Swarm robotics focuses on designing and coordinating large groups of relatively simple robots to perform tasks in a decentralised and collective manner. The swarm provides a resilient and flexible solution for many applications. However, contemporary swarm robots have a significant power problem in that secondary (i.e. rechargeable) batteries are slow to charge and offer lifetimes of only a few years, increasing maintenance costs and pollution due to battery replacement. We imagine a different future, wherein battery-free robots powered by supercapacitors can be recharged in seconds, offer long-life autonomous operation and can rapidly pass charge between one another using trophallaxis. In pursuit of this vision, we contribute the CapBot, a battery-free swarm robot equipped with Mecanum wheels, a Cortex M4F application processor and Bluetooth Low Energy networking. The CapBot fully recharges in 16 s, offers 51 min of autonomous operation at top speed, and can transfer up to 50 % of its available charge to a peer via trophallaxis in under 20 s. The CapBot is fully open source and all software and hardware source is available online.

Bluetooth Low Energy and IEEE 802.15.4 are commonly used wireless communication protocols in IoT applications. Both operate in the 2.4 GHz ISM band, where their coexistence can lead to interference. We study the bit error rate (BER) under controlled timed interferences within the physical payload, varying interference power and frequency offsets. Measurements with a co-located software-defined-radio antenna are captured and shown to validate the experimental setup. IEEE 802.15.4 proves more robust to BLE interference than vice versa, consistent with results in literature. Interference at lower relative frequencies is found to have a greater impact on BER. Controlled interference causes persistent bit errors after it ends, suggesting receiver desynchronisation.