Robots often need a wireless link so a phone, laptop, or base station can send commands and receive sensor data. Bluetooth and Wi-Fi are two common choices because they are inexpensive, widely supported, and built into many development boards. Choosing the right link matters because it affects driving range, response time, battery life, and the amount of data the robot can send.
A small wheeled robot may work well with either system, but the best choice depends on the job.
Key Facts
- Bluetooth is usually best for short-range robot control, often about 10 m to 30 m depending on the version, antenna, and environment.
- Wi-Fi usually offers longer range than Bluetooth, often about 30 m to 100 m indoors or nearby outdoors with a good access point.
- Bandwidth measures data rate: bandwidth = data transferred / time.
- Latency is delay between command and response: latency = receive time - send time.
- Wi-Fi generally has higher bandwidth than Bluetooth, so it is better for video, maps, and large telemetry streams.
- Bluetooth Low Energy is designed for low power, so it is often better for battery-powered robots sending small packets.
Vocabulary
- Telemetry
- Telemetry is data sent from a robot to a controller, such as battery voltage, motor speed, position, or sensor readings.
- Bandwidth
- Bandwidth is the amount of data a communication link can carry per second.
- Latency
- Latency is the time delay between sending a command or data packet and receiving it at the other end.
- Bluetooth Low Energy
- Bluetooth Low Energy is a Bluetooth mode designed to send small amounts of data while using very little power.
- Access Point
- An access point is a Wi-Fi device, such as a router, that lets wireless devices connect to a network.
Common Mistakes to Avoid
- Choosing Wi-Fi just because it is faster is wrong because high bandwidth may waste power when the robot only sends small sensor readings.
- Choosing Bluetooth for live video is wrong because many Bluetooth links do not have enough bandwidth for smooth camera streaming.
- Ignoring latency is wrong because a robot can feel hard to control if commands arrive late, even when the signal strength looks good.
- Assuming the rated range always applies is wrong because walls, motors, metal frames, antennas, and radio interference can greatly reduce real range.
Practice Questions
- 1 A robot sends 1200 bytes of telemetry 20 times per second. What bandwidth is required in bytes per second and in bits per second?
- 2 A controller sends a drive command at 2.000 s and the robot receives it at 2.045 s. What is the latency in milliseconds?
- 3 A classroom robot must run for a long time on a small battery and only reports temperature, distance, and battery voltage once per second. Should the design favor Bluetooth Low Energy or Wi-Fi, and why?