Rafiki & Simba · High Stakes Competition Robots

High Stakes rewarded Ring scoring, Mobile Goal control, and climbing. The highest-value repeatable objective available to a VEX-U team was a Tier 3 Buddy Climb, which doubled Simba's 12-point Tier 3 Climb to 24 points.

Following the team's principle that strategy dictates design, our goal was to create a system that could establish a high score before opponents had a chance to interfere. Rafiki and Simba needed to dock, use opponent Rings to complete Rafiki's Tier 1 Climb, lift Simba to Tier 3, and score on the High Stake.

Together, these actions could score 39 points using a single scored Ring:

The system also needed to declimb, control Mobile Goals and Positive Corners during driver control, deny opponent Rings, and repeat the climb at the end of the match.

The original concept used an extremely lightweight mini-bot that could fit within the space occupied by two Rings. Rafiki would lift the mini-bot while using the same manipulator for Ring scoring.

We later determined that the robots needed to remain connected throughout the match so opponents could not prevent Rafiki from retrieving the smaller robot before climbing. Once the two-Ring packaging constraint was removed, the smaller robot could support its own arm and claw. This became Simba.

The final strategy used both robots as one combined system:

1. 1Dock Simba to Rafiki
2. 2Intake two opponent Rings beneath Rafiki
3. 3Contact the Ladder
4. 4Extend Rafiki's platform lift and sit on the two Rings for a Tier 1 Climb
5. 5Raise Simba with the double reverse 4-bar for a Tier 3 Buddy Climb
6. 6Use Simba's claw to score a Ring on the High Stake
7. 7Declimb during driver control when additional field interaction was required
8. 8Protect the Positive Corner, control Mobile Goals, and deny opponent Rings
9. 9Return to the Ladder and climb again before the match ended

High Stakes limited how many horizontal Ladder planes a Robot could break based on whether it was still touching the floor. This created a major constraint because Rafiki's double reverse 4-bar needed to raise Simba more than 5' to reach the High Stake and complete a Tier 3 Buddy Climb.

While Rafiki was touching the floor, its effective height limit was 32", corresponding to the plane between Ladder tiers 2 and 3. I designed the lift with a software-controlled floor mode that limited its maximum height to 27-7/8", leaving 4-1/8" of margin beneath that limit.

To access the height needed for the complete climb, Rafiki first intaked two Rings beneath its chassis and contacted the Ladder. Four pneumatic cylinders then extended the Platform Lift, raising the robot onto the Rings and completely removing it from the floor.

V5RC Q&A 2093 confirmed that contact with a Ring did not prevent a Robot from being considered Climbed. Once Rafiki was supported by the Rings, no longer touching the floor, and contacting the Ladder, it qualified as a Tier 1 Climb.

Entering the climbed state changed which Ladder planes Rafiki could legally break. Its effective height limit increased from 32" to 46", allowing the double reverse 4-bar to raise Simba to Tier 3 and position the claw above the High Stake.

In climbed mode, the lift was software-limited to a maximum height of 42-3/16", leaving 3-13/16" of margin beneath the 46" limit. The software used separate limits for the floor and climbed states so the same mechanical lift could operate legally throughout the complete sequence.

The climb sequence was:

1. 1Dock Simba to Rafiki
2. 2Intake two Rings beneath Rafiki
3. 3Contact the Ladder using the Ladder arm or flexible contact brushes
4. 4Extend the pneumatic Platform Lift to get off the ground and onto the Rings for a Tier 1 Climb
5. 5Switch the double reverse 4-bar to its climbed software limit
6. 6Raise Simba to a Tier 3 Buddy Climb
7. 7Have Simba cross the top most plane and score on the High Stake using Simba's claw

This approach did not bypass the expansion rule. The robot architecture deliberately changed Rafiki's legal climbing state before extending the lift past the floor-based height limit. Mechanical stops, Ladder-contact mechanisms, the Platform Lift, and state-based software limits worked together to keep both robots within the permitted planes.

Alpha, Beta, and Gamma were internal revision names for the season-long development of Rafiki and Simba rather than separate project entries.

Rafiki retained the same core robot structure and was continuously modified throughout the season. Simba retained the same role and functional architecture, but the Gamma version was completely redesigned after Alpha and Beta established the geometry, subsystem interfaces, and strategy requirements.

Alpha established the core architecture used throughout the season:

• 6-motor double reverse 4-bar
• 8-motor Rafiki drivetrain
• Pneumatic docking between Rafiki and Simba
• Pneumatic platform lift
• Simba virtual belted 4-bar
• Two-Ring claw
• Mobile Goal clamp
• Autonomous climb and High Stake sequence

Alpha competed at the West Michigan Holiday Tournament and RiverBots III. These events exposed weaknesses in Simba's printed base and arm pivot, the docking mechanism, Rafiki's lift rigidity, Ladder contact, and vertical-expansion stability.

Beta retained the same overall architecture and continued using a 6-motor double reverse 4-bar with an 8-motor drivetrain.

Major improvements included:

• Ratchet system to hold the double reverse 4-bar in position
• Reinforced lift plates, motor caps, and gear spacing
• Improved hot-swap access for lift motors and gears
• More reliable Ladder contact mechanism (arm to linear slide)
• 0.5" stroke to 1" stroke pneumatic platform lift
• Side and vertical skirts for more climb alignment opportunities
• Improved docking durability and alignment
• Faster declimb sequence
• Greater serviceability between matches

Beta competed at the Purdue Slam and Jam qualifier.

Gamma was the final Worlds configuration. Rafiki received another major revision, while Simba was completely redesigned around the architecture proven by Alpha and Beta.

The redesign was easier to complete because Simba's core requirements were already understood. It still needed to dock with Rafiki, use a virtual belted four-bar, manipulate Rings, score on the High Stake, and function as the lifted robot during the Tier 3 Buddy Climb. Instead of developing a new concept, I could focus the redesign on structure, packaging, reliability, weight, and serviceability.

Major Rafiki improvements included:

• Reduced the double reverse 4-bar from 6 motors to 4 motors
• Added 2 x 10 lbf gas struts to assist the lift
• Reallocated the removed lift motors to create a 10-motor drivetrain
• Reinforced the lift with polycarbonate plates and improved gear support
• Improved the docking geometry and mounting interfaces
• Added more robust Ladder contact and climb-alignment features
• Tripled pneumatic storage capacity
• Refined pneumatic, electrical, and mechanical packaging
• Improved replacement-part access and between-match maintenance

Major Simba redesign changes included:

• Completely rebuilt the robot while retaining its established functional architecture
• Replaced the reinforced printed base with a pocketed 1/4" aluminum baseplate
• Reduced the baseplate weight from approximately 1.225 lbs to 0.6 lbs
• Repackaged the drivetrain, Robot Brain, Battery, Radios, docking hardware, and arm structure
• Redesigned the arm pivot and mounting structure
• Revised the virtual belted four-bar and claw power transmission
• Improved the docking interface using geometry developed through the Alpha and Beta revisions
• Increased structural rigidity around the arm, drivetrain, and docking loads
• Improved access to motors, electronics, fasteners, and replaceable components
• Created cleaner and more repeatable mounting interfaces between subsystems
• Created a modular mounting system for the claw to be able to swap out different claw types (roller claw and simple claw)

Gamma competed at VEX-U Worlds and VEX AI Worlds.

Rafiki served as the primary drive platform and supported the combined climb, docking, and field-control systems.

• Lifted Simba to a Tier 3 Buddy Climb
• Used a 12:84 gear reduction
• Used 6 motors during Alpha and Beta
• Used 4 motors and 2 x 10 lbf gas struts during Gamma
• Used 1/2" x 1/2" x 1/16" wall box-tube arms for rigidity and compact packaging
• Ran the linkage joints on 1/4" aluminum standoff dead axles
• Used polycarbonate outer plates, 3D printed motor cap, inner polycarbonate reinforcement plates, and a polycarbonate gear-tensioning plate
• Used a pneumatic ratchet to hold the lift in position
• Allowed the lift motors and gears to be serviced between matches

• Used four 1" stroke, 0.75" bore pneumatic pancake cylinders to raise Rafiki off the floor
• Supported the combined weight of Rafiki and Simba (39 lbs)
• Trapped two Rings beneath the chassis using a Ring fence
• Used a concave platform shape to improve Ring alignment
• Completed a Tier 1 Climb while Rafiki contacted the Ladder
• Reduced the climb's dependence on precise Ladder alignment

• Connected Simba to Rafiki at the beginning of the match
• Used two 0.5" stroke, 0.75" bore pneumatic pancake cylinders producing approximately 88 lbf at 100 PSI
• Used matching positive and negative alignment geometry between the robots
• Guided the docking hardware into chamfered locating features
• Kept both robots connected during scoring, driving, climbing, and declimbing
• Developed through multiple revisions to improve alignment and prevent printed-part damage

• Used two 1" stroke, 0.75" bore pneumatic pancake cylinders
• Produced approximately 88 lbf of clamping force at 100 PSI
• Captured the lower edge of the Mobile Goal against fixed standoffs
• Allowed Rafiki to control Mobile Goals for scoring and point denial
• Used a wide engagement area to reduce alignment sensitivity

Simba served as the Ring manipulator and the elevated portion of the Tier 3 Buddy Climb. The Gamma version was a complete mechanical redesign that preserved the role, docking relationship, virtual four-bar architecture, and scoring capabilities established by Alpha and Beta.

• Used a printed and steel bar reinforced structural base during Alpha and Beta
• Repeated cracking in the printed base and arm-pivot structure helped define the Gamma redesign requirements
• Replaced the previous base with a cnc'ed billet 1/4" aluminum baseplate for Gamma
• Reduced the baseplate weight from approximately 1.225 lbs to 0.6 lbs
• Repackaged the Robot Brain, Battery, Radios, drivetrain, docking interface, and arm pivot
• Used tapped and clearance holes for repeatable subsystem mounting
• Integrated the docking interface directly into the redesigned structure
• Improved rigidity, service access, and replacement-part consistency

• Used two 105T HTD 9 mm timing belts
• Maintained the claw's orientation while the arm moved
• Used printed gear inserts at the pivot to prevent the bores from rounding
• Ran the claw pulleys on 3/8" aluminum standoff dead axles
• Allowed Simba to manipulate Rings while docked to Rafiki

• Held up to two Rings
• Scored on Mobile Goals, Wall Stakes, the Alliance Stake, and the High Stake
• Used a 100 rpm 11W motor
• Used herringbone gears for Gamma to reduce backlash
• Used replaceable 1/8" polycarbonate claw plates to play with claw geometry
• Allowed claw geometries to be changed by removing six screws

The climb relied on a detailed interpretation of High Stakes scoring and expansion rules.

• V5RC Q&A 2093 confirmed that a robot could achieve a Tier 1 Climb while sitting on Rings, provided it no longer contacted the floor and met the other climb requirements
• V5RC Q&A 2026 confirmed that Rafiki carrying Simba did not make Rafiki possess the Rings held by Simba and that possession was not transitive
• Rafiki used Ladder contact mechanisms and flexible skirts to establish climb contact
• The lift used software limits to prevent the robots from breaking more vertical-expansion planes than allowed
• Rafiki's lift height was limited differently while on the floor and while supported by the platform lift
• The ratchet held the double reverse 4-bar extended without relying only on motor torque

For Gamma, the team developed a roller claw intended to collect one Ring, two stacked Rings, or a second Ring after the first had already been captured.

The design used printed rollers with integrated sprockets, rubber tubing, and a deployment system released by rotating the roller. Although the claw could collect Rings during testing, its deployment was not reliable enough before VEX Worlds.

With approximately one week remaining before the event, the roller claw was abandoned and Simba returned to the proven claw. This protected the reliability of the complete robot system instead of introducing an unfinished mechanism at Worlds.

I contributed to the documentation, graphics, and media used to communicate the Rafiki and Simba project throughout the season.

This work included:

• Engineering notebook entries
• Robot reveal videos
• Team and robot brochures
• Recruitment flyers
• Sponsor packets
• Team shirts
• Competition graphics
• Technical diagrams and CAD renders
• Photos and media used for judging, sponsors, outreach, and recruitment

The robot media received more than 45,000 YouTube views. Rafiki and Simba were also presented on the VEX Worlds Finals stage in front of a live audience of more than 8,000 people.