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Courtesy of FRC Team 4817: One Degree North
Robot Design Concept
Robot Design Concept
Designed by students who were new to FRC during the 2021 FRC season, this robot utilizes simple mechanisms for maneuvering, intaking and shooting. Coupled with a limited budget and limited available parts, a lot of shortcuts were taken in designing the robot.
As the focus was on building basic skills rather than functionality, simplicity in design was the byword for this project.
A tank drive base was chosen as it was super easy to design and build.
For the intake, mecanum wheels are used to simultaneously bring balls towards the robot and to push them toward the center gap between the bumpers. Balls are then stored at the indexer and eventually launched by the double vertical flywheel.
There was a single motor limit on the intake as there were no additional motors available. To get around this problem, a ratchet was utilized to allow the motor to flip down the over bumper intake at the start of the game before switching to powering the intake. A cheap in-house solution for creating this ratchet involved the use of the head of a screw as the ratchet's pawl.
Diag. 11.5, Taken from Preparing for the Game Drop
For a more indepth discussion of how a ratchet works, refer to Macro Design: Preparing for the Game Drop chapter 11.2.
Robot Design Learnings
Robot Design Learnings
This robot has many shortcomings that could have been avoided with prototyping or an indepth knowledge of mechanisms prior to robot design. Macro Design: Preparing for the Game Drop would have had been a valuable resource to pre-empt a number of issues with this robot design.
What Worked Well
What Worked Well
Considering that this is a project for new FRC members to get their feet wet, it was commendable that a "functioning" robot was designed and built with little supervision.
Robot design is about problem solving within constraints - budgetary, parts, time, experience. The incorporation of a ratchet is a more advanced technique that the team attempted to overcome the budget and parts constraints.
With an awareness of time and experience limitation, the team presented a simple robot with less functionality within the available timeframe.
What Could Be Improved
What Could Be Improved
The tank drive base was easy to design but the robot moved very poorly. The design team imagined that with such a simple and flat design, the robot would turn well enough. However, this was not the case. A West Coast Drivebase would have been a better solution.
During intaking, balls would choose the path of least resistance, resulting in balls jumping over the bumper, instead of shifting along the bumper. An additional plastic wall had to be added, post assembling the robot, to get the intake to work properly.
Diag. R1.1: The Additional Wall
The inclusion of this additional wall was successful in allowing the mecanum wheels to redirect the balls towards the indexer.
The ratchet worked well initially. However, with enough wear and tear, the custom ratchet broke down in a number of ways, with the head of the screw falling out, bearings supporting the ratchet popping out of the stock, etc. In general, a good rule of thumb is to not put bearings directly inside of pieces of stock, and instead in plastic plates, as they can be cut more accurately for a close fit. If ratchets need to be used, buying an off the shelf ratchet solution would be more reliable and durable.
Infinite Recharge Robot Comparisons
Infinite Recharge Robot Comparisons
Compare this design against an improved version in Ref 17 and a more advanced version in Ref 11. A top of the class solution can also be found at Ref 20.
Game Manual: 2021 FRC Game Infinite RechargePrimary Game Piece: 7" ø Yellow Power Cells (Dodgeballs)Secondary Game Piece: N/ARobot Storage Capacity: 5 Dodgeballs3D Render: 4817 Competition Design AMechanisms in Bot: Tank Drivebase, Ratchets, Mecanum Wheels, Filtering, Over Bumper Intake, Linear Indexer, Double Vertical FlywheelCompare & Contrast: Ref 11, Ref 17 & Ref 20
* Further explanation of mechanisms in FRC Handbook Volume 1.
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