Failed Attempt At Built-In Servo Saver

In the world of remote-control vehicles, there’s a category of devices called “servo savers”.  For RC cars, this shock usually comes from driver error sending the car into a wall. The obstacle tries to push the wheel in a different direction than what the steering servo was told to hold. If the obstacle is immovable enough and the collision occurs fast enough, this sharp and sudden force usually dissipates by turning a servo gearbox into little fragments of gears. A servo saver absorbs this sudden shock and releases the stress over a longer period of time, softening the blow to prevent component damage.

Sawppy the Rover is not expected to drive at high speeds, but sharp shocks to the system are still possible. For example, if someone kicks a rover wheel or a wheel drops off a rock. As the steering mechanism was being redesigned to accept a common servo bracket, it incorporated an outlet for sudden shock in the form of a narrow neck connecting servo bracket to the rest of the steering joint.

Here’s the steering joint with experimental shock absorption (left) and without (right)

Aborted Built-in Servo Saver

A little testing with the tricycle steering test rig showed a servo saver is more than just a point to absorb shock. It is also important for a servo saver to be rigid in normal operation so it does not affect normal behavior of the device.

While this narrow neck does indeed bend to absorb sharp shocks to the system, it also bends in response to small forces. This makes normal steering sluggish and unreliable. With this narrow neck, some unpredictable amount of steering force is absorbed instead of transmitted to the wheel as intended, then that lost steering force may reappear at unreliable times as the neck snaps back to being straight.

A proper servo saver would hold rigid until a threshold force is encountered, then it gives way to absorb shock. Without such capability, this narrow neck design was not a real servo saver… it’s just an unreliable steering mount.

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