Friction estimation for a vehicle

A vehicle, comprising:

• at least one wheel that drives a tire to move the vehicle along a support;
• a radio-frequency (RF) transceiver that transmits an RF signal toward the support and measures a reflected signal;
• a drive unit that drives rotation of the at least one wheel;
• and
• control circuitry in communication with the RF transceiver and the drive unit, the control circuitry configured to:
• control the RF transceiver to output the RF signal at a first phase;
• compare a second phase of the reflected signal to the first phase to detect a phase difference;
• estimate a moisture content of the support based on the phase difference;
• determine a type of soil comprising the support based on the estimated moisture content;
• determine a level of friction between the tire and the support based on the moisture content;
• and
• communicate an output to adjust a force between the tire and the support in response to the level of friction, wherein the force adjustment is at least in part based on predefined shear strength values associated with the type of soil.

The vehicle of 15, further comprising:

• a time-of-flight device configured to detect a distance from the vehicle to the support along a path of the RF signal, wherein the control circuitry is further configured to:
• determine a target delay for the RF signal based on the distance;
• and
• compare the target delay to the propagation delay to estimate the moisture content.

A vehicle, comprising:

• at least one wheel that drives a tire to move the vehicle along soil;
• a radio-frequency (RF) transmitter that transmits an RF signal toward the soil;
• an RF receiver that receives a reflected signal reflected by the soil;
• a drive unit that drives rotation of the at least one wheel;
• and
• control circuitry in communication with the RF transmitter, the RF receiver, and the drive unit, the control circuitry configured to:
• control the RF transmitter to output the RF signal at a first phase;
• compare a second phase of the reflected signal to the first phase to detect a phase difference;
• estimate a moisture content of the soil based on the phase difference and determine a type of soil based on the estimated moisture content;
• determine a level of friction between the tire and the soil based on the moisture content;
• and
• communicate an output to adjust a force between the tire and the support in response to the level of friction, wherein the force adjustment is at least in part based on predefined shear strength values and internal friction force angles associated with the type of soil, and wherein the volumetric moisture content may be between approximately 15% and 25% for sandy soils, between approximately 35% and 45% for loam soils, and between approximately 45% and 55% for clay soils.