L L P T V
(Large Low-Pressure Tire Vehicle)

by John Nordlie
For Dr. Dick Parkers 491 Space Mission Design course

1.1 INTRODUCTION
 The LLPTV (Large Low-Pressure Tire Vehicle) is a roving platform designed for use in planetary exploration.

1.2 BACKGROUND
After the success of the Viking exploration mission to Mars, many people have realized the advantages of having a roving exploratory probe, as opposed to a stationary one. Many exciting schemes have been developed for creating a mobile probe, ranging from aircraft to huge bouncing balls. One interesting plan involves using large (relative to the vehicle) inflatable tires which are pumped up to relatively low pressures. This allows the tires to have a substantial "flat spot" or area of contact where they meet the ground. The size of the contact area determines both the traction limit of the tires and the weight loading on the tire surface area. As any fan of the "monster trucks" can tell you, larger contact area means more traction and the ability to absorb large obstacles, enabling the vehicle to pass over very rough ground. Since larger contact area also means a lower loading of weight per square unit of tire, the risk of puncture is also lessened. Exploration probes are required to pass over rough, hilly terrain without damaging themselves, yet they must also be close enough to the ground to enable them to collect samples. Since the LLPTV can do all these things, we feel that the LLPTV is ideally suited to the task.

1.3 TEST VEHICLE
The test prototype of the LLPTV will be built in several stages. The vehicle has four large diameter, low inflation pressure tires, connected to live axles. The front axle is steered by means of a servo, and is otherwise unpowered. The rear axle is driven by a six volt gear motor through a belt system. The chassis is made from 1" x 1" wood, joined by steel corner braces. The chassis provides mounts for the steering servo, the drive motor, a battery power pack, and a 27.095 MHz radio control receiver, which also contains the motor control electronics. Provisions have also been made for the mounting of dead weight to the chassis for test purposes. The LLPTV test model is built in a series of six stages: 

	1 - Assemble front axle and axle mount, add wheels and
         steering linkage.

	2 - Assemble rear axle, mounts, and drive pulleys.  Add
         rear wheels.

	3 - Assemble main chassis.  Add wheel/axle units.

	4 - Mount drive motor to chassis.  Mount steering servo
         on chassis.  Connect drive belt and steering linkage.

	5 - Mount battery power packs and radio receiver to 
         chassis.  Wire receiver to steering servo and drive
         motor.  Mount radio antennae.

	6 - Mount the body, which also serves as payload carrier.
         test systems for shorts and mistakes.
1.4 TESTS OF LLPTV
Testing of the prototype LLPTV will involve operating the vehicle in a variety of differing terrain's, using different tire pressures and payload weights. The object is to get an idea of the optimal tire inflation pressures and payload limits for given terrain environments.


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