Snow Cat Real Time PC μ C Snow Cat Track Controls UHF DL 7400

In recent years, break-through in GPS-navigation has led to a whole new range of robotic control applications. The Stanford University GPS laboratory has pioneered research in fields ranging from unmanned aerial vehicles, robotic open-pit mining trucks, and autonomous farm tractors. This same technology can also find use in grooming the slopes of a ski area! With safety paramount, snow grooming is always performed after closing time of a ski resort, i.e. evenings and nights. Robotic snow cats have great promise for reducing current operating costs of snow grooming, partly due to cost of operators working extremely odd hours of the day. With a state-of-the-art navigation system, one may operate even in full whiteout conditions. Furthermore, a robotic vehicle could be more readily used in avalanche prone areas. From the standpoint of a manufacturer, an autonomous snow cat has no need for an operator cabin (w/ chairs, controls, radios/CD-players etc.). Removing that cabin may well save weight as well as cost of production. Finally, cabin removal will open new degrees of freedom in snow cat design. A lower snow cat would be more stable, and it could more easily access areas under lifts. As a first step towards the ultimate goal, a GPS-based autopilot for a Bombardier MP Plus snow cat has been implemented and tested. This paper gives a general system overview and presents results from field tests at Alpine Meadows Ski Resort. All tests were performed without any attitude system, but the results still show total system errors in the 10-cm range. 1.0 Introduction GPS based robotic systems are currently finding their way into the market place. GPS has enabled tractors to plow perfectly straight rows in farm fields [1], and huge trucks to navigate open pit mines [2]. The purpose of this paper is to explore similar technologies for robotic grooming of ski slopes. There's more to using a snow cat than simply driving it around the ski slopes. Unlike most comparable heavy machinery, snow cats use both front and rear mounted implements. Whereas a front blade levels major snow unevenness, like moguls, a rear tiller removes snow lumps and residual surface unevenness. Both implements are 46 degree of freedom systems, and they're controlled through separate joysticks. Finally, snow cats are steered around either using steering wheels, or 2 "tank like" trackspeed control sticks. Due to the plethora of controls involved in handling a snow cat, fully mastering such a vehicle is a skill that usually takes several seasons to acquire. Not only must a snow cat operator guide the vehicle along paths with minimum mutual overlap, but the operator must also make constant changes to the attitude of the front blade and rear tiller in order to ensure best possible grooming performance. Furthermore, a groomer must judge the oncoming snow surface in order to cut down all bumps and fill in all ruts, all while constrained by following natural terrain features. Finally, operators must adapt to a wide spectrum of snow conditions. Still, an expert groomer needs only one single pass through a mogul field to level it perfectly. Snow grooming is always done after closing time of a ski resort, when no one is on the hills. Although public safety is maintained such scheduling means extremely odd working hours for snow groomers. Night work during weekends is rather expensive for ski resorts. Furthermore, some ski hills run only one shift of grooming. This means they require more $200k snow cats to do the same job that other ski resorts do by grooming all night. In the quest to remain open to the public, snow cats are often run during whiteout conditions. Robotic snow cats with state-of-theart navigation systems should greatly improve grooming performance during low visibility conditions as well as reducing regular operating costs. Such robotic vehicles would have no use for an operator cabin. Removing that cabin should open new doors in snow cat design, e.g. enabling lower vehicles for easy access under lifts. Although making a snow cat fully autonomous is the long-term goal of this project, systems for operator assistance can be achieved more readily. Removing some of the workload from an operator should improve grooming and cut down on initial training time. Thus, a GPS-based snow cat autopilot was implemented to test one possible technology. 2.0 Experimental set up In this work we had the great fortune of borrowing a Bombardier MP Plus snow cat from Alpine Meadows ski resort. We mounted a dual-frequency GPS antenna on the roof of the operator cabin and a UHF data link antenna to its right side-view mirror. A Trimble 7400 RTK-GPS receiver, a Pacific Crest Blue Brick UHF data radio, and a 300W power inverter were fastened to the inside of the operator cabin. Then, an Industrial Computer Source PC with a DBI "sunlight readable" LCD display and a 12V battery were fit snuggly on the passenger-side floor. Finally, a Phytek 515C microcontroller was attached to the top of the PC. See picture below for passenger-side equipment. Figure 1 Technical equipment As GPS reference, another 7400/Blue Brick pair was put on top of the start tower of the Subway lift at Alpine Meadows. See picture below. Figure 2 GPS reference station The full system overview is shown in the figure below.