Last month, we discussed the design and performance compromises that accompany
the use of an asymmetric weapon. If
you decide that this design is right
for your robot, the next step is to
start concocting your weapon.
First, you need to decide
whether you want to use a bar or a
disk. If you are a more advanced
builder and decide to design a full-body horizontal spinner or vertically
spinning drum, the principles are very
similar to those for a disk. Assuming
the same diameter, a disk is able to
store more energy, but a bar will be
lighter and spin up faster.
The most important term to
understand in designing an
asymmetric weapon is "center of
mass." The center of mass of your
weapon is the point that represents
the average position of its mass.
When we say that a weapon is
"balanced," this means that the
center of mass is at the center of
rotation (center of the weapon
shaft). If your weapon is not
balanced, it will create vibration as it
spins and your robot will become
As your weapon spins faster,
Although it is possible to use
manual calculations to balance a
simple weapon design, the help of a
CAD program makes it much easier.
Here, we'll use SolidWorks to go
through the steps to design an
asymmetric disk. You can apply these
same concepts to any design.
If you are new to SolidWorks,
you may want to find some basic
tutorials online before you get
started. You'll need to know how to
sketch, dimension, and extrude.
There are basic commands that you
will learn quickly.
Step 1. Start by opening SolidWorks
and creating a new part. Select a
plane (I'll use the top plane) and start
a new sketch. Draw a circle at the
center of the coordinate system.
This circle represents the
diameter of your weapon without
the tooth. Dimension the circle
according to your weapon design.
In this example, I'll make the circle
Step 2. Now, we're going to sketch
the tooth. Create a new sketch on
the same plane as your first sketch
(I'll choose the top plane again).
Draw your tooth geometry and
dimension it. Make sure your tooth
touches or overlaps the circle you
drew in the first sketch.
Here’s how to dimension the tip
of the tooth to the circle you drew in
the first sketch: Using the Dimension
tool, click on the tip of the tooth and
the perimeter of the circle. With that
dimension selected, click the Leaders
tab in the Dimension menu. Then,
select Min under the Arc Condition
section of the Leaders tab.
Step 3. Next, we're going to extrude
our first sketch to create the main
body of the disk. Select the circle
sketch and select the Extrude
command. Enter the value that you
want for the thickness of your disk.
In this example, I'll enter 0.125
Step 4. Now, we'll extrude the tooth
geometry and merge it with the solid
Don’t Bite Off More Than
You Can Chew
; by Andrea Suarez Part 2: Designing an Asymmetric Weapon
32 SERVO 03.2014