A minimum competitive concept (or MCC) is a robot specifically engineered to be a valuable asset to any alliance, while still being simple and accessible to any team, regardless of experience or resources. Around a week ago Ayush from 1961Z, Carter from 13907A, and the team behind 6007R decided to take on the challenge of designing an MCC for this year’s Vex game Tower Takeover. As the definition states, the robot should be simple and accessible, and we prioritized this throughout the design process. We also wanted to stay below the motor limit to allow teams to use the last motor(s) in a creative and unique way. The original goal was to use 6 motors, but doing a roller intake with only 1 motor got too complex, so we had to move it up to 7. We each have our own unique game analysis, or approaches to the game based on what we think will be the most effective. This explains why all the robots are different and are better suited to different parts of the game. The 6007R team designed a simple tower focused 6 bar with a 2 cube capacity roller intake. Carter designed a robot with an even more simple 4 bar that has a 3 cube capacity claw. Ayush designed a robot that can quickly put 4 cubes in each scoring zone and then play defense. The game analysis behind each robot will be included with the descriptions below.
When analyzing Tower takeover our team concluded that the most important part of the game is the tower multiplier. A newer team would be a great addition to any team focusing on a single color in the match.
This design would fall under the previously stated tower bot, it is able to do 6/7 of the towers or all but the highest tower. When using a robot like this you want to try to maximize your points by letting your partner stack while you push the other teams around and maintain control of the 6 towers you are able to reach. Doing this would allow your partner to have to stack fewer cubes in order to win. This robot utilizes a simple and effective 6 bar lift, as well as a hinged intake, this hinged roller allows the robot to pick a cube up at any orientation. (this can be seen in the photo section)
The goal for this robot was to be an all-around robot that would suit beginner and inexperienced teams well. Based on my game analysis, the best strategy is to score as many cubes in the scoring zone as possible and then do towers based on what color you have most of in the zone. However, you may find it more advantageous to focus on 1 or 2 colors and then put those in the towers. This could change because of the quality of your opponent and how much driver practice you have. Based on this analysis, I determined it would be best to design a simple robot that could place cubes in the shortest tower, place cubes at least 6 high in the scoring zone, and have a 3 or 4 cube intake. Having an ability to hold more than 1 or 2 cubes at a time is important because you will spend a lot of time driving between the scoring zones and wherever cubes are if you have a very low cube capacity. If the cube capacity is very high, say greater than 5, the robot would become very difficult to maneuver, and I wouldn’t really recommend this for a rookie or inexperienced team.
The second goal for this robot was to only use the parts from the Vex Competition Super kit plus two motors. You could use a 2 motor drive, but I wouldn’t recommend this because you wouldn’t be able to play much defense and would probably get pushed around. Another requirement for the design is that none of the parts could be cut, as I know many teams don’t have a metal saw or aren’t allowed to cut metal. This is a very difficult challenge as designing a robot with only 35 long and 25 long parts is not an easy task and the metal available is also very limited. Unfortunately, I came up slightly short of this goal. To get the intake up to a standard that I thought was acceptable, standoff couplers were necessary. I would recommend the .5 inch star drive couplers, as these are the appropriate size and you can use the tools included in the kit with them. Note that the build techniques used on the intake aren’t all ideal, as this was impossible to reasonably do within the requirements of this challenge. I am also aware that the robot is not perfect; it is designed in a way where there will be obvious improvements and fixes teams can make. The possibilities open up even more when the teams utilize the two extra motors they are allowed.
Now, let’s talk about the actual robot. The drivetrain uses four 200 rpm motors (1 per wheel) and is a tank drive. This is a very simple drive to build, and it has proven to be very reliable. In fact, almost every vex world champion has used a tank drive. It doesn’t have the ability to strafe, but that isn’t necessary with this kind of design. The lift is a 4 bar geared 1:5 with a 200 rpm motor. The gear ratio allows the motor to be able to power the lift. If you are unfamiliar with how gear ratios work, look at the link below. The lift also uses screw joints, which are the best way to keep friction and slop low using vex parts. The use of a 4 bar allows the piece the intake is connected to parallel to the ground. This is beneficial because it allows you to reach the various different heights required (including towers, intaking cubes, and stacking cubes) and have the intake still have the correct orientation. The lift is able to stack cubes on top of 3 already stacked and 3 cubes in the intake, and 4 cubes already stacked with 2 cubes in the intake. It is also able to place cubes in the shortest tower. The intake uses 1 200 rpm motor and is a claw. This claw allows you to have a high cube capacity, low motor count, and a simple design. The downside is that the claw can’t correct much for the cubes being in different orientations, so it may be harder to intake cubes in certain situations. On the intake, it is recommended that you use the mesh included in the super kit on the plate to grip the cubes better. If you didn’t buy the super kit, you can find mesh at a local dollar store or on the vex website. You may also find that the standoffs come loose from the couplers on the intake. If this becomes too much of an issue, loctite is recommended. This can be found at a local hardware or auto parts store (links are included at the bottom of the post).
This design is more suited for defensive play while still being capable of offensive play in terms of scoring cubes quickly and efficiently. With the two spare v5 motors left, the team could take on the challenge of building a proper lift for being able to capture and contest stationary towers to help boost their alliance’s point values or to make opponent point values diminish.
In terms of the overall build, the base is kept simple with 4 motors being used in a generic tank-drive setup with 200 RPM cartridges along with using four 4” Omni-wheels. The tray is mostly built with lexan (shown as black plates) along with a few 2-wide C-Channels. The open back allows the user to potentially expand the overall cube capacity up to their desire. In order to pivot the tray/intake setup, there is a basic 4b (four-bar) set up in the back to transfer rotational motion into lateral motion. The bar (figure 1) that is highlighted as red is left out from the CAD to encourage teams who take on this style of design to fine tune how far and how deep they want their tray/intake setup to move.
One key aspect that this robot has is its one motor intake setup. The robot utilizes two 24-tooth rollers that would be paired alongside tank treads with medium-sized flaps to grip cubes well. While later on, we decided to increase the motor count to 7 to make having a roller intake easier, I decided to to take on the challenge of making both rollers run off of only one v5 motor. The end result was a motor attached onto one side of the roller setup with a gearing system to reverse the direction of the output motor. This allows the motor to power one roller directly while also powering a gear that will run in the opposite direction, which the opposite side of rollers need. By linking the opposite side of rollers with a chain run from the input shaft of the roller to the gear that has the reversed direction of the motor, the robot is able to maintain a double roller setup while only being powered by one motor. (Figure 2 gives a basic visual explanation on how the mechanism works)
External links and resources:
Vex V5 Competition Super Kit:
Anti-Slip Mat (Mesh)
Video on Vex Joints
Drivetrain Types Document
Gear Ratio Document
4 Bar and 6 Bar Explanation