Turning System

The turning system provides active steering for the front and rear wheel assemblies. To ensure high reliability during operation, the subsystem uses a direct-drive arrangement engineered to withstand heavy vertical static loads while eliminating mechanical play and plastic material deformation. It was desinged in a way to provide rotation while preventing vertial load transfer to the stepper motor as their axial load limit is much lower than the load of an individual turning system.

System Architecture & Components

The finalized design (Version 2) replaces indirect mechanical transmission with direct motor drive to simplify the assembly and maximize torque transfer efficiency.

Stepper Motor: Directly drives the steering shaft without intermediate reduction gears. This eliminates backlash, reduces total part count, and removes gear-tooth wear as a potential failure point.

Custom Interface Shaft: Machined shaft tapped at the side and secured to the stepper motor shaft via a set screw. It translates the rotational output of the motor shaft into a rigid mechanical connection for the turning core.

Lower Core Block (Plastic Cube): Connected securely to the upper interface shaft it aids in a more even tranfer of torque form the shaft to the vertial square tubes, provides support for the screws connecting the U-shaped bracket to the vertical square tubes and interface shaft, and supports the U-shaped bracket in the center where the thrust bearing load is.
Vertical Square Tubes: Act as the primary load-bearing rotating columns for both the front and rear steering assemblies.
U-Shaped Steel Brackets: Mounted to the exterior of the vertical square tubes. They provide a flat, rigid metal surface that prevents localized plastic crushing under heavy structural loads.
Thrust Bearings: Positioned flush against the steel brackets. They isolate the axial (vertical) forces caused by the weight of the rover from the motor shaft, enabling smooth rotational motion under full payload.

Design Rationale & Failure Mode Analysis

V1 Concept vs. V2 Real-World Performance

Version 1 (Failed Prototype): The initial concept attempted to use a 3D-printed gear (30 mm diameter) driven by an M6 60 mm bolt and hex nuts pressed into embedded cutouts inside the plastic cube. This was done to prevent the

Primary Failure Mode 1 (Gear Shear): The main probelm foreseen with this concpet was that under high torque the gear could bend causing jumping/slipping whihc would not be ideal. Another probelm was the gear would degrade quite quickly.
Primary Failure Mode 2 (Interface Stripping): High torque from the stepper motor concentrated immense torsional forces onto the sharp corners of the embedded hex nuts. Because plastic yields easily under point loads, the nuts quickly stripped out their plastic pockets, causing total loss of rotational control.
Primary Failure Mode 3 (Nut loosening): Since the system relies on two nuts that are screwed into each other to create a lock; under high amounts of torque and continuous vibration, these nuts would eventually loosen making the turning system useless.

Version 2 (Current Production Design):

Direct Drive Integration: Eliminating the printed gears entirely removed the primary shear risk. Driving the turning column directly ensures 100% torque transmission from the stepper motor without intermediate mechanical slop.
Metal-on-Metal Fastening: Switching to a tapped metal interface block with set screws distributes clamping pressure evenly across the flat of the motor shaft. This prevents the rounding and stripping experienced in plastic cutouts.
Axial Load Isolation via Thrust Bearings: Standard radial bearings or plain plastic bushings degrade quickly when subjected to heavy vertical loads down the steering axis. Placing thrust bearings against rigid U-shaped steel brackets creates a dedicated path for vertical forces to pass through the frame. This protects the internal stepper motor bearings from dynamic impacts during travel and maintains low rotational friction.