CURRENT ISSUE
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Feature Article
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Issue #200 March 2007
Inertial Rolling Robot
by Jeff Bingham & Lee Magnusson
Start | Electronics | Drive Motor | Servo Motor | Pressure Sensor | Software | DC Drive Motor Control | Servo Motor Control | Mechanical Components | Manufacturing | Assembly | Findings | Sources & PDF
MECHANICAL COMPONENTS
In this article, we present our parameters for constructing this robot;
however, customization is the spice of life. In order to modify this robot,
you should keep a few things in mind. The ideal implementation of this
robot has its weight as far away as possible from the robot’s driven axle.
This allows the robot to convert a maximum amount of momentum or torque
into rolling, because the robot essentially moves based on the “falling”
of the pendulum. If the pendulum rotates too far, the ball will counter-rotate,
so balancing motor torque and pendulum torque is important (see Figure
5).
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| Figure 5—Driving the internal pendulum causes the robot sphere to rotate. |
Simulating the robot’s motion can also help. Using the motion equations in Figure 6, different physical parameters and motor-control scenarios can be modeled to determine the optimal design. These equations can be solved using any numerical solver and plotting the output. In order to model the motion in the tilt direction (the plane perpendicular to rolling), the same equations can be simplified and used. However, the simplest and most important analysis of the tilt motion is the turning radius:
where j is the tilt angle of the pendulum. These two-dimensional simulations should be more than adequate for predicting the robot’s basic motion.
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