Project Caribou - September 2026 Progress Report

General
1

Project Caribou — September 2026 Progress Report

1. Summary

Caribou Phase 2 is approved and already running. September turned into PT1.5 planning: a lighter, faster-to-build frame, with two builds planned, one in Germany and one in the US in November.

Done in September:

  • The DAO approved Phase 2 on Snapshot (closed September 1: 100% For, 6 votes).

  • Designed the PT1.5 layout: a carbon-fiber tube sandwich frame replaces PT1’s welded steel inner frame.

  • Moved the tube adapters from 3D-printed aluminum to CNC machining. The parts are now in manufacturing.

  • Started ordering parts for both PT1.5 builds: folding connectors, tube clamps, CNC adapters, motors, propellers. Thomas started his build prep in Texas: batteries ordered, enclosures printing.

  • Created nine GitHub issues covering the work needed before the November build.

  • Continued PT1 testing. The gathered data led to an adjusted control tune.

2. Team

September core contributors:

Contributor Role September allocation
Julius Project lead 30 h/week
KBM CAD / PCB 20 h/week
Alex Avionics / Caribou Hub 10 h/week

Erick supported the project in calls and reviews without a paid allocation this month. Alperen and Zeynep gave design and general feedback.

3. Progress

PT1.5 layout

PT1.5 is an improved build of PT1. Size, layout, and motor angles stay almost the same.

What changes:

  • Frame: a sandwich layout of 60 mm carbon-fiber tubes and CF sheets (with foam or honeycomb core) replaces the welded steel inner frame. PT1’s frame took a long time to weld and needed jigs. The new frame aims at fast assembly.
  • Weight: the goal is about 40 kg less than PT1. The estimate still has to be confirmed.
  • Payload: two tank bays that act as universal cargo mounts. They take DJI T50 agricultural tanks. The spray and the granule-spreading tanks give us two payloads to test right away.
  • Batteries: a printed slide-in mount replaces PT1’s sheet-metal holder.
  • Landing gear: bent aluminum tubes, with an added centre support.
  • Electronics: unchanged from PT1. Both PCBs get small revisions: a buzzer and precharge voltage sensing on CBC_PCB, and a USB power-path check on CMAIN_PCB.

The design discussion runs in the PT1.5 thread. KBM added his earlier PT2 suggestions there. Alperen suggested square tubes for better bending stiffness.

Tube adapters: from printed to CNC

The first plan was to 3D print the tube adapters in aluminum. The supplier quoted 1–3 mm tolerance. That was too loose, so we redesigned the adapters for CNC machining. The redesign used Build123d and produced machining drawings and an RFQ package. The CNC adapters are now in manufacturing. One batch covers both builds.

Two builds: Germany and the US

  • Germany: Julius builds a PT1.5 with the same frame parts, on a similar timeline to the US build. The US meetup preparations take priority, so the German build may finish after it.
  • US (November): Thomas builds a PT1.5 in Texas at the November meetup. Thomas has ordered batteries and is printing the battery and main PCB enclosures. Julius is shipping foldable motor-beam connectors to him.
  • The next PCB order (with assembly) runs through Thomas’s JLC account, so the boards ship straight to Texas.
  • We are preparing a cable table for JLC, so the meetup crew doesn’t have to crimp harnesses by hand.

The build plan and parts list live in the PT1.5 planning sheet (Sources).

PT1 testing

PT1 started basic testing in September. We analyzed some test logs and adjusted the control parameters. The new tune is validated in simulation. The test flight should confirm it on the real aircraft.

Flight approval: we submitted the SORA 2.5 FastFlight application to the LBA on August 18. Seven weeks in, no decision yet. The fast-track process takes a few weeks.

New GitHub issues for October

Nine issues cover the work before the November build:

  • #58 CBC_PCB: add a buzzer and precharge voltage sensing, fix the precharge relay
  • #59 CMAIN_PCB: check whether internal devices draw power from the FC USB port
  • #60 PT1.5 landing gear design
  • #61 Finish the CF sandwich sheet design
  • #62 Cable table for manufactured JLC harnesses
  • #63 Printed battery slide-in mount
  • #64 Wire routing in CAD with mounting points
  • #65 T50 tank mounts for the cargo bays
  • #66 Overview of the T50 electrical, fluid, and pellet systems

Some issues are unassigned. Contributors can pick them up.

4. Outlook

  1. Finish the CF sandwich panels and freeze the PT1.5 design.
  2. Receive the CNC tube adapters and place the PCB order.
  3. Do more testing on PT1.
  4. Follow up on the LBA flight approval.
  5. Build PT1.5 in Germany and at the November US meetup.
  6. Close the open October issues, starting with landing gear and the battery mount.

5. Budget

September contributor streams (September 1 – October 1, executed from the Caribou Safe on September 30 in a single batch):

Contributor Stream amount
Julius 9,000.00 USDC
KBM 3,840.00 USDC
Alex 1,920.00 USDC
Total streams 14,760.00 USDC

The same batch sent 1,280.00 USDC to Erick, who returned it the same day. His September allocation was zero.

September reimbursements (executed from the Caribou Safe on October 1, sheet items 0038–0040):

Item Amount
8× 60 mm foldable motor-arm connectors + 20× 60 mm tube clamps (DAO share: 50% of invoice) 1,606.65 USDC
5× CNC tube adapters (3W-Adapter_Edge_v4) + shipping 2,433.00 USDC
Hobbywing X15 propeller set 935.00 USDC
Total reimbursements 4,974.65 USDC

August interim payment (executed September 24): Julius, two weeks of August at the project-lead rate, 4,200.00 USDC. It came out of the remaining Phase 1 balance, as the Phase 2 proposal set out for the August interim month.

After the August payment, 1,676.33 USDC remained. On September 30 the Safe received 28,323.67 USDC from the treasury, which brought it to exactly 30,000 USDC. After the September payouts the balance is 10,265.35 USDC. It reconciles exactly with the transfer history.

Total September allocation: 19,734.65 USDC (streams + reimbursements). The August interim payment (4,200.00 USDC) came from the Phase 1 budget.

6. Key Sources