Bill of materials and costs

Stage 6 · Toward hardware · ~30 min · Before this: 04 Actuators · 11 Sensors and compute · 09 Power and battery · numbers from the repository as of 2026-11-02

Marvin Bot costs about $17,600 in parts to build from nothing at November 2026 prices. This page takes that number apart: which 65 lines make it up, which few lines dominate it, what it leaves out, and how buying one phase at a time changes when the money leaves your account and how much is at risk if a test fails.

You will learn

• What a bill of materials (BOM) is, how bought and made parts differ, and why every price carries a date and a basis.
• Why two groups, actuators ($6,339) and compute and sensors ($4,723), are 62% of the total, and what is deliberately not counted.
• How quantity tiers and staged buying trade a small saving against money committed before a test has passed.
• How to compare actuators by price per N·m, and which alternatives the project looked at.

The idea in one picture

A bill of materials is the complete shopping and making list for a product: every item, how many, what each costs and where the price came from. Engineering organisations treat it as a product-oriented tree that every cost estimate hangs from: if a part is not on the list, it is not in the budget.^[1] For a one-off robot the BOM answers three practical questions: what will this cost me?, what do I buy first? and which few lines matter?

Marvin Bot’s BOM lives in one spreadsheet, bom/bom.xlsx, with one sheet per group and a Summary sheet. Its total, $17,574.86 for 65 lines, is the full cost to replicate: what someone starting from an empty bench would pay for parts. The bars below are that total split by group; the playground lets you change the assumptions.

Two ideas from elsewhere in the guide help here. The robot is built in seven phases (page 22): 0 foundations and 1 simulation (both free in parts), 2 a bench test of two motors, 3 one leg, 4 the lower body, 5 torso, arms and head, 6 perception. And each actuator (a motor with its gearbox and electronics, page 4) is named by its RobStride model, from the large RS04 down to the small RS00.

Playground: BOM cost explorer

Presets

Marvin Bot today Staged buying I own the Orin and hands Two robots Import shock (hypothetical)

View

By groupBy build phase

Actuator and kit pricing

Single-unit prices (the BOM) Staged: one order per phase, 10+ price where an order reaches 10 Everything in one order now One order for two robots (cost per robot)

Seeed's 10+ tier: RS04 $242, RS03 $214, RS00 $131.99 (no tier listed for the RS10P), hand kit $97, debug adapter $14.

I already own…

Jetson AGX Orin developer kit ($3,499) AmazingHand kits ($198) Tooling group ($710) 48 V bench supply ($250) Backup USB IMU and gamepad ($95)

Owned lines keep their price in the full cost (as in the workbook) but drop out of "still to spend".

What-if (hypothetical)

Duty on parts shipped from China

Applied to the actuator, servo and hand-kit lines only. Not a real tariff rate: check yours.

Shipping allowance

Percent added to what you still have to buy.

Show amounts in US dollars Euros (illustrative 0.92 per $) Pounds (illustrative 0.78 per $) Rupees (illustrative 84 per $) Australian dollars (illustrative 1.52 per $)

Fixed illustrative rates, not live. The BOM itself is in US dollars.

Cost by group

Full cost to replicate

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Still to spend

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Change vs BOM total

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Actuators share

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Committed before the leg test

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to buyownedhypothetical dutycumulative

Reading the numbers: Full cost to replicate counts every part at today's price, even ones you own; Still to spend is what actually leaves your account. Committed before the leg test is money paid through phase 2, before the one-leg build (phase 3) has shown the design works: lower means less at risk if a test fails.

Try this

1. Press Marvin Bot today: the full cost reads $17,575. Switch to By build phase. Phases 0 and 1 cost nothing in parts: simulation is free once you have a training computer (which the BOM does not count).
2. Choose Everything in one order now. Only the RS03 reaches ten units (9 + 1 spare), so the saving is 10 × $11 = $110. Now look at “Committed before the leg test”: it rises by about $1,900, because the whole RS03 order (~$2,100) is paid before the actuator bench has said whether the RS03 is any good. Then try Staged: the 9 RS03 for phase 3 fall one short of the tier, because the tenth was bought alone for the phase 2 bench test, so staging keeps none of the $110.
3. Tick the Orin. “Still to spend” drops by a fifth. That is why the repo once quoted “about $12k”: it counted owned parts at $0 (docs/decisions.md, 2026-10-29).
4. Drag the duty to 25%. Only about $6,400 of lines ship from China, so what you spend rises by about $1,600, not by a quarter.

All 65 lines

Every line of the workbook, with its quantity, spares, unit price, line total (quantity plus spares, times unit price) and the price basis exactly as recorded. The phase column is this guide’s mapping of each line to the build phase that first needs it (see below). Click a heading to sort.

All groups All phasesPhase 2Phase 3Phase 4Phase 5Phase 6 Any price basisEstimates onlyDated listings onlyShips from China

Group	Item	Qty	Spares	Unit $	Line $	This scenario $	Phase	Price basis
Shown lines

From first principles

Bought parts and made parts

A robot’s parts come in two kinds. Bought parts arrive finished: actuators, the computer, the camera, battery cells, bearings, connectors. Their cost is a price on a listing. Made parts are designed in the project and produced from raw material: Marvin Bot’s code-CAD generates 97 CNC-machined aluminium parts (about 6.4 kg of finished 6061 and 7075), 20 printed structural parts and 24 printed body-shell pieces, plus 12 plates too large for a desktop mill that go to an online machining service (the Made parts (CAD) sheet, generated by python -m cad.export). Made parts appear in the costed BOM only as their inputs: aluminium stock, filament, end mills, and the three “online machining” lines. Their real extra cost is machine time and your time, which the BOM does not price.

That split explains why the structure is cheap ($2,452, 14%) even though it is most of the part count, and why the bought groups dominate.

Line totals, spares and the sum

Each line is priced as

line total = (quantity used + spares) × unit price

and the BOM total is the sum of the 63 line totals. Spares exist only where a failure would stop the project for weeks: one RS04, one RS03 and one RS10P, the three actuator models with long lead times and several joints each. For example the RS03 line is (9 + 1) × $225 = $2,250. The arithmetic is trivial; the judgement is in the quantities (do you need a spare?) and the unit prices (where did this number come from, and when?).

Price basis and dating

A price without a date and a source is a guess dressed up as a fact. Every line in the workbook has a price basis column that says what the number is: a dated listing (“Seeed 2026-10-29: $225 each, $214 at 10+”), an “estimate” with nothing behind it yet, or a listing marked “unverified”. Prices move: the Jetson AGX Orin developer kit’s list price went from $1,999 to $3,499 in July 2026, a 75% rise, reported from NVIDIA’s developer FAQ.^[2] In this BOM 37 of 60 lines are still estimates, mostly power parts, wiring, safety gear and online machining; the playground’s table can filter them. They total about $4,500 (26%), so most of the headline number rests on dated listings.

What drives the total

Sort the table by line total and the shape is obvious: the top five lines (the Orin, the RS03s, the RS04s, the RS10Ps and the primary IMU) are 56% of the money. Two groups carry the budget:

• Actuators, $6,339 (36%). 23 RobStride actuators plus 3 spares and 4 Feetech servos. RobStride’s own datasheets give the torque figures;^[5] Seeed Studio lists the RS00, RS03 and RS04 at RobStride’s list price with about 5% off at ten or more of one model; the RS10P comes from another reseller’s listing, a pre-order not yet confirmed.^[3][4]
• Compute and sensors, $4,723 (27%). The Jetson AGX Orin 64 GB developer kit alone is $3,499,^[2][9] the Orbbec Gemini 335L depth camera $359 list,^[10] and the primary IMU an estimated $730.

Everything else (structure $2,452, power $1,633, electronics $844, tooling $710, safety $470, hands $224, fasteners $180) adds up to $6,513. Cutting 20% of the fasteners saves $36; finding a cheaper computer could save thousands. Cost work starts at the top of the sorted list.

What is not counted

The total is parts for one robot, delivered free, with no tax. The Summary sheet and bom/README.md list what is left out:

• A training GPU. Isaac Lab training and GR00T fine-tuning want a desktop RTX card with 24-32 GB; the repo notes an RTX 5090 at $1,999 list but about $4,000 or more street price in late 2026. A rented cloud GPU also works.
• The desktop CNC mill and 3D printer (requirement R60 assumes you have them).
• Shipping, import duties and tariffs. Most actuators and the hand kits ship from China. Duty depends on your country, the goods’ tariff classification and the year;^[13] the RobotShop price of the camera, $413 against the $359 list, shows the kind of difference it makes (the Sourcing sheet notes it “includes US tariffs”).
• Your time, failed parts, and anything you break on the bench.

Quantity tiers and staged buying

A quantity tier is a lower unit price for ordering at least a set number of one item. At Seeed the RS03 is $225 singly and $214 at ten or more.^[3] The robot needs 10 RS03 (with the spare), so ordering them all at once saves 10 × ($225 − $214) = $110. But it commits about $2,100 before the phase 2 actuator bench test has confirmed the RS03’s torque, heating and CAN behaviour. The decision log weighs exactly this (docs/decisions.md, 2026-10-26) and chooses: buy one RS04 and one RS03 singly for the bench, then order the rest together after the bench passes. Since the RS10P replaced the RS03 at the shoulder roll (2026-11-02) that order is 9, one short of the tier unless the spare goes with it; either way you risk $225 instead of $2,250. The RS04 (7) and RS10P (7) never reach ten for one robot, so their tiers only matter for a second robot.

The general rule: a discount for committing early is worth taking only if it is larger than the expected loss from committing to the wrong part. A 5% discount against even a 10% chance of needing a different actuator is not worth it.

Playground: cost per N·m

Torque is what an actuator is for, so dividing price by torque gives a fair first comparison between sizes and brands. There are two torques to divide by: peak torque (short bursts) and continuous (rated) torque (what it holds without overheating). For a walking robot the rated figure is usually the binding one (see 04 Actuators and 05 Leg loads and stairs).

Divide by

Peak torqueRated torque

Price

Single unit10+ tier

Compare with

Alternatives (reseller listings, not in the BOM)

Damiao DM-J10010L-2EC about $230 (120 / 40 N·m)^[8]; CubeMars AK80-64 about $890-1,240 (120 / 48 N·m)^[7]. Prices October 2026, low end used.

US dollars per N·m of peak torque

Cheapest per N·m (BOM models)

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Robot's actuator $ per N·m installed

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Try this

Switch to rated torque. The RS04 stays cheapest per N·m, and the small RS00 and the Feetech servo get much worse: small actuators carry a fixed cost (housing, encoder, driver board) that does not shrink with torque. That is why Marvin Bot uses the big RS04 for the three most loaded leg joints and only uses small units where the torque is genuinely small. Then tick the alternatives: on these listings the Damiao is slightly cheaper per N·m than the RS04, and CubeMars several times dearer.

How Marvin Bot does it

In the repo

• bom/bom.xlsx is the single source of truth: Summary, one sheet per group, Sourcing (where each part is sold, with tiers, availability and the date checked) and two generated CAD sheets. Each line has a Status column (owned, ordered or empty for “to buy”); owned lines keep their price so the total stays the full cost to replicate.
• tools/bom/book.py tidies the workbook and rebuilds the Summary formulas; --check runs in CI (the automatic checks run on every change to the repository); tools/bom/summary.py prints the totals ($17,574.86, 65 lines).
• Groups: actuators $6,338.91; compute and sensors $4,723; structure and materials $2,452; power $1,633.05; electronics and wiring $843.90; tooling $710; safety $470; hands $224; fasteners $180.
• Requirement R61 (docs/requirements.md): about $14k excluding the onboard computer, about $17.6k with it. $17,575 − $3,499 = $14,076.
• One line per item with a spares column, not one line per purchase phase; docs/plan.md says what each phase needs (docs/decisions.md, 2026-10-29).

Spend per build phase

The workbook has no phase column, so the phase view in the playground is this guide’s mapping, built from the work column of docs/plan.md and the decision log. Where the plan names parts, the mapping follows it; elsewhere it is an inference, marked below. At single prices:

Phase	Spend	What it buys (main lines)	Basis

• Inference: the Orin, NVMe drive and on-board CAN transceivers are put in phase 2 because phase 2’s pass check is “CAN at the planned rates works on the Orin”, although the plan’s work column lists the Orin under phase 4. If you already own one (the repo’s builder did), this does not matter.
• Inference: the wired e-stop and hand tools are put in phase 2 because docs/safety.md applies its rules “from the first actuator bench test onward”.
• Inference: lump-sum lines that serve several phases (harness, CAN cable, fasteners, 6061 stock, leg machining, filament) are split between them in rough proportions; the split is illustrative.
• From the decision log: two bench actuators bought singly in phase 2; the other 11 RS03 in one order in phase 3; the remaining RS04 as the legs need them.

Trade-offs and alternatives

Option	Cost effect	Why not (yet)
CubeMars actuators	2-3× the price per N·m (decision log); on October 2026 reseller listings the AK80-64 is ~$890-1,240 for 120 N·m peak[7]	Price; the RobStride range covers every joint.
Damiao DM-J10010L (120 / 40 N·m)	About the same as the RS04 (~$230 at a reseller[8])	Fewer verified specifications; kept as the second source for the 120 N·m class (it also speaks MIT mode, the same CAN command format, so the driver would carry over).
Self-built cycloidal actuators	Cheaper parts, much more labour	More work, lower torque; the project’s risk is learning and integration, not actuator design.
Orin module on a carrier board	Module $2,999 since July 2026[2] plus a carrier board; about −1.0 kg	Little saving at today’s prices; the developer kit was already owned. Kept as a mass reduction (docs/decisions.md). A carrier board is the third-party board that gives a bare module its connectors.[6]
Jetson Thor T4000 for a second robot	Module $2,999 since July 2026 (was $1,999)[2]; NVIDIA quotes up to 1,200 sparse FP4 TFLOPS (trillion low-precision arithmetic operations per second, a measure of AI compute), 64 GB, 40-70 W[6]	Same module price as the Orin 64 GB; a newer platform for a second robot, not worth re-porting the first one.
13S2P battery instead of 13S3P (13 cells in series, 2 rather than 3 in parallel; page 9)	−13 cells (−$129) and −1.1 kg	Runtime would sit at the 1 h requirement with no margin (docs/decisions.md).
Count owned parts at $0	The old “about $12k”	Understates the cost for anyone else; replaced on 2026-10-29.
Order all actuators at once for the tier	−$110	Commits ~$2,100 before the bench test; staged buying keeps the saving only if the spare RS03 goes in the phase 3 order.

Where sources and the repo disagree

• CubeMars price per N·m. The decision log says CubeMars is “2-3× the price per N·m”. The one model checked here, the AK80-64 at $890-1,240 on October 2026 reseller listings for 120 N·m peak, is $7.4-10.3 per N·m against the RS04’s $2.13: 3.5-4.9×. The log may have compared other models or other prices; either way the conclusion (RobStride is cheaper) holds.
• Damiao. The log lists Damiao as an alternative with “fewer verified specs”. On current reseller listings the DM-J10010L-2EC (~$230) is slightly cheaper than the RS04 ($255) for the same 120 / 40 N·m. The repo’s reason for not choosing it is the specifications and software support, not price.
• Orin dev kit version. CNX Software’s report gives the developer-kit price change ($1,999 to $3,499) without naming the memory size;^[2] the repo and SparkFun’s listing^[9] apply it to the 64 GB kit, the only AGX Orin developer kit sold.
• Inside the repo: docs/plan.md lists the Orin as phase 4 work, but phase 2’s pass check needs it; this guide’s phase view puts it in phase 2.

Decisions you can make here

• Which parts you already own, and so what you actually have to spend (mark them owned in your copy of bom/bom.xlsx).
• Whether to take a quantity tier now or after the bench test.
• Whether a second robot is planned (it puts the RS04 into the 10+ tier too, and the RS10P if a reseller offers one).
• How much to allow for shipping and duty in your country, before ordering (roadmap open item 1 asks for a direct RobStride quote and current tariffs).
• Which estimate lines to get real quotes for first: sort the table by line total with “Estimates only”.

Your decision noteCopy

Built from your settings above. Paste it into an issue, a design discussion or an AI assistant session.

Further reading

• NASA Work Breakdown Structure Handbook: how large projects organise every deliverable into a tree that cost estimates hang from; the same idea at a much larger scale.
• RobStride Product_Information: the actuator manuals and datasheets behind the torque figures in the cost-per-N·m chart.
• CNX Software on the July 2026 Jetson price rise: a reminder that the biggest single line can move by 75% overnight.
• AmazingHand: the open-source hand, with its own parts list if you would rather build than buy the kit.
• 22 Build phases and roadmap: when each phase’s spend falls due and what it must prove first.

Sources

1. NASA, Work Breakdown Structure (WBS) Handbook — used for: a cost estimate hangs from a product-oriented breakdown of every deliverable.
2. CNX Software, “NVIDIA increases the price of Jetson modules and devkits by up to 101%”, 22 July 2026 — used for: AGX Orin developer kit $1,999 → $3,499; AGX Orin 64 GB module $1,599 → $2,999; T4000 module $1,999 → $2,999.
3. Seeed Studio, RobStride 03 actuator listing — used for: $225 each, $214 at 10+, 60 N·m peak, 880 g (checked October 2026).
4. Seeed Studio, RobStride 04 actuator listing — used for: $255 each, $242 at 10+ (as recorded in the BOM’s price basis).
5. RobStride, Product_Information repository — used for: peak and rated torque of the RS00, RS03, RS04 and RS10P.
6. NVIDIA Technical Blog, “Accelerate AI inference for edge and robotics with NVIDIA Jetson T4000 and JetPack 7.1” — used for: T4000 compute, memory and power figures; Jetson modules are used on carrier boards.
7. RobotShop, CubeMars AK80-64 listing — used for: 120 N·m peak, 48 N·m rated, ~$1,238 (other resellers from ~$890), October 2026.
8. AIFit Lab, Damiao DM-J10010L-2EC listing — used for: 120 N·m peak, 40 N·m nominal, ~$230, October 2026.
9. SparkFun, NVIDIA Jetson AGX Orin 64GB Developer Kit (DEV-22099) — used for: $3,499 listing for the 64 GB kit.
10. Orbbec store, Gemini 335L — used for: the camera’s $359 list price.
11. 18650 Battery Store, Molicel P45B — used for: cell price around $9.95-9.99, and the advice to buy from an authorised dealer.
12. Pollen Robotics, AmazingHand repository — used for: the open hand design (CC-BY-4.0) and its build-from-parts option.
13. US International Trade Commission, Harmonized Tariff Schedule — used for: duty depends on the goods’ classification and country; the slider is hypothetical, not a rate from here.