Mechanical Design
The mechanical design of the height-adjustment subsystem evolved through several iterations, each addressing a different engineering problem. The earliest concern was simply how to provide vertical adjustability. As the design matured, however, it became clear that the real challenge was how to do so without compromising structural integrity under punching. This caused the subsystem to evolve from a simple adjustment problem into a load-path-driven mechanical design problem.
Phase 1: Basic adjustment concepts
The earliest concept space included fixed-height and manually adjustable configurations. These were useful in framing the problem but were not serious long-term solutions. Fixed height could not satisfy the user-adjustability requirement, and manual telescoping solutions were too coarse and inconvenient for repeatable, user-friendly setup. This phase was important mainly because it showed that vertical adjustment had to be treated as a real subsystem, not as a one-off manual convenience feature.
The fundamental requirement to provide a 400 mm vertical stroke ensures that the robot's striking targets (head, liver, solar plexus) align anatomically with users ranging from 150 cm to 190 cm in stature. This 400 mm travel distance dictates the minimum required length of the inner sliding column and the effective thread length of the screw jack mechanism. Proper target-zone placement is critical to anthropometric validity, ensuring every user trains against a realistic opponent.
Phase 2: Rear linear-guide plus central screw-jack concept
The first serious structural concept used two rear-mounted vertical linear rails, spaced as far apart as practical, with a lift carriage plate supported on multiple linear blocks. The screw jack was positioned near the centreline to minimise torsional effects, and a compliant jack interface was proposed to absorb minor angular misalignment.
This phase was significant because it established the correct mechanical principle of the subsystem: the guides should determine motion accuracy and resist moments, while the jack should supply vertical force only. In other words, this concept was the first explicit recognition that the lifting mechanism and the lateral load path should be separated.
However, although structurally sound, this arrangement required many precision-mounted parts. It introduced alignment sensitivity, tolerance stack-up, and additional potential failure points at rail blocks, mounting plates, and bracket interfaces. This was the point at which the design team began looking for a way to preserve the same structural principle with fewer fitted components.
Phase 3: Transition to a telescopic lift column
The next major refinement was the move from exposed rear linear guides to a custom telescopic lift column. This was not a change in structural logic, but an improvement in how that logic was implemented. The telescopic concept consolidated the guide function into one structural column assembly.
The final layout uses:
- an 8080 aluminium extrusion as the moving inner member,
- Delrin wear pads as the guide interface,
- and a welded steel outer tube with integrated plate as the fixed outer sleeve.
Mechanically, this is a stronger subsystem because it reduces the number of precision-critical components, simplifies the overall load path, lowers the chance of misalignment-induced binding, and makes the structure more robust for prototype conditions and repeated handling.
The height-adjustment column does not only carry the vertical gravitational payload of the upper structure; it acts as the main structural spine of the robot. It experiences massive side loading and overturning moments transferred from boxing impacts. The nested tube design effectively channels these violent lateral and bending forces away from the fragile internal screw jack, reacting them safely into the base structure.
Delrin (POM) wear pads are utilized at the interface between the moving aluminium inner column and the fixed steel outer tube. These low-friction polymer pads serve multiple crucial functions: they reduce sliding friction, eliminate harsh metal-to-metal contact, and compensate for minor manufacturing misalignments. More importantly, they distribute localized contact loads over a wider area and act as a dampening layer to reduce wear, chatter, and vibration travelling down the frame when the robot is struck.
Phase 4: Screw-jack integration
Once the telescopic guide structure had been defined, the screw jack was retained as the dedicated lifting mechanism. The selected actuator is the HK2T screw jack with a travelling nut, connected to the 8080 inner column through a dedicated mount. In this arrangement, the screw jack is no longer expected to guide the robot body or resist large bending loads; it acts as a lifting device only. That makes the subsystem mechanically safer and easier to reason about.
Because the column houses a powerful motorized screw jack with high mechanical advantage, end-of-travel safety features were considered paramount. While physical limit switches were initially planned to prevent overtravel at the top and bottom of the 400 mm stroke, they were ultimately not implemented in the final prototype. Instead, robust motor control logic and operator awareness are required to prevent the travelling nut from crashing into the mechanical hard stops, which would risk jamming the column, stalling the motor, or causing electrical damage.
Phase 5: Fabrication-driven refinement
As the design matured, fabrication realism became more important. The earlier notes show that the final structural solution was developed with stiffness, weldability, and durability in mind. Large SHS members were retained at at least 6 mm wall thickness, welded plates were kept sufficiently rigid, and gusseted joints were preferred where aluminium extrusion met steel platework. These details matter because the final performance of the subsystem depends not only on the actuator and guide concept, but also on whether the surrounding structure preserves alignment under load.
The required height of the outer steel tube cannot be based on the 400 mm stroke alone, because the moving inner member must remain fully supported even at maximum extension. The final height is derived as:
Houter_tube = stroke + minimum_retained_overlap
Houter_tube = 400 mm + 200 mm = 600 mm
The 200 mm retained overlap within the 600 mm outer tube was deliberately selected to fulfill strict structural guidance requirements. This generous overlap ensures sufficient guided engagement at full extension, drastically improving bending restraint. By maximizing the lever arm between the upper and lower Delrin pads, it reduces wobble and angular misalignment, lowers the risk of the column binding, and ensures a superior distribution of impact loads through the guide region.
Final mechanical design state
The final height-adjustment subsystem can therefore be summarised as follows:
- it moved from basic adjustability concepts toward a structurally guided lifting concept,
- it initially clarified its load-path logic through a rear-linear-guide plus screw-jack concept,
- it then consolidated that same logic into a custom telescopic lift column,
- it retained the HK2T screw jack as the lifting device,
- and it now separates axial lift from lateral load resistance in a much cleaner and more integrated way than the earlier concepts.