# Turret wiring and harness (v0, the bench build) The electrics of the foam-ball turret as built for the bench (docs/decisions.yaml D42): every connector and its pinout, every conductor's gauge and length, the one fuse, the hardware arm chain (the safety pulses across the slip ring, the overspeed trip, the phase-short brake), the current budget, and the boards laid out part by part. Part numbers are the catalogue keys of `exports/turret/bench/bom.json`; the order sheets are `exports/turret/bench/orders/`. The physics numbers are docs/turret-physics.md's (v0 sections). ``` BENCH STAND (fixed) | BASE (fixed) | SLIP RING | TURRET (pans) | CT | CARTRIDGE (tilts, XT60E-M <- 24 V supply | DT04-12PA receptacle (-y pad) | stator | rotor -> the board bay (-y arm): | | lifts off) rocker, 5 A time-lag fuse | 5 A MINI in line | -> rotor | L0 12 V regulator (always on) | | 2 x AM32 ESC mini-XLR <- pendant | base board (+x): 12 V PAN, | | L1 safety switch, 5 V, 2 x 1000 uF| | cartridge board: USB-CAN <- laptop | the 555 pulse oscillator | | opto, one-shots | | 6 brake FETs and terminal board (70 x 50) | pan servo (STS3215, ID 1) | | L2 Feather M4 CAN, trip latch, | | their driver, DT06-12SA plug | index magnet | | ARM gate, servo bus buffer | | gate comparator | | | | | feed servo (ID 3) | | | tilt servo (ID 2, +y arm), laser, | | 2 gates | | | hall switch | | ``` The pan joint is the slip ring (continuous pan). The tilt joint (yoke to cradle) is a lead loop: everything that rides the cradle or the cartridge leaves the bay as one bundle and crosses the tilt axis in a 40 mm loop beside the -y pivot. The cartridge (CT) is unplugged by hand: two Micro-Fit connectors on a short pigtail. **What v0 changed from the plan's wiring (docs/turret-prototype-plan.md 4.4), and why:** 1. **The flywheel regulator is always on and the safety switch is on its 12 V side.** The fixed 12 V regulator (D24V150F12) feeds 12 V MAIN; the tilt servo takes 12 V MAIN directly, and the Pololu 2815 switches 12 V MAIN to 12 V FLY (the two ESCs and the feed servo). The separate 12 V AUX regulator for the tilt servo is gone. The speed ceiling is unchanged (the ESCs only ever see the fixed 12 V regulator's output), the safety line still cuts the flywheels and the dial in hardware, and pan and tilt stay live (D7). Reason: the bay's three 52 x 50 boards could not hold the plan's parts (section 6 shows each board). 2. **One fuse: 5 A MINI in an in-line holder in the +24 V lead in the base.** It protects the slip ring's paralleled 2 A circuits (the plan's 10 A ATO would not) and everything after it; the stand's 5 A time-lag fuse protects the stand's wiring. No PCB blade holder fits: a blade fuse standing in its holder is 15-25 mm tall, against 11 mm under the base board and 11 / 12.5 / 8.5 mm on the bay's levels. The servos' leads have polyfuses (MF-R300) and the 5 V rail an MF-R250. 3. **The Pololu 2815's slide switch is set to OFF.** Pololu: "If the physical switch is in the 'off' position, the switch state can also be controlled by a digital signal" (pololu.com/product/2815); with the switch ON the MOSFET is on whatever ARM does, so the plan's "slide switch left ON" would defeat the safety line. **Check it before every power-up (bench test 3.2).** Its ON pin left open is off (Pololu). 4. The cartridge's power connector carries 12 V FLY on three contacts and GND on three: no 24 V and no CAN node on the cartridge at all. The feed servo takes 12 V FLY through its polyfuse on the cartridge board. 5. The bank is 2 x 1000 uF (the X2216's 300 ms soft start draws 2.5 A at the ring, 3.6 A with 200 ms: 2 mF rides a 2 ms contact bounce at 3.6 A with 4 V of droop). 6. **The arm chain's logic runs on the Feather's 3.3 V** (section 3): the plan's 5 V logic would have put 5 V on the Feather's pins (ARM_IN, TRIP_IN, PULSE_MON; the SAMD51's are not 5 V tolerant), and its gates' 3.3 V pull-ups were below a 5 V 74HC input's 3.5 V threshold. The servo bus comes back to RX through a Schottky diode (3.5). 7. **The 555 runs on the pendant loop's 12 V, with no 78L05.** A 5 V 555 drives the opto's LED through 4.4 k at about 0.5 mA, too little for a 4N35 to pull its input low reliably; at 12 V it is 2 mA, and a diode (D1) keeps a +24 V fault on the line out of the 555. 8. **The brake FETs short each phase to GND**, driven from ARM by a 74HCT14 on the cartridge board (section 3.3). The plan's common star floats: the FETs' gate drive would be referred to wherever the ESC's phase-sense dividers held the star, and they could stay off. Phases to GND is what AM32's own brake does. 9. **No CAN terminator on the boards**: the Feather M4 CAN has its own 120 R between H and L (Adafruit); a second one would leave the bus at 60 R at one end. 10. **From the part-by-part review (D47):** the trip latch is set-only (its D tied high, clocked by GATE_2 AND the window), where the plan's D = window would have let the next slower ball clear a trip; the Feather reads PULSE and ARM through 100 k, so a firmware fault cannot raise ARM; the one-shots are the CD74HC423E, which a rising reset never triggers, with an MCP120 supervisor making the power-up reset (a 10 ms RC edge is far too slow for HC inputs); each brake FET has 100 nF from gate to source (the ESC's phase edges would otherwise lift its gate past threshold) and three inverters share the six gates; PULSE_MON moved to A3 (A4 shares an interrupt line with D10); the Feather's USB pin, the 2815, 12 V FLY, the pendant loop and a reversed supply each got their protection (3.6); AM32's complementary PWM is off, so a slowing wheel never pushes energy into the 12 V rail. ## 1. Connectors and pinouts ### 1.1 TM connector: DT12 (base, -y pad) TE Deutsch DT04-12PA-L012 receptacle on the pan base (`te-dt04-12pa-l012`, W12P wedgelock `te-w12p`, 12 x size-16 pins `te-0460-202-16141`, crimped with the IWISS IWD-1620); the mating DT06-12SA plug with its W12S wedge and sockets on the stand's harness (`te-dt06-12sa-kit`). Size-16 contacts, 13 A each. | Pin | Signal | Wire | |---|---|---| | 1, 2 | +24 V | paralleled, 18 AWG PTFE each, from the stand's fuse and switch | | 3, 4 | GND | paralleled, 18 AWG each | | 5, 6 | CAN_H, CAN_L | 24 AWG twisted pair; terminated by the Feather's own 120 R on the turret and the USB-CAN's on the stand | | 7, 8 | SAFETY_A, SAFETY_B | 24 AWG twisted pair: the pendant's dry loop (closed = run) | | 9-12 | spare | | ### 1.2 The slip ring SparkFun ROB-13065 (`sparkfun-rob-13065`: twelve 2 A gold-on-gold circuits, 28 AWG leads 250 mm, Ø22 x 26.5, flange Ø44.5), two circuits in parallel for each power rail, two kept for a camera (D41): | Circuit | Signal | Notes | |---|---|---| | 1, 2 | +24 V (after the base's 5 A fuse) | joined on both boards | | 3, 4 | GND | joined on both boards: the only power return | | 5, 6 | CAN_H, CAN_L | adjacent circuits, twisted on both sides of the ring | | 7, 8 | SAFETY+, SAFETY- | the 1 kHz pulse loop (section 3.1) | | 9 | SERVO_TTL | the half-duplex bus to the pan servo in the base (500 kbit/s across the ring) | | 10 | SIG_GND | the TTL and pulse reference: joined to GND on the base board and on level 2 (a third ground circuit beside 3-4) | | 11, 12 | CAM+, CAM- | kept for a camera; to GND through 100 k on level 2 until then (R22, R23) | Two 2 A circuits in parallel carry the power. The flywheels' **300 ms soft start** keeps the ring at 2.5 A (1.25 A a circuit); a stepped start would be 12 A, so the firmware never steps. 8 shots at 10/s peak at 2.3 A (0.65 A RMS); the game averages well under 2 A (section 5). ### 1.3 The ring's two connectors: Micro-Fit 3.0, 2 x 6 Each end of the ring ends in a Molex Micro-Fit 3.0 dual-row 12-way pair, so the ring is changed by unplugging two connectors: the stator side at the base board, the rotor side at level 2. **The ring's own 28 AWG leads carry the receptacles** (`molex-43025-1200`, with the 26-30 AWG female crimps `molex-43030-0010`, one lead per contact); the boards' 24 AWG tails carry the plugs (`molex-43020-1200`, male crimps `molex-43031-0001`). Pin n = circuit n at both ends; the power pairs (1+2, 3+4) are joined on the boards. ### 1.4 The CT connectors (turret to cartridge): power 2 x 3 and signal 2 x 5 The cartridge brings a 150 mm pigtail with two plugs; the cradle carries the two receptacles on its -y rail (behind the latch) on the harness from the bay. The three Micro-Fit sizes in the turret (2 x 3, 2 x 5, 2 x 6) cannot go into each other's places, and Micro-Fit housings are polarised. Power, Micro-Fit 3.0 2 x 3 (`molex-43025-0600` receptacle on the bay's harness, `molex-43020-0600` plug on the pigtail; 18 AWG crimps `molex-43030-0038` / `molex-43031-0021`; **18 AWG PTFE wire, 1.75 mm over the insulation**: Molex allows 1.85 mm at most, so silicone wire does not fit): | Pin | Signal | Load | |---|---|---| | 1, 2, 3 | +12 V FLY | the two AM32 ESCs and, through an MF-R300 on the cartridge board, the feed servo; 3 contacts x 8.5 A | | 4, 5, 6 | GND | | **No contact of this connector ever carries 24 V**: the only 24 V on the turret is the ring's pair into the bay's levels 0 and 1. A cartridge plugged into anything in this turret sees 12 V at most. Signal, Micro-Fit 3.0 2 x 5 (`molex-43025-1000` / `molex-43020-1000`, 24 AWG crimps `molex-43030-0001` / `molex-43031-0001`, 24 AWG UL1007 wire): | Pin | Signal | Notes | |---|---|---| | 1 | ESC_L | bidirectional DShot300 from the Feather (eRPM telemetry back on the same wire) | | 2 | ESC_R | as above | | 3 | FEED_TTL | the servo bus to the feed servo (ID 3) | | 4 | spare | | | 5 | ARM | the arm chain's output (3.3 V, high = armed); the cartridge's brake driver makes BRAKE from it (section 3.3) | | 6 | +5 V | the gates' emitters and comparator | | 7 | GATE_1 | first chronograph gate (LM393, open collector) | | 8 | GATE_2 | second gate | | 9 | spare | (the hopper-full beam in v1) | | 10 | SIG_GND | | ### 1.5 Small connectors on the turret | Run | From | To | Connector | |---|---|---|---| | Tilt servo (ID 2) | level 0: 12 V MAIN through an MF-R300 in the lead; TTL from the 74AHCT125 on level 2 | STS3215 on the +y arm | its own 3-pin lead (Molex 5264-type), 200 mm extension | | Pan servo (ID 1) | base board: 12 V PAN through its MF-R300; TTL from ring circuit 9 | STS3215 in the base | its own 3-pin lead | | Feed servo (ID 3) | cartridge board: 12 V FLY through its MF-R300; FEED_TTL from CT signal 3 | STS3215 under the dial floor | its own 3-pin lead | | Laser | level 0: 5 V to the laser's +, its - through the 2N7000 (Q1); its gate at 5 V from the bus buffer's second channel on level 2 (U11, from LASER_EN on A5) | Quarton VLM-650-03 LPT on the cradle tab (2.6-6 V, < 35 mA) | 2-pin, 24 AWG, across the tilt loop | | Hall index | level 2 (5 V, GND, PAN_INDEX) | A1120LUA-T in the turntable's underside, C23 100 nF across its VCC and GND at the sensor | 3 x 24 AWG up the Ø2.8 hole beside it | ## 2. Conductors Lengths from the CAD's points (cad/turret.py: the DT pad, the base board's wall, the ring, the bay on the -y arm at z 71-128, the cradle's rail, the cartridge board at z 63 over the cage); cut each wire 20 % long and trim at the connector. | # | Run | Conductors | Gauge | Length | Strain relief | |---|---|---|---|---|---| | C1 | stand: XT60E-M -> rocker -> 5 A fuse -> terminal board -> DT06 plug pins 1-4 | 2 + 2 | 18 AWG PTFE | 250 mm | the DT06's backshell | | C1b | stand: the pendant socket (TB3M mini-XLR, pins 1-2) -> DT06 pins 7-8; USB-CAN H/L -> pins 5-6 | 2 pairs | 24 AWG twisted | 250 mm | same | | C2 | base: DT04 pins 1-2 -> **5 A MINI in-line holder** -> base board (D8 across +24 V and GND at its input pads); pins 3-4 -> base board; 5-6 (CAN) -> base board; 7 <- base board's 12 V PAN through F4 (in line); 8 -> the 555's VCC | 4 + 4 | 18 / 24 AWG | 120 mm round the housing | a tie to the housing at 60 mm | | C3 | base board -> the ring's stator plug (the ring's own 250 mm leads, 28 AWG, end in their receptacle) | 12 | 24 AWG tails | 60 mm | a tie at the board | | C4 | the ring's rotor leads -> level 2 (up the Ø40 bore beside the coupling, through the driver's crescent, the yoke's slot and the -y arm's window) | 12 | 28 AWG (the ring's) | 160 mm | tied to the driver's crescent | | C5 | level 0/1 -> CT power receptacle on the cradle's -y rail (through the 40 mm tilt loop) | 6 | 18 AWG PTFE | 220 mm | a tie at the yoke arm, one at the cradle rail | | C6 | level 1/2 -> CT signal receptacle | 10 | 24 AWG | 220 mm | same | | C7 | cartridge pigtail: the two plugs -> the cartridge board's pads (power GND 4-6 and SIG_GND 10 join on its ground bus) | 6 + 10 | 18 / 24 AWG | 150 mm | a tie at the cartridge's base plate | | C7b | cartridge board's pads -> each ESC's + and - leads (12 V FLY, GND) and signal lead (through R55 / R56) | 2 x (2 + 1) | 18 AWG / 24 AWG | 40 mm | a tie at the cage plate | | C8 | level 0/2 -> tilt servo on the +y arm | 3 | its own lead + 200 mm | | ties on the bridge | | C9 | level 0 -> laser on the cradle tab | 2 | 24 AWG | 250 mm in the tilt loop | a tie at the cradle tab | | C10 | hall -> level 2 | 3 | 24 AWG | 90 mm | the pocket's hole | | C11 | cartridge board -> each motor's three phases (the ESC's motor pads, the FETs' drains) | 3 + 3 | 18 AWG (the motor's own leads to the ESC; 22 AWG taps to the FETs) | 60 mm | a tie at the lead slot | | C12 | cartridge board -> the two gates (TSAL4400 and TEFT4300 in the barrel's bosses) | 4 + 4 | 24 AWG | 120 mm | a tie at the barrel socket | | C13 | level 0 <-> level 1 <-> level 2 (inside the bay) | from the rotor plug on level 2 down: +24 V and GND to levels 1 and 0, SAFETY+/- to the opto (level 1); 12 V MAIN up from level 0 to level 1; 5 V from level 1 up to level 2 and down to level 0 (the laser); 3.3 V from the Feather down to level 1; PULSE (through R50), Q_A, Q_B, BUS_V up to level 2; ARM, GATE_1 and /CLR_PU down to level 1; LASER_5V down to level 0 | 18 AWG (power) / 24 AWG | 30 mm each | along the standoffs | Twisted pairs: CAN, SAFETY, the gates' signals with SIG_GND. Ring circuit 10 (SIG_GND) joins GND on the base board and on level 2: a third ground circuit beside 3-4, for the TTL and pulse references. 5 mm clearance from anything that moves at every pose (the clash sweep checks the Ø7.5 bundle the CAD draws for the ring's rotor leads). **The +24 V path, end to end** (the acceptance trace): the 24 V supply -> the stand's XT60E-M -> the rocker -> the 5 A time-lag fuse -> the terminal board -> DT06 pins 1-2 -> DT04 pins 1-2 -> the 5 A MINI in-line fuse -> the base board (D36V50F12 for 12 V PAN; the rest straight on) -> the ring's stator plug pins 1-2 -> ring circuits 1-2 -> the rotor plug pins 1-2 on level 2 -> the bank on level 1 -> (a) the D24V150F12 on level 0 -> 12 V MAIN -> the Pololu 2815 on level 1 (ON = ARM) -> 12 V FLY -> CT power pins 1-3 -> the pigtail -> each AM32 ESC's + -> its three phases -> the motor; (b) the D36V28F5 on level 1 -> 5 V. Nothing on the cartridge connects to anything upstream of the D24V150F12. ## 2.1 Crimps, by connector | Connector | Housing | Contacts | Wire | |---|---|---|---| | DT12 receptacle (base) | DT04-12PA-L012 + W12P | 12 x 0460-202-16141 (size 16) | 18 AWG (power), 24 AWG (signals) | | Ring, ring side (x 2) | 43025-1200 receptacle | 12 x 43030-0010 (26-30 AWG) | the ring's 28 AWG leads | | Ring, board side (x 2) | 43020-1200 plug | 12 x 43031-0001 (20-24 AWG) | 24 AWG tails | | CT power, bay side | 43025-0600 receptacle | 6 x 43030-0038 (18 AWG) | 18 AWG PTFE | | CT power, pigtail | 43020-0600 plug | 6 x 43031-0021 (18 AWG) | 18 AWG PTFE | | CT signal, bay side | 43025-1000 receptacle | 10 x 43030-0001 | 24 AWG | | CT signal, pigtail | 43020-1000 plug | 10 x 43031-0001 | 24 AWG | The open-barrel Micro-Fit crimps go on with the ratcheting crimper (`tool-microfit-crimper`, 18-28 AWG; it is not a Molex tool: test one crimp of each wire size with a pull first); the DT contacts with the IWD-1620. ## 3. The arm chain (no microcontroller in it) Every part below has a designator; `exports/turret/wiring/parts.md` lists them board by board with their values, their catalogue keys and where each pin goes (generated by `cad/turret_boards.py`, which also lays the boards out). The logic that decides ARM runs on **3.3 V** from the Feather's 3V pin (U7, U9, U10, U14 and the pull-ups), so every signal the Feather reads is a 3.3 V signal; the bus buffer, the brake driver and the gates' comparator run on 5 V. The design was reviewed part by part against the datasheets before anything was soldered (D47; the review's fixes are in this section). ### 3.1 Safety pulses across the ring ``` BASE (base board) RING TURRET (level 1) (level 2) 12 V PAN ─ F4 MF-R010 ─> DT12 7 ─ pendant (dry loop) ─ DT12 8 ─> U1 NE555 VCC (C3 1 uF) U1 astable: R1 1.0 k, R2 6.8 k, C1 100 nF film -> 986 Hz U1 out ─ D1 1N4148 ─> R3 2k2 1 W ─> circ 7 SAFETY+ ─> R8 2k2 1 W ─> U6 4N35 LED (D2 reversed across it) base GND <─ circ 8 SAFETY- <──────────────── U6 LED cathode U6 transistor: PULSE (R9 39 k to 3.3 V) ─ R50 100 k ─> Feather A3 (PULSE_MON) PULSE ─> U7 1A: one-shot A (CD74HC423E), retriggerable 18.5 ms (R10 39 k, C6 1 uF) U7 1Q = Q_A ─────────────────────> U10 74HC08: ARM = Q_A AND /TRIP │ U4 Pololu 2815 ON (> 1 V = on; ITS SLIDE SWITCH OFF, glued) <──────────────────────────────┤ 12 V MAIN (D24V150F12) ─> U4 ─> 12 V FLY (CT power 1-3): the ESCs, the feed servo ├─ R53 100 k ─> Feather D12 (ARM_IN) └──> CT signal 5 ─> the brake (3.3) ``` - Pendant released, a loop wire cut, the 555 unpowered or stuck, a ring contact open or shorted to +24 V or to GND, mains hum: no 1 kHz edges, so one-shot A's Q falls within 16-21 ms, ARM falls, the 2815 removes 12 V FLY from the ESCs and the feed servo, and the cartridge's brake shorts the motors' phases 5-14 ms later. The MCU, the pan and tilt servos, the laser supply and the gates stay powered, so the turret reports what happened. - The LED current: the 555 runs on the pendant loop's 12 V, so its output is ~10.6 V high and the loop carries (10.6 - 0.7 - 1.15) / 4.4 k = **2 mA**. The 4N35's saturated transfer ratio at 2 mA is about 0.45 of its 10 mA value (Vishay fig. 2), so a minimum part sinks about 0.9 mA at 25 C and 0.36 mA at its temperature extremes, against the 0.085 mA that R9 (39 k) needs. A +24 V fault on SAFETY+ drives a steady 10 mA through R8 and the LED (no edges: released) and cannot reach the 555 (D1 blocks it); SAFETY+ to GND stops the LED; D2 keeps any reverse voltage off the LED. The 555's 1 uF holds it up for about 0.5 ms after the pendant opens. F4 (0.1 A) limits a short of the hand-held loop to GND. - **The Feather reads ARM and PULSE but cannot drive them:** each reaches its pin through 100 k (R53, R50). A pin set as an output by a firmware fault moves PULSE (39 k to 3.3 V) only to 2.7 V and ARM by millivolts, so it can neither retrigger one-shot A nor turn the 2815 on (> 1 V). Its own conditions sit on top (ARM_IN high, a CAN heartbeat no older than 200 ms, the 1 kHz train on PULSE_MON) and only ever command zero throttle when they fail. - A bouncing ring contact drops a pulse or two (< 1 ms) and the 18.5 ms one-shot rides through it. - One-shot A: t = K x R10 x C6 = 18.5 ms (K = 0.475 at 3.3 V, TI's fig. 5; C6 a 10 % ceramic: 16-21 ms, inside the bench's 25 ms; 18 periods of the train). U7 is the CD74HC423E, not the '123: a rising /R never triggers it, so the power-up reset (3.2) releasing /CLR_PU cannot fire one-shot A while PULSE is low. - **What the hardware does not see:** a retriggerable one-shot only checks that edges keep coming, so a wrong frequency (300 Hz, 3 kHz, 50-60 Hz hum) also holds ARM up. The ring's real faults (open, shorted to GND or +24 V, a DC level, the 555 stopped or unpowered) all stop the edges and are caught in hardware; a wrong-frequency train can only come from a broken 555 or a test generator (hum cannot drive the opto's LED through 2k2). The Feather's PULSE_MON input checks the period (0.85-1.15 ms, 870-1,176 Hz; the 555 is 986 Hz, about +-9 % worst case) and zeroes the throttle and refuses to feed within 1-6 ms of a wrong train (firmware/turret; bench test 3.2). A hardware frequency window (a 74HC221 pair: too fast and too slow) is a v1 item. ### 3.2 The overspeed trip: a set-only latch ``` GATE_1 (U13 LM393, high while the beam is cut; R17 1 k to 3.3 V) ─> U7 2B: one-shot B, t = K x R11 x C7 = 3.01 ms U7 2Q = Q_B ─┐ GATE_2 (R18 1 k to 3.3 V) ─────────────────────────────────────────────> U10 gate 2: TRIP_CLK = GATE_2 AND Q_B └─> U9 74HC74 CLK, D = 3.3 V U9 Q = TRIP ─> Feather A1 (polled); U9 /Q = /TRIP ─> U10 gate 1 (3.1) /CLR_PU: U14 MCP120 (open drain, low until the 3.3 V is up), R12 10 k to 3.3 V, SW1 RESET (recessed) to GND ─> U9 /CLR and U7 1/R ``` A ball that reaches gate 2 while the 3.0 ms window from gate 1 is still open is faster than 66 fps: TRIP_CLK rises, the flip-flop clocks its D (tied high) and TRIP latches; ARM falls exactly as for a released loop. Its D is tied high and its clock only runs while the window is open, so no later edge can clear it (a slower ball, a finger in the barrel, a reseated plug): only the recessed button or a power cycle does. U14 holds /CLR_PU low at power-up until the 3.3 V is up, then lets it rise in one clean edge (the HC inputs want edges under 1 us, which a 10 ms RC is not). The window: C7 = 100 nF film 5 %, R11 = 63.4 k 1 % to start (K = 0.475 at 3.3 V: 3.01 ms); K varies part to part, so bench test 3.3 sets the final R11 by selection from 60.4 / 63.4 / 66.5 / 69.8 / 73.2 k (all in the parts list), never a trimmer. The gates' 1 k pull-ups give the latch's clock (no Schmitt input) edges well under 1 us. The Feather times both gates too and logs every shot's speed; it refuses to feed after any ball over 66 fps on its own. It reads GATE_1, GATE_2 and TRIP directly: driving them could only set the latch, never clear it. ### 3.3 The phase-short brake (on the cartridge board) ``` ARM (CT signal 5) ─┬─ R24 100 k to GND (a pulled plug reads as released) ├─ R25 6.8 k ──────────────┬─ BRK_RC ─ C15 1 uF to GND └─ D3 1N4148 ─ R26 1 k ────┘ │ U12 74HCT14 (5 V): three inverters in parallel, each driving two gates 1Y ─ R27, R28 1 k ─> Q2, Q3; 2Y ─ R29, R30 ─> Q4, Q5; 3Y ─ R31, R32 ─> Q6, Q7 each gate: 100 k (R33-R38) and 100 nF (C17-C22) to GND Q2-Q4 (right motor), Q5-Q7 (left): IRLZ44N, drain to a phase, source to GND (the cartridge's power GND) ``` Six IRLZ44N (`infineon-irlz44npbf`), one from each phase of each motor **to GND**. Shorting all three phases to GND brakes the motor exactly as shorting them together does (the winding's neutral is free), and it is what AM32 itself does on a stop (`brake_on_stop`), so the two never fight; with the sources at GND the gates see 4.95 V (the 100 k pull-downs take nothing). Each gate has 100 nF to its source, right at the FET's legs: while the ESC runs, every 0-12 V phase edge pushes the FET's gate-drain charge into its gate, which through 1 k alone would lift it 2-3 V, past the 1-2 V threshold; with 100 nF the kick is under 0.1 V. Three inverters share the six gates (two each): an output starts at 10 mA, inside the 74HCT14's 25 mA. BRAKE = NOT BRK_RC: when ARM falls, C15 empties through R25 and BRAKE rises when BRK_RC crosses the 74HCT14's lower threshold, **6.8 ms x ln(3.3 / V_T-) = 5-14 ms (about 8 ms) after ARM**; by then the 2815 has cut the ESCs and the Feather has commanded zero throttle. When ARM rises, D3 and R26 fill C15 (tau 0.9 ms) and the short opens 0.6-1.4 ms later, long before the ESCs can drive (AM32 arms only after 0.5 s of zero throttle). The 74HCT14's TTL thresholds read the 3.3 V ARM correctly on 5 V. The motor's own back-EMF drives the braking current: through the motor's 117 mOhm, two FETs (25 mOhm each at 5 V on the gate) and the taps, tau 10.2 ms at low speed; the winding's inductance (not published; 35 uH est) limits it at full speed, so the wheels reach 5 % speed **40-57 ms** after release (48 ms at 35 uH) and are stopped (< 0.1 %) by the 96 ms when the first ball still in the chute could arrive (docs/turret-physics.md section 5). The peak braking current is 13-58 A for a few ms; at a 5 V gate the IRLZ44N's channel carries about 60 A (its fig. 1), so the 58 A of the zero-inductance case is at its limit and the estimated 21 A is well inside. The FETs' tabs are the motor phases: they stand apart, never on a shared heatsink. ### 3.4 The chronograph gates Each gate: a TSAL4400 940 nm emitter (D4, D5) on 5 V through 100 R (R39, R40: ~37 mA) in one side of the barrel's gate boss, a TEFT4300 phototransistor (Q8, Q9) with a 10 k pull-up (R41, R42) in the other, the 1 x 2 mm slit between them (cad/turret.py `GATES`). The beam holds the phototransistor on (its collector low); a ball cutting it lets the collector rise. U13 (LM393, one package for both gates, on 5 V) compares each collector (through 10 k, R43/R44) with 2.5 V (R45/R46), with 100 k from each output back to its input (R47/R48: 0.3 V of hysteresis). Its open-collector outputs are GATE_1 and GATE_2, high while the beam is cut, pulled up to 3.3 V on level 2 (R17, R18, 1 k) for the Feather (D9, D10), one-shot B and the trip's clock. The light through the slits is not confirmed (the TEFT4300 gives at least 0.8 mA at 1 mW/cm^2, and the TSAL4400 gives about 0.85 mW/cm^2 at the gate's 26.5 mm before the slits): bench test 3.10 reads each collector, under 1 V with the beam clear and over 4 V when cut; if the clear level stays over 1 V, R41/R42 go to 39 k (in the parts list). A ball cuts a 1 mm beam in 47-60 us: well inside the comparator's microsecond response. ### 3.5 The signals into the Feather Nothing above 3.3 V reaches a Feather pin. ARM_IN (D12) and PULSE_MON (A3) come through 100 k (3.1); GATE_1 (D9), GATE_2 (D10) and TRIP_IN (A1) come straight from 3.3 V logic or 3.3 V pull-ups; PAN_INDEX (D11) is the hall's open drain with R19 10 k to 3.3 V; BUS_V (A0) is +24 V through 91 k / 10 k (2.4 V at 24 V, 2.6 V at 26 V: R20, R21, C13 on level 1). The Feather's own pull-ups and pull-downs stay off on all of them. **Interrupts:** the SAMD51 has one external-interrupt line per number, shared between pins: D10 and A4 are both EXTINT 4, A1 and D11 both EXTINT 5. So PULSE_MON is on A3 (EXTINT 9), not A4, and TRIP_IN is polled (it is a latch); the gates (EXTINT 3, 4), the index (5) and ARM_IN (6) keep their interrupts. The servo bus (5 V, R14 4.7 k pull-up) comes back to RX (D0) through D6, a BAT85 Schottky with its anode at RX and R16 10 k from RX to 3.3 V: the bus pulls RX down to about 0.5 V when it is low, and a high bus, whether a servo drives it to 3.3 V or the pull-up holds it at 5 V, leaves RX at 3.3 V. The buffer (U11, 74AHCT125 on 5 V) takes the Feather's 3.3 V TX on its TTL input; its /OE (SERVO_DIR, D4) has R13 10 k to 3.3 V, so the bus is released until the firmware drives it. The laser's 2N7000 needs more than the Feather's 3.3 V on its gate (its threshold is up to 3 V), so LASER_EN (A5, R49 100 k to GND) goes through U11's second buffer and reaches Q1 at 5 V. LASER_EN is not D13: that pin also lights the Feather's red LED, which the bootloader pulses on a reset. **The Feather's USB pin is its USB-C port's VBUS.** The turret's 5 V reaches it through D7 (a 1N5817 in line, anode at the 5 V), so a laptop on the USB-C port and the turret's 5 V never feed each other. CAN uses the Feather's own 120 R (its Trm jumper left closed): no other terminator on the turret; the USB-CAN adapter terminates the stand's end (its terminator switched on). ### 3.6 Protection around the switched rail - **The 2815** (Pololu: "do not use this switch as an emergency cutoff"; the robot's radio stop cuts the head rail upstream as well). Pololu's own advice for switching large currents is followed: a TVS across its input (D9, P6KE15A on 12 V MAIN) and a Schottky across its output (D10, 1N5822 on 12 V FLY), both on level 0. Its slide switch is set to OFF and glued there (it sits under level 2, out of sight); the release check (12 V FLY off when the pendant is let go) opens every session (bench test 3.2). - **No energy back into the 12 V rails.** With complementary PWM a slowing ESC pushes the wheels' energy back into its supply (3 J a wheel at 8,855 rpm: 0.3 J into the rail's ~1 mF would lift 12 V to 27 V), and the D24V150F12 is a buck that cannot take it. So AM32's complementary PWM is off (firmware/turret/am32_settings.md): a slowing wheel coasts or brakes in its own windings, never into the rail, and the firmware slows the wheels only through zero throttle (brake on stop) or a slow ramp. D11 (P6KE15A across 12 V FLY at the cartridge's pads) catches what is left. - **Signals into unpowered parts.** With 12 V FLY off, the feed servo and the ESCs are unpowered while their signal lines may still be high: R55-R57 (1 k in ESC_L, ESC_R and FEED_TTL on the cartridge board) limit what reaches their inputs, and the firmware holds the DShot pins low while ARM_IN is low. - **A reversed supply:** D8 (1N5822 across +24 V and GND right after the in-line 5 A fuse) conducts and the fuse blows; the regulators have their own reverse protection, the 2 x 1000 uF bank has none. - **The cartridge's plugs** go in and out only with the stand's rocker off: a pulled signal plug floats both gates high together and takes the brake driver's 5 V with it. ## 4. Power rails and protection | Rail | Where | Source | Feeds | Protection | |---|---|---|---|---| | +24 V in | base | DT12 1-2 | everything | **5 A MINI** (`littelfuse-0297005-wxnv`) in the in-line holder (`littelfuse-0fhm0001zxj`) in the lead to the base board; D8 (1N5822) after it for a reversed supply | | 12 V PAN | base board | D36V50F12 (`pololu-d36v50f12-4095`) | the pan STS3215; the 555 through the pendant loop | MF-R300 (`bourns-mf-r300`) to the servo; F4 MF-R010 (0.1 A) to the pendant loop | | +24 V ring | turret | ring circuits 1-2 | the bank, the D24V150F12, the D36V28F5 | (the base's 5 A) | | 12 V MAIN | level 0 | D24V150F12 (`pololu-d24v150f12-2885`), always on | the tilt STS3215; the 2815 | MF-R300 in the tilt servo's lead; D9 TVS (P6KE15A) | | 12 V FLY | level 1 | the Pololu 2815 (`pololu-2815`) switching 12 V MAIN, ON = ARM | the two AM32 ESCs; the feed STS3215 | MF-R300 on the cartridge board for the feed servo; D10 Schottky (1N5822, level 0), D11 TVS (P6KE15A, cartridge); no regeneration (AM32 complementary PWM off, 3.6) | | 5 V | level 1 | D36V28F5 (`pololu-d36v28f5-3782`) | the Feather (its USB pin, through D7), the bus buffer, the cartridge (brake driver, gates), the hall, the laser | MF-R250 (`bourns-mf-r250`) in line | | 3.3 V | level 2 | the Feather's own regulator (3V pin, 500 mA peak) | the arm chain's logic (U7, U9, U10, U14) and every pull-up the Feather reads: under 5 mA | (the Feather's) | | Bank | level 1 | 2 x 1000 uF 35 V low ESR (`panasonic-eeu-fr1v102`) across the ring's +24 V | rides a 2 ms contact bounce | | Every fuse is DC-rated (MINI blades: 32 VDC). The regulators have their own reverse-voltage protection; the bank does not, so D8 turns a reversed supply into a blown fuse. The 5 A fuse is for shorts: a sustained 4-6 A, over the ring's two 2 A circuits, is the firmware's to prevent (the soft start, the current budget). The bench supply (Mean Well LRS-350-24) has no current limit as such: its overload protection is hiccup mode at 110-140 % of its rated power. ## 5. Current budget (24 V side, at the ring) From the physics' power model with the X2216 (docs/turret-physics.md section 9, 60 mOhm ring): | Case | Ring peak | RMS over 1 s | Notes | |---|---|---|---| | Flywheel spin-up, 300 ms soft start (the firmware's) | 2.5 A | | 95 % speed in 0.285 s | | Flywheel spin-up, 200 ms | 3.6 A | | not used: 1.8 A a circuit is too close to 2 A | | Flywheel spin-up, stepped at the AM32 10 A limit (never) | 12.0 A | | | | 8 shots at 10/s | 2.3 A | 0.65 A | the X2216 loses 1.3 % a shot | | Feed servo step, tilt servo move | ~0.8 A each | | 12 V servos at the firmware's torque limit | | MCU, logic, gates, laser, the D24V150F12's own 0.1 A at no load | 0.25 A | | | | **Game average** | | **<= 1.5 A** | inside the ring's 4 A (two 2 A circuits) and the 5 A fuse | ## 6. The boards, part by part `cad/turret_boards.py` lays every board out on its 0.1 in grid and checks each part against the board's edges, its standoff holes, the other parts and the height its level allows (`exports/turret/wiring/boards.json`; none fails). The pictures show the components side; wire on the back. Each part's footprint includes its leads. | Board | Picture | Parts | |---|---|---| | Base board, 50.8 x 30, on the base's +x wall | ![base](../exports/turret/wiring/board-base.png) | D36V50F12 (12 V PAN), the NE555 on the pendant loop's 12 V with its R1, R2, C1-C3, D1 and R3 (the 1 kHz pulses), MF-R300 (pan servo), the pan servo's 3-pin, the ring plug's tails, CAN through; D8 and F4 in the harness beside it | | Bay level 0, 52 x 50 | ![level 0](../exports/turret/wiring/board-level0.png) | D24V150F12 (12 V MAIN, always on), the 2N7000 laser switch with R6, R7, the 2815's TVS (D9) and Schottky (D10), the 12 V and 24 V pads | | Bay level 1, 52 x 50, on 12 mm standoffs | ![level 1](../exports/turret/wiring/board-level1.png) | Pololu 2815 (slide switch OFF, glued), D36V28F5 (5 V), 2 x 1000 uF, the 4N35 with R8, D2, R9 and R50, the CD74HC423E (both one-shots, on 3.3 V) with R10, R11, C6-C8, the BUS_V divider | | Bay level 2, 52 x 50, on 14 mm standoffs | ![level 2](../exports/turret/wiring/board-level2.png) | Feather M4 CAN, 74HC74 (the set-only trip latch) and 74HC08 (ARM, the trip's clock) on 3.3 V, the MCP120 power-up reset, 74AHCT125 (servo bus, laser gate) on 5 V, the recessed RESET, the pull-ups, R53 and the RX diode | | Cartridge board, 50 x 44, on four posts over the cage | ![cartridge](../exports/turret/wiring/board-cartridge.png) | 6 x IRLZ44N in a row along the front edge (phases to GND, 100 nF and 100 k at each gate), the 74HCT14 brake driver (three inverters, two gates each) and its RC, LM393 (gates), MF-R300 (feed servo), D11 (TVS), R55-R57 in the ESC and feed signals, the gates' resistors, the pigtail's pads; the two ESCs lie on the cage plate under it | | Stand terminal board, 70 x 50 | ![stand](../exports/turret/wiring/board-stand.png) | the 24 V, pendant and CAN junctions to the DT06 plug | The perfboard is SparkFun's PRT-08619 (80 x 100 mm, plated through; one board cuts into two 52 x 50 pieces). Drill the corner holes to Ø3.2 at the standoff pattern (46 x 44 on the bay's boards). The Feather goes in on its two header rows, USB towards the bay's open face; nothing on level 2 stands taller than 8.5 mm. ## 7. Building the electrics, in order 1. The stand's harness (C1, C1b) and the DT06 plug; continuity and polarity at the plug before the turret is fitted. 2. The base: the DT04 with C2 and the in-line fuse; the base board; the ring's stator plug. With the turret off the stand, bench test 3.1 on the base alone: 12 V PAN present, the 555 at 1 kHz only while the pendant is held. 3. The bay: level 0, then 1, then 2, each tested before the next goes on (the regulators' outputs with no load; then the 2815's ON from a lamp with its slide switch OFF; then glue the slide switch in OFF). 4. The ring's rotor plug, the hall, the tilt servo and the laser; then the CT receptacles on the cradle. 5. The cartridge board and its pigtail, on the bench with the cartridge off the turret: the brake FETs to the phase leads, the gates, the feed servo. 6. Then docs/turret-bench-tests.md section 3 (the electrics without motors): the pulse train's fault list, the trip window, the brake timing with a lamp. Rules for every session: the CT plugs go in and out only with the rocker off; the Feather is programmed over its USB-C port with the turret powered or not (D7 keeps the laptop and the turret's 5 V apart); the release check (12 V FLY off when the pendant is let go) opens the session.