The Segway Human Transporter (HT) is a unique two wheel, self balancing locomotion device. It was designed to allow humans to move more quickly, cover more distance, and carry more than they could by walking. The manufacturer asserts that the Segway can go anywhere one can safely walk. The maximum speed a Segway can travel is 12.5 mph, which is about 3 times the average walking speed.
The Segway Mobility Evaluation was initiated with the concept that if the Segway could provide convenience for the everyday person, perhaps it is versatile enough to enhance the tasks of military personnel. Military personnel are often presented with situations that deem the use of full sized military vehicles inconvenient or even impossible, yet it would be advantageous to have use of a device that would provide for greater versatility than walking. With its small size and its capability for speed, the Segway appears to be such a device. However, military personnel are often situated on surfaces and terrains that pose a greater challenge to maneuvering over than the average person faces. The paths can be rough, scattered with obstacles, and may include a variety of surface irregularities. Hence, it was necessary to determine if the Segway HT would still provide convenience if placed in an environment that is rougher and less predictable than the environments it was designed for.
2.0 Summary of Test Plan
In order to obtain performance results that would be meaningful to the military, it was important to conform the Segway testing to a set military standard. The NATO Reference Mobility Model II (NRMMII) is a series of algorithms used by the US Army and other North Atlantic Treaty Organization (NATO) countries to compute the maximum velocity of a specific vehicle over a specific terrain. It is a comprehensive program that computes the maximum possible speed of the vehicle for a variety of different variables including tire pressure, tire type, ground terrain, and obstacles. The variables applicable to the Segway testing included tire type, terrain type, surface roughness, and obstacles. Other things to note are: battery life, dismounts, weather conditions, damage to Segway, and rider comfort.
2.1 Terrain Categorization
The NRMMII specifies 8 different terrain types: primary road, secondary road, sand soil on trail, other soil on trail, operation in snow on trail, sand off-road, other soil off-road, and snow off-road. Given physical limitations, snow was unavailable for use at the time of testing. Additionally, the other soil on trail and other soil off-road categories were omitted because of obscurity of definition and limited terrain type in the designated test area (Seaside, SSC San Diego). Self-Imposed definitions of the terrain types allowed testing of the other four types within the limited testing area. Primary road is defined as any maintained paved road. Secondary road is defined as un-maintained paved road or maintained gravel road. Sand soil on trail is characterized as compacted sand that does not show significant ruts upon Segway crossing. Uncompacted (loose, uncompressed) sand located off trail is designated as sand off-road.
2.2 Surface Roughness
The term surface roughness is used here to describe the relative quantity of surface irregularities in the terrain. In this experiment, a quantitative estimate of roughness was obtained by laying a yardstick flat on the terrain and measuring the difference in height between the yardstick and two lowest points (to the nearest ј inch). This was repeated along the entire length of the test course and the values were then averaged and the standard deviation computed. The average value was then placed into one of five predetermined ranges: 0-.2, 0-.5, 0-1, 0-1.5, or 0-2, inches. For each terrain type, two or three distinct areas were found each of which fell into a different range of roughness.
For testing purposes, an obstacle was defined as an object at a height greater than or equal to .75 inches that impedes the motion of the Segway. Obstacles encountered in nature include rocks and vegetation. Additionally, other varieties of objects may be stumbled upon on maintained roads. Since obstacles vary greatly in size, shape, and location, it would be difficult to obtain informative results by performing tests on geographical obstacles. Hence, to evaluate the Segway’s performance over obstacles, a set of model obstacles was created for testing purposes. The obstacles consisted stacking several 2 x 4 pieces of lumber and a 0.75 inch thick sheet of plywood in various combinations to attain different heights. Additional pieces were added until the Segway was no longer able clear the obstacle.
2.4 Tire Type
For the initial testing, three different tires were tested. The standard Segway HT tires (the tires that come with the Segway), the Segway HT enhanced traction tires, and Dunlop D739 dirt bike tires. Since the Segway tires are tubeless, in order to use the Dunlop D739 tires, it was necessary to modify the Segway rims by drilling a hole through the plastic to accommodate a tire inner tube (size 3 x 14 inches). The Dunlop tires are mini bike tires of size 14 90/100, while the tires designed to be used with a Segway are 14 65/100. In order to install the Dunlop tires, the Segway fenders had to be removed. As a safety precaution, new fenders were fabricated using Segway e-series bag mounting brackets and slightly alternating their shape to accommodate the Dunlop tire. The onboard software of the Segway was not updated from the original configuration to accommodate the larger tires.
2.5 Experiment Set Up
Before testing could begin, it was necessary to explore the testing area for assorted terrain types and roughnesses. Regions were sketched out and marked on a map of the Seaside division of SSC San Diego (appendix VI). The course length for each test varied from 30 feet to 72 feet. The boundaries were marked off with cones and two pieces of rope to facilitate timing.
For the testing of the Segway over obstacles, the plywood was arranged in such a way that it wouldn’t shift during testing (see photo). The course length for obstacles was set at 92 inches (7.67 feet).
2.6 Testing Procedures
The Segway was driven over the surface roughness course length three times in each direction. Time was recorded using a stop watch with accuracy of 1/100 of a second. The 6 obtained times were then averaged and an average speed computed. Similarly, for obstacle testing, the tester rode the Segway over the obstacle course 3 times in succession and time was recorded. The obstacle course consisted of a 7.67 foot long track with the obstacle in the center of the course. For obstacle testing, given that there was often be multiple attempts before passing over the obstacle, the actual distance covered varied from test to test (depending on how many runs it took to overcome the obstacle). Although “speed” is technically defined as the change in distance over the change in time, for comparative purposes and to simplify data analysis, “speed” was freely defined to be the course length (displacement) divided by the total time it takes to complete the test.
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