Thermal design for compact robots

Heat is what kills electronics. Motor drivers, power supplies, Jetsons, BLDC motors — every component dissipates power, and that power has to leave somehow. In a compact robot enclosure, "somehow" isn't automatic. Get thermal design wrong and your $500 motor controller smokes its silicon in five minutes; get it right and the same component runs cool for years.

Where heat comes from

Three primary sources in a typical robot:

• Power-handling components: motor drivers (10–60 W), regulators, BLDCs themselves. The largest dissipators by far.
• Compute: Jetson Orin (10–25 W), ESP32 (1 W), MCUs (mW).
• Mechanical / friction: gearboxes (1–10 W of inefficiency), bearings, friction in joints.

Estimate total dissipation: sum the worst-case wattages. A typical mobile manipulator: 50–200 W of heat to dissipate.

Where heat goes

Three paths:

1. Conduction

Heat travels through solid materials toward cooler regions. Copper traces, heatsinks, mounting plates. Aluminum and copper conduct well; plastic and FR-4 (PCB substrate) conduct poorly.

To improve: bigger thermal pads under hot ICs, copper pours under power components, thicker copper layers (2 oz instead of 1 oz costs $5 more per batch).

2. Convection

Air carries heat away from surfaces. Natural convection (still air): ~5 W/m²·K. Forced air (fan): 25–100 W/m²·K. Liquid cooling: 500+ W/m²·K (rare in robotics).

Most compact robots in 2026 use forced air. A small 5V fan moves several watts of heat for ~0.5 W input.

3. Radiation

Surfaces emit IR radiation; rate scales with T⁴. Significant only at high temperatures (>80°C). Black surfaces radiate better than shiny ones.

For a Jetson Orin at 70°C, radiation is ~10% of total cooling. Negligible for design.

Thermal resistance

The unit of thermal flow analysis: K/W (kelvin per watt). Total thermal resistance from junction to ambient:

θ_JA = θ_JC + θ_CS + θ_SA

• θ_JC: junction-to-case (inside the chip).
• θ_CS: case-to-sink (thermal interface material — paste or pad).
• θ_SA: sink-to-ambient (heatsink to air).

Junction temperature: T_J = T_ambient + (Power × θ_JA).

Example: a motor driver dissipates 5 W; θ_JA = 30 K/W (with heatsink); ambient is 25°C. T_J = 25 + 150 = 175°C. Above the chip's max (typically 125°C). Add a fan or larger heatsink.

The thermal interface materials

Material	Conductivity	Use
Air gap	0.025 W/m·K	Worst case — avoid
Thermal paste	5–10 W/m·K	Standard CPU/heatsink interface
Thermal pad	3–8 W/m·K	Easier to handle than paste
Liquid metal	70+ W/m·K	Niche; corrosive to aluminum

Use thermal paste for one-time installs (Jetson + heatsink). Use thermal pad for components that might need to be re-mated.

The hot components in a typical robot

• Motor drivers (BLDC, stepper): 1–20 W per driver. Need heatsinks; sometimes fans.
• Buck regulators: 1–5 W lost as heat per stage.
• BLDC motor windings: 5–100 W under load. Largely cooled by airflow; sometimes water-cooled.
• Jetson SoC: 5–25 W. Active fan + heatsink usually sufficient.
• Battery during charge: 0.5–5 W; usually self-managed.

Cooling strategies

Passive (heatsink only)

Works for <5 W components in well-ventilated cases. Larger surface area = better cooling. Black anodized aluminum is standard.

Active (fan)

Required for 5–50 W components in compact enclosures. Standard Jetson fans (40 mm) move ~1.5 W of heat per W input.

Pick fan flow rate (CFM) based on heat load: ~1 CFM per watt is a working rule.

Liquid

Rarely needed; appears in racing drone ESCs and some industrial robotic arms. Adds complexity.

Phase-change

Heat pipes; vapor chambers. Used in very compact high-performance compute (modern laptops). Niche in robotics.

Air flow patterns

For a fan-cooled enclosure:

• Cool air enters one side; hot air exits the other. Don't recirculate.
• Place the fan near the hottest component.
• Avoid dead spots (corners; behind cables) where air doesn't move.
• Use computational fluid dynamics (CFD) for serious designs; for hobby, intuition + thermocouple readings.

The thermistor / temperature sensor

Add temperature sensors to your robot. Monitor:

• Motor driver case: log; throttle / shut down at threshold.
• Jetson SoC: tegrastats reports; built-in thermal management.
• Battery: critical for safety. Lithium chemistry runaway above 60°C.
• Enclosure ambient: tells you if cooling is adequate.

Cheap thermistors (NTC) connect to ADC pins. Set firmware to alarm at thresholds.

Common gotchas

• Sealed enclosures: look great, cook electronics. Always allow some ventilation, even if it's small slots.
• Fan reverse-mounted: blowing inward instead of outward, or vice versa. Check airflow direction with a tissue.
• Heatsink without thermal paste: air gap adds 30–50 K/W. Use paste.
• Hot in summer, cold in winter: 20°C ambient swing → 20°C component swing. Designs that work in lab fail outdoors.
• Component above PCB: heat from the chip rises through air to nearby components. Position thermally.
• Black plastic chassis: absorbs sunlight; outdoor robots in summer cook themselves. White / metal performs better.

The 2026 production reality

For typical robotics projects:

• Compute: Jetson with stock fan + heatsink. Works.
• Motor drivers: heatsinks + active airflow. Don't bury them.
• Power: external buck modules (DROK, Pololu) with built-in heatsinks. Usually adequate.
• BLDC motors: rely on convection through the casing; large motors include fans.

For dense or long-running robots, do the math. For hobbyist projects, oversize the cooling and forget about it.

Exercise

Take a robot you've built. Run it under load for 15 minutes. Measure the temperature of every hot component (cheap IR thermometer). Note the components closest to their max-rated temperature. That's where future thermal failures will originate. Add cooling there.

That's the Embedded & Hardware track done

You've covered the full progression: microcontrollers → actuators → encoders → IMUs → power → wiring → Jetson → TinyML → protocols → RTOS → PCB → thermal. With this and the 11 other completed tracks, you have twelve complete tracks covering the entirety of robotics from the math foundations to the silicon. One track left: Frontiers — the differentiator topics no other curriculum covers.