Project files

Assembly Guide — Hsiwu

This guide covers the complete assembly process for the Hsiwu bionic bat robot, from manufacturing the parts to a fully operational flapping-wing system.

Preparation

Required Tools

• Soldering iron (temperature-controlled, fine tip)
• Solder (lead-free or 63/37 SnPb, 0.5–0.8 mm diameter)
• Desoldering braid / desoldering pump
• Tweezers (pointed, anti-magnetic)
• Flux pen (no-clean type)
• Digital multimeter (DMM)
• Oscilloscope (optional but recommended — Tektronix TDS1001B-SC or equivalent)
• Hex drivers: 1.5 mm, 2.0 mm
• Small Phillips screwdrivers (#00, #0)
• Needle-nose pliers
• Diagonal cutters
• Third-hand tool / PCB holder
• Isopropyl alcohol (99%) + brush (for cleaning PCBs)
• FDM 3D printer (if printing parts yourself)
• Digital caliper

Required Materials

• Finished PCB (from the Gerber files in electronics/output/gerber/)
• All components listed in the BOM (BOM/PCB_Base_BOM.xlsx)
• 3D-printed structural parts (STEP files located at mechanical/output/3dp/)
• Laser-cut or 3D-printed linkages
• M2/M3 screws and lock nuts
• 3.7V lithium battery (single cell)
• Motor wire (AWG 26–28 stranded)
• Double-sided foam tape (for securing the battery)

Step 1: PCB Assembly

1.1 Inspection

Inspect the bare board before soldering:

• No visible shorts between adjacent traces (check with a magnifier)
• All pads are intact and undamaged
• Silkscreen is clear and legible (reference designators match the BOM)
• Board outline matches the mechanical frame profile

1.2 Soldering Order

Solder in order from smallest to largest and from low thermal mass to high thermal mass:

1. 0805 resistors (R1–R11) — ceramic, heat-tolerant
2. 0805 capacitors (C1–C2, C4, C6, C8) — MLCC small capacitors
3. 0805 LED (LED1) — mind the polarity (cathode marking)
4. SOT-23-6 (U4, MT3608) — fine pitch, use flux
5. SOIC-8 (U6, U7, U8 — L293D) — align the pin 1 marking
6. SOIC-14 (U5 — 74HC04) — align the pin 1 marking
7. SOP-20 (U1, U2, U3 — NE555 carrier board) — use the drag-soldering method
8. SMC diode (D1) — mind the polarity (the colored band is the cathode)
9. SMD inductor (L1) — high thermal mass, preheat the pads
10. SMD electrolytic capacitors (C3, C5, C7) — mind the polarity
11. Through-hole switch (SW2) — solder from the bottom side
12. XH-2A connectors (U9 × 3) — make sure they sit flat against the board
13. Battery connector — solder the wire leads and add strain relief

1.3 Soldering Techniques

0805 passive components:

1. Tin one pad
2. Hold the component with tweezers and reflow the tinned pad
3. Solder the other pad
4. Reflow the first pad so it is shiny and neat

SOIC/SOP chips:

1. Align pin 1 (dot/notch marker) with the silkscreen marker
2. Tack-solder two diagonally opposite pins to hold the chip in place
3. Apply flux to all pins
4. Drag-solder along each row of pins
5. Use solder wick to remove solder bridges

1.4 Post-Soldering Inspection

• Visually inspect all solder joints (shiny, concave fillets, no solder bridges)
• Continuity test: no short circuit between power rails and ground
  • Multimeter continuity mode: probes between VCC and GND — should read open circuit
• Diode test: D1 cathode→anode should read open circuit (multimeter diode mode)

Step 2: PCB Power-On Test

Before connecting the motors, confirm the power supply is working:

1. Preparation — Place the PCB on an insulated surface, with the oscilloscope probe ready
2. Check the input — Measure the battery voltage with a multimeter: 3.7–4.2 V
3. Power on — Flip SW2 to ON
4. Confirm the LED — LED1 should light green
5. Measure each voltage rail:
   • 5 V rail: between the VCC and GND of any IC → 5.0 V ± 0.25 V
   • 7.35 V rail: between L293D pin 8 (VCC2) and GND → 7.35 V ± 0.5 V
6. Check the oscillation (oscilloscope):
   • Connect the probe to the NE555 output pin (pin 3 of U1/U2/U3)
   • You should see a ~4.8 Hz square wave, from 0 V to ~5 V
   • Check all three channels
7. Verify phase inversion (dual-channel oscilloscope):
   • Channel 1: NE555 OUT
   • Channel 2: the corresponding /OUT of the 74HC04
   • The two should be complementary (when one is HIGH, the other is LOW)

If any check fails: Cut the power immediately and debug. Common problems:

• No 5 V: check the LDO, C2, C4
• No 7.35 V: check the MT3608 feedback resistors, L1, D1
• No oscillation: check the RC network and the trimmer potentiometer position
• Wrong phase: check the 74HC04 pin connections

Step 3: Mechanical Assembly

3.1 3D Printed Parts List

3.2 Linkage Inventory

3.3 Fastener List

3.4 Assembly Order

3.4.1 Frame Subassembly

1. Press the bearings into center_bearing_cap and head_bearing_cover
2. Attach head_support to central_support with M2 × 10 mm screws
3. Attach tail_bracket to central_support with M2 × 10 mm screws
4. Install lead_screw together with the bearings and end caps
5. Install head_drive_shaft
6. Insert head_pin and tail_pin into the pivot seats

3.4.2 Motor Installation

1. Install the three coreless cup motors onto the motor mounts of central_support (M2 × 12 mm)
2. Connect 2-to-3_coupling to each motor shaft
3. Verify that each motor shaft rotates freely by hand

3.4.3 Linkage Assembly (Each Wing Section)

1. Mount rod_a (crank) on the motor output shaft → secure with set screw
2. Connect rod_bc (connecting rod) to rod_a with a hinge pin
3. Connect rod_d (rocker) to rod_bc and the wing pivot pin
4. Install rod_h, rod_ij, rod_kf to form the scissor linkage
5. Repeat the above steps for all three sections on each side
6. Assemble the other wing as a mirror image

3.4.4 PCB Installation

1. Place the PCB on the mounting posts of central_support
2. Secure with M2 screws (do not overtighten—FR-4 may crack)
3. Connect the motor wires to the XH-2A connector
4. Manage the wiring with cable ties or small adhesive cable clips

3.4.5 Battery Installation

1. Install the lithium battery on the bottom surface of central_support
2. Secure it with double-sided foam tape and a Velcro strap
3. Connect the battery to the PCB input

Step 4: Final Integration Test

4.1 Pre-Flight Checks

• All screws are tightened (without stripping)
• All linkages move freely through their full range of motion
• No wires interfere with moving parts
• Battery is secured and connected
• PCB is mounted firmly
• All XH-2A connectors are fully inserted

4.2 Power-On Procedure

1. Place the robot on a soft surface (foam pad or towel)
2. Flip SW2 to ON
3. LED1 should light up
4. The wings should begin flapping within about 1 second
5. The three segments on each wing should move in a coordinated wave-like motion

4.3 Tuning

• Wing 1 (leading-edge segment) speed — adjust trimmer potentiometer R4
• Wing 2 (middle segment) speed — adjust trimmer potentiometer R10
• Wing 3 (trailing-edge segment) speed — adjust trimmer potentiometer R11
• Ideal pattern: the leading edge leads slightly and the trailing edge follows, creating the "wave" motion characteristic of a bat

4.4 Common Issues

Step 5: Maintenance

• Bearings: Add one drop of light machine oil every ~10 hours of operation
• Linkage joints: Check for wear every ~5 hours of operation; replace the linkage if play develops
• PCB: If flux residue is attracting dust, clean it with isopropyl alcohol
• Battery: Store at 3.7–3.8 V when not in use
• Motors: Brushes have a limited lifespan; expect to replace them after roughly 50–100 hours of continuous operation

Happy flying! 🦇