One of the initial design considerations for the robot is how it will navigate through rubble. Although tank treads are often considered, wheels are recommended for better maneuverability. Wheel size is an important factor in the speed, stability and navigation of the robot. In addition to size, other wheel features will need to take into account the size of the rubble as well as the type of terrain. For these tests, however, you will only be varying the wheel size and navigating the robot on one type of terrain at a set distance.
You’ll use gears, of course, to vary the force turning the wheels. The gear test stations in the Innovo test engineering laboratory are set up with spur gears in three different configurations. You will be measuring the rotational speed in rpm (rotations per minute) and the torque, or force, each gear axel can pull in Newtons.
Download the notes and procedures for the wheel and gear/mechanical advantage tests.
Please note: The procedure for the wheel test is included in the downloaded notes, while the gear test procedure is a separate attachment in addition to the downloaded notes.
Wheel test notes:
http://www-education.rec.ri.cmu.edu/
vex_online/lessons/wheel_size_basic/
wheel_size_starter_kit_procedures.pdf
Gear test notes:
http://www-education.rec.ri.cmu.edu/vex_online
/lessons/gearbox/docs/student_notes.pdf
Please review the background information below and refer to the Requirements for more detail. We have developed a list of questions for you to answer to help make sure you understand the concepts you need to apply in making your measurements and interpreting your data. These are included in a document called “Training Assessment (Checking your Understanding)”, which is also attached. Use the attached Excel worksheets to record your data for the wheel and gear tests. You will be submitting these to your project manager along with your lab reports.
Important Background
Recall from simple machines that the wheel and axle is a lever that rotates in a circle around a fulcrum, and therefore the principles of levers also apply to wheels. As a lever that can turn 360 degrees, the effort or resistance force can be applied either on the outer wheel or the axle.
To vary the speed and strength of the force turning the wheels, engineers use gears. A gear is simply a wheel with teeth, or cogs, on the outside, which fit into the teeth of another gear. When the gear turns, it then turns the other gear, transferring forces from one gear to another and causing the other gear to turn in the opposite direction. If the two gears are different sizes with different number of teeth, the speed of the turns also changes from one gear to the next. The gear that originates the rotation is called the driving gear, and it is usually attached to a motor. The gear that is then turned by the driving gear is the driven gear, and is often attached to the wheel.
A gear's most important feature is that gears of unequal sizes (diameters) can be combined to produce a mechanical advantage, so that the rotational speed and torque1 of the second gear are different from that of the first. When a system of gears is combined with the wheels on a vehicle, it can be used to vary the speed and direction the wheels travel. Spur gears are the most common type of gears. They have straight teeth and are mounted on parallel axels, or shafts. Sometimes, many spur gears are used at once to create very large gear reductions.
1 Recall that torque is a measure of the rotational influence that a force has on an object. It is measured by multiplying the force by its distance from the object’s center of rotation.
“A robot must obey the orders
given it by human beings except where such orders would conflict
with the First Law" [The Second Law of Robotics]” (Isaac
Asimov , 1920-1992)
