Written by IIan Redodique

Lava Monkey is a 3 lb Beetleweight combat robot designed for durable, control-oriented engagement using a high-energy vertical spinning weapon. The chassis is constructed around a polycarbonate top and bottom plate skeleton for structural rigidity, with flexible armor components printed in SainSmart PEBA filament to absorb impacts through controlled deformation rather than cracking or permanent bending. PEBA is used primarily in the outer chassis armor and fork elements to improve survivability in repeated high-force collisions while maintaining flexibility and rebound characteristics.

This robot competed at East Valley Attack Robotics (EVAC): Bring Water Slaughter in the Beetleweight class. Final competition placement was influenced by an intermittent radio control failure encountered during matches and is not indicative of the mechanical performance of the PEBA filament.

Figure 1: Onshape model of Lava Monkey showing blue PEBA chassis and fork components.
Figure 2: Lava Monkey following competition at EVAC: Bring Water Slaughter.

Why PEBA Was Selected for This Combat Robot Test

PEBA was selected for evaluation based on its reported material properties, particularly its lower density compared to TPU, high elasticity, and strong rebound characteristics. The initial hypothesis was that SainSmart PEBA filament could provide improved elastic energy absorption relative to TPU while reducing overall part mass.

In the context of a 3 lb combat robot, this reduction in density could allow additional mass allocation to structural or functional components without compromising durability.

Initial Printing Experience with PEBA

Unless otherwise noted, all testing was performed using Orca Slicer v2.3.2 with a 0.4 mm nozzle and the "0.20 mm Standard" process profile. The Elegoo Neptune 4 Plus was the sole exception, using a process profile specifically optimized for flexible filaments. For reproducibility, this process profile has been included separately as an attachment. Printer-specific machine profiles were retained, while filament settings were adjusted as required throughout testing.

Initial testing was conducted on a Flashforge Adventurer 5M using Orca Slicer’s Generic TPU filament profile. Aside from adjusting the nozzle temperature to the manufacturer's recommended 240 °C and increasing the maximum volumetric flow rate to 7.2 mm³/s, all settings were left unchanged from the default profile.

The observed failure mode differed from typical FDM layer delamination. Rather than separating cleanly along layer boundaries, parts could be peeled apart through the wall thickness in long, straight sections. This behavior was most prominent in regions composed of parallel extrusion paths with minimal overlap between adjacent toolpaths. Areas containing overlapping or intersecting extrusion paths generally remained intact, likely due to mechanical interlocking effects rather than filament bonding.

Once separated, the peeled sections themselves exhibited good internal cohesion, indicating that failure occurred primarily between neighboring extrusion paths rather than within the deposited strands. The resulting failure mode resembled peeling layers from an onion, with separation propagating through contiguous straight sections of the print.

Figure 3: Delamination observed using the initial PEBA profile. Separation occurred through straight extrusion paths while overlapping regions remained intact. (FlashForge Adventurer 5M)

Final Print Settings for PEBA

To improve filament-to-filament bonding and eliminate the peeling delamination, the Generic TPU profile was adjusted as follows:

• Extrusion flow increased to 1.08
• Nozzle temperature raised to 250 °C
• Maximum part cooling fan speed reduced to 20%

As a consequence of these changes, parts exhibited substantial stringing and a noticeable reduction in print quality. This behavior was not exclusive to PEBA but was a general result of prioritizing strong interlayer and inter-bead bonding over surface finish.

This was considered an acceptable tradeoff for the intended application, as combat robot components prioritize structural integrity and impact resistance over surface finish and cosmetic appearance. The resulting profile was used for all subsequent testing unless otherwise noted.

Figure 4: Stringing produced by the finalized PEBA profile. Increased flow and reduced cooling were intentionally retained to maximize part strength despite reduced surface quality. (Elegoo Neptune 4 Plus)

Figure 5: Close-up of stringing observed with the finalized PEBA profile. (Elegoo Neptune 4 Plus)

Creality Ender 3 Compatibility

Printing was also attempted on a Creality Ender 3; however, it was ultimately unsuccessful. Despite tuning and multiple print attempts, the printer consistently exhibited under-extrusion and poor filament feeding, resulting in incomplete and mechanically unusable parts.

While settings were adjusted throughout testing, none provided reliable operation. Given the successful performance of the material on three other printers, the observed issues are believed to be associated with flexible filament handling limitations of the printer rather than the material.

Figure 6: Under-extrusion observed during PEBA testing. (Creality Ender 3)

Figure 7: Cross-section revealing uneven shell and poor perimeter bonding. (Creality Ender 3)

Combat Results from EVAC: Bring Water Slaughter

During competition at EVAC: Bring Water Slaughter, PEBA components were subjected to repeated impacts from high-energy spinning weapons. The material was primarily used in outer chassis armor and fork structures.

Across matches, PEBA components remained mechanically functional, with no catastrophic shattering or complete structural failure observed. Damage was generally localized to high-impact zones, with deformation and tearing occurring in heavily loaded regions while surrounding structures remained intact.

For comparison, the baseline TPU chassis was printed in 95A TPU (Overture), which is one of the most commonly used 95A TPU materials in combat robotics and serves as a practical reference baseline for flexible filaments.

All parts were printed using identical structural parameters to allow for a reasonable comparison between TPU and PEBA parts. This included 4 perimeters (with alternating extra wall), 3 top and bottom layers, and 10% gyroid infill. Layer height, process settings, and general print methodology were kept consistent across both material sets.

A PEBA fork assembly experienced complete cutting under impact loading. A comparable TPU fork, while slightly larger in overall geometry, exhibited a similar failure method under similar impact conditions. In both cases, damage was concentrated at the point of impact. The PEBA fork was printed using 10% cubic infill to increase stiffness.

Figure 8: PEBA fork assembly after impact failure, showing fracture location at point of impact. (Elegoo Centauri Carbon)

Figure 9: TPU fork assembly after impact failure, showing fracture location at point of impact. (Elegoo Neptune 4 Plus)

The most significant damage occurred on the rear chassis armor. On the PEBA chassis, this manifested primarily as localized tearing at the primary impact site, while the surrounding structure remained largely intact with no evidence of widespread cracking, delamination, or propagation of damage.

A previous TPU chassis sustained rear-section damage in a comparable location. However, the nature of the damage differed slightly: the PEBA showed more tearing, while the TPU exhibited cleaner cuts/shearing. This is likely because the TPU chassis was struck by a sharpened weapon, whereas the PEBA was hit by an unsharpened, though high-energy, weapon.

Despite these differences in opponent weaponry, both materials displayed localized failure modes with minimal damage propagation beyond the contact point. Overall damage severity remained comparable under combat conditions.

Figure 10: Rear left impact damage comparison. Left: PEBA chassis after competition. Right: TPU chassis after competition.

Figure 11: Rear right impact damage comparison. Left: PEBA chassis after competition. Right: TPU chassis after competition.

Figure 12: Raw in-pit photo of PEBA rear damage immediately after major impact (before hot glue repair).

Combat Highlights

Lava Monkey put on some entertaining performances throughout the event. The PEBA armor held up well while the robot delivered strong hits, tossed opponents, and even shattered a stainless-steel weapon in one match. Below are some of the more fun action shots from the tournament:

Figure 13: Lava Monkey tossing Wisp during competition. Photo credit: Alec Miller

Figure 14: Lava Monkey weapon contact with PopPopPop Cat during competition. Photo credit: Alec Miller

Figure 15: Lava Monkey breaks Jimbo’s stainless steel weapon during competition. Photo credit: Alec Miller

Conclusion: Is SainSmart PEBA a Viable TPU Alternative?

Within the scope of this field testing, SainSmart PEBA filament demonstrated impact durability comparable to the TPU baseline. PEBA successfully absorbed and dissipated impact forces without catastrophic failure, suggesting it is a viable alternative (or potential upgrade) to TPU for flexible combat robot applications.

While PEBA is marketed for high elastic energy return and rebound behavior, in this application high-energy impacts exceeded the material’s elastic limit, resulting in localized fracture or tearing before significant elastic recovery could be observed.

However, during operation and lower-intensity impacts, the robot subjectively exhibited a “bouncier” response compared to previous TPU configurations, suggesting increased elastic compliance in non-failure regimes. This observation is qualitative and not instrumented, and therefore cannot be rigorously quantified, but was consistently perceived during handling and post-impact recovery.

Despite this, the reduction in material density provided a meaningful benefit, with PEBA components achieving approximately 20% lower mass compared to equivalent TPU parts, providing valuable mass savings in the 3 lb class.

Key Findings

• PEBA components were successfully printed on 3 of 4 tested printers after profile optimization.
• Initial prints exhibited an unusual peeling-type delamination that was resolved through increased flow, higher nozzle temperature, and reduced cooling.
• The finalized profile prioritized strength over appearance, resulting in increased stringing but substantially improved part integrity.
• During combat testing, PEBA demonstrated impact resistance comparable to previously used TPU components.
• PEBA provided an approximate 20% weight reduction compared to equivalent TPU parts, allowing additional weight allocation elsewhere in the robot.