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Why are my joints moving / stretching under force?

I could use some help/advice. I can not figure out why these joints are deflecting/stretching from the chassis in the y direction under load. I understand that there is a force being applied to cause them to do this, but I don't understand why the joint is not constraining them, since z is set as the axis of rotation.

image description

They are currently configured as revolute as shown below:

<joint name="front_left_steer_bearing" type="revolute">
    <origin xyz="0.09 0.057 -.079" rpy="0 0 0"/>
    <child link="front_left_strut"/>
    <parent link="chassis"/>
    <axis xyz="0 0 1" rpy="0 0 0"/>
    <limit effort="20" velocity="1.0" lower="-0.3" upper="0.3"/>
</joint>

<joint name="front_left_wheel_bearing" type="continuous">
    <origin xyz="0 .0175 0.01" rpy="0 0 0"/>
    <child link="front_left_wheel"/>
    <parent link="front_left_strut"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="100" velocity="100"/>
</joint>

The struts (white boxes) are attached to the chassis, and the wheels are in turn attached to the struts. I assumed that by only allowing the struts to rotate around the z axis, x and y would be fixed (relative to the chassis). Clearly this was a bad assumption.

Any insight into where my understanding is breaking down would be much appreciated. Thanks!

Why are my joints moving / stretching under force?

I could use some help/advice. I can not figure out why these joints are deflecting/stretching from the chassis in the y direction under load. I understand that there is a force being applied to cause them to do this, but I don't understand why the joint is not constraining them, since z is set as the axis of rotation.

image description

They are currently configured as revolute as shown below:

<joint name="front_left_steer_bearing" type="revolute">
    <origin xyz="0.09 0.057 -.079" rpy="0 0 0"/>
    <child link="front_left_strut"/>
    <parent link="chassis"/>
    <axis xyz="0 0 1" rpy="0 0 0"/>
    <limit effort="20" velocity="1.0" lower="-0.3" upper="0.3"/>
</joint>

<joint name="front_left_wheel_bearing" type="continuous">
    <origin xyz="0 .0175 0.01" rpy="0 0 0"/>
    <child link="front_left_wheel"/>
    <parent link="front_left_strut"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="100" velocity="100"/>
</joint>

The struts (white boxes) are attached to the chassis, and the wheels are in turn attached to the struts. I assumed that by only allowing the struts to rotate around the z axis, x and y would be fixed (relative to the chassis). Clearly this was a bad assumption.

Any insight into where my understanding is breaking down would be much appreciated. Thanks!image description

Why are my joints moving / stretching under force?

I could use some help/advice. I can not figure out why these joints are deflecting/stretching from the chassis in the y direction under load. I understand that there is a force being applied to cause them to do this, but I don't understand why the joint is not constraining them, since z is set as the axis of rotation.

image description

image description

They are currently configured as revolute as shown below:

<joint name="front_left_steer_bearing" type="revolute">
    <origin xyz="0.09 0.057 -.079" rpy="0 0 0"/>
    <child link="front_left_strut"/>
    <parent link="chassis"/>
    <axis xyz="0 0 1" rpy="0 0 0"/>
    <limit effort="20" velocity="1.0" lower="-0.3" upper="0.3"/>
</joint>

<joint name="front_left_wheel_bearing" type="continuous">
    <origin xyz="0 .0175 0.01" rpy="0 0 0"/>
    <child link="front_left_wheel"/>
    <parent link="front_left_strut"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="100" velocity="100"/>
</joint>

The struts (white boxes) are attached to the chassis, and the wheels are in turn attached to the struts. I assumed that by only allowing the struts to rotate around the z axis, x and y would be fixed (relative to the chassis). Clearly this was a bad assumption.

Any insight into where my understanding is breaking down would be much appreciated. Thanks!image description

Why are my joints moving / stretching under force?

I could use some help/advice. I can not figure out why these joints are deflecting/stretching from the chassis in the y direction under load. I understand that there is a force being applied to cause them to do this, but I don't understand why the joint is not constraining them, since z is set as the axis of rotation.

image description

image description

They are currently configured as revolute as shown below:

<joint name="front_left_steer_bearing" type="revolute">
    <origin xyz="0.09 0.057 -.079" rpy="0 0 0"/>
    <child link="front_left_strut"/>
    <parent link="chassis"/>
    <axis xyz="0 0 1" rpy="0 0 0"/>
    <limit effort="20" velocity="1.0" lower="-0.3" upper="0.3"/>
</joint>

<joint name="front_left_wheel_bearing" type="continuous">
    <origin xyz="0 .0175 0.01" rpy="0 0 0"/>
    <child link="front_left_wheel"/>
    <parent link="front_left_strut"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="100" velocity="100"/>
</joint>

The struts (white boxes) are attached to the chassis, and the wheels are in turn attached to the struts. I assumed that by only allowing the struts to rotate around the z axis, x and y would be fixed (relative to the chassis). Clearly this was a bad assumption.

Any insight into where my understanding is breaking down would be much appreciated. Thanks!

EDIT So in trying to troubleshoot, it looks like the joints are in general springy. They not only translate in the y direction, but in the x and z directions as well. If I change them to fixed, they are rock solid but as revolute's they are like limp noodles. image description

Why are my joints moving / stretching under force?

I could use some help/advice. I can not figure out why these joints are deflecting/stretching from the chassis in the y direction under load. I understand that there is a force being applied to cause them to do this, but I don't understand why the joint is not constraining them, since z is set as the axis of rotation.

image description

image description

They are currently configured as revolute as shown below:

<joint name="front_left_steer_bearing" type="revolute">
    <origin xyz="0.09 0.057 -.079" rpy="0 0 0"/>
    <child link="front_left_strut"/>
    <parent link="chassis"/>
    <axis xyz="0 0 1" rpy="0 0 0"/>
    <limit effort="20" velocity="1.0" lower="-0.3" upper="0.3"/>
</joint>

<joint name="front_left_wheel_bearing" type="continuous">
    <origin xyz="0 .0175 0.01" rpy="0 0 0"/>
    <child link="front_left_wheel"/>
    <parent link="front_left_strut"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="100" velocity="100"/>
</joint>

Gazebo is version 7.0.0

The struts (white boxes) are attached to the chassis, and the wheels are in turn attached to the struts. I assumed that by only allowing the struts to rotate around the z axis, x and y would be fixed (relative to the chassis). Clearly this was a bad assumption.

Any insight into where my understanding is breaking down would be much appreciated. Thanks!

EDIT So in trying to troubleshoot, it looks like the joints are in general springy. They not only translate in the y direction, but in the x and z directions as well. If I change them to fixed, they are rock solid but as revolute's they are like limp noodles. image description