Spectrum Resources
Guide to the FRC MCC (Minimum Competitive Concept)
Spectrum's guide to building a simple, robust, and high-value FRC robot that maximizes playoff alliance potential within your team's resource limits.
1. What is an MCC?
Section titled “1. What is an MCC?”An MCC is a robot designed for FRC games that uses few resources (money, time, equipment, knowledge, etc) to play the game at a level where the robot is valuable on any playoff alliance. When tuned, the MCC is often an alliance captain due to its robust and consistent nature. These robots often have a lower potential score ceiling than some of the superstar robots but are still key contributors to their alliances.
2. MCC Principles
Section titled “2. MCC Principles”1. Keep it Simple
Section titled “1. Keep it Simple”- Most MCCs have only a few moving parts above the drive train.
- 3 or fewer motors and 3 or fewer pneumatic actuations.
- Karthik’s Golden Rule #1: Always build within your team’s limits. (Effective FIRST Strategies)
2. Don’t do everything!
Section titled “2. Don’t do everything!”- Every MCC leaves some game tasks unaccomplished, and that helps make them great. By avoiding the most complicated tasks in any game the MCC builders are able to focus on the rest of the game and make their robots more effective at what they do.
- Choose early what you aren’t going to do and don’t compromise. 2017 Example: “Maybe we’ll shoot fuel later if the gear and climber stuff is working,” is almost as bad as focusing on fuel from the beginning. You will make sacrifices to the gear mechanisms to allow for the addition of fuel in the future and that will hurt your performance.
- Karthik’s Golden Rule #2: If a team has 30 units of robot and functions have a maximum of 10 units, better to have 3 functions at 10/10 instead of 5 at 6/10.
3. Drive train
Section titled “3. Drive train”- Don’t drive sideways (mecanum, swerve, h-drive, etc) or use tank treads. It’s never needed to be competitive.
- Use the kit chassis or another proven and tested chassis design:
- Most teams should use the kit of parts chassis (for 2022, the AM14U4) but other COTS chassis options (VersaChassis, etc) are acceptable if you have the experience to build them.
4. Driver Practice and Tuning
Section titled “4. Driver Practice and Tuning”- Quickly get your robot to a state where you can start driving it and tuning it. Small iterations that improve your consistency and speed up your game tasks can dramatically improve your performance.
5. Autonomous Mode
Section titled “5. Autonomous Mode”- In most games moving in Autonomous mode is an absolute must.
- There is often a less difficult autonomous task, such as scoring in a low goal or hanging a gear that MCC robots should be able to do.
6. Clean, Organized, Robust Wiring and Pneumatics
Section titled “6. Clean, Organized, Robust Wiring and Pneumatics”- The most effectively engineered MCC will fail to have success if the wiring is messy and causes field disconnects or has trouble being maintained.
7. Be able and prepared to play defense
Section titled “7. Be able and prepared to play defense”- Defense is critical to many FRC games. As the level of competition rises during the season there may be times where it is strategically best for your robot to play defense. Think about defense in this game and make sure your robot is able to play solid, legal defense.
3. MCC Robot Examples
Section titled “3. MCC Robot Examples”2013 - Ultimate Ascent
Section titled “2013 - Ultimate Ascent”- Simple design to get disks from the feeder station, score them in the high goal, and hang on the pyramid for 10 points. These were the same tasks that many Einstein robots were able to accomplish.
- What it took to build it:
- 2 pneumatic actuators
- 1 spinning wheel
- Plywood and a bucket
- How’d they do?
- Rank 3
- Fixed Angle Shooter, Passive 10 point climber, simple alignment for a high goal shot. Expertly executed simple design.
- What it took to build it:
- 2 spinning wheels
- 1 pneumatic actuation for feeding disks
- How’d they do?
- Ranks 2, 1, 14, 12
- 2 District Wins, Championship Division Win
2014 - Aerial Assist
Section titled “2014 - Aerial Assist”- A simple robot built to be an inbounder or low goal scorer. Well practiced drive team.
- What it took to build it:
- KOP Chassis
- 1 pneumatic actuation
- 1 spinning shaft with wheels
- How’d they do?
- Ranks 15, 26
- Championship Division Winner
2016 - Stronghold
Section titled “2016 - Stronghold”- Single joint arm and intake. Able to go over defenses and score in the low goal. Added another motor-driven wedge for the portcullis later in the season.
- What it took to build it:
- KOP Chassis with Pneumatic wheel upgrade
- 1 motor for arm
- 1 spinning shaft for intake
- How’d they do?
- Ranks 10, 1, 52, 10
- District Winner, District Finalist, District Championship Winner
2017 - Steamworks
Section titled “2017 - Steamworks”- Passive Gear pocket, and velcro climber. Side gear auto modes.
- What it took to build it:
- Lexan and aluminum extrusion for the human gear mechanism, no moving parts
- 1 Motor-powered shaft with velcro on it
- How’d they do?
- Ranks 3, 3, 4
- Regional Finalist, Regional Winner, Championship Division Winner
2018 - Power Up
Section titled “2018 - Power Up”- Single joint with an intake, “claw on a stick”. Awesome switch autonomous modes. Great at the vault and defending the home switch.
- What it took to build it:
- Pneumatic actuation for the arm uses a door hinge.
- Intake 2 motors + belts and pulleys. Designed based on public CAD.
- How’d they do?
- Ranks 6, 7, 1, 5, 55
- Excellence in Engineering Award, District Event Winner, Championship Division Winner
118’s Everybot
Section titled “118’s Everybot”- Designed to be a simple and inexpensive robot built using common tools. Everybot designs are usually published after the first week of build season.
- Simple intake allowed the robot to score cubes in the vault. A simple dumper arm allows scoring in opponent switches.
- What it took to build it:
- 2 motors & gearboxes for the intake
- 1 motor and gearbox for the arm
- No pneumatics
2019 - Destination Deep Space
Section titled “2019 - Destination Deep Space”118’s Everybot
Section titled “118’s Everybot”- Designed to be a simple and inexpensive robot built using common tools. Everybot designs are usually published after the first week of build season.
- Simple Cargo intake and belt for scoring on the cargo ship. Simple single motor hatch intake for scoring on the cargo ship.
- What it took to build it:
- Kit motor and gearbox + a chain reduction for the intake and belt
- Single motor hatch mechanism
- Kit of parts drive train
- Pneumatics could be used to improve the hatch mechanism
- Designed after the season to be a simple and effective robot for this game.
- Single-stage elevator with simple cargo and hatch intakes. Can score in every location except for Rocket level 3.
- What it took to build it:
- 1 gearbox elevator, 1 motor ball intake, pneumatic wrist, pneumatic hatch grabber
- Elevator based on COTS Kit Design (Greyt Elevator). Other COTS elevator designs could work as well (AndyMark Elevator Kit, VEXpro linear motion)
- The space on the back allows for the future addition of a climber.
4. MCC Mechanism Examples
Section titled “4. MCC Mechanism Examples”VEXpro Versaframe Arm Example
Section titled “VEXpro Versaframe Arm Example”- Uses a planetary gearbox (likely 50:1 or more), then a 20DP gear stage on a VEXpro clamping gearbox. That is connected to a 12t #35 sprocket and a chain runs up the arm to a 60t sprocket and a VEXpro VersaBlock on the tube.
- You can recreate this easily using similar components but you can replace many of the gussets with cheaper options such as ones from Home Depot. You can use regular aluminum extrusion instead of much of the VersaFrame since you don’t need all the holes.
- The VEXpro VersaPlanetary gearbox can be replaced by a large reduction Dual Sport or 57 Sport gearbox and directly connect to the 12t sprocket for driving the large sprocket on the arm. That would work just as well.
- You should look at adding limit switches and an encoder or a potentiometer to this arm.
5908 Intake / WCP 2016 MCC
Section titled “5908 Intake / WCP 2016 MCC”- Simple Ball Intake used for defense crossings.
- Able to be deployed and retracted using pneumatics (not shown).
- Simple thru tube mounting of a VersaPlanetary Gearbox (could be a VP lite gearbox) using a Versaframe bearing mount gusset or a Sport gearbox mounted on top of the rail.
- The chain connects the motor to the roller shaft.
- Lower wheels are free spinning on 1/2” Tube axle, could be polycarbonate 1/2” tube.
- Many of the Versaframe gussets shown could have been Home Depot steel or any other gusset. In fact, some of the steel corner Ls or Keystone 4337 brackets would work better here.
1257 - 2016 Intake
Section titled “1257 - 2016 Intake”- Simple Intake with VP and belt drive.
- Hex shaft with small wheels (Banebots) and spacers.
- The shaft is able to flex up which gives compliance on the ball. The elastic cord at the front of the intake pulls it down.
- Simple Lexan and square tube construction.
- Arm powered by a simple gear on a hex shaft.
5. MCC Details, Tips, and Tutorials
Section titled “5. MCC Details, Tips, and Tutorials”Use CAD sketches to design pneumatic linkages
Section titled “Use CAD sketches to design pneumatic linkages”It’s often a struggle to find the correct mounting points for a pneumatic cylinder to actuate your mechanism in the path that you want. This FRC#973 RAMP video explains a simple process for getting the right spot every time. DesignSheet.Spectrum3847.org has a tab devoted to pneumatics that lets you get the correct lengths.
Use 1:1 Scale paper printouts when you don’t have CNC tools
Section titled “Use 1:1 Scale paper printouts when you don’t have CNC tools”You can still take advantage of CAD programs (Onshape, Solidworks, Fusion 360, etc) even if you don’t have CNC machines. FRC#558 details this method in a YouTube video. This is useful for getting the chain or belt spacing correct or finding the right place to put a pivot for your pneumatic cylinder.
Face mounting an AndyMark Sport Gearboxes
Section titled “Face mounting an AndyMark Sport Gearboxes”You can use two .25” thick #10 nylon spacers to be able to face mount an AndyMark Sport gearbox to many of the mounts for a CIM, including the Versaframe Bearing plate and VEXpro Single Speed Gearbox. AM sells a spacer for this as well and a flange mount adapter. When using a 12:1 or higher ratio with a flat plate on the far side of a 1”x1” tube, a Keystone 4337 L Bracket can be used on the other side to mount into the side mounting holes of the motor. You could just mount to the side hole by drilling clearance holes in the tube to match the mounting holes on the gearbox. The Keystone L brackets could still be used in that configuration for support. The angle bracket prevents the single gusset from bending.
Face mounting a VersaPlanetary v2 Gearbox
Section titled “Face mounting a VersaPlanetary v2 Gearbox”A similar feature can be created with a VP v2 but you will need to space off the Keystone 4337 from the tube. Use a 0.125” spacer for one stage and add a 0.5” for each stage over 1. A two-stage gearbox is shown.
Clip Nuts or Rivet Nuts
Section titled “Clip Nuts or Rivet Nuts”Clip Nuts (McMaster 94850A129) and Rivet-Nuts are useful in allowing you to quickly bolt things to sheet metal without needing access to the other side of the plate for the nut. Here is a video on installing Rivet Nuts into the kit bot to use as bumper mounting fasteners.
Drill Templates for patterned holes
Section titled “Drill Templates for patterned holes”Garnet Squadron “WorseAFrame” Hole Guides. Used to drill 1” hole patterns into normal 1” rectangular or square tube, to make it similar to VersaFrame. You can also use graph paper templates to make quick hole patterns as well.
Drilling 1.125” Bearing Holes on a Drill Press
Section titled “Drilling 1.125” Bearing Holes on a Drill Press”Triple Helix Video Guide. Drilling correctly-sized bearing holes is a difficult process for most teams without a mill or CNC equipment. Triple Helix did some testing to find the best cutting tool to use. They suggest purchasing these two tools to use on a drill press:
How to strip and crimp wires for FRC
Section titled “How to strip and crimp wires for FRC”Buy the correct wire crimpers for the terminals you are using.
- Code Orange Wiring Tutorial
- Spectrum 3847 Electrical Guide - Includes what and where to buy items.
- Introduction to FRC Robot Wiring (WPILib)
Pneumatics
Section titled “Pneumatics”Pneumatics are a very common part of many MCC robots. They are robust and simple to control. The rookie kit of parts comes with most of the items needed for a pneumatic system.
Shoulder screws in bearings allow for easy shaft removal
Section titled “Shoulder screws in bearings allow for easy shaft removal”The Versaroller System is based on using shoulder screws to easily remove rollers from your robot. The same process can be used with a hex shaft if you drill and tap the ends to 5/16-18”. Shoulder Bolts can be purchased from multiple sources — Grainger is by far the cheapest source right now. The VersaRoller User Guide in the ‘Additional Info’ tab at the bottom of the page explains the system.
Counter Balance
Section titled “Counter Balance”For any mechanism that needs to work against gravity, it is advisable to counter the force of gravity with some type of spring. Common springs used for counterbalancing a mechanism are:
- Rubber Tubing / Latex Tubing / Surgical Tubing / Speargun tubing
- Often included in the kit of parts. Latex tubing comes in a wide variety of thicknesses, diameters, and use cases.
- McMaster 3/8“ 1/4“, AndyMark 3/8“, Amazon 3/8“ 5/8“ Extra Thick
- Extension Spring
- A common spring type that is often harder to adjust than rubber tubing.
- McMaster
- Constant Force Springs
- Commonly used on FRC elevators or other linear motion applications.
- Vulcan Spring Voucher, McMaster
- Torsion Springs
- Used for arms or other pivot joints. These springs are similar to those used on a mousetrap.
- McMaster
- Gas springs
- Probably the most difficult to design for but can provide the most force and are very consistent. They do also dampen motion, so don’t expect anything using gas springs to move very fast.
- Spectrum Design Sheet has a tool to help calculate the length of gas springs.
- McMaster
Suggested tips for counterbalancing mechanisms:
- 846 Counterbalancing Resources - Video, Presentation
6. Suggested FRC Build Items
Section titled “6. Suggested FRC Build Items”Please see the links below for updated purchasing suggestions for cost efficient FRC robots:
- Suggested FIRST Robotics Competition Items Document
- Suggested FRC Purchase Lists - Each tab is different combinations of vendors