allowing for 4 or 6 wheels to be used with variable positioning possible for the 4 corner mounted wheels.

80/20 As Frame 80/20 as frame has several pro and cons.

Pros: Orderable cut to length, strong, highly modular, and strong customer support.

Cons: Difficult to assemble for complex structures, requires significant foresight for fastener placement during assembly, and large amount of disassembly required for re-configuring the frame or replacing some parts.

Small Scale Programming and Circuitry
Signal Receiving As per the customer requirements, the system shall be controlled by a pilot using remote control; this presented the problem of how to interpret the signal from the receiver. Using an Arduino Uno, attempting to quantify the signal as pseudo analog measure of voltage intensity proved to not be possible. It was discovered that the signal is entirely digital and required a measure of the period between high (5V) pulses. This pulse width varies linearly depending on user input allowing for simple quantification.

Signal Processing Reading the signal from the receiver created an additional problem for processing the signal. The measure of pulse width requires a pause in processing to count the time between pulses which distorts the signal once too many inputs are being read at once. This led to the discovery that the maximum number of inputs readable from the receiver is 2.

This problem suggests two viable solutions. Use a controller with larger processing power, use more than one controller, or create a control algorithm can translate and rotate the platform with only two input signals.

Circuitry To distribute power to the DC motors, H-Bridges capable of controlling two motors each were used which placed restrictions on safe current levels. The TI-L293D H-Bridge has a current limitation of 600 mA, and the current drawn by our motors was measured to be vastly below this at 1.4 mA each. Despite the safe levels, H-Bridges were rendered inoperable after more than 20 minutes of total run time. This means that to build a fully operational early control system that wont burn up 24 volt motor controllers with heat sinks will have to be used for the small scale proof of concept.

Full Scale Programing and Circuitry
Signal Processing Utilizing (2) Arduinos ((1) for translational and (1) for rotational) for signal processing is a viable solution. Additionally, the (2) Arduinos may be used without a master/slave relationship preventing latency issues that would otherwise occur.

Operating the motor drivers requires use of servo outputs on a scale of 0-180 degrees with 0 and 180 dictating both direction and speed. When operating the motor drivers, a soft acceleration limiting algorithm is essential to the longevity of the motor drivers. Failure to limit acceleration can result in over-current to the motor drivers.

Circuitry To safely charge and discharge lithium ion batteries, a battery control circuit must be utilized. This battery control circuit will help to ensure balanced cells and that no continuous over/under current/voltage occurs.

Power to the motor drivers should be conditioned to create a more "steady-state" circuit. To condition the power capacitors maybe used parallel to the motor drivers to help minimize fluctuations in the load. Additionally linear 5V power supplies should be used to power the Arduinos and RC receiver to avoid using the battery eliminating circuits built into the motor drivers. These BEC circuits are more appropriate for the powering of cooling fans for motor drivers.

The 12 ga. wire currently used by the motors is under for the 80A continuous max rating at 24V. Wires of ga. 4 or 8 would be more appropriate depending upon wire lengths.

=Final Design= Sub Assemblies

Status of Completion

=Validation=

=Future Work=
 * Electrical System
 * 1) New Motors and/or Motor Drivers for Larger Scale
 * 2) New Charging Appropriate Power Supply or Battery Charging System Needs to be Redesigned to Charge with a 6S Charger
 * 3) 5V Linear Power Supply for Replace Battery Elimination Circuit Power for Arduinos and RC Receiver
 * 4) New Acceleration Limiting Algorithm
 * 5) Power Conditioning Circuit for Motor Power
 * 6) Alternative DC-AC Inverters for 24V System
 * 7) Addition of Lighting System

=Team Members=

=Additional Documentation and Information=

Notable Dates
Controls Proof of Concept: 07/16/19 Final Design: 07/22/19 Small Scale Build: 08/02/19 Wheel Assembly Prototype: 08/24/19 Fully Assembled Prototype: 09/18/19 Validation Completion: 10/16/19 Delivery to Customer: 10/22/19 Game Day Demonstration: 11/02/19

Documentation
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Budget
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Meeting Minutes
Team Meetings



Mentor Meetings



Customer Relations
Client Interview