iRobot Definitely Developing Robot Lawn Mower, Astronomers Very Upset

Evan Ackerman
This picture of my Roomba on some grass is not intended to be representative of an actual iRobot lawn mower. Also, Roombas function poorly on grass.

We’ve been assuming for years now (years!) that sooner or later, iRobot would come out with a robotic lawn mower. The reason it's been later and not sooner, we're guessing, is that iRobot has been trying to figure out how to make a lawn mower that’s as easy to use as a Roomba, which could be impossible. Based on a recent FCC filing, it sounds like iRobot is working on a lawn mower that uses a wireless beacon system as opposed to an edge wire, which is a pretty cool idea. It’s too bad astronomers are doing their level best to kill the whole thing.

Since we’re a robotics blog, let’s first have a look at what iRobot is working on, before we delve into the drama that is iRobot versus radio astronomy.

Just about every single robotic lawn mower that currently exists (and there’s a bunch of them) requires you to first bury a loop of wire called an edge wire around the perimeter of your lawn to keep the robot contained. The robot senses the wire under the ground and won't cross it. This is a pain in the butt to set up, and historically it’s not the sort of thing that iRobot wants to ask users of its robots to do.

The ideal option would be to develop a robotic lawn mower that can sense when it’s on your lawn and when it isn’t, but this is an extraordinarily difficult problem to solve, because of the amount of complex variation that most lawns have, not to mention all of the issues that you run into trying to get sensors to work outside. Is it possible? Of course. Is it practical in a mass-produced consumer robot? Probably not right now.

iRobot’s approach, according to a waiver that they’ve filed with the FCC, is to replace that edge wire with a series of small wireless beacons. The average lawn (between a quarter and a third of an acre) would need somewhere between four and nine beacons that you’d drive into the ground around the perimeter of your lawn at the beginning of the summer. iRobot’s robotic lawn mower (referred to in the FCC filing as a “RLM”), after an initial user setup, would use the beacons to calculate its position using time-of-flight of transmitted ranging packets:

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The reason that iRobot has to apply for a FCC waiver for this system is that its beacons operate in the 6240-6740 MHz range, over which the FCC prohibits “fixed outdoor infrastructure.” iRobot wants the FCC to agree that the beacons aren’t fixed, and besides, they’re very low power, not running most of the time, close to the ground, and this particular frequency range is being used by almost nobody. Almost.

At the very end of the iRobot’s FCC filing is this:

iRobot recognizes that the Radio Astronomy Service ("RAS") uses 6650-6675.2 MHz for spectral line observations. There is little risk of interference...

That 6650-6675.2 MHz range is used by the National Radio Astronomy Observatory (NRAO) to spot the spectral signature of methanol out in space, or, as the NRAO somewhat bizarrely calls it, “interstellar wood alcohol.” Methanol denotes star-forming activity, and is also used to “measure distances to star-forming regions with high precision, charting the course of galactic evolution.” This is important enough that the FCC says that “all practicable steps shall be taken to protect the radio astronomy service from harmful interference.”

As you might expect, the NRAO got a little bit upset that iRobot wanted to set up its beacons to broadcast on a protected frequency, because they're worried that people's lawn mower beacons would start to mess with their radio astronomy data. So, they’ve filed a comment to that effect on iRobot's FCC waiver application, to which iRobot responded, and then NRAO responded to that.

We’ve read through these documents (including iRobot’s waiver application, NRAO’s comments, iRobot’s response, and NRAO’s reply), and they’re full of amusingly passive-aggressive commentary from both sides as they argue back and forth in front of the FCC. Some choice excerpts that are worth the read:


iRobot: “Use of the iRobot RLM [robot lawn mower] will increase lawn mower safety. An estimated 1,517 lethal accidents occurred with lawn mowers through the years 1997 to 2010. It is reasonable to assume that many of these injuries and deaths would not occur if consumers used a robotic mower. More than 17 million gallons of fuel, mostly gasoline, are spilled each year while refueling lawn equipment. A battery powered RLM will reduce emissions, gasoline spills, fires and other such accidents.”

NRAO: “iRobot cited multiple statistics of grim accidents and spilt gasoline to assert the public benefit of approving its wireless robotic lawn mowers. However, there is already a competitive market for robotic lawn mowers using wire loops [buried edge wire], which has somehow failed to stanch the stream of ghastly accidents and spilt gasoline that iRobot associates with the mundane practice of lawn-mowing.”


NRAO: “The protection criterion for detrimental interference to [radio astronomy] operations [implies] a line of sight separation distance of 89 km.”

iRobot: “NRAO calculates that an 89 km exclusion zone is necessary to protect radio telescopes from harmful interference. This radius is overstated. The claimed radius of interference [should be] a maximum of 19.3 km, before considering other factors.”


iRobot: “The NRAO observatories for the most part are not closely surrounded by residential areas, at least no residential areas with lawns. A review of the observatory locations on Google maps also shows that many are surrounded by desert or forests, not environments where residential lawn equipment is used.

NRAO: “This claim is most charitably characterized as silly.”


iRobot: “The iRobot RLM will be marketed for consumer use only, and iRobot has offered to place a notice in the user manual and on the robot that states: Consumer use only; use must be limited to residential areas.

NRAO: “A toothless admonition to use only in residential areas does not suffice.”


So who’s right? Well, NRAO has a point: these frequencies are restricted for a reason, and if iRobot’s beacons would mess with radio astronomy, they shouldn’t be allowed. But iRobot also has a point that the odds of this actually occurring are very, very small, and they reiterated this to us in a statement:

iRobot has reviewed comments filed by the NRAO and believe that there is an infinitesimal likelihood that the proposed RLM system will impact any radio astronomy measurements. The FCC staff is highly competent in determining these technical matters and will determine whether there will be any negative repercussions to radio astronomy. We trust that the FCC will make the right decision.

Honestly, we’re not sure which way to go on this one, except to wonder if it really would be that big of a deal for iRobot to adjust its beacons to keep out of restricted frequency ranges. For its part, NRAO has suggested that iRobot might instead incorporate some sort of geolocation feature to keep the beacons from operating near radio astronomy sites at all, but iRobot didn't seem to like that idea. Strictly speaking, whether these two parties agree or not is moot, because it’s up to the FCC to make the final decision, which it will undoubtedly do at its typical blistering bureaucratic pace.

[ FCC Filing ]

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