MODULE 26 / PHYSICAL WORKSHOP
Power and communication
Understand power rails, connector details and CAN as a system. Build an electrical worksheet while the exact BDX-R hardware configuration is reconciled.
By the end, you can…
- Separate power and signal paths
- Read a CAN topology and bus map
- Create a power budget with explicit unknowns
Actuators and sensors
Manufacturing and 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.
Energy and information follow different paths
A battery supplies energy. Distribution, protection and switching route it to motor drives and regulated computer/sensor rails. The computer sends information over communication links. A CAN message does not supply the mechanical power that moves a leg. Drawing those paths separately helps you understand the architecture.
Voltage is electrical potential difference, current is charge flow, and simple DC power is voltage times current. A 12 V load drawing 2 A consumes 24 W. A converter delivering that load from a higher voltage draws a different input current and loses some energy as heat. Wiring and protection also depend on transient and fault conditions, not just average watts.
DC power [W] = voltage [V] × current [A]A battery label is not a rail specification
Record chemistry, nominal and fully charged voltage, permitted discharge current, protection behavior, connector and charger. Do not infer these from a “40 V” product label. Compare the full voltage range with every device on the rail. Motor drives can return energy while decelerating, so the source and protection design must account for regeneration according to the exact hardware documentation.
Give each regulated rail its own row: voltage, continuous/transient current, regulator input range, thermal conditions and grounding/isolation requirements. A computer reboot during motor movement may be a supply problem. Later voltage measurements under controlled load are more informative than a no-load reading alone.
CAN is a shared differential bus
High-speed CAN signals use CAN_H and CAN_L. Termination belongs at the physical ends under the transceiver/cable design. Two ordinary 120-ohm end resistors give an ideal parallel resistance of 60 ohms. That is a topology calculation, not a universal diagnostic for every connected circuit. Resistance measurements require power removed and the exact circuit understood.
A name such as can0 identifies an operating-system interface; a motor ID is a device/protocol address on a bus. Linux SocketCAN exposes CAN through network interfaces. A USB adapter that appears as a serial port is not automatically interchangeable. Verify driver, mode, bitrate, protocol, termination and electrical interface together.
Match the actual hardware generation
The early BDX-R paper used a BNO055 and two USB-to-CAN adapters. Later code expects an MTi-3 serial setup and three CAN interfaces with fourteen mapped motors. The full design includes two ear actuators. Exact sensor board, adapter variants and power details still need verification; an old pinout does not resolve them.
A connector specification includes mating halves, contacts, wire range, pin numbering and ratings. Draw its viewing direction: a mating-face view can mirror a wire-entry view. Add strain relief and service loops that accommodate motion. A clear harness record preserves electrical and mechanical behavior as the robot moves.
WORDS YOU NOW KNOW
- Rail
- A supply line with specified voltage and electrical capability.
- Regeneration
- Mechanical energy converted back to electrical energy.
- Termination
- A network at bus ends used to control reflections.
YOUR CALL
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Primary references for this module. Use the version and hardware revision named in the lesson.
Linux SocketCANTI CAN physical-layer fundamentalsPinned hardware backendRobStride official information