« Team Members Alin Dobre, Aaron Brookshire, Wiljariette Hernandez, Jayson Clifford, Jason Firanski, Michael Harris, Edward Muller, Tim Bentley, ...»
Alin Dobre, Aaron Brookshire, Wiljariette Hernandez, Jayson Clifford, Jason Firanski, Michael Harris,
Edward Muller, Tim Bentley, Alex Gregg
Charles Reinholtz, Richard Stansbury, Keith Garfield, Shane Barnett
Faculty Advisor Statement
I certify that the engineering design of the vehicle described in this report, Reagle, has been significant,
and that the student effort is equivalent to a senior design capstone project.
Charles F. Reinholtz, Mechanical Engineering, Embry-Riddle Aeronautical University
1.0 Introduction The Autonomous Vehicle Team of Embry-Riddle Aeronautical University is proud to introduce Reagle, a new vehicle platform designed to compete in the 2008 Intelligent Ground Vehicle Competition (IGVC). Embry-Riddle last competed in the 2002 IGVC, finishing 8th in the Autonomous Challenge and 2nd in the Navigation Challenge.
Reagle incorporates many of the successful features and subcomponents used by other IGVC competitors in recent years, but the design also includes several key innovations specifically developed for the 2008 competition. Our goal is to make use of the knowledge and experience gained by previous teams while attempting to address the most critical problems and provide the best overall value.
The name Reagle (pronounced ˈrē-gəl) is a contraction of the University founder’s last name (aviation pioneer and barnstormer John Paul Riddle) and the eagle mascot that represents the University’s aviation heritage. The word “regal” (same pronunciation) means, “Of notable excellence or magnificence.” We hope to live up to the lofty expectations our vehicle name and heritage may suggest.
1.1 Base Vehicle Overview Reagle is a three wheel, differentially driven and steered vehicle. The drive/steering wheels are located in the rear and a passive caster wheel is mounted in the front. The overall
vehicle specifications are provided in table 1.1:
Table 1.1: Vehicle Specifications Overall weight: 185 lbs (not including 20 lb payload) Overall length and width: Length: 44 inches Width: 33 inches Weight Distribution: 80% rear, 20% front caster Wheelbase: 29 inches Track width: 31 inches Wheel Sizes: 14 inch rear, 10 inch front caster Height: 17 inches (without sensor mast and payload box) 67 inches (with sensor mast)
Reagle uses two Quicksilver brushless DC drive servomotors with integrated 10:1
reduction planetary gear heads. All system power is provided by four sealed lead acid
1.2 Innovations In developing Reagle, the team attempted to understand the strengths and weaknesses of past designs. Whenever possible, the team made use of commercial, off-the-shelf (COTS) components to expedite development and to ensure reliability. As part of the design process, five former IGVC participants, Jesse Farmer, Jon Weekley, Peter King, Patrick Currier and Michael Fleming, were invited to the Embry-Riddle campus to work with the current design team. Jesse Farmer was a member of the Bluefield State College team. All other former participants were members of teams advised by Dr. Reinholtz at Virginia Tech.
Discussions and interviews with these successful former competitors revealed a number of critical requirements and design specifications for the new vehicle. While many of the requirements were achieved by past vehicle systems, the team identified three key innovations endorsed by the former IGVC participants. These innovations, which will be 2 discussed in detail in the subsequent sections, are the SoftRide© chassis, the Portable Electronics Case and the Hybrid-Electric Trailer for extended field testing and operations.
1.2.1 Innovation #1: SoftRide© Chassis The SoftRide© chassis was developed to provide a passive suspension and vibration damping without adding complexity or weight to the system. As qualifying and competition speeds have approached the 5 mph speed limit in recent years, and with the introduction of actual potholes, vehicle dynamic response has become a factor in both perception and control. Several recent vehicles, such as Chimera in the 2006 competition [Chimera Design Report, http://www.igvc.org], have attempted to add traditional spring-damper suspension systems to vehicles with rigid frames. The result has been larger, heavier and more complex vehicles.
Reagle takes a completely different approach to solving the suspension and vibration problem. Rather than adding a spring-damper suspension to a rigid vehicle frame, Reagle has these properties built in to the chassis of the vehicle. In figure 1.1, the blue rigid tubular box frame at the rear of the vehicle is designed to support the high torques and loads associated the drive motors. This frame section also supports the heavy lead acid batteries and the competition payload. The white front portion of the vehicle chassis is fabricated from high-density polyethylene, which provides both compliance and damping to the system.
This results in a vehicle that is lighter and less complex than a comparable rigid frame vehicle with a spring-damper suspension.
To help demonstrate the effectiveness of the integrated SoftRide© suspension, the dynamic response of Reagle was compared to Johnny-5 (a retired Virginia Tech vehicle from the 2007 competition currently housed at Embry-Riddle for joint research). Johnny-5 is a rigid aluminum frame vehicle of similar size and configuration. Figure 1.2 shows the typical accelerometer response to a step input at the sensor mast for the two vehicles. Peak accelerations on Reagle are reduced by a factor of three and peak velocities are reduced by a factor of two.
3 Figure 1.2: Sensor mast acceleration comparison (SoftRide© chassis in Red) 1.2.2 Innovation #2: Portable Electronics Case The Portable Electronics Case shown in figure 1.3 is another innovative aspect of Reagle’s design. This weather-resistant enclosure allows all of the system electronics to be removed from the vehicle for quick replacement of the electronic subsystem. An additional benefit is interoperability and interchangeability.
This same system can be directly integrated into another vehicle. The Embry-Riddle team has registered to participate in the 2008 AUVSI Autonomous Surface Vehicle Competition. Our goal is to use the same Pelican Case electronic subsystem and the same root software on our differentially steered surface vehicle. Although the surface vehicle uses SeaBotix thrusters rather than Figure 1.3: Pelican Case 1520 Portable Electronics Enclosure wheels, and it must navigate a course defined and Components by buoys rather than lines, the electronics and controls of the two systems are remarkably similar.
Figure 1.4: Reagle without (left) and with (right) Hybrid‐Electric Conversion Trailer Reagle is an all-electric base vehicle platform with four on-board Odyssey batteries that provide enough energy to run the vehicle in competition events for more than an hour. To substantially increase run time, a Hybrid-Electric trailer-based charging system has been developed and implemented. This trailer system includes a 1000 watt Yamaha four-stroke gasoline powered generator and a Deltran BatteryTender microcontroller-based charger. The Hybrid-Electric trailer provides extended operating times of eight hours or more. It also provides an auxiliary 120 volt AC, 12 volt DC and 24 volt DC power station. This field power station is remarkably handy for charging notebook computers, radio control units, cell phones and other common field equipment. Note that the trailer limits the vehicle’s ability to make zero-radius turns greater than 180 degrees, which must be controlled through software.
2.0 Design Process The 2008 competition will be the first IGVC for all of the student members of the EmbryRiddle team. Fortunately, the team has experienced faculty advisors and significant technical support from former IGVC participants now in graduate school or working in the industry,
2.1 Team Organization Members of the 2008 Reagle team are listed in table 2.1. The team includes two graduate students and seven undergraduate students. Every member of the team contributed to the overall design process. The graduate students, along with Alin Dobre and Aaron Brookshire focused primarily on electronics and software development, while the other members of the team focused on mechanical design, fabrication and testing. It is estimated that the team spent 1000 hours developing Reagle.
Table 2.1: Student Team Members Name Academic Major, Year Primary Team Functions Alin Dobre Computer Engineering, Senior Electronics, Software, Documentation Aaron Brookshire Mechanical Engineering, Freshman Software, Electronics, Documentation Wiljariette Hernandez Mechanical Engineering, Junior Mechanical Design, Documentation Michael Harris Mechanical Engineering, Freshman Mechanical Design Edward Muller Aerospace Engineering, Freshman Mechanical Design, Testing Tim Bentley Mechanical Engineering, Freshman Software, Testing Alex Gregg Mechanical Engineering, Freshman Mechanical Design Jason Firanski Computer Engineering, Masters Electronics, Software Jayson Clifford Computer Engineering, Masters Electronics, Software
2.2 Design Methodology As can be seen in the table above, the Embry-Riddle team includes a mix of students with widely varying levels of experience and with different academic backgrounds. This made it imperative to adopt a design process that everyone on the team could quickly understand and implement. Professor Reinholtz introduced the team to two tools that met this criterion. The first tool was the six-step process described in Product Design and Development (Ulrich and Eppinger, 2000). This process focuses on customer needs and the iterative steps followed in design. To ensure that innovation would be effectively represented in the design, the team also adopted the Kano design method described in Attractive Quality and Must-Be Quality Method (Kano, Seraku, Takahashi and Tsuji, ASQC Quality Press, 1996) during the conceptual design phase. Figure 2.1 illustrates this simple, common-sense approach to design.
6 Figure 2.1: Kano design method diagram
For a customer to be fully satisfied, a product must first meet the basic needs such as complying with the 5 mph maximum speed limit. According to the Kano model, customer satisfaction will increase linearly with improvements in performance parameters such as battery life. Finally, the Kano model suggests that customer satisfaction is strongly enhanced by unexpected features that are not found in competing products, Kano refers to these features as “delighters”. We believe that the SoftRide© chassis, the Portable Electronics Case and the Hybrid-Electric Trailer ideas generated in the brainstorming phase and later implemented in the design are delighters.
3.0 Mechanical Design Reagle was developed based on the requirements specified in the 2008 IGVC rules as well as the feedback provided by experienced advisors and former competitors. Our emphasis was on simplicity of design and operation and on efficiency and value.
3.1 Vehicle Chassis As noted in the innovations section of this report, the vehicle chassis combines an aluminum frame aft section for relatively rigid support of the motors, batteries and payload, and a front component deck made of marine-grade high density polyethylene sheet. The high density polyethylene deck provides the desirable compliance and damping properties described earlier, and it has the added benefit of lightening and simplifying the overall structure. In a rigid frame 7 vehicle, a separate deck plate would have been required for component mounting and protection.
The structural polyethylene sheet deck provides both the structural and protective functions.
3.2 Vehicle Drive Train Reagle is driven by two Quicksilver SilverMax 34HC-1 brushless DC servomotors. Each motor provides a maximum 444.7 watts (0.6 hp) at 2.47 N-m (1.82 ft-lb) of torque with a continuous stall torque of 4.77 N-m (3.52 ft-lb). Integral with the motors are 10:1 reduction NEMA 34 single-stage planetary gear heads. When joined with eccentric locking bearing and a custom machined steel hub, the motor and gear head provide a simple and reliable drivetrain, as shown in figure 3.2.
Figure 3.2: (a) CAD exploded view of the drive shaft assembly, (b) Reagle’s drive train
4.0 Electronics The electrical system on Reagle is an innovative aspect of its design. Many of the power distribution and control problems that hampered past teams have been effectively eliminated.
Because of the inexperience of the team, we collaborated with former team members and TORC Technologies to develop an integrated circuit power management board that regulates and distributes power to Reagle’s components.
4.1 Power System Reagle’s flexible power system allows it to adapt to different mission requirements. In its base configuration (i.e. without the auxiliary power trailer), Reagle is powered by sealed lead acid batteries. This safe power source allows Reagle to operate in environments where noise and exhaust fumes would pose safety or operational concerns. When longer runtimes are needed, the
5.0 Sensors and System Integration Reagle uses the four sensors shown in table 5.1 to perceive the surrounding environment.
Table 5.1: Sensor Suite Unibrain Fire-i board digital color CCD IEEE 1394 Firewire camera SICK LMS-221 scanning laser rangefinder system Pacific Navigation Instruments TCM2-20 3-axis digital compass Novatel SMART ANTENNA™ with Omnistar Subscription Correction The generalized sensor system architecture is shown in figure 5.
1. The selected sensors have been used by a number of past IGVC teams and have proven to be reliable and readily integrated through serial, USB and firewire busses, as shown in the figure below.