Project Longshot — Custom 21700 Li-ion Battery Pack

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This vote is to approve or reject the creation of ‘Project Longshot'. If approved, an amendment to AIP-007 would be made to add ‘Project Longshot’ to the list of projects. Its current status would be listed as ACTIVE along with relevant information such as project lead, funding status, spending caps, start and expiration dates.

1. Project Summary

This project develops a custom 14S9P 21700 Li-ion battery pack as a drop-in replacement for the Tattu 14S 30Ah smart battery used in Quiver. The pack targets the same form factor (220×330×90mm usable interior, ≤11.5kg) while delivering approximately 45% more energy — ~2,200–2,300Wh versus ~1,554Wh — through 126 high-capacity 21700 cells in a shifted upright layout.

Beyond raw energy density, Li-ion chemistry offers a significantly better safety profile than LiPo for commercial field operations, and typical cycle life is 2–3× longer. The pack will use a 3D-printed enclosure with aluminum reinforcement, laser-cut copper bus bars, and a custom STM32-based BMS developed against the VESC BMS architecture. The main connector is a Samtec ET60S-D06-0-00-D06-L-V1-S with integrated CAN H/L, handling both charge and discharge.

The project runs in two phases. Phase 1 delivers a functional prototype by beginning of May 2026, with mechanical design, cell assembly, and a dummy BMS sufficient for bench and flight testing. Phase 2 — scoped after prototype validation — delivers the full smart BMS with protection, balancing, and CAN communication.

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2. Project Phases

Phase 1 — Prototype (target: beginning of May 2026)

All Phase 1 work is delivered through bounties. Work packages cover cell layout CAD, enclosure design, bus bar design, cell voltage connector integration, and the v0 BMS dummy PCB — but these are examples of how the project will run, not fixed sequential tasks. Bounties will be created, scoped, and assigned as the design matures.

Phase 1 prototype definition:

• 3D-printed enclosure (with aluminum reinforcement) manufactured and assembled

• 14S9P cell array assembled via spot welding

• Bus bars and cell voltage connections integrated

• BMS v0: PCB dummy exposing individual cell connections for external balancing; handles main power path from cells to main connector; no active protection circuitry

• Flight tested on Quiver

Phase 2 — Smart BMS & Refinement (timeline TBD)

Scoped after Phase 1 completion and flight validation. Indicative scope:

• Full smart BMS (v1): OVP, UVP, OCP, OTP, passive cell balancing, CAN interface

• Communication protocol implementation: Tattu protocol mirror and/or DroneCAN battery node

• Design refinements from prototype lessons

• Validated production-ready pack design

Phase 2 will be proposed as a separate project or amendment after Phase 1 delivers.

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3. Project Timeline

No intermediate deadlines are set within Phase 1. Bounty contributors manage their own delivery against the May target. Julius as Project Lead tracks progress and unblocks where needed.

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4. Budget Cap

Phase 1 only. These are caps, not spend commitments.

The BMS specialist budget is included here because identifying and engaging the right person early accelerates Phase 2. If no suitable candidate is found in Phase 1, this budget is not spent. It would be a great way to get experience with our own open-source BMS design.

Additional 10,000 $ARROW are requested to create the bounties from a mix of $USDC and $ARROW.

All bounties paid in $USDC or $ARROW at prevailing rate. Hardware costs reimbursed in $USDC.

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5. Project Lead

Julius serves as Project Lead for this project.

Responsibilities:

• Architectural and technical decisions

• Defining, scoping, and issuing bounties

• Managing development progress and unblocking contributors

• Flight testing and validation

Vector (vector-arrow) supports as project coordinator: GitHub project management, tracking open items, documenting decisions, and helping coordinate between contributors.

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6. Project Team

Julius will assemble the project team under the approved project budget. Positions are filled via bounties — there are no pre-assigned team members beyond the Project Lead.

Contributors interested in working on any aspect of this project (mechanical CAD, PCB design, BMS firmware, manufacturing) should express interest in the forum thread. Julius will evaluate and assign bounties as work packages are ready.

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7. Deliverables

Phase 1

Phase 2 (indicative — to be scoped)

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All design files released open-source under Arrow DAO standard licensing.
Questions or interest in contributing: comment in the forum thread or reach out to Julius or the Arrow team.