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Robot Power Sources
Batteries, voltage, current, and runtime
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Robots need a steady source of electrical energy to run motors, sensors, lights, and controller boards. The power source affects how long a robot can run, how fast it can move, and how safe it is to use. Educational robots often use battery packs because they are portable and easy to replace or recharge. Choosing the right power source is an engineering decision that balances voltage, current, capacity, size, cost, and safety.
Different robot jobs need different power options. AA alkaline batteries are simple but may drain quickly in motor-heavy robots, while NiMH packs are rechargeable and handle repeated classroom use well. Lithium-ion and LiPo batteries store more energy for their size, but they require careful charging and protection from damage. Wall power works well for stationary robots, and solar panels can extend runtime for outdoor rovers when sunlight is available.
Key Facts
- Electrical power is found with P = V * I, where P is power in watts, V is voltage in volts, and I is current in amperes.
- Battery capacity is often measured in mAh, and 2000 mAh = 2 Ah.
- Approximate runtime in hours is runtime = capacity in Ah / current in A.
- Example: a 7.4 V 2000 mAh battery powering a 1 A robot lasts about 2 hours because 2 Ah / 1 A = 2 h.
- Higher voltage can make motors spin faster or provide more torque only if the motor and controller are rated for that voltage.
- LiPo and lithium-ion batteries have high energy density, while alkaline AA and NiMH packs are often safer and simpler for beginners.
Vocabulary
- Voltage
- Voltage is the electrical push that moves charge through a circuit, measured in volts.
- Current
- Current is the rate at which electric charge flows through a circuit, measured in amperes.
- Capacity
- Capacity tells how much charge a battery can supply over time, often measured in milliamp-hours.
- Energy density
- Energy density is the amount of stored energy compared with a battery's size or mass.
- Power regulator
- A power regulator is a circuit that changes or stabilizes voltage so robot parts receive the correct supply.
Common Mistakes to Avoid
- Using the highest voltage battery available is wrong because motors, controllers, and sensors can overheat or fail if their voltage rating is exceeded.
- Treating mAh as power is wrong because mAh measures stored charge, while power depends on both voltage and current using P = V * I.
- Ignoring motor current spikes is wrong because motors can draw much more current when starting, turning, or climbing than when rolling smoothly.
- Charging lithium-ion or LiPo batteries with the wrong charger is wrong because these batteries need specific charging control to prevent damage, overheating, or fire.
Practice Questions
- 1 A robot uses a 6 V battery pack and draws 0.5 A while driving. What electrical power does it use?
- 2 A 7.4 V 2000 mAh battery powers a robot that draws 1 A on average. Estimate the runtime in hours, then find the average power in watts.
- 3 A classroom robot stays on a table all day for demonstrations. Explain why wall power might be better than a battery, and name one disadvantage of using wall power.