Eric L. Wang

Teaching freshmen design, creativity and programming with LEGOs and Labview

For the past 3 years LEGOs have been used to teach design, creativity, and structured programming to freshmen mechanical engineering students at the University of Nevada, Reno. MECH 151 is a 3-credit hour course offered as the second semester of a first year mechanical engineering design sequence. The class utilizes a project-based learning environment, which consists of approximately 10 design projects of increasing difficulty and scope. The course culminates with a robot battle and a presentation to local K-12 schools. Assessment methods include student surveys, external evaluators, evaluation of projects, and enrollment data. The use of LEGOs was found appealing to the students while providing an excellent medium for teaching design, programming, and creativity. Student enrollment has grown over 2 fold since the introduction of LEGOs.

LEGO-based Robotics in Higher Education: 15 Years of Student Creativity

Our goal in this article is to reflect on the role LEGO robotics has played in college engineering education over the last 15 years, starting with the introduction of the RCX in 1998 and ending with the introduction of the EV3 in 2013. By combining a modular computer programming language with a modular building platform, LEGO Education has allowed students (of all ages) to become active leaders in their own education as they build everything from animals for a robotic zoo to robots that play childrens games. Most importantly, it allows all students to develop different solutions to the same problem to provide a learning community. We look first at how the recent developments in the learning sciences can help in promoting student learning in robotics. We then share four case studies of successful college-level implementations that build on these developments.

Augmenting heat transfer from fail-safe magneto-rheological fluid dampers using fins

This paper presents a lumped system model for predicting the heat transfer from fail-safe magneto-rheological fluid dampers. For this study, a fail-safe damper is defined as a damper which retains a moderate damping capacity in the event of a power systems failure. To evaluate the validity of the theoretical model, two automotive size dampers were constructed, one with fins to augment heat transfer and one without fins. The results show that the model slightly over predicts the temperature rise when compared to experimental data. Despite the error, both the experimental and theoretical results clearly demonstrate that the heat transfer can be considerably enhanced with the use of the fins. Finally, the results also indicate that both the mechanical and electrical power input contribute substantially to the temperature rise.

Theoretical and Experimental Studies of an Electro-Rheological Grease Shock Absorber

One method of achieving fail-safe, semi-active damping is to utilize a controllable fluid with a high zero-field damping capacity. To this end, this paper introduces a prototype electrorheological grease (ERG) as a new concept in electro-rheological fluids (ERFs). The general properties of grease-like fluids imply a non-Newtonian post yield viscosity. The fluid model developed in this paper considers the influence of a non-Newtonian post yield viscosity by using a power law model to account for shear thinning behavior. This model can be applied to all controllable fluids since it reduces to a Newtonian viscosity as a special case. The theoretical study includes a lumped parameter dynamic system model to predict the behavior of an actual damper, which takes into consideration inertial and compressibility effects. To validate the proposed models, a prototype damper was designed and used to collect data for a known ERF and the new ERG. Results from the ERG test data indicate that a good match between experimental and theoretical data was achieved. A sensitivity analysis shows that the model was insensitive to the mass of the fluid, but sensitive to the bulk modulus of the fluid. Comparisons are also made between the performance of the ERG and the existing ERF. The ERG demonstrates higher zero-electric field damping capacities than those of the ERF, yet produces an increase in damping when an electric field is applied.

Minimization of pedaling induced energy losses in off-road bicycle rear suspension systems

SUMMARY This paper presents the results of an optimization analysis performed on off-road bicycles in which the energy loss induced as a result of pedaling action was minimized. A previously developed computer-based dynamic system model (Wang and Hull, Vehicle System Dynamics, 25:3, 1996) was used to evaluate the power dissipated by a single pivot point rear suspension while pedalling uphill on a smooth surface. By systematically varying the location of the pivot point, the relationship between power dissipated and pivot location was determined. The optimal location was defined as the location which resulted in the least power dissipated. The simulation results show that the power dissipated was very dependent on the height above the bottom bracket but not the fore-aft location of the pivot point. If the pivot point is constrained to the seat tube, then the optimal pivot point was found to be 11 cm above the bottom bracket. Compared to a commercially available design, the optimal pivot point reduced the p...

Flight Testing of a 1-DOF Variable Drag Autonomous Descent Vehicle

This paper details the hardware development and testing of an autonomous descent vehicle. The developed vehicle utilizes a circular parachute and wind data to control the landing location. The benefit of this system over alternative precision aerial delivery techniques is the envisioned ability to use the large inventory of circular parachutes already in use for uncontrolled cargo and personnel deliveries with minimal training or system modifications. Parachute control is obtained via reversibly reefing of the canopy, thereby modifying the descent speed. For this study, the parachute size is assumed to be constant for the remainder of the descent; however, the desired parachute size computation is periodically updated to assist in reducing landing errors due to inaccurate wind data. A small mechanical reeling system has been developed, comprising a microcomputer, RF modem, electronic speed controller, and an electric motor. The hardware is coupled with a quarter-spherical canopy with four suspension lines, similar to those used in automotive drag racing. The combined weight of the parachute-payload system is 53.5N (12.0lb). Flight testing was conducted using a small single engine aircraft (Cessna 172), with preliminary flight testing conducted using an Arcturus T-20 UAV. Release ceilings were approximately 3050m (10,000ft) MSL. Typically, dropsondes were used to collect predicted wind for the descent vehicle. The time needed to collect the wind data, upload it into the descent vehicle software, takeoff, and reach the desired deployment location was approximately two hours. Preliminary testing of the parachute-payload system was performed to determine the appropriate control gains for the motor angle control routine to achieve the desired descent rate. Release altitudes were between 450m (1,500ft) and 610m (2,000ft) AGL. Using Zeigler-Nichols gain tuning rules and an experimental step response, gains were determined for both a Proportional-Integral (PI) controller and a Proportional-Integral-Derivative (PID) controller. Additional testing was conducted to verify the ability of these control gains to achieve a desired descent speed prior to flight testing the full path planning system and control algorithm. Flight testing results demonstrate the ability for the autonomous descent vehicle (ADV) to successfully navigate towards a target line segment when using accurate wind prediction data. As previously published results have noted, when the predicted wind data is inaccurate, the vehicle is not always capable of improving the landing location accuracy compared to an uncontrolled parachute. Additional considerations in developing a descent rate control system for use in circular parachutes are also presented.

Time-Varying Descent Rate Control Strategy for Circular Parachutes

This paper presents a time-varying control methodology for a variable-sized circular parachute to reach a target landing location. A trajectory is calculated for the immediate control horizon using wind forecast data. To create a parachute–payload trajectory, a three-degree-of-freedom kinematic model is developed. Using this, the performance envelope is determined, revealing the potential target range of the system during a descent. Next, this model is further developed into a control methodology to determine the necessary descent rate, to reach the desired landing target, to be controlled via parachute size manipulation. Finally, simulation results are presented to validate the control scheme. Various release locations were simulated with paired uncontrolled/controlled parachute descents from within the performance envelope. Results demonstrate the feasibility of the system, with controlled parachute descents actively navigating toward the target. With accurate wind data, the vehicle can overcome release...

Electrorheological grease (ERG) shock absorber

A fluid model for the evaluation of electrorheological grease (ERG) is presented. This model considers the influence of a Non-Newtonian fluid using a Herschel-Bulkley fluid model. Fluid compressibility was included using a lumped parameter dynamic system model. The optimal model parameters were determined by matching theoretical and experimental data for an existing ERG damper. Results indicate that a good match between experimental and theoretical data was achieved using the Herschel-Bulkley fluid model. A sensitivity analysis indicated that the model was insensitive to the mass of the fluid, but sensitive to the bulk modulus of the fluid.

In-flight Landing Location Predictions using Ascent Wind Data for High Altitude Balloons

This paper presents a hardware and software system in which the landing location of a balloon–payload system is continually predicted and improved. Initial prediction parameters are corrected by estimating flight parameters using GPS data. The focus of this study is on small (less than 10 kg payload) balloon systems. For these systems, flight missions typically have a duration of a few hours (minimal loitering at altitude) and descend after the balloon bursts at an altitude in the range of 15-30 km. Prior to launch, weather predictions are typically used to predict the flight path and landing location of the balloon-payload system. The prediction accuracy greatly depends on the stability of wind data, as well as the accuracy in predicting the balloon ascent speed, balloon burst altitude, and parachute descent speed. Differences between the predicted and actual landing locations of 60 km are not atypical. Rather than relying on the pre-flight predictions, the system developed here measures ascent/descent speeds and wind speed during the balloon’s ascent. Unlike the pre-flight predictions, the system provides chase and recovery personnel with an accurate prediction of the landing location that is periodically updated as the mission progresses. During ascent, GPS data is logged to provide both actual ascent speed and up-to-date spatial and temporal wind data. The ascent speed along with the logged wind data and initial estimates of the parachute-payload flight characteristics (mass, parachute size, etc.) are used to correct the flight model up to the time of balloon burst. During descent, the actual descent speed is used to further enhance predictions as the mission progresses. Results calculated from post-processing actual balloon flight GPS data validate the methodology developed. Prediction accuracy is improved from an average predicted landing location error of 36% of the traveled range prior to launch. At the balloon burst location, prediction quality improves to 3.5% of the total range traveled on average. Additionally, real-time, in-flight prediction results verify the ability to perform the in-flight prediction updates on-board a balloon using a microprocessor and off-the-shelf radio communication equipment.

Path Planning of a Circular Parachute Using Descent Rate Control

This paper presents a time-varying control methodology for a variable-sized circular parachute to reach a target landing location. A trajectory is calculated for the immediate control horizon using wind forecast data. In order to create a parachute–payload trajectory, a 3–DOF kinematic model is developed. Using this, the performance envelope is determined, revealing the potential target range of the system throughout a descent. Next, this model is extended to develop a control methodology to determine the descent rate, via parachute size manipulation, needed to reach the desired landing target. Finally, simulation results are presented to validate the control scheme. Various release locations were simulated with paired uncontrolled/controlled parachute descents from within the performance envelope. Results demonstrate the feasibility of the system, with controlled parachute descents navigating towards the target. With accurate wind data the vehicle can overcome release location errors as well as vehicle uncertainties and perform significantly better than an uncontrolled parachute.