Power faults and ESD
Diagnose robot resets, voltage sag, shared servo limits, static discharge, and electrical noise.
When a resets or an stops, record what was happening before changing parts. Driving into a load, moving several , and touching a charged surface can produce different faults with similar symptoms.
First checks
| Symptom | Start here |
|---|---|
| A hub reboots during combined motion | Battery condition, power connections, and under load |
| One actuator stops working | Its cable, port, configuration, and mechanical load |
| Several servos fail together | Their shared supply and port-pair limits |
| A reset follows contact or movement on a dry surface | Check power first, then investigate |
| An analogue reading changes when a runs | supply, ground connection, and cable routing |
Save the logs and note the battery, payload, and action. Repeat only a normal operating movement; do not deliberately motors or overload a supply to reproduce a failure.
Voltage loss
The voltage at the hub can fall as current rises. Some loss occurs inside the battery; more occurs in cables, the switch, and connectors. A poor connection adds resistance to that path.
For example, a 0.03 Ω power path carrying 20 A loses 0.6 V and dissipates 12 W. These are illustrative values. If much of that resistance sits in one damaged terminal, heat is concentrated there.
A battery's internal resistance changes with condition, temperature, and charge. Compare a suspect pack with a known healthy, charged pack under the same normal robot load.
An unloaded voltage reading is only a starting check. Compare voltage at the battery and hub during the movement that causes trouble. A battery voltage that holds up while hub voltage drops points toward the intervening wiring and connections.
Inspect damaged, loose, or hot connections with power disconnected. Stop using a damaged or abnormally hot battery and have a check it. limits cannot make a faulty power connection reliable.
Servo power
Servo current limits apply to the controller's servo supply, not directly to the battery current. On a , ports 0–1, 2–3, and 4–5 each share a 2 A limit. The total servo supply and auxiliary 5 V ports share a 5 A limit.
Two loaded servos on one pair can reach its limit while the total remains below 5 A. Check the pair assignments as well as the combined demand. A servo pushing against a hard stop can draw heavily even when it appears stationary.
Power conversion also matters:
Here is conversion efficiency, written as a fraction. Suppose several servos draw 3 A at 5 V, spread across port pairs within their individual limits. Their output power is 15 W. With an assumed 90% conversion efficiency and 12 V input, that is about 1.39 A from the battery for this load alone.
The lower battery-side current does not increase the servo-port limits. Other robot loads still add to battery demand. If using a separate servo power device, check that it is permitted, follow its wiring instructions, and match the voltage to the exact servos.
Combined loads
Test the actions that happen together: accelerating the , raising a loaded slide, holding a gripper, and feeding a shooter. Record voltage and useful current readings during normal use. Use those readings to plan a current for the combinations your robot actually uses.
Once the hardware is sound, reduce unnecessary peaks. Avoid commanding a servo beyond its mechanical travel, stagger large accelerations where the task permits, and wait for a flywheel to recover before feeding the next ball. Verify that these changes improve the actual movement without causing a new failure elsewhere.
A fuse rating is not an instantaneous current ceiling. Opening depends on both current and time, as well as the fuse's characteristics. A brief peak and a sustained overload are different. Never bypass a fuse, increase its rating to hide a fault, or use repeated fuse trips as a test method.
Static discharge
Contact and separation between materials can build static charge. A discharge through the robot may disrupt communication, reset electronics, or damage a component. ESD is worth investigating when failures correlate with contact or surface conditions, but first rule out loose power and data connections.
Use the supported mitigations in the official ESD guidance. An approved resistive grounding strap can reduce the voltage difference between the frame and control-system ground while limiting discharge current. Install it exactly as instructed.
This is not an earth connection, and it does not prevent every source of charge. Do not use the frame as the normal power return, replace the strap with a direct negative-to-frame wire, or connect the robot to the field. Do not apply your own treatments to event flooring.
Check exposed electrical contacts, mounting, cable protection, and USB retention. Retest under the conditions associated with the original fault; a successful run on a different surface does not establish that it is fixed.
Sensor noise
An analogue signal needs a compatible voltage range and a sound ground connection. Check the sensor pinout and output against the controller input before adjusting software.
Log the raw value with the actuator stopped and moving. Inspect the supply and return path, then try a known good cable or sensor while changing one thing at a time. Disconnect power before changing wiring. Moving a signal cable away from a high-current run can help, but it will not fix an intermittent terminal.
Apply filtering only after the electrical cause is understood. A filter can hide a fault and adds delay to the reading used by a control loop. See sensor integration for mounting and validation.
Meter connections
Measure voltage across the two points of interest. Check resistance or continuity only with power disconnected and the circuit isolated. Never place a meter in current mode across a battery; that creates a short circuit. Use a suitable current clamp or controller measurement for load checks, with a mentor if you are unfamiliar with the equipment.