MODULE 27 / PHYSICAL WORKSHOP
Build the harness
Turn a verified electrical design into labeled, inspected cable assemblies. Separate motor power, regulated compute power and communications, then check routing and continuity with the system de-energized.
By the end, you can…
- Build and inspect a cable against a pin-to-pin wiring schedule.
- Explain power distribution, CAN topology and termination.
- Complete unpowered verification before commissioning.
Completed electrical design and component datasheets
Accessible mechanical assembly
- 1Energy source
- 2Protection & isolation
- 3Power distribution
- 4Actuators / regulated logic
Select voltage, current ratings, wire, connectors and protective devices as one system. A high-current motor supply and logic supply have different requirements.
A harness is a built electrical design
Download wiring-schedule.csv and joint-map.csv from the build-files hub. A wire color alone is not a connection definition. Each cable needs named endpoints, connector orientation, pin numbers, signal/power function, conductor specification and a test result. View connector drawings from the stated mating or wire-entry side; those views can appear mirrored.
Before making cables, resolve the actual battery, motor generation, regulators, adapters and sensor carrier. The paper’s BNO055/two-bus setup differs from the audited MTi-3/three-bus backend. This lesson provides fabrication and verification steps, not an interchangeable pinout for those systems.
Keep power paths and signal paths explicit
Draw battery power through the selected protection and isolation hardware to its loads. Show the regulated branch for the computer separately from motor power. Fuse ratings, wire sizes, contacts, switching devices and regulation must be selected for the actual voltage, current, fault conditions and component limits. Do not copy the nominal battery voltage into a computer input.
Have the completed design and protection choices checked by someone competent in DC power wiring before first energization. This is a concrete dependency: a power-tool battery can deliver damaging fault current. The review should resolve the drawing and parts, not merely label them safe. Keep exposed conductors insulated and the battery removed throughout this fabrication lab.
CAN is a network with a physical route
For the usual high-speed CAN physical layer, use the specified twisted signal pair along a bus with termination at its two physical ends. Check which selected devices already contain or enable termination. Adding a resistor at every motor overloads the network. Grounding and shielding follow the chosen adapter/transceiver documentation.
Two 120-ohm end resistors appear as approximately 60 ohms in parallel across CAN_H and CAN_L on an unpowered, correctly configured bus. That measurement is a useful diagnostic only when the expected topology is known. It does not prove pin assignment, signal quality, bitrate or unique motor identity. Never measure resistance on an energized circuit.
Good terminations are inspected before hidden
Use the connector manufacturer’s contacts, conductor range, stripping length and crimp tool/procedure. A terminal can look attached while having damaged strands or poor retention. Inspect the conductor and insulation crimps, perform the specified retention check and confirm the contact locks into the housing. Practice on spare material first.
Route the finished harness away from sharp edges, moving pinch points and hot surfaces. Put strain relief on stationary segments while allowing a deliberate loop at each moving interface. Labels belong at both ends. Keep power disconnected for all connection changes; hot-plugging is permitted only where the actual equipment explicitly supports it.
WORDS YOU NOW KNOW
- Harness
- A grouped, routed set of wires and connectors implementing an electrical design.
- Pinout
- The defined function of each connector contact, with a specified viewing direction.
- Termination
- The electrical load at the ends of a communication bus used to control signal reflections.
YOUR CALL
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Primary references for this module. Use the version and hardware revision named in the lesson.
Selected RobStride hardware documentationAudited BDX-R bus and motor mappingCAN termination measurementCAN implementation and topology