Chonkii

Introduction

This robot had a name before a design. It born when Brian thought to himself, "Hey, it would be really funny if we named a robot Chonki and made it really, really big and really really loud..." Throughout the design process the robot lived up to its name. Chonkii is a 45lb shuffling shell spinner competing in the 30lb weight class that serves as an iteration on the original Chonki, which was never fully constructed. It was developed during 2021-2022. The drive system was iterated from that of Apachi and Chonki. The weapon system was a brand new concept for BattleBots. The goal of Chonki was to evaluate the viability of shell spinners while taking advantage of the 1.5 times weight multiplier afforded by using a mechanism other than wheels for movement. Competed at Motorama 2022 and finished with a 2-2 record.

Members:

• Mihir Nagaraj (Lead)
• Brian Epstein (Mentor)
• Janie Edgar
• Sydney Baker
• Thomas Jackson
• Cole Sosnowski
• Christopher Bellflowers
• Emily Liu

Drive System

Chonki utilizes a shuffler system for drive. It consists of two shuffler modules, each with 4 UHMWPE feet. The feet sit on two parallel, keyed cam shafts. These allowed for the four feet to be positioned 90 degrees from each other, so feet would always be in contact with the ground through the cam shaft's rotation. To fit inside the feet get smaller as they move away from the chassis. The longer feet have fillets to clear the rollers and support which they sit under. The cams have offset keyed holes to accommodate the shafts and sit inside circular cutouts in the feet, which keep them parallel with the ground as it walks. The use of the shuffling system allowed Chonki a weight bonus, bringing the max weight to 45 lbs.

Foot Profile

The shuffler feet are shaped as such for several reasons. The decreasing lengths are such that the module will fit inside the circular profile of the shell. In the future, the lengths could be further shortened so that the modules could have armor plating in front of them in case a weapon is able to penetrate the shell. The downward slopes of the feet are to provide space for the rollers on which the shell rides. The needle roller bearings are placed into the circular cutouts.

Cams and Bearings

Weapon System

Design Considerations

Since the weapon on this bot also serves as its armor, it was imperative that the weapon be large enough for the robot to fit inside. An additional constraint was that it must be small enough that a reasonable thickness could be attained while still remaining under the desired percentage of the total weight of the robot (~50%).

Shell Design

Shell was milled out of a 250 lb block of A36 steel. It took forever but was very effective in absorbing damage.

Pros:

• Less expensive than the nested ring design
• Made from one solid piece so it didn't have connection points to fail at
• Lives up the it's name, super THICCC
• Its SHINY!

Cons:

• Expensive, had to get Speed Machine to have them use a larger machine to mill the shell out.
• One piece, parts that got damaged on shell were not replaceable - dents needed to be pressed or hammered out.

Weapon Shaft Interface

A tapered roller bearing fits into a housing that is attached to the top of the shell.

Weapon-Drive Mechanism

• Inspired by Hyperpolarized, it was later decided to drive the weapon by using a single driven wheel at the top of the bot, with rollers along the surface to give additional support. A central shaft was used as a dead axle support.

Chassis System

• The chassis mostly consisted of aluminum, featuring of a ¼” top and side plates and ⅛” bottom plate.
• The front and back plates were made of HDPE, which bent to form Chonkii’s robustly round shape.
• The chassis had multiple rollers spaced out along its top, giving additional support to the shell track above.
• The central dead axle was constrained by two blocks, mounted to both the top and bottom plates. However, it was later determined that a single longer block with a key would constrain the shaft better than the two block system.
  • While drilling through the blocks into the shaft, a drill bit melted inside, acting as a makeshift pin (that was instantly destroyed in competition).

Electronics

Drive Motors	Turnigy Aerodrive SK3 - 5055-280KV Brushless Outrunner Motor
Drive Motor Controllers	Flipsky Dual FSESC6.6 Based upon VESC6 with Aluminum Heatsink Mini Size (was too big)
Weapon Motor	Scorpion SII-4035-250KV
Weapon Motor Controllers	Tribunus 06-120A (6S) Brushless ESC
Receiver	Hobby King 2.4Ghz Receiver 6Ch V2
Remote Control	Hobby King 2.4Ghz 6Ch Tx and Rx V2
Battery	Turnigy Heavy Duty 5000mAh 6S 60C LiPo Pack w/XT90 Turnigy Graphene Panther 3000mAh 3S 75C Battery Pack w/XT90

Competitions

Motorama 2022

• Results: 2-2
  • Bracket Style: Double Elimination
    • [Chonkii (winner) V.S. Marathon (loser): YouTube Link]
      • This match saw Chonkii head to head with a
      • Chonkii got a bunch of good hits in, sparks flew multiple times.
      • Shove, wall , stay
      • More Description
    • [Chonkii (loser) V.S. Yahoo (winner): YouTube Link]
      • turtle
      • More Description
    • [Chonkii (winner) V.S. Pigeon (loser): YouTube Link]
      • Trick shots, smacked off titanium front plate
      • More Description
    • [Chonkii (loser) V.S. Lockout (winner): YouTube Link]
      • Forfeit (5 thou)
      • More Description
  • Robojacket Rumble
    • [Chonkii vs Everyone: YouTube Link]
      • Description
      • More Description

AVC 2022

• Results: 1-2
  • Bracket Style: Double Elimination
    • [Chonkii (winner) V.S. Boost (loser): YouTube Link]
      • Expecting to get immediately bum-rushed by the flipper, Chonkii took evasive action directly into the wall
      • After a little shuffling, we bent their front and they tapped out
    • [Chonkii (loser) V.S. Wedgeham (winner): YouTube Link]
      • So we kind ajust got pushed around for a bit without having enough not to spin up the shell
      • After being pushed around, we go launched onto the wall where we stayed for the remainder of the match
    • [Chonkii (loser) V.S. Yahoo (winner): YouTube Link]
      • The rematch of the century was cut short by a wire that was: too short
      • This was caused by us removing our 3D printed esc enclosure because we "didn't want to putt it back in"

Issues

• Weapon
  • Weapon speed is too slow to inflict a ton of damage
  • PAIN to manufacture
  • Weapon wheel drive does not maintain consistent contact with track
  • Shell is too high off the ground, undercutters = scary
  • Once one hurricane deforms it is the only one that is hit
• Drive
  • Not enough traction to win in a pushing match
  • Needs more protection, if it got hit it would likely be destroyed
• Chassis
  • Too big and not dense enough
  • No self righting mechanism

Changes to make

• Weapon
  • Spring load weapon drive wheel
  • Add another weapon motor to increase reliability and top speed
  • Smaller weapon motor to decrease bot height
  • Switch to angled shell to deflect hits instead of absorbing them??
  • Increase number of hurricanes/teeth
  • Make hurricanes/teeth one part
  • Make hurricanes/teeth replaceable
• Drive
  • Improve traction
    • Wooden arenas: join blade meta
    • Magnets on shufflers
• Chassis
  • Optimize wiring and make everything more compact
  • Reduce overall diameter and add extra weight to weapon
  • Self righting mechanism
    • Active: piston with a spike on it?
    • Gigabyte bar

Trivia

• The Vectrax was rendered inoperable twice by Chonki members (mainly Brian) during its construction.