LigerBots 2877 FRC OpenAlliance Build Thread 2023!

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Welcome to the LigerBots 2023 Open Alliance thread! We are excited to continue to be part of this great community of teams this season. We appreciate the opportunity to learn more from other teams and hope that this thread can be used as a resource for anyone looking for new ideas.


The LigerBots, team 2877, is composed of members from both Newton South and Newton North High Schools in Massachusetts. We are a student-led team and have over 140 members. Doubling the amount of students we had last year

We have spent the last few months training our new team members for this upcoming season.

Open Alliance

Our goal is to post bi-weekly thread updates. We will compile summaries of the day from each build team with pictures of our mechanisms and links to our online resources and then on Mondays and Thursdays we will upload updates to the thread. We hope that this thread will show the complete picture of our design and mechanical process.



Distance Learning with Zoom: LigerBots Distance Learning Whitepaper
Vision Processing: LigerBots Vision Whitepaper
Camera Latency: LigerBots Camera Latency Whitepaper
Electrical Test Bench: LigerBots Electric Testbench Whitepaper

Training materials:

FIRST Robot Mechanisms: FIRST Robot Mechanisms.pptx
Drive trains/chassis: Drive trains and chassis.pptx
Robot Recipes: Robot Recipes.pptx
Intro to Robots and FIRST Strategy: FIRST Robots and Strategy.pptx
Sensors: Sensors Presentation.pptx
How Motors Work: Motors Presentation.pptx
Intro To Manufacturing and Assembly: Intro to Manufacturing
Nuts and Bolts of Nuts and Bolts: Nuts and Bolts of Nuts and Bolts Presentation
LigerBots Build Season Process: Ligerbots build season process 2021.pptx
LigerBots branding standards: LigerBots Branding Standards
LigerBots Chairman’s booklet 2022: LigerBots Chairman’s Booklet 2022
LigerBots Robot Flyer: LigerBots Robot Flyer 2022
LigerBots Sponsor benefits flyer: LigerBots supporter benefits flyer
Pumpkin Smash:Pumpkin Smash Design Presentation

Training Cad:

Mock 3DD Cad: 3DD Cad
Cascade Elevator: Cascade Elevator
Swerve Chassis: Swerve Chassis

Past Year Cad:

2022 Robot: 2022 Cad
Citrus Circuits CADathon 2021: Citrus Circuits CADathon 2021
2020 Robot: 2020 Robot Cad
2022 Chain in Tube Drivetrain: Chain In Tube WCD

Public LigerBots code repos: LigerBots - FRC Team 2877 · GitHub


LigerBots 2877 Preseason Update

During this preseason we worked hard on training our CAD team and our new members. Our CAD team worked on making complex mechanisms that our team has never tackled like continuous elevators.

This design is based on the GreyT elevator. It uses a 2x1 boxtube with custom bearing blocks that we designed for manufacturing with the machines we have available.

Just like the GreyT elevator we used Falcon 500’s as the motors and instead of making our own gearbox we used planetary gearboxes. This made it so that when we prototyped the elevator we would be able to assemble it easier because we wouldn’t have to assemble our own gearbox.

the people working on Mechanical focused on prototyping and building the mechanisms

This is the elevator after finishing Prototyping!

In addition to working on CAD this year, our team noticed that during the three day design of last year, many of the new members did not know how to participate in it which led to long zoom calls and an overall bad three day design experience.

To fight this problem this year, we did a mock three day design for the 2018 Power Up game. Eight groups where chosen and over the next three meeting we met and did preliminary designs on paper

This is an example of a drawing by a student in the Blue group; it shows an elevator with an intake on it so that the robot is able to move the cubes up to the scale and drop them off on top of it.

Even though the drawings were very preliminary over Thanksgiving break the CAD team and people interested in learning CAD met together and CADded some of the ideas that came up during the mock three day design.

This was one of the intakes that one of the teams came up with

After Thanksgiving break we voted on which mechanisms we should prototype and this intake won!

We used 80-20 aluminum to prototype this because that way we would not need to cut or use the CNC as much which cut down on prototyping time.

The pistons on the side where designed to let the intake open and close to the shape of the cube because since it is such a strange shape to manipulate our intake had to be adapted to it

This is the final prototype of the intake!

Elliot’s 5 Robot concepts from simple to not simple

This was mostly my thing but after kick-off, I wanted to come up with a few robot concepts for brainstorming. I mostly came up with these concepts on Day 0.

Robot 1-Bumpers are hard enough

  • Tank drive
  • No intake
  • Very short nothing above 7in off the ground


  • Very simple to build
  • Extremely low center of mass
  • Very light
  • Not much can break


  • Can not score in mid and high goals
  • Hard to move game pieces around


Robot 2- How about moving things

  • Tank drive
  • Very short nothing above 7in off the ground
  • Arm that goes over bumper and traps game object to drag it around on the floor


  • Simple to build
  • Extremely low center of mass
  • Very light


  • Can not score in mid and high goals
  • Cones might get james on carpet


Robot 3 - Big arm

  • Through the bumper intake
  • Big arm with graber
  • Scores in low and mid


  • Relatively simple - one degree of freedom
  • Can score on both low and mid
  • Can get link ranking point because it can score on the mid level


  • Can not score on high level
  • High center of mass

Side View Top View


Inspired by Kettering’s Ri3d Onshape


Robot 4 - Big Huge Arm

  • Through the bumper intake
  • Huge arm with graber
  • Scores in on all goals


  • Relatively simple - one degree of freedom
  • Can score on all goals
  • Can get link ranking point because it can score on the mid level


  • Very high center of mass
  • High likelihood of being very shaky


Robot 5 - Elevator with a Huge arm

  • Elevator
  • Extremely long arm


  • Huge reach at any height
  • Can score on all goals
  • Low center of mass when carriage is at the bottom
  • Only have to build one moving mechanism


  • High center of mass when scoring (carriage is high up)
  • Complicated to build elevator
  • Elevators are Heavy
  • Big lever arm on the elevator

Elevator with fixed arm on it

Robot 6 - arm with and elevator on it

  • Rotating arm
  • Arm extends


  • Low center of mass
  • Can score on both sides or robot


  • Complicated
  • Constant for spring arms can be unreliable under load when trying to extend


3dd Recap 1/11/23

This three day design was intense!. The Ligerbots met to watch the kickoff at the local library and from there we split off into 10 different design teams tasked with designing all the mechanisms for the Robot this year.

Some of the ideas that were brought up

  • Suction to grab onto the ball and the cone instead of a cone
  • An elevator on a pivot to reach onto the ground to pick up the game pieces and place them on the pegs and shelves
  • A robotic arm
  • A robo drone (As a joke)
  • An accordion like intake that extends to pick up game pieces and retracts into frame perimeter
  • Square vs Rectangle Robot
  • Swerve vs Tank

Some strategy ideas:

  • Can we steal game pieces from the other team’s side, lowering our cycle time and hindering the opposing team?
  • If we use swerve on the charging station can we beach ourselves by going to the side and forcing our wheels off the ramp and giving space for a third robot?
  • Do we even need to pick up game pieces from the ground?

Today 1/11/23

The build leaders met and finalized our drivetrain as swerve

The first things we talked about where intakes

Our criteria: Touch and Control, Simplicity

We are thinking about different strategies for intakes

  • Lance
  • Grippers
  • Just taking game pieces from the loading zone

We also thought about the different wants for our robot:

  • Simplicity
  • High goal
  • Creative solutions

We want to be able to finish our CAD by next week so we are trying to choose as simple of mechanisms as we can so that our CAD can be done as soon as possible and people can start manufacturing

In addition we looked at different designs for our arm mechanisms

  • Two rotating joints
  • An elevator arm on a rotating joint
  • Two elevators on each other at a 90 degree angle
  • Just one elevator that at an angle that is able to reach the high goal, but it moves all the complexity of getting the cone in a suitable position into the intake

The intake will be prototyped more this week and our main plan is to use a roller claw intake or a pneumatic claw right now, but that is subject to change as the prototyping keeps going on

OA post 1/18/23

As the end of the First week and CAD weekend came to a close a lot of updates have happened.

We began CAD weekend by making simple skeleton sketches of our arm mechanisms and choosing one to pursue.

We narrowed it down to a static arm and a rotating 1 stage arm but after many many hours of work we were simply unable to get the static arm working and the rotating arm’s geometry would only work with 2 stages.

We settled on a rotating 2 stage elevator because it would let us pick up from the ground.

The elevator uses a 2.5 inch box tube for the largest box and uses constant force springs as well as a cascade elevator rigging to move. This allows us to put less stress on the motors to pull up the elevator but still lets us move like a cascade elevator.

In addition we are adding a pivot to the arm which will be very similar to roboteers 2019 robot.

As well as CADding many big parts of the robot, this weekend we also focused on CADding prototypes for intake mechanisms.

We CADded a linear intake arm which has bearings on the side so that the grippers can rotate and the Cone can self correct with its low center of gravity.

Yesterday we started Prototyping the linear pinch claw with 80-20

As well, yesterday we started cutting chassis parts, currently our dimensions are 25x30 as this will allow us to have a thin robot so we don’t have to beach when we go to the ramp and we can fit three robots for more points.

Unfortunately, while cutting, we experienced melting on the box tube so next meeting we will cut the box tube slower to prevent melting

OA 1/22/23

AS the end of week two, and the start of week three approaches, we got a lot done.

This week we

  • Started assembling the chassis
  • Started CADding our main assembly’
  • Prototyped Intakes
    • Mechanically and with in CAD

For our intake we will be using perforated polycarbonate sheets as the belly pan and we plan on putting a U shaped bumper as this allows for our arm to clear the bumper easier as the arm swings

Our Current Part Studio for the chassis (top)

Our current Main assembly right now

As the season goes on and as more of the CAD gets finalized the different arm stages will begin to appear and our robot will begin taking shape.

One of the main goals this year for the robot was to have motors low to the ground. While this is hard to do with an end effector that uses motors; we can still have the pivot motors low to the ground. This also lets us use an in line chain tensioner rather than having to make a slot and have our subsystems on a slotted space.

We started assembling some of the CADded intakes that we did over three day design.

Here we are testing a linear claw mechanism that utilizes the material that goes under rugs as it is able to grip onto things very well. The linear claw mechanism is very strong due to the fact that it does not have to be motor powered and can be powered only by pneumatics. This means that we would not need to route wires and motors to the top of the arm which helps the electrical team when it is time to wire the robot.

Here we are testing a pneumatic powered roller claw. This roller claw will use motors to move the wheels, but its opening and closing mechanism is powered by pneumatics. The rollers would be useful for an intake because it means that the driver can touch-and-control a game piece, which would in turn lower our cycle time.

IMG_6158 (1)

Attached is a GIF of the roller intake pulling in cones. This shows that with a roller claw we would be able to touch-and-control. Yet the downside is that we would have to route wires to the top which would be difficult for electrical.

OA 1/30/22

Week three saw lots of new developments especially on the swerve chassis

We were able to get the chassis fully made and dry fitted, in addition, we made some mock swerve modules, as we want to still build our robot while letting the drive team practice with swerve!

The swerve modules are 3D printed with wood to attach caster wheels so the chassis can still move like it is swerve.

Here is a video of our chassis with the “swerve dummies” as we have coined.

In addition we faced some problems with perforated polycarbonate for the chassis. We had one sheet left over from last year, and we were unable to find any new sheets. This led us to have to split up the belly pan into 3 different sections. We wanted to maximize the amount of our belly pan that uses perforated polycarbonate because it makes it easier for electrical to put the PDH and other essential electronics.

The Highlighted zones are going to be using perforated polycarbonate while the center zone is using solid polycarb as we do not have enough perforated.

Programming worked very hard this week, using the test chassis with the swerve modules, they were able to get an auto leveling system to work

More exciting things to come!

I know we have not posted anything in a while so I am just going to post something. I don’t know any specifics and some of these are my best guesses

BattleCry, we did awesome we were part of the 16th alliance and beat thr Number 1 alliance in match 1. Then we went on to lose twice…
In that second match we had 3 main problems.
1, When we initialized the arm it was not fully down so the arm position was off. This resulted in the arm beeing off by a few inches when extended. We ended up smashing the arm on the dubble feeder station. Crazy enough the arm was fully functional after expect the arm lost appears to have lost it’s position.

2, we had the bumper mount de mount them selves from the frame of our robot. We have 2 rivets attaching each bracket to our robot. We have seen them slowly come lose but in that match we had some fully ripped off. This did not cause us any problems in the match because we have a bunch of attachment points.

3, This is the big failure we had at the event. Our frame on the right side was bent and the Rev 2x1 box tube unzippered it self. I have been told by my coach that they checked the robot before the match so it most likely did not happen before this final match.
One interesting thing is when watching the match we noticed no big hits to the left side of the robot.

Match video:

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Was great playing with y’all at battlecry! Was even better that you and Team Phoenix had the same colors… and tie dye :slight_smile:

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OA 11/13/23

I know that our blog posts have been non-existent for the latter half of the season and I just wanted to post some final documentation to wrap up 2023. If you have any questions please feel free to ask. Thank you to all of our alliance partners this season for an amazing season full of crazy upsets and nail biting moments.

Rhode Island Event: 4908, 5813

Greater Boston Event: 246, 238

New England District Championship: 8724, 78

BattleCry: 1153, 2342

NERD: 4909, 9986

Some documentation:

Crab Claw

CAD: Onshape


Worked awesome, we made a backup but never had to use it.

  • 3:1 reduction for Neo550.
  • Very heavy but the overkill gearbox handled it like nothing.
  • Pistons worked well to allow us to drop pieces onto nodes instead of spitting them out.

We also made a different claw design that made a final version of but decided against using it. I can post about it if people are interested.


CAD: Onshape

  • 3 Stage cascading Elevator.
  • CADed and manufactured in house by students
  • Dimensions:
    • Stage zero: 3 in (1/8in)
    • Stage one: 2 in (1/16in)
    • Stage two: 1.5 in (1/16in)
  • Neo with a 10:1 Reduction.
  • Used 1/8th rope for cascade, we tried thinner rope but it kept breaking.
  • Made with Mill and CNC router

Super Structure & Arm gearbox

CAD: Onshape

  • Max Tube,
  • 60t top sprocket for arm
  • 3D printed RSL mount
  • Custom Milled blocks to attach arm to sprocket. Made on manual mill.
  • Designed for 2 Falcons but we think we could try set coast mode(we have not tried that yet)
  • 480:1 gearbox was overkill
    • Hude acceleration but slow final speed
    • Broke gears when blocked(quite spectacularly)
    • Replaced with a gear set to get to a more reasonable 120:1
    • Top speed too fast to handle, limited in software