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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
MANUFACTURING
We used off-the-shelf mechanical components for this design. Most of the
parts can be purchased at your local hardware store.
The mechanical components that you must build must consist of several plates, which when assembled make up a pendulum and the inner-workings of the rolling robot. The pendulum is essentially a box with a series of threaded holes that are used to attach the drive motor and servomechanism.
The first step is to cut out the rough shapes of the different plates that make up the pendulum and a custom universal joint. The method of creating these plates depends on the materials you work with. We chose aluminum, which requires machining with a water-jet or milling cutter. However, the body could just as easily be made from polycarbonates or acrylics and cut out with a scroll saw.
Once you cut out the parts, you must drill holes to attach the drive components. Next, tap the drilled holes. Taps can be purchased as a set or individually at your local hardware store. Make sure the taps match the screws used in the project.
The brackets used to attach the servo pushrod should be made slightly different than the other plates. First, cut out a strip of 18-gauge sheet metal, drill the holes, and then bend the bracket. The part is small enough so that drilling the holes before bending makes the manufacturing process much easier.
The pushrod itself is easily made by cutting a short length of threaded rod and connecting two pushrod clevis pins. The next step is to cut the shafting to length in order to create a drive shaft, gear shaft, and a support shaft. There are several ways to accomplish this. The simplest is to use a hacksaw. Once you cut the shafts to size, carefully round the ends with a file. Any raised burrs will make it difficult to slide anything onto the shaft. Finally, use a die to thread the drive shaft, you should need to thread only about 1" on either end of the shaft.
The final step is to cut two holes into the rubber kick ball. First, determine an axis through the ball. This can be accomplished by deflating the ball and folding it into quarters. The points of the quarters should approximate the location of an axis through the ball. Next, inflate the ball. Using a compass, trace two circles on the ball and use the lock ring from the drain assembly to determine the necessary diameter of the circles.
Lastly, deflate the ball and use a pair of scissors to cut out two holes defined by the circles you have drawn. Make sure you don’t cut the ball’s plug; otherwise, it will be impossible to inflate.
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