The vehicle has a small platform in its center. When this platform is raised, the wheels touch the ground and the vehicle can proceed. In this configuration the vehicle has no turning ability at all; on the contrary, it has been designed to go as straight as possible.
To change direction, the vehicle lowers the platform and lifts itself a bit so as the wheels don't touch the ground anymore. At this point, the platform rotates, actually making the robot change the direction toward which it is pointed.
When the desired direction is reached, the platform is raised again and the vehicle can resume its motion.
Here you can see the complete turning sequence. Initially, the platform is raised and the main wheels touch the ground.
When the time to turn comes, the robot stops and lift itself using two large pneumatic cylinders that connect the platform to the body. Notice that the two small wheels attached to the base of the platform cannot rotate; they have the purpose to increase the friction of the platform on the ground.
With the main wheel lifted, the platform turns in respect of the body of the vehicle, acutally making the vehicle itself change its direction.
The rotation of the platform continues until the vehicle reaches the desired direction. For this specific contest, the platform was designed to turn precisely 180°.
A bottom view reveals some details of the platform, and the turntable it is attached to.
The main drivetrain is rather simple. In this picture you see also the light sensor used to measure the travelled distance in conjunction with a black&white rotating disc. The short axle pointing downward is the reference point used to measure the distance from the starting/arrival point.
Front view. The supply of air is provided by two air tanks, loaded manually before each run of the robot. They provide enough air for the single lift-lower cycle required to turn the robot 180°.
By removing the central platform, the chassis reveals its simplicity. The front side mounts the drive motor and the touch sensor to detect the wall. The rear side mounts a simple motorized valve switch to operate the pneumatic cylinders.
Side view of the platform, taken apart from the robot. The most critical point of this assembly is the high torque needed to turn the robot when its entire weight acts on the turntable. The friction is so high I had to adopt a 144:1 ratio to make the motor able to rotate the robot.
The other side of the platform.
Top view of the platform. There's a gearbox inside, which helps in reaching the high reduction rate mentioned above. The axle coming out of the 24t gear inside the gearbox is connected to an 8t gear, engaged to the inner geared side of the turntable.
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