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The OSSM motorhead middle section connects the motor and pulley assembly to the bottom plate, completing the motorhead housing. This component is available in two variants: with a built-in pivot for mounting flexibility, or without a pivot for a simpler design. The assembly process differs slightly depending on which variant you’re using.

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Required Components and Tools

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Components

ComponentCountSpecification / Notes
OSSM Motorhead Middle1The middle section, with or without a pivot
M5 35 mm Bolts4Used to secure the middle piece to the bottom plate
M5 Nuts4For the M5 35 mm bolts

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Tools

ToolCountSpecification / Notes
4 mm Hex1To fit the M5 bolts
Small Flathead Screwdriver1Or equivalent tool to help place nuts
The motor and pulley assembly should already be installed on the bottom plate from previous assembly steps. You may have used temporary bolts to hold these components in place.

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Step-by-Step Assembly

1

Remove temporary bolts

Remove any temporary screws or bolts used to hold the motor and pulley assembly in place from the previous step.
All temporary fasteners have been removed, and the motor and pulley assembly remains properly positioned on the bottom plate.
2

Prepare nuts for pivot design (if applicable)

If your middle section has the built-in pivot, use a bolt to temporarily push and secure the four M5 nuts into their designated slots on the middle piece.Once the nuts are in place, unthread and remove the bolt, leaving the nuts secured in the slots.
A small flathead screwdriver or similar tool can help position the nuts if they’re difficult to place by hand.
All four M5 nuts are securely seated in their slots on the middle piece (pivot design only).
3

Align and position middle piece

Set the OSSM Motorhead Middle piece on top of the motor and bottom plate assembly.Ensure the piece’s protrusions line up with the larger protrusions on the bottom plate’s corners.Hold the entire unit in place and turn it over to access the bolt holes from the underside.
The middle piece is properly aligned with the bottom plate, and all protrusions match up correctly.
4

Insert and lightly secure bolts

Insert the four M5 35 mm bolts according to your design variant:With Pivot: The bolts go in from the underside (opposite the motor) and thread into the nuts you pre-installed in the middle piece.Without Pivot: The bolts go in from the top down (near the motor) and are secured by the nuts placed on the back of the motor.Lightly secure each bolt in an X-pattern until the bolt begins to bite into the corresponding nut.
Starting with an X-pattern (top-left, bottom-right, top-right, bottom-left) ensures even pressure distribution and prevents misalignment.
All four bolts are inserted and lightly secured, with each bolt beginning to engage its corresponding nut.
5

Final tightening

Perform a final tightening pass on all four bolts in a cross pattern.Tighten them firmly (hand-tight, or until the Allen key starts to visibly torque) as this is a critical connection, but do not use excessive force.
This is a critical structural connection. While it needs to be secure, excessive force can damage threads or warp components. Tighten until you feel resistance, then stop.
You can choose to leave space for the electronics input (the green plug) on the bottom if preferred. Ensure the bolt placement doesn’t interfere with the electronics connection.
All four bolts are securely tightened in an X-pattern. The middle piece should be firmly attached to the bottom plate with no play or movement.

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Next Steps

With the OSSM motorhead middle section installed, the motorhead housing is now complete. You can proceed to install the cover in the next section to protect the motor assembly and complete the motorhead enclosure.