Inventory philosophy.
The right inventory level is neither "everything possible" nor "buy when you need it." Both extremes fail predictably — over-stocking ties up capital and produces shelf-life waste; under-stocking produces missed missions and emergency-shipping costs. Cohort default approach: identify what you actually use, calibrate par levels to that usage plus a reasonable buffer, and reorder before you run out, not when you do.
The four inventory principles:
Par level math: the formula
For a given item, the cohort default par level calculation:
Par level = (lead time in days × daily usage) + safety buffer
Worked example for cohort default props:
- Lead time: ~3 days from local sources.
- Daily usage: ~1 set per 25 flight hours; alumna flying ~8 hours/month uses ~0.32 sets per month, or ~0.01 sets/day.
- Lead time × daily usage: 3 × 0.01 = 0.03 sets needed during reorder cycle.
- Safety buffer: 2 sets (covers crash scenarios, mission-day surprises).
- Par level: 2 sets minimum, 4 sets recommended for active alumni.
Reorder point: when stock hits 2 sets, place an order. By the time the order arrives, you should have ~1.97 sets, well above zero.
Repeat this calculation for each spare. The downloadable kit's spreadsheet has these calculations built in for cohort default builds; updating your usage rate over time produces refined par levels automatically.
The capital trade-off. Stock costs money tied up. Cohort default individual alumna stock is ~₱8,000; partner-org fleets run ~₱25,000-50,000 in inventory. That capital sits idle until used.
The trade-off math:
- Too little stock: emergency-shipping costs (₱200-500 per rush order), missed missions (~₱5,000-15,000 per missed mission in revenue), customer-relationship damage.
- Too much stock: capital tied up at zero return; storage space; shelf-life waste on perishables.
Cohort default thresholds: spend up to ~5% of annual operating revenue on inventory. For an alumna doing ~₱200,000/year in surveys, ~₱10,000 in inventory is reasonable. For a partner-org fleet doing ~₱2M/year, ~₱100,000 in inventory makes sense. Below these thresholds, the operations are inventory-constrained; above them, capital is being wasted on shelf-life-risk items.
Critical spares.
Critical spares are the items where running out means your operations stop. These are the spares with the highest cost-of-stockout: missed missions, emergency-shipping costs, possibly cohort-relationship damage. The cohort default is to keep these items above zero at all times, with reorder points well above zero to absorb supply variability.
The cohort default critical-spares list:
Why critical-spares are critical
Each item on this list shares a property: running out blocks operations entirely. Specifically:
- Props: a damaged prop means the drone can't fly safely. Without spares, the day stops.
- Batteries: depleted packs can't mid-mission swap. Below ~3 packs, capacity is mission-constrained.
- Motor: a failed motor stops flight. Without a matching spare, multi-day repair turnaround.
- USB cables: required for FC configuration. Without them, no mission upload, no firmware updates, no diagnostics.
- Charger: required to charge mission batteries. Without it, only one battery cycle per day at best.
- Radio (partner-org only): without RC, drone can't fly. Backup unit prevents day-stop on radio failure.
The category is short by design — only items where the consequence of stockout is operations-stopping qualify. Adding more items to "critical" reduces inventory discipline; treating non-critical items as critical wastes capital. Be strict about what counts.
Total critical spares investment for individual cohort alumna: ~₱9,000-19,000 depending on build size. The bulk of this is batteries (the largest item category by cost).
Critical spares should be inspected at every monthly thorough check (maintenance.html Section 3). Counts verified; condition checked; reorder triggered if at or below reorder point. Don't assume critical spares are intact just because you remember buying them — verify physically.
For partner-org operations, critical spares scale with fleet size. A 5-drone fleet doesn't need 5x the props (volume discounts apply) but does need 3-4x; the par-level math is in Section 6.
Routine spares.
Routine spares are the items consumed during scheduled maintenance per maintenance.html Section 2-3. Predictable usage, predictable replenishment — these are the easiest items to manage well, since the schedules tell you what you'll need and when. Cohort default approach: order in batches when ordering critical spares; bulk discounts apply at moderate quantities.
Cohort default routine spares list:
Bulk vs single-unit ordering
Routine spares are where bulk ordering pays off most consistently. The economics:
- Single-unit pricing from individual sources includes their margin and your shipping. Convenient but expensive.
- Bulk pricing at moderate volumes (10+ units of a category) typically offers 10-15% discount.
- Wholesale pricing (100+ units) offers 20-30% but exceeds single-alumna needs and may exceed shelf-life.
Cohort recommendation: order routine spares as a batch every 6 months. By accumulating needs across many small items, you reach the bulk-discount threshold without exceeding shelf life. Cohort cells often coordinate group orders — pooling needs across 4-6 alumni gets to wholesale-volume pricing while staying within useful timeframes.
The downloadable stocking pack includes a coordination form for cohort group orders. Lumipad engineering can help facilitate larger group orders that involve multiple cooperatives or partner orgs.
Storage discipline for routine spares. Most routine items have shelf life that's years, not months — but the cohort default storage discipline applies anyway:
- Sealed containers: Tropical humidity affects everything. Even items that seem moisture-resistant degrade slower in sealed containers.
- Cool, dry storage: ambient room temp is fine; direct sun is not. Workshop drawer is better than truck dashboard.
- Visible labeling: by category and quantity. "Look at the box and know what's there" is the goal.
- FIFO rotation: First In, First Out. Use older stock first; don't leave items at the bottom of the bin.
Total routine spares investment: ~₱2,000-3,500 for individual alumna; this stock typically lasts 6-12 months at cohort default usage rates.
Repair spares.
Repair spares are the items kept for reactive use — components that fail or get damaged and need replacement. Usage rate is unpredictable; you might go 6 months without needing one, then need three in a single month after a difficult mission. Cohort default approach: hold lower par levels than critical/routine, but don't let any go to zero. The ones below are the ones cohort alumni actually use, ranked by frequency.
The cohort default repair-spares list:
The "spare drone" question
Should an individual alumna keep an entire spare drone? Cohort default answer: not typically, but consider it carefully. The trade-offs:
- Pro: zero downtime if primary drone has serious damage; no waiting for spare-component delivery.
- Pro: parts harvest possible if primary needs urgent repair (cannibalize the spare).
- Pro: secondary drone for training, personal practice, simpler missions.
- Con: ~₱25,000-40,000 capital tied up in something that may rarely fly.
- Con: maintenance burden doubles even if flight time doesn't.
- Con: decision fatigue — which drone for which mission?
Cohort default thresholds:
- Single-mission alumna with backup income: spare drone overkill; spare-parts inventory sufficient.
- Full-time alumna doing 5+ paid missions/month: spare drone makes sense; downtime cost exceeds capital cost.
- Partner-org operations: backup drone is essentially mandatory at fleet scale.
For most cohort alumni in their first year, individual repair spares (this section) are sufficient. The spare-drone decision becomes relevant as commercial operations mature.
Repair spares storage discipline. Several repair spares have specific storage requirements:
- FCs and ESCs: anti-static bags; sealed containers; away from magnets (motors). Cohort default: original packaging if available, anti-static bag otherwise.
- Receivers: same as FCs; anti-static-sensitive.
- Cameras: lens cap on; foam-padded storage; away from heat sources. Direct sun damages lens elements over time.
- Frame arms: flat storage to prevent warping; carbon fiber survives most storage but can crack if dropped.
Total repair spares investment for individual alumna: ~₱5,000-10,000 depending on whether spare FC/camera are stocked. Partner-org operations typically stock ~2x this per drone, with shared inventory pools.
The "use it within 12 months" rule for repair spares. Components in storage tend to lose currency — newer firmware versions emerge; better alternatives become available; cohort default BOM evolves. Repair spares stocked for over 12 months without use should be evaluated:
- Is the component still cohort-default? Or has the BOM moved on?
- Is firmware still current? (FC, ESC, RX firmware ages even unused.)
- Does the storage condition still preserve the item?
Cohort default: cycle through repair spares by using them in scheduled maintenance work where possible (e.g., a 12-month-old spare FC becomes the operational FC; the operational one becomes the spare; cycle continues). Items that genuinely sit unused for 18+ months are usually wasted capital.
Sourcing & lead times.
Where you order from determines lead time and cost. Local sources are fastest but priciest; domestic online is middle-ground; international orders are cheapest but slowest. Cohort default approach: tier sources by lead-time tolerance — critical items from local supply, routine items from mid-tier, occasional bulk orders internationally for capital efficiency.
The four sourcing tiers:
The cohort sourcing strategy
Cohort default approach to sourcing matches lead-time tolerance to category:
- Critical spares: hold buffer high; refill from Tier 2 (domestic online) for routine refills, Tier 1 (local) for emergency. Never let critical spares run to zero.
- Routine spares: order in Tier 2 batches every 6 months. Bulk-order pricing within volume tier 1; reasonable lead time.
- Repair spares: Tier 2 for individual restocking after use; Tier 3 (international) for occasional capital-efficient batch purchases.
- Bulk routine items (props, screws, basic supplies): Tier 4 group orders capture the best pricing; cohort cells coordinate to reach volume thresholds.
The tier mix balances speed against cost. Operations that depend on fast restocking lean toward Tier 1-2; operations with predictable consumption lean toward Tier 3-4. Find your balance based on actual missions cadence and risk tolerance.
Lead-time realities for Davao operations:
- Same-day Davao stock: limited to drone-specific shops; carries cohort-default-build components but limited brand choice.
- 24-hour Davao + Manila: motorcycle-courier delivery from Manila; emergency option for critical-item stockout. ~₱500-1,000 shipping cost.
- 3-day domestic: standard domestic shipping; cohort default routine restocking timeline.
- 2-week international: AliExpress standard; works for non-urgent items; price advantage usually 30-50% vs local.
- Customs delays: international orders sometimes held in customs for 1-3 additional weeks. Plan accordingly.
Currency hedging: international orders are typically PHP-denominated at point of purchase but settle against USD or RMB. PHP weakening between order and delivery shifts effective cost. Cohort recommendation: budget 5-10% above quoted price for currency drift; settle in PHP at order time when possible.
Reliability of sourcing channels: cohort experience is that local sources are most reliable for stock availability; domestic online occasionally stocks out unexpectedly; international orders are most variable in delivery time. The reliability ranking: local > domestic online > international. Match this to your operational risk tolerance.
Fleet inventory.
Individual alumna inventory (~₱8,000) doesn't scale linearly to fleet operations. Partner-org fleets benefit from inventory pooling, dedicated stock management, and bulk purchasing power that individual alumni can't access alone. This section covers what changes at 5+ drone scale and the cohort recommendations for partner-org inventory management.
What changes at fleet scale:
Cohort default fleet inventory size for 5-drone partner org: ~₱25,000-35,000 in inventory. This breaks down roughly:
- Critical spares (~50%): ~10 prop sets, 12-15 batteries, 3 spare motors, multiple USB cables, 2 chargers, 1 backup radio.
- Routine spares (~20%): 6-month batch of consumables (solder, heat shrink, screws, etc.).
- Repair spares (~30%): 2-3 spare ESCs, 2 spare FCs, 2 spare receivers, 2 spare GPS, frame arms for 2 drones.
For 10-drone partner org: ~₱50,000-70,000 inventory. Critical spares scale ~1.8x, not 2x — the consolidation produces real savings. Repair spares scale ~1.5x — same logic plus the per-drone failure rate isn't additive.
The inventory dashboard
Cohort default fleet inventory dashboard (spreadsheet-based) tracks per-item:
- Current stock: physical count, updated weekly minimum.
- Par level and reorder point: target stock and trigger threshold.
- Lead time: typical days from order to delivery.
- Consumption rate: actual usage over the past 3-6 months.
- Last reorder: date and quantity of most recent purchase.
- Notes: shelf-life concerns, sourcing notes, etc.
The dashboard auto-flags items at or below reorder point, items approaching shelf-life expiry, and items with consumption rates that suggest par-level adjustments. Updated weekly by inventory manager; reviewed monthly by operations team.
The downloadable stocking pack includes a Google Sheets template that maps to this structure. Partner orgs can fork it; individual alumni can use a simplified version. The discipline is the same; the scale differs.
Cross-fleet inventory sharing can multiply the leverage of fleet inventory:
- Cohort cell pooling: 4-6 alumni in the same region share a pooled inventory for less-frequently-used items. ~30-50% capital savings vs each holding individually.
- Inter-partner-org coordination: when one partner org has surplus and another has stockout, lateral transfer is faster than reordering. Requires inter-org coordination but works.
- Cohort emergency loan: alumni borrow critical spares from cohort engineering inventory in genuine stockout situations. Used rarely; available as backstop.
The capital efficiency at the highest tier of coordination — cohort-wide group orders + cell pooling + emergency loan backstop — produces the lowest effective cost per drone of any approach. Partner orgs operating in isolation pay more for the same inventory; integrated cohort participation produces inventory leverage individually impossible.
The annual inventory review closes the inventory cycle. Each year, an inventory manager (or alumna for individual case) reviews:
- Total inventory cost vs operations cost — is the ratio reasonable (~5-10% of annual revenue)?
- Items consumed faster than expected — par levels need increase?
- Items consumed slower than expected — par levels can decrease, or item should be removed?
- Items that have aged on shelf — any approaching shelf-life expiry that need use-or-disposal decision?
- Sourcing reliability — any changes needed for next year?
The annual review calibrates the inventory shape for the coming year. Without it, par levels drift from operational reality; with it, inventory stays aligned with how operations actually work. Inventory discipline is iterative — initial setup is rough; refinement over years produces optimised stock that supports operations without wasting capital.