Motors are typically Direct Current (DC), and are fairly small.
Torque is a measurement of how much weight a given motor can move.
Current Draw is a measurement of how much power a given motor requires to
move with a given torque a given weight. The more current draw, the faster your
batteries discharge, the larger the control circuitry you have to have, and
(typically) the heavier the motor.
Shaft encoders are a way to measure angular changes in output shafts,
such as the one coming out of your motor. In the discussion that follows,
modern optical shaft encoders are the primary thing discussed, but there are
other, more mechanical (or audio things) that can be used.
A given shaft encoder, attached to the direct output wheel of a robot, generates
a train of pulses to the CPU that indicates that the given wheel moved a
number of degrees of rotation. When you turn on your motor to move in a given
direction, the shaft encoders, in returning the information to the CPU, give the
robot a sense of how much distance it is covering.
Odometry is the engineering task of using this type of feedback to
ESTIMATE where the robot is in its physical environment. It is
strictly an estimate because of a number of physical limitations on the motors,
gear boxes, interconnections, etc. that are involved, along with inertia, vary
Let's face it, the size of most modern wheels is a bit of a guess. Perfect no
load wheel diameter (i.e., no deformation due to weight) is different than when
the same wheel is under load. Some production wheels are not perfectly
circular, even under no load.
In summary, here are a few of the questions that need to be discussed to
determine what is best for a given physical system.
Knowing the answers to these questions, you can then go about creating
a wheel encoder. This web page/form helps you see a narrow
range of results using different values.
Hence, what this page attempts to do is just to give you some idea
of how much travel your wheel will make given one pulse back on your
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Given that you want to determine some specs on your motors,
here is a tool that might well help you out. Once you insert
the values for your physical constraints, this tool will give
you various bits of information that you will hopefully find