Robot Drivetrain

A robot drivetrain is the most fundamental robot subsystem. The drivetrain commonly refers to the robot frame configuration, the drive system, and the power transmission system (including gearboxes, belts, or chains).

Importance and Fundamental Considerations

The drivetrain is the single most important component of a winning robot. Good drivetrains are built robustly, are easily repaired, are built within the resources of the team, and are tailored to meet strategy goals. A good drivetrain may be one which can be adapted for more than one design, such as in the case our 2013 robot, Orangahang (also known as Mk. II and Mk. III). Optimally, the drivetrain should be able to be fixed within 4 minutes, as this is the longest allowable timeout that a team can call before a match.

When designing a drivetrain, it is crucial to understand your team's resources. The first is cost. How much can the team afford to spend on this subsystem? The robot budget must include manipulators, drive station pieces, and other components. While a drivetrain is the most important part of the robot, we must be aware that it isn't the only part. The more complex the drivetrain design is, the more time and money it will take to perfect. When in doubt, keep the design as simple as possible (KISS). A simpler design is quicker to design and build, faster to get up and running, easier to fix in an emergency, and easier to maintain for future years. During build season, time is everything. Getting the robot driving early will allow the team time to discover and fix the design's shortcomings. It will allow drivers time to practice, and also give the team more time to fine-tune its performance. Don't forget the electronics and software teams!! They also need time to configure the drivetrain before it can be effective.

Types of drivetrains

Deciding the type of drivetrain is crucial to accomplish early. It depends on team strategic focus for that years game, which needs to be decided as quickly as possible following kickoff. Attributes of a robot drivetrain which can aid in effectively implementing a strategy might include:

• Speed
• Power
• Pushing force
• Climbing
• Maneuverability
• Acceleration
• Accuracy
• Obstacle handling
• Reliability
• Durability
• Ease of control
• Available team resources

It's important to realize that we have to sacrifice some attributes for others. No single system will perform all of the above functions. As with every engineering decision, we must weigh the pros and cons of each design aspect.

High Speed

Drive systems with a high top speed might employ the following features:

• High power output
• High efficiency
• Optimized gearing ratios

Robot designs optimized for speed obviously require an open playing field to be effective. The 2008 game, Overdrive, provides an excellent example of a challenge where speed won regionals. In 2013, Ultimate Ascent saw fast robots reduce their cycle times and contribute to their alliance score very efficiently.

Acceleration

• High power output
• Low inertia
• Low mass
• Optimal gear ratio

The single most important factor in designing a robot which can accelerate quickly is the robot's mass. It requires significantly more force to accelerate a heavy robot, which we know from Newton's Second Law: F=ma. An accelerating robot would perform well for games with a divided or confined field, where speed is important but there is not enough room to attain high velocity. Look to Rebound Rumble(2012) and Logomotion(2011) for examples of challenges where acceleration was important.

Pushing/Pulling force

• High power
• High traction
• High efficiency
• Proper gearing

When designing a robot for a defensive role, pushing force is almost always a desirable trait. Pushing or pulling is often a question of traction and power output. Almost every year provides an opportunity to push against other robots while playing defensively. In 2009, Lunacy required robots to tow trailers on a traction-limited field, and being able to put power down without slipping was crucial.

Obstacle Handling

• Ground clearance
• Obstacle protection
• High traction
• Drive wheels on the ground

2015, Stronghold, provides the best example of a challenge in which obstacle handling mattered. Robot drivetrains were required to mount challenging obstacles to traverse the field and score points. Ground clearance mattered much, as did protecting from collisions and hard landings (using skid plates and reinforced hardware). It's important to design an obstacle handling robot so that it can have wheels in contact with the ground at all times, so that it does not risk getting high centered or being unable to drive over an obstacle. Again, traction matters more than anything else.

The robot chassis refers to the metal or wood frame which forms the core structural component of the robot. The frame can be crafted from sheet metal, aluminum tubing, or even laser cut wood and plywood.