odometry in place

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I am setting up a Gazebo model for use with the navigation stack. I have been reading the Navigation Tuning Guide and am confused about the lidar data in the odom frame. I would think that the tuning guide, when it says:

"The first test checks how reasonable the odometry is for rotation. I open up rviz, set the frame to "odom," display the laser scan the robot provides, set the decay time on that topic high (something like 20 seconds), and perform an in-place rotation. Then, I look at how closely the scans match each other on subsequent rotations. Ideally, the scans will fall right on top of each other, but some rotational drift is expected, so I just make sure that the scans aren't off by more than a degree or two. (Nav Stack Tuning)"

it means that the lidar data is supposed to be in approximately the same place before, during, and after the rotation. I have been reading and it seems that these sweeping swirls that I see are correct? I have been trying to use gmapping in my simulation and whenever I rotate the map gets horridly disfigured - I believe that odometry is to blame.

I have recorded what the lidar data looks like in the odom frame. Is this correct or should it look differently?

Edit 1: I followed this tutorial to build the initial model and simulate it. I created a (visually) crude model with two wheels (left and right) that move and two frictionless casters (front and back) using their general framework. I changed the shape of the robot but just followed their procedure and tried to reproduce it. I have tried to flip the x rotation for the left and right wheels from -pi/2 to pi/2 and that just reversed the direction of motion, which I expected, but does not change the issue of streaky lidar from the odom frame. I am puzzled because the straight odometry data keeps the laser scans in the same position (as one would expect) but when I rotate the robot I get the streaks. I don't really know the mechanism behind calculating the odometry data in Gazebo so I am stuck as to fixing this issue.

The urdf file is shown:

<?xml version="1.0"?>
<robot name="bender" xmlns:xacro="http://ros.org/wiki/xacro">

    <xacro:property name="pi" value="3.141592653589794" />
    <xacro:property name="base_len" value="0.89" />
    <xacro:property name="base_wid" value="0.80" />
    <xacro:property name="base_height" value="0.20" />
    <xacro:property name="caster_length" value="0.10" />
    <xacro:property name="caster_radius" value="0.15" />
    <xacro:property name="wheel_length" value="0.10" />
    <xacro:property name="wheel_radius" value="0.15" />
    <xacro:property name="update_rate" value="50"/>
    <xacro:property name="hokuyo_size" value="0.05"/>

    <xacro:macro name="default_inertial" params="mass">
        <inertial>
          <mass value="${mass}" />
          <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0" />
        </inertial>
    </xacro:macro>


    <material name="white">
       <color rgba ...