Design and Simulation of Human Powered Vehicle for ASME HPVC

Introduction

Human Powered vehicles (HPVs) come in many different sizes and configurations. A human powered vehicle can be as simple as a paddle boat and as complex as an airplane.

HPVs include vehicles built for air, water, or ground transport, but the common denominator is the integration of a human into the design.

Objective

1. The goals for the HPV design were for it to be agile, lightweight, and efficient in both daily use and events. To reduce the air drag of the vehicle the rider is placed in the supine position which is referred to as a recumbent bicycle.
2. To further reduce the drag the addition of an aerodynamic enclosure, known as a fairing, can be added.
3. Design of HPV provides the team a field knowledge of challenges faced during Designing, Manufacturing, and Dealing with local markets and information gained from a lengthy experience

ASME HPVC

The American Society of Mechanical Engineers sponsors the Human Powered Vehicle Challenge (HPVC) as a way to promote the use of human powered vehicles

The HPVC tests Mechanical Engineering students to design and manufacture a HPV that is to be judged in categories such as design, safety, and performance. Ultimately, the HPV will be driven in both a time trial and endurance race against entries from ersities across the United States and around the world.

ASME DESIGN STANDARDS

DESIGN-ASSEMBLY AND PARTS

Frame/Chassis Configuration:

Two wheels & Three wheels: ?It has been noted that some teams in the past from last years competition , have had trouble on sharp, low speed corners?with a two wheel design resulting?in their vehicle losing stability and falling over

?We had decided to go with a three wheel design for one main reason and that is stability.

Three Wheeled Configurations?

When one looks at the basic layout of each design and does a visual vector analysis of forces while cornering, one can see that two wheels in the front is more stable than two wheels in the rear. So combining the forward momentum and the centrifugal force as shown by the vectors in blue, they combine to give the vector in green, which, as one can see, points in the directions of the tires in the case of the three-wheel front design, and points outside of the front tire in the case of the three-wheel rear design. This basic proof of concept shows why two-wheels in the front are a more feasible design choice than two wheels in the rear. It was also noted that handlebars for the first configuration would be conflicting with a narrow fairing design. So for the frame configuration it is decided to do a three wheel design with two wheels in the front.

Frame materials:

Seat & its Adjustment

Having the correct posture and seat distance can help the drivers maximize their potential.The seat angle was fixed at about 30° from the horizontal based on studies done on pre-existing designs. To adjust for different driver heights, a commercial quick-release mechanism was chosen to allow the seat to slide forward and back.

Wheel selection

The main difference between road style and mountain bike style is tire/wheel diameter and width. The reason we might be interested in mountain bike tires is because they might provide more traction because they have more tread, but they would also provide more rolling resistance. Road style tires are narrow and larger, so we could attain a higher top speed and have less rolling resistance.

Most wheel hubs use 5mm skewers to hold them onto dropouts, like the rear tire will. But these hubs are mounted in double shear. The way we are going to mount the front wheels is cantilevered like a common car wheel is, that is, it is mounted on the side and the axle is in single shear with the uprights. For this reason a 5mm skewer may not be strong enough for the expected loads and would interfere with the braking system.

Braking system

Disc brakes generate far more braking power than standard rim brakes. A faster ride - It is considered that disc brake bikes can provide a faster ride. It consist of 2 main pa

1. Disk pad
2. Breaking mount

Steering system

?Ackerman steering system:

Ackermann steering geometry results in all wheel axes intersecting at the same point while the vehicle is turning, eliminating the tire scrub that would occur if the front wheels simply turned by the same amount. Perfect Ackermann geometry makes tight turns at low speeds smooth and easy, but causes oversteering due to tire deformation at higher speeds. Magnum was designed to have perfect Ackermann geometry at its minimum turn radius of 5.5 meters. At larger turn radii, the wheels would be slightly closer to parallel.

Drivetrain components

It is the?gearing system that translates power from the human to the drive axle.?As one can see a theoretical speed, based purely on gearing ratios and possible rider cadence, of 47.3mph might be obtainable as long as a cadence of 100rpm can be reached in top gear. This speed could be increased in the cadence can be increased as determined by the rider or if the upper chaining is switched to the 55 tooth. This system is also beneficial since it is compatible with 9-speed Flat-bar gear shifters which will make shifting and rider use easier.

Fairing Design

• ?The fairing is an aerodynamic shell built around the frame. It is used to improve air flow and also protects the rider.
• ?There are a several different design possibilities. To begin we will?design the fairing to be as safe and aerodynamic as possible
• The fairing must be designed to fit around the RPS and give enough room for the rider to pedal without hitting the sides
• ??It would begin with a round nose and end with a tapered edge.
• ?This helps to maintain laminar flow over the entire shape.
• ?When the air flow does not hug the surface of the fairing this causes turbulent flow and increases drag.

Rollover Protection System (RPS)

The roll protection system or RPS for short is the most important safety feature on the vehicle and a necessity to participate in the ASME competition. It protects the driver from contact with the ground in the event of a rollover. It must also resist a side load of 300lbs and 600lbs 12° from vertical at the top. An illustration has been provided by ASME in their HPVC Rule Book.

Design Analysis

Frame Design Analysis:

Frame must be able to withstand a load of 600lbs applied to the top of our roll bar at an angle of 12 degrees toward the rear of the vehicle and have a deflection of no greater than 2 inches. Second, there must be a side roll bar able to withstand a horizontal load of 300lbs with a deflection of no greater than 1.5 inches. Having selected the material, the necessary diameters and wall thicknesses will be calculated using beam deflection formulas.

Complete Design