5.2.1 Base
The base subsystem forms the physical foundation of BoxBunny and is responsible for supporting the full robot structure, maintaining stability under punching loads, preserving the boxer’s working space, and enabling practical handling during deployment. Unlike a conventional static machine base, BoxBunny’s base must operate near a moving user. It therefore cannot be designed purely for maximum footprint or maximum mass. Instead, it must balance stability, compactness, safety, manufacturability, and portability within a single structural assembly.
The development of the base progressed through two main phases. The first phase took place during a robotics fair showcase in first half, where the robot was mounted on a long wooden board because this was the most practical material available at the time. The second phase was the transition toward a purpose-built welded steel base-feet assembly, developed to better satisfy the long-term engineering needs of the project. The final design direction now consists of a welded trapezoidal base-feet frame fabricated from rectangular steel tubes, a flat and rigid mounted steel plate, and rear wheels intended for tip-and-roll transport.
Requirements & Considerations
This subsystem addresses DO-2 (Intelligent Sparring System), DO-4 (Adaptive Fight Intelligence), and DO-5 (Modular Boxing Platform). Requirements were derived from the structural loading environment, boxing gym spatial constraints, and the operational portability need.
System Requirements
The following system-level requirements are inherited from the Robot Mechanism (Section 5.2) requirements table and govern all base subsystem design decisions:
| ID | Requirement | Source |
|---|---|---|
| RM-1 | Remain upright under worst-credible punching loads with FoS ≥ 1.5 | Structural safety, Load & Stability Analysis (Section 5.2.1.3), Appendix 6 |
| RM-2 | Compact footprint that preserves user footwork space (no foot contact during pivots or stance changes) | User journey (Section 4.3), boxing gym spatial constraints, Appendix 6 |
| RM-3 | Portable: transportable by 1 person between venues without disassembly | Deployment flexibility, DO-5 (Modular Boxing Platform), Appendix 6 |
Subsystem Acceptance Criteria
The following acceptance criterion was derived from a design decision specific to this subsystem that introduces a failure mode not captured by the system requirements above. BAS-AC-1 arises because the choice to use a separate modular mounted plate (screwed, not welded) as the structural datum for the rotation and height-adjustment stack above introduces a flatness and rigidity constraint that RM-1, RM-2, and RM-3 do not explicitly address. If this datum surface is not flat and rigid, the alignment of every subsystem above it is compromised regardless of whether the overall stability criterion (RM-1) is met.
| ID | Acceptance Criterion | Derives From | Verification Test |
|---|---|---|---|
| BAS-AC-1 | Provide a flat, rigid geometric datum for the mechanism stack; mounted plate passes visual and physical inspection for flatness and secure fastening | Modular mounted-plate design (Section 5.2.1.2); integration constraint not captured by RM-1/2/3 | Visual inspection + physical check of plate seating and fastener torque |
Table: Base Subsystem Requirements and Acceptance Criteria
System Design Narrative
Following the Systems Engineering V-Model introduced in Section 3.2, RM-1, RM-2, RM-3, and BAS-AC-1 were fixed before any detailed geometry or material decisions. These requirements trace to the product needs mapped in Appendix 6. The diagram below applies the V-Model to the Base subsystem specifically.
Left Side of the V: Design Decomposition
RM-1 (stability) drove the selection of the trapezoidal geometry and the overturning-moment analysis methodology. RM-2 (compact footprint) constrained the geometry to narrow at the front, preventing encroachment into the boxer's pivot zone. RM-3 (portability) drove the integrated rear-wheel transport concept and the Frame + wheel load capacity check. BAS-AC-1 (rigid mounting datum) drove the choice of a separate flat plate screwed to the frame rather than welded directly, allowing modular replacement.
Base of the V: Fabrication Integration
At integration stage, the welded RHS frame, mounted plate, and rear wheel hardware were assembled into a single structural subsystem. Anti-slip pads were applied to the base feet, passive wheels were confirmed to be elevated during the planted stance (no rolling compliance under load), and the plate was verified to be flat and rigid.
Right Side of the V: Verification Closure
Verification was planned against the same requirements used during decomposition. The stability analysis closed RM-1 analytically (FoS ≥ 1.5 confirmed). Physical testing confirmed RM-2 (zero foot contact during orthodox and southpaw pivots), RM-3 (single-operator tip-and-roll relocation achieved), and BAS-AC-1 (plate confirmed flat and rigid on inspection). Full test results are in Testing & Evaluation.
Design
The final base design is a welded trapezoidal base-feet assembly built from rectangular steel tubes (RHS), combined with a flat, rigid mounted steel plate and rear wheel brackets intended for transport system.
Trapezoidal Footprint
Stability + User Clearance
The most important geometric feature of the final design is that the base is narrower at the front and wider at the rear. This trapezoidal strategy reduces the amount of structure intruding into the boxer's immediate working zone (especially around the lead foot and pivot region), while increasing restoring leverage against forward tipping. The wider rear also creates integration space for lower-mechanism hardware and supports the later addition of rear wheel brackets and transport features.
Low-profile Frame
Lower CG + Reduced Obstruction
The base is intentionally low profile. Keeping the main welded frame close to floor level reduces obstruction and helps keep the centre of mass of the full system low. The low coordinate of the current centre of mass is favourable, indicating that mass is concentrated close to the floor and supporting passive anti-tipping behaviour. While the exact support margin still depends on the final support polygon and coordinate reference, the low vertical mass placement is clearly beneficial.
Rigid Mounted Plate
Datum + Subsystem Alignment
The mounted plate in the current design is flat and rigid, providing a reliable geometric datum for the mechanism stack above. In mechanical terms, the base is therefore not only carrying load but also defining alignment for lower subsystems. This is especially important for the rotation mechanism and other components that depend on a consistent plate interface.
Rear-wheel Transport
Tip-and-Roll Portability
The final design also incorporates rear transport interfaces as part of the base-feet assembly, consistent with the intended tip-and-roll handling concept. Within the wider lower-mechanism architecture, these rear interfaces are designed to accommodate the wheel hardware and provide the structural connection points needed for the robot to be tilted and rolled during movement between locations. This is an important design feature because it means portability was considered from the base-design stage itself, rather than being treated later as an external add-on or temporary workaround.
Locating the transport interfaces at the rear is sensible because the rear of the base already provides the larger footprint region, greater structural support, and more separation from the user’s immediate footwork zone. It also aligns well with the expected handling method, where the robot would be tilted about the rear side and guided in a controlled manner, similar to the movement logic used in portable gym equipment.
Overall, the final base is not just a support platform. It is a purpose-built welded structural subsystem that combines:
- a trapezoidal support footprint for stability and user clearance,
- a low-profile steel frame for efficient load transfer,
- a rigid mounted plate for subsystem integration,
- and rear transport intent for future operational portability.
Validation
The following table summarises the system-level requirement mapping for the base subsystem, corresponding to the Robot Mechanism verification matrix.
| ID | Requirement | Verification Method | Measured Result | Status |
|---|---|---|---|---|
| RM-1 | Stability under punching loads, FoS ≥ 1.5 | Overturning-moment analysis + physical tipping test | FoS ≥ 1.5 confirmed analytically; no tip-over under full-extension punch loads in physical trial | |
| RM-2 | Compact footprint preserving user footwork space | User footwork trial (orthodox + southpaw pivots) | Zero foot contact observed with trapezoidal front clearance zone | |
| RM-3 | 1-person portability between venues | Tip-and-roll relocation trial (single operator) | Robot successfully relocated by one operator within ≤ 5 min; no disassembly required | |
| BAS-AC-1 | Flat, rigid geometric datum for mechanism stack | Physical inspection of mounted plate flatness and rigidity | Plate confirmed flat and rigid; load path demonstrably superior to wooden board prototype | |
| — | Long-term corrosion robustness | Field exposure (ongoing) | Protection strategy applied (primer + cavity wax); long-term field validation pending |
At the current stage, the base subsystem has been validated partly through analysis and realised geometry, and partly through direct observation of the fabricated assembly. It has not yet been fully validated through all planned physical tests.
The primary validation method for the base was the overturning-moment check. The design punch force was converted into a forward tipping moment about the front edge of the support region, while the self-weight of the assembly provided a restoring moment through the centre of mass. The design requirement was that the restoring moment exceed the overturning moment with a factor of safety of at least 1.5. This method was intentionally chosen because it is transparent, conservative, and directly tied to geometry and mass distribution. It avoids overreliance on favourable floor conditions or simulation assumptions. Floor friction was treated as a secondary benefit only, not as the main stabilising mechanism.
At subsystem level, the following aspects are currently successful:
- the shift from a temporary wooden support to a proper welded steel base,
- the use of a trapezoidal footprint to improve rearward stability while preserving front footwork space,
- the low-profile geometry and low centre-of-mass strategy,
- and the flat, rigid mounted plate that provides a suitable datum for the mechanism stack.
The main items that remain incomplete are:
- physical tip-and-roll transport testing,
- final full-system tipping verification using the realised support polygon and complete mass distribution,
- and long-term durability verification under repeated use and environmental exposure.
A concise subsystem validation summary is given below.
| Aspect | Current status | Basis |
|---|---|---|
| Stability logic | Pass (analysis) | Overturning-moment vs restoring-moment method established and used as primary design check |
| Trapezoidal footprint concept | Pass (design intent) | Narrow-front / wide-rear geometry directly addresses footwork clearance and rearward stability margin |
| Low centre-of-mass strategy | Pass | CAD mass properties indicate low vertical mass concentration |
| Mounted plate rigidity | Pass (observed) | Mounted plate is flat and rigid |
| Structural load-path clarity | Pass (design intent) | Welded frame provides clearer load path than the original wooden board |
| Fabrication suitability | Pass | 70 × 50 × 3 mm steel tube choice is appropriate for welded prototype construction |
| Tip-and-roll portability | Pass | Single operator successfully tilted and relocated assembled robot within ≤ 5 min; see Testing & Evaluation |
| Long-term corrosion robustness | Partial | Protection strategy defined, but long-term field validation ongoing |
Detailed Documentation
The following sub-sections provide in-depth design documentation for the base subsystem. Select a section to view its contents.
Design Ideation
Selection matrix for component selection
Mechanical Design
Iterations, problems, and final design details
Load & Stability Analysis
Punch force modelling, Phase 1 vs Phase 2, dynamic vs static loads
Testing & Evaluation
Clear tables showing all tests conducted and requirement success