VFD direction/speed control lever mechanism

I wanted a lever control that controls both motor direction and speed/acceleration/deceleration (similar to a hydraulic directional control valve) on a screw press motor using a variable speed (variable frequency) drive.
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This mechanism is designed to trigger a VFD that is configured to operate in 2-wire control mode for motor direction, and with an external potentiometer to control the motor speed:

• 2x normally open microswitches (body 20mm x 10mm x 6mm), one for forward, one for reverse rotation
• 1x 16mm diameter linear potentiometer with 6mm spline shaft

At rest, the lever is in the centre position, and the motor is stopped (both microswitches depressed). A spring holds the lever in the centre/off position.

• When the lever is moved away from the centre position, one microswitch is released and the motor starts; the further the lever is moved away from centre, the faster the motor runs runs (potentiometer is rotated as the lever is moved).
• As the lever is moved back toward the centre position, the potentiometer is rotated back toward its start position, the motor slows down, and stops when the lever is returned to the centre position the potentiometer is returned to its start position, and the microswitch is depressed thus breaking the run signal..
• If the lever is moved in the opposite side of centre, the second microswitch is released the motor turns in the opposite direction.
• The mechanism rotates the one/same speed potentiometer regardless of which way the lever is moved: ie as the lever is moved away from centre in either direction, the potentiometer is rotated clockwise. As the lever is moved toward centre in either direction, the potentiometer is rotated anticlockwise.

The hardware:

• 8mm bolt for main axle & nut
• I used a metal shaft for the lever: 8mm diameter x desired length. Knob end with 8mm thread x 10mm long, and other end with 6mm thread x 10mm long. I have included an STL file for this shaft if you prefer to print this part: I preferred a metal shaft though.
• 2.5mm mounting screws & nuts for microswitches
• M3 countersunk stews to mount assembly in the case
• Extension spring with loop at either end as shown in photos: strength of spring according to user preference.

Before assembly ream the 8mm holes on the following parts to ensure the holes are round and correct size:
Chassis
potentiometer arm
Shaft rod end
Slot cover
Spur gear

Prior to assembly, refer to the 3D CAD images to see part orientations

To assemble:

1. First wire the "inner potentiometer and mount
2. Mount the "inner potentiometer to the chassis
3. Fit the potentiometer onto the potentiometer arm
4. Fit the potentiometer gear onto the potentiometer shaft
5. Fit the potentiometer arm into the chassis: rotate to maximise space for next step
6. Fit the spur gear: as you put this in, ensure that the potentiometer is rotated fully anticlockwise when the potentiometer arm and spur gear are seated against one another
7. Fit the lever shaft rod end
8. Fit the 8mm bolt through all of the above parts
9. Fit the spring to hold the arms together: there are 4x pairs of spring mounting points to enable adjustment of spring tension.
10. Slide the slot cover in between the chassis and inner mechanism, and align hole with hole between potentiometer arm and spur gear.
    Insert 6mm end of shaft through the slot in the chassis, slot cover and screw into lever rod end.
11. Screw knob onto 8mm end of lever.
12. Wire the microswitches and potentiometer to VFD.
13. Install assembly into case.

Note: as per photos, I did drill a hole in the side of the chassis to attach a "P-clip" using a M4 button head screw to strain relieve the control cable as shown in the photos