Each side of the 4-wheel drivetrain is mounted on a "rocker", which connects to the chassis on a pivot joint

PROS

• Lighter, simpler design
• Can scale obstacles in either direction
  • Provides another way out if our rover becomes trapped

CONS

• Has to lift more of the rover's weight at a time
• Requires a lot traction to scale tall obstacles
• More bounce to chassis
• Higher potential to tip over sideways from climbing tall obstacles

Queen's Space Engineering Team

• Tied for #12 overall ranking for SAR 2020
• Trapezoidal rocker design to improve the members' ground clearance
  • Slightly heavier design
• Constructed using aluminum boxtube, gussets, and rivets
• Minimal footage of it traversing terrain, but appears to move carefully
• Appears to have minimal issues with turning. Has a small turning radius

UW 2020/2021 Drivetrain

• Experieneces resistance while turning. Has a large turning radius
• Very capable of traversing uneven terrain

The front part of the rocker has the first set of wheels, while the back of the rocker implements a bogie system that hosts the other two sets

Idea is that all six wheels passively contact the surface at all times

NOTES:

• The lengths of the rocker and bogies and the position of each joint should be defined such that the front pair of wheels experience the lowest normal force
  • More normal force on the rear wheels increase the ability to generate forward thrust
• Appears that some URC teams are doing rocker-bogie but backwards? The front wheels should be the ones mounted at the end of the rocker arm

PROS

• Less forward thrust required for climbing obstacles, since the rover is only lifting 1/3 of its weight at a time
• Provides more traction while scaling obstacles. This is because it has four wheels pushing the front wheels over
• Equal wheel pressure with the ground at all times

CONS

• More calculations and simulation required to design effectively 
• Heavier, complex design
• Requires one actuator per wheel, as a gearbox and chain rigging would be hard to implement while still maintaining ground clearance
• Rover is optimized to traverse obstacles in one direction 
• Unstable at high speeds, as it risks damage to the suspension arms due to the suspension speed

Resources...

• The Challenges of Designing the Rocker-Bogie Suspension
  for the Mars Exploration Rover 
• Design and terramechanics analysis of a Mars rover utilising active suspension

• Dynamic Rocker-Bogie A Stability Enhancement for High-Speed Traversal

Has front and rear bogies that pivot off of the middle wheel and are constrained by the V-shaped linkage mounted to the chassis

Like the rocker-bogie design, idea is that all six wheels passively contact the surface at all times

PROS

• Easier to design for low CoG while maintaining similar flexibility to a rocker-bogie
• Easier to mount dampeners to increase stability at high speeds 
• Less forward thrust required for climbing obstacles, since the rover is only lifting 1/3 of its weight at a time
• Provides more traction while scaling obstacles. This is because it has four wheels pushing the front wheels over
• Equal wheel pressure with the ground at all times
• Can scale obstacles in either direction
  • Provides another way out if our rover becomes trapped

CONS

• Few resources available
• More calculations and simulation required to design effectively 
• Heavier, complex design
• Requires one actuator per wheel, as a gearbox and chain rigging would be hard to implement while still maintaining ground clearance

Front wheels on bogies with a 4-bar mechanism between the wheels to divide the load

Intention is to have all wheels passively contact the ground and be able to traverse tall obstacles with more stability

PROS

• Rear rocker increases stability and reduces chances of tipping over
• Can climb over very tall obstacles
• Simpler to design? Don't have to optimize for member angles
• Less forward thrust required for climbing obstacles, since the rover is only lifting 1/3 of its weight at a time
• Provides more traction while scaling obstacles. This is because it has four wheels pushing the front wheels over
• Equal wheel pressure with the ground at all times

CONS

• Increase pivoting joints and mounting locations off of the chassis
• Requires one actuator per wheel, as a gearbox and chain rigging would be hard to implement while still maintaining ground clearance
• Rover is optimized to traverse obstacles in one direction 
• Unstable at high speeds, as it risks damage to the suspension arms due to the suspension speed

Idea is that each wheel can move independently to allow for passive contact with the ground

Keeps the wheel perpendicular to the ground by using a 4-bar linkage

No differential bar used – held up exclusively by its suspension system

PROS

• Individual drive systems → can easily repair with a replacement
• Suspension provides force on the wheels into the ground, therefore increase traction
• Stable at high speeds

CONS

• Chassis jostles around more, nothing attempting to balance it between the suspended wheels
• Higher potential to tip over sideways from climbing tall obstacles
• Requires a separate mounting point for each wheel (heavy, makes the frame larger)
• Complex design, not easy to maintain
  • Requires springs
• Requires one actuator per wheel

Idea is to have the front wheels with an individual, spring-loaded suspension system and to have the rear wheels roll over the already conquered obstacles

PROS

• Simplified version of the Independent Wheel Suspension type of drives → only the front requires spring-loaded suspension
• Suspension provides force on the wheels into the ground, therefore increase traction
• Rear, rocker wheels allow for the use of a differential bar that keeps the chassis more stable

CONS

• Optimized for traversal in one direction
• Requires springs
• Higher potential to tip over sideways from climbing tall obstacles
• Additional mounting points for each wheel

• Provides less traction, so theoretically experiences less turning resistance
  • Depends on the wheel type (i.e. if the front and rear wheels end of contacting a large portion of the ground anyways – like the 2020/2021 drivetrain – then there's no difference)
  • At the same time, the front and rear wheels are far from the pivot point so they experience a lot of sideways force while turning → not the most efficient for turning control
• Less actuators and suspension required. Simple to maintain and lighter
  • Offers more weight to be used by the mechanism

• Provides less traction for climbing obstacles, therefore increasing the amount of slippage
  • Requires more precise driver control to climb over tough obstacles
• Chance of beaching

• Provides more traction for climbing obstacles, therefore reducing the amount of slippage
• The extra wheels reduce the normal force on each wheel by 1/6 the weight of the rover
• Has an advantage at turning, since it has a pair of middle wheels close to the rover's pivot point
  • Even better if it's closer to the rover's centre of mass?
• Allows for a lower centre of gravity

• Provides more traction, therefore experiences more turning resistance (cleaner turns)
• Requires more actuators, suspension → overall, more complex and heavy

Rocker-Bogie

• Bogie as the front wheels