Robot power board v0.11: plain-language walkthrough

What this board does

It is the robot's power strip and USB hub in one. Two battery packs come in, pass through your external master switch, and the board hands out every voltage the robot needs. It also gives the Jetson one USB cable that reaches the speakers, the Dynamixel servos and three small hobby servos.

• Motors: battery voltage goes straight through a fuse to your existing motor controllers. The board does nothing clever here.
• Jetson Thor: a 24.3 V supply good for the 8 A the Thor kit can draw.
• Servos: 5 V for the XL330s, 10.8 V for the XL430s, and a separate 5 V for three MG90S servos.
• Sound: a USB sound chip and a stereo amplifier for two speakers.
• Spare outputs: a 5 V / 5 A output and an 11.7 V / 5 A output ("AUX") for your own gear.

What plugs in where

The board is 228 mm wide and 155 mm tall. This sketch is to scale, seen from the top.

Orange: battery-side wiring you solder. Grey: fuses you fit. Blue: outputs. Purple: signal and audio.

The actual board

Top copper layer of v0.11. The bottom strip holds the hobby-servo supply (left), its fuse, the three servo headers and programming header on the bottom edge, and the servo controller chip (right of centre).

What changed in v0.11

v0.10 had an empty quarter because the hobby-servo circuitry was still sitting where a much older version of the board had put it. In v0.11 that one area was laid out again; everything above it, and the USB area on the right, is copper-for-copper the same as v0.10.

The connections between the moved pieces were re-drawn by the project's routing program and passed the design-rule check, but no person or second AI has reviewed that corner yet.

What changed from v0.9 to v0.10, and why

v0.10 is not a new design. A script takes the reviewed v0.9 board and applies a short list of changes. Every part and every trace sits in the same place relative to everything else. The saved v0.9 order was $535.15; v0.10 was $294.18. (v0.11 then undid the Thor inductor line below.)

Savings are approximate and overlap; the totals at top are the real quotes.

What to buy

Shipping, tax and any coupon are added at checkout. The factory's estimate for shipping the bare boards alone was about $32.

Three things to decide before you click pay

1. Mounting holes. The board is 75 mm shorter than v0.9 and the bottom row of holes moved (positions in New in v0.11). Check that your robot's mounting can take the new pattern.
2. Finish. The order uses lead-free tin ("HASL"). A gold finish ("ENIG") is flatter and kinder to the tiniest chip on the board, for about $15.60 more (about $321 total). I left it off.
3. Stock. Two chips were low at the factory earlier today (30 and 52 pieces). If the cart flags a shortage at checkout, stop and ask rather than accepting a substitute.

Also buy separately

• One TLV3011BIDBVR chip per assembled board (about $2.78). The "B" matters. The factory had none, so you fit it by hand at position U9903.
• Fuses: two 30 A (Littelfuse 0505030.MXEP) and one 5 A (Schurter 8020.5075.PT) per board, plus fuses at each battery pack.
• The Thor cable (Molex 2147551042), XT60 pigtails, your master switch, pin headers, M3 standoffs.
• Chargers for your own gear: see Powering your gear.

After you pay

The order is set so the factory will not start on its own. Expect two emails asking for approval:

1. Production file. Their engineers show how they will build the bare board. Check that the layer build says JLC04161H-7628 and that they have not changed hole sizes or trace widths.
2. Parts placement. A picture of every part on the board. The remark on the order asks them to check pin 1 and polarity on every chip, diode and capacitor. Look especially at the parts with a dot or stripe: they must line up with the board marking.

The factory's own preview of the final upload. The yellow XT30s and the USB switch chip were corrected against this view. One capacitor (C20, below the big coil) shows as an empty outline because the factory has no 3D picture of it; it is on the parts list.

When the boards arrive

You get five bare boards; two have the surface parts and most connectors fitted. They are not ready to run.

Soldering you must do on each assembled board

1. Fit the TLV3011BIDBVR at U9903. It is a small six-leg chip; this is the fiddliest job.
2. Solder the three fuses (F1, F2, F7000).
3. Solder the battery pigtails (J1, J4), the motor pigtail (J2) and the four switch wires (J5). Use 12 AWG and add strain relief; the board must not carry cable weight.
4. Fit the three servo headers and the 5-pin programming header.
5. Optional: seven small two-pin "OFF" headers. Putting a jumper on one switches that supply off, which is handy for testing one section at a time.

Programming

The chip that drives the three MG90S servos arrives blank. It needs its firmware loaded once through J7008 before those servos will do anything. Everything else works without programming.

First power-up, in order

The full procedure is the bring-up checklist; it applies unchanged. The short version:

1. Look over the board for solder bridges, then check with a meter that no output is shorted to ground.
2. Use a current-limited bench supply at 27–33 V on one pack input, not a battery. Nothing plugged into the outputs.
3. Bring up one supply at a time (use the OFF jumpers) and measure each: 24.3 V, 5 V, 5 V, 10.8 V, 11.7 V, 5 V.
4. Load the Thor supply with a dummy load up to 8 A before connecting the Jetson. Meter the Thor cable's polarity first.
5. Then USB: plug into the Jetson and confirm the sound card, both serial ports and the servo controller appear. Try the USB-C plug both ways up.
6. Only then batteries, then servos, then motors.

Powering your own gear

"AUX" is just the name of the 11.7 V output. The connector is an XT30, the small yellow two-pin plug. Both spare outputs use it, so each lead you plug in needs an XT30 on the end.

A Pi 5, a tablet and two small monitors add up to more than AUX can supply on its own (about 58 W, shared with the amplifier). Spread them out:

• The Pi 5 only takes its full 5 A after negotiating with a smart supply. From a plain 5 V source it runs, but limits its own USB ports to 0.6 A unless you add usb_max_current_enable=1 to its config file.
• A battery-side charger module must be rated well above 33.6 V input (look for 40 V or more). Ordinary "12–24 V" car chargers are not safe on the battery.
• If you would rather run the Pi from an AUX charger module with a plain USB cord, that works too; AUX then runs warmer. Move the tablet to the battery-side module in that case.
• Building USB charge ports into the board is possible in a later revision, but would add roughly $20–30 and new layout to this one.

Heat

Thinner copper is the main thing given up to hit the price. I modelled how warm the board gets from its real copper shapes, in still air, with Thor drawing 8 A and typical loads elsewhere (about 12 W of waste heat in total).

These are rises above the surrounding air. In a 25 °C room the hottest spot would be about 70 °C; in a closed, warm robot body it would be higher. The chips themselves run hotter than the board under them.

• This is an estimate, good to roughly ±30%. With pessimistic airflow the worst spot is +59 °C.
• The hottest spot is AUX because the model loaded it at 4 A. Following the split in Powering your gear brings it down to about 2 A.
• On the bench: run each supply at its real load for 15 minutes and check the regulators with a thermometer or a fingertip-near test. If something is too hot to keep a finger near, add airflow or a stick-on heatsink before trusting it.

Known risks, plainly

The 30 A motor fuse is a fuse rating, not a promise that the board carries 30 A all day. The design assumes about 10 A to the motors.

How it was checked

• Design-rule check: zero errors and zero unconnected pads. Thirteen cosmetic warnings, the same ones v0.9 has.
• v0.11 difference audit: a second script compares v0.11 against v0.10 and passes only if nothing outside the servo corner changed (apart from the shortened USB run to the servo controller), no part or connection changed inside it, everything is connected, and the schematic still matches.
• v0.10 difference audit: a script compares v0.10 against v0.9 and passes only if every difference is on the list above. It covers all 366 parts, 1,195 pads, 3,488 trace segments, every hole and every copper pour, and confirms the schematic and board agree.
• Factory upload: for v0.11 the factory read the files as a 4-layer 155 × 228 mm board, matched all 81 lines of the parts list, and priced it on the cheaper assembly line. The moved parts sit on their pads in its preview.
• Second opinion: Google's Gemini (Argon) reviewed it twice. Its first verdict was "do not order". The findings that held up were fixed: the first replacement inductor was too small, and three parts were rotated wrongly. Two of its "blockers" were its own mistakes, which it accepted on the second pass, when its verdict became "order with named changes". Those changes are in the final build. Argon has not seen v0.11.
• Not done: nothing has been built or measured. The heat figures and USB trace sizes are calculations.

Files: board revisions/v0.11/kicad/robot_pdb.kicad_pcb (fingerprint starts 1c351a03d3f0), factory package outputs/v11-order-preparation/package-1c351a03d3f0/, quote record outputs/v11-order-preparation/factory-quote.json.

Glossary