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The Chassis is the base of the robot. The chassis design can affect how the robot drives, scores, and moves around the field. A chassis can have the added benefit of protecting important and fragile parts like the motors, wiring and cortex. It can also prevent the robot from tipping over.
There are some common chassis shapes that students build in VEX robotics. Each has pros and cons, so choose your chassis wisely. However, the most important thing to know is that the axles holding wheels or gears need support from both sides. When only one metal side is used, the drive shaft or axle sit on a pivot point like a teeter totter. This creates a loss of structural integrity and less precision when driving because the axle is not secure. Using two pieces of metal (as shown below with the grey rectangles) keeps the axle and wheel sturdy and secure. It is also important to use the bearing flats to reduce the friction when the axles turn in the metal square holes. |
You also need to consider how many motor and wheels you think your robot needs. The more motors, the more power. Remember to follow the constraints related to the number of motors allowed as described in the game manual.
Turning scrub is also something you will need to keep in mind. Turning scrub is the friction that resists turning. This friction is created from the wheels dragging sideways on the ground as a robot turns. Ideally, you want to reduce turning scrub in your design using Omni Directional wheels. However, there are some instances where friction may be beneficial.
The shape of the chassis also affects the turning scrub as shown below.
Turning scrub is also something you will need to keep in mind. Turning scrub is the friction that resists turning. This friction is created from the wheels dragging sideways on the ground as a robot turns. Ideally, you want to reduce turning scrub in your design using Omni Directional wheels. However, there are some instances where friction may be beneficial.
The shape of the chassis also affects the turning scrub as shown below.
Common Chassis Shapes
Square/Rectangular Base
The square or rectangular shaped chassis is a sturdy structure that can handle a lot of stress from the mechanisms moving above. It also blocks the game pieces from entering the inside of the robot and getting stuck. In some instances, the metal frame acts as a plow to move objects around the field. It is important to consider how the robot will need to interact with the game pieces. The four walls may get in the way of grabbers and intake systems. Make sure to design all three subsystems of the robot together before beginning to build the chassis. |
H-Shaped Chassis
The H-shaped chassis is another sturdy base and uses less metal than the square or rectangular shaped. It also allows areas for the others subsystems of the robot to operate in the front and back of the robot. It is important to consider how the robot will need to interact with the game pieces. The central bar may get in the way of larger grabbers and intake systems so design all three subsystems of the robot together before beginning to build the chassis. |
U-Shaped Chassis
The U-Shaped chassis loses a bit of structural integrity along the front of the robot. The central bar can be moved forward a bit and several screws can be used to help reinforce the back to help with maintaining the structural integrity. However, the benefit is that there is ample room to operate a grabber or intake system inside of the robot. Consider the game pieces as they may get trapped inside the U-shape when driving on the field. |
Holonomic Shaped Chassis
The holonomic U-shaped and H-shaped chassis are built so that the wheels are at 45 degree angles. This is a difficult chassis to build and program. It also has a bit less space to operate mechanisms and attach sensors. However, if built correctly, the big advantage of a holonomic drive is getting to exact X and Y coordinates on the game field. The holonomic allows for driving left or right while keeping your claw parallel to your goal. This can be especially beneficial in autonomous programming. |