IGVC Mechanical 2015

Background

Current Robot

The team has taken part in IGVC for many years. Generally the mechanical base is a rugged design intended to serve as a platform for offroad autonomous navigation, In recent years, the vehicles generally exhibit 4 wheel drive with significant emphasis on suspension and power transmission.

Previous Issues

The primary robot used in the 2013 and 2014 competition was a 4 wheel drive vehicle that utilized chains and sprockets to transmit power. Due to the suspension setup and the weight of the robot, there was significant misalignment with the interior and exterior sprockets, causing the chain to derail. Efforts in 2014 to improve this design proved to be insufficient.

Additionally, these robots utilized skid-steer/differential drive, which works very well in the terrain encountered in competition, but presents odometry problems that needlessly complicate the efforts of the software development team. It is also not uncommon for inclement weather to occur during the competition, which further complicates the odometry issues.

Improvements

The primary goals of the 2015 build season are to rebuild the drivetrain such that it is robust, while making drivetrain changes to also improve the odometry of the system.

Requirements

Primary Goals

The team for the 2015 competition year has met several times to discuss the primary goals for the system rebuild. These requirements are outlined below, in order of highest priority to lowest priority.

1. Eliminate chain and sprocket design and replace with a more reliable design given our suspension setup.
2. Maintain the use of our wheel decoupling mechanism
3. Eliminate skid-steer/differential drive design
4. Improve weatherproofing
5. Add a newer, more low-profile LIDAR.
6. Hot-swap batteries/recharging circuit

Secondary Goals

The team has also considered other desired characteristics of the robots that are not necessarily competition-oriented goals. The list is below (in no particular order).

1. Make a more compact, lightweight gearbox
2. Improve vehicle aesthetics

Specifications

• Robot dimensions should not exceed AA x BB x CC inches for competition
• Robot dimensions should not exceed DD inches in width for ease of transportation through common door thresholds
• Robot dimensions should not exceed EE inches in height for ease of transportation in our trailer.
• E-stop should be located at FF inches from the ground
• E-stop to be located at approximately GG inches from the ground for safety purposes while testing (RoboJackets criteria)
• Mechanical chassis to exhibit rounded corners for safety purposes

Mechanical Systems

System Components and Bill of Materials

Current Mechanical Tasks

For progress timelines see our meeting notes

Caster Wheel:

• Press out bearing cups 
• Press bearing into new wheels 
• Determine need for spacer between rim and bearing plates 
  • Design spacer if necessary
  • Fabricate Spacer
  • Remove tabs and install spacers
• Wirebrush steel sides 
  • coat with WD-40/lubricant to avoid rust
• Cut steel for turntable mount
• Prep for welding
  • Training
• machine axle

Suspension:

• Confirm control arm mounting points and shock absorber bracket
• Design physical support for brackets
• Machine control arms and brackets

Drivetrain:

• Generate BOM
• Place order
• Generate G-Code
• Machine Gearboxes
• Verify and machine decoupled axle
• Add retaining ring grooves to worm axle cad
• Machine worm axle
• Waterjet uprights

Development

Inventor Autodesk Inventor 

We model our robot in Autodesk Inventor, and perform FEA with the inbuilt stress analysis tools.

Structure

Our robot frame consists of primarily 1" steel tubing that has been custom designed and welded in-house. Steel tubing is chosen largely for its rigidity, with design emphasis on ruggedness and high payload capabilities, similar to that seen in military environments. The frame provides partitions for electronics, motors and sensors.

Suspension

Much emphasis has been placed into the design of the robot's suspension. The primary objectives of off-road capability and vibration damping (for sensors) have been achieved by allowing for independent suspension for the rear wheels. The robot sports 3 ATV wheels and heavy-duty shock absorbers, allowing it to traverse rough terrains at high speeds while damping residual and transient vibrations to the sensors and giving each wheel up to 5 inches of vertical travel.

Drivetrain

The vehicle utilizes caster wheel mechanics by with each of the two rear wheels being powered by a motor through a gearbox with a reduction of 30 to 1. The two 4.5 HP Ampflow motors ensure that the robot will not get bogged down in muddy or rocky terrain. Additionally, this allows for a top speed upwards of 20 MPH to be achieved.

Weatherproofing

Heavy emphasis is placed on making the robot resistant to weather. The custom-machined gearboxes are sealed shut and snap-on body panels cover the entirety of the robot to keep water from directly seeping in. Additionally, water run-off flaps are attached to all sides of the body panels. Splash guards are also employed to keep water and debris thrown from the wheels from entering the region with the motor controllers and other electronics.

The button panel and electronics mounted on the mast also reside in weather resistant enclosures.

Other things

The robots sports a variety of features that make it easy to maintain and operate. The body panels are easily removed via thumbscrews from any location, providing easy access to anywhere on the robot.

Emphasis is also being placed on ensuring ease of testing and transportation of the robot. Basic design parameters have been adhered to, such as making the width of the vehicle fits through a standard doorway and making vehicle such that the overall height fits with the transportation trailer.