Johnstone says his herd seems to be happier for it, and some opt to be milked four times a day.
The process, which is based on a "black box" collar on each animal, generates vast amounts of data.
The collars communicate with the shed gates, and also measure the cows' rumination, their movements and activity.
The technology details how milk they have, the time they came into the shed to milk, the amount of feed they were given, their weight, data around milk composition, their preferred robot, and whether they are in heat.
Johnstone's robotic shed means his 320 cows are available for milking 24 hours a day, seven days a week.
He says the machines are "pretty advanced and pretty robust".
Johnstone, an early adopter of the technology, bought the farm three years ago and installed the gear soon after.
The 100ha farm, which was converted from a sheep farm nine years ago, was one of the first in New Zealand to use robotics.
Johnstone says there is no "huge" economic benefit from going robotic but there were savings in terms of improved animal health. Labour costs were not a big consideration.
Including himself, it takes two to three people to run the farm.
That's a little higher than the one to 1.5 people required to a conventional farm of a similar size.
Johnstone's farm has its own support blocks and is quite self-contained. Silage is made on the property, so there is a higher workload in that respect.
"It's not really a big labour saver. You end up doing other things that can fine tune your performance."
There are slightly higher maintenance costs, plus higher capital costs.
Johnstone, who supplies Fonterra, says robotics are becoming more popular among older farmers who want to cut back on the physical demands of the job.
"We all want better quality time and a better work/life balance," Johnstone says.
"It's not for everyone, but for us it fits in with what we want to do."
- Video: Andrew Luxmoore, Fonterra