In a sweltering factory in southern India, Royal Enfield motorcycles are being painted and lacquered by giant robotic arms that move at twice the maximum speed of a human limb, day in, day out, never making a mistake.

Only a few workers are still needed on the paint line at Royal Enfield Motors Ltd.'s plant in Oragadam, doing touch-ups on the iconic two-wheelers coveted for their classic design. Four robots can do the work of 15 human painters toiling across three shifts.

Robots and automation are invigorating once-sleepy Indian factories, boosting productivity by carrying out low-skill tasks more efficiently. While in theory, improved output is good for economic growth, the trend is creating a headache for Prime Minister Narendra Modi: Robots are diminishing roles for unskilled laborers that he wants to put to work as part of his Make in India campaign aimed at creating jobs for the poor.