> ## Documentation Index
> Fetch the complete documentation index at: https://docs.researchanddesire.com/llms.txt
> Use this file to discover all available pages before exploring further.

# 4. OSSM Motorhead

> Install bearings and attach the OSSM motorhead bottom plate to the linear rail

The OSSM motorhead bottom plate serves as the foundation for the motor assembly and provides mounting points for the bearings that guide the belt. This step involves pre-threading the mounting holes, stacking and securing the bearings, and attaching the motorhead to the linear rail.

## Required Components and Tools

### Components

| Component                   | Count | Specification / Notes                                     |
| --------------------------- | ----- | --------------------------------------------------------- |
| OSSM Motorhead Bottom plate | 1     | Bottom plate for the motor head assembly                  |
| Bearings                    | 3     | Stacked onto one of the M5 bolts                          |
| M5 20 mm Bolts              | 2     | Used to secure the bearings to the motorhead bottom plate |
| Linear Rail                 | 1     | With previous components attached                         |
| M3 8 mm Bolts               | 4     | Used to attach the motorhead to the linear rail           |

### Tools

| Tool       | Count | Specification / Notes |
| ---------- | ----- | --------------------- |
| 4 mm Hex   | 1     | To fit the M5 bolts   |
| 2.5 mm Hex | 1     | To fit the M3 bolts   |

<Info>
  The linear rail should already have the belt, tensioners, and end effector installed from previous assembly steps.
</Info>

## Step-by-Step Assembly

<Steps>
  <Step title="Pre-thread the M5 holes">
    Use one of the M5 20 mm bolts to lightly pre-thread the two M5 holes on the OSSM Motorhead Bottom plate.

    Thread the bolt in just enough to ensure it fits correctly and is perpendicular to the surface. This step helps verify the threads are clean and properly aligned.

    <Check>
      The M5 bolt should thread in smoothly without binding or requiring excessive force.
    </Check>
  </Step>

  <Step title="Stack and secure bearings on first bolt">
    Stack all three bearings onto one of the M5 20 mm bolts.

    Thread this bolt into the motorhead bottom plate until it bottoms out, but do not overtighten.

    <Tip>
      The bearings should stack neatly on the bolt. Ensure they are properly aligned before threading the bolt into the plate.
    </Tip>

    <Warning>
      Do not overtighten the bolt. The bearings need to spin freely, and excessive torque can damage the threads or prevent proper bearing movement.
    </Warning>
  </Step>

  <Step title="Install second M5 bolt">
    Thread the second M5 20 mm bolt into the remaining hole in the motorhead bottom plate.

    This bolt does not need any bearings stacked on it—all three bearings are on the first bolt.

    <Check>
      Both M5 bolts should be securely threaded into the motorhead bottom plate.
    </Check>
  </Step>

  <Step title="Test bearing movement">
    Verify that all three bearings spin freely on the first M5 bolt.

    Each bearing should rotate independently without binding or excessive friction.

    <Check>
      All three bearings rotate smoothly and independently. If any bearing is stuck or difficult to rotate, check for proper alignment and ensure the bolt is not overtightened.
    </Check>
  </Step>

  <Step title="Attach to linear rail">
    Align the motorhead bottom plate assembly with the linear rail.

    Insert the four M3 8 mm bolts into the holes that attach the motorhead to the rail.

    <Info>
      The motorhead bottom plate should align with the mounting holes on the linear rail. Ensure proper orientation before inserting the bolts.
    </Info>
  </Step>

  <Step title="Tighten in X-pattern">
    Tighten the four M3 bolts in an X-pattern to ensure even pressure distribution.

    First, lightly secure all four bolts, then go around again to tighten them fully.

    <Warning>
      This is a critical connection that must be hand-tight. Use an X-pattern tightening sequence (top-left, bottom-right, top-right, bottom-left) to ensure even clamping force and prevent warping or misalignment.
    </Warning>

    <Check>
      All four M3 bolts are securely tightened in an X-pattern. The motorhead bottom plate should be firmly attached to the linear rail with no play or movement.
    </Check>
  </Step>

  <Step title="Route the belt">
    Route the loose end of the belt so that it passes above the three stacked bearings.

    The belt should follow a smooth path over the bearings without kinks or twists.

    <Tip>
      The belt should make contact with the top of the stacked bearings. This ensures proper belt guidance and reduces friction during operation.
    </Tip>

    <Check>
      The belt is routed above the three stacked bearings and follows a smooth, unobstructed path.
    </Check>
  </Step>
</Steps>

## Next Steps

With the bearings installed and the motorhead bottom plate attached to the linear rail, you're ready to proceed with installing the motor and pulley assembly in the next section of the build guide.