Evolution Robotics’ Mint sweeper robot made its debut at CES 2010, where we got a demo of it exhibiting its cleaning behaviors on video. Mint offers flexibility by doing away with the vacuum entirely, and using either wet or dry cleaning pads, Swiffer style. It’s certainly simpler, but does it work as well as the competition? Our review, after the jump.
Mint is adorable. I like its clean lines and straightforwardly modern black and white color scheme. It’s compact (10 inches wide, 3 inches high), but at about 4 pounds I wouldn’t call it light. On top, it has three backlit operation buttons and three small indicator lights, and that’s the extent of the interface, although it also sings to you to let you know when it’s charging, finished, stuck, etc.. The big black diamond is how Mint localizes itself on your floor; more on that later.
Mint’s ‘chin’ is a pressure-actuated bumper, similar to other robot vacuums. It also has a frontal proximity sensor with which it can detect impending obstacles to prevent itself from running headlong into walls and stuff.
Underneath, Mint has two drive wheels and two casters that also serve as edge sensors… Mint is heavily weighted towards its butt, so if the casters drive off a ledge, the robot won’t tip forward and has plenty of time to stop and back up.
The system for attaching Mint’s cleaning pads is ingenious. There’s a detachable panel that sticks to the bottom of Mint’s chin with strong magnets, and the cleaning pads wrap around that. To get the pads to stay on, you “zip” them into two sets of rubber teeth, and then snap the panel onto Mint and you’re good to go.
It’s very secure while also being very easy to change. The modularity of the system also means that you can stick just about anything on there, from Swiffer pads to the reusable cloths that come included with Mint to something of your own.
Mint doesn’t have a charging dock. To charge it, you use a wall adapter that plugs in underneath the robot. The manual suggests that you charge Mint while its standing on its butt, which makes it take up less space, but then you can’t easily grab it by the butt-mounted handle. It might have been better to put the charging port on the side of the robot instead, which would allow for a bit more flexibility, but I suppose that’s a pretty minor quibble.
First, let’s just get one fact out of the way: Mint does not clean carpets. The manual spells it out on page one… Mint is for indoor use on hard surface floors only, specifically wood, tile, vinyl, linoleum, and laminate. So, if you have lots of carpet, Mint may not be for you.
If you have carpet and hardwood or tile, Mint can deal with that. Mint is supposed to avoid getting on any area rugs you might have by registering their edges with its sensors, but if your rugs are too flat, Mint will get on them anyway. If this is a problem for you, the manual suggests that you place obstacles around carpet to dissuade Mint from getting on them, but this isn’t necessarily a very practical thing to do for most people. In our testing, Mint avoided thick shag area rugs, but once (out of six trial runs) got onto a thinner rug that had rounded edges.
The way Mint approaches cleaning isn’t pseudo-random like the Roomba; it’s more like the Neato XV-11 in that it actively builds a map of each area it cleans. Mint doesn’t have any integrated localization sensors, but instead depends on an external reference point to tell it where it is in a room.
This is a NorthStar cube. It’s essentially a little infrared projector that shines some spots onto your ceiling. The big black diamond on top of Mint can spot those spots, and Mint uses their relative orientation to figure out where it is and which way it’s going. You don’t really have to pay much attention to where exactly you stick the cube, as long as it’s in the same room that you want Mint to be cleaning and it has a clear view of the ceiling. This location information, combined with Mint’s proximity and drop sensors, allows it to build a map of the entire area that it’s cleaning.
NorthStar isn’t strictly necessary to get Mint to work, and it’s not a problem if Mint gets underneath something and can’t localize for a little while. If you don’t use NorthStar at all, Mint won’t be able to localize itself, and consequently will clean a smaller area and not do its edge cleaning behavior. This can actually be a good thing, though, for small areas like a bathroom. If you want Mint to clean more rooms, you can buy additional NorthStar cubes to help it navigate.
Mint uses two different cleaning techniques depending on whether you tell it to sweep or mop, based on what motions are most effective with what type of cleaning pad. The dry sweeping technique is a straight line approach, where Mint covers open areas in a back and forth pattern and then makes a complete edging circuit. For mopping, Mint also does straight lines, but while moving along each line it goes forward and back and to each side in a sort of “Y” motion. We’ve got some long exposure pictures that show this very well just below.
As discussed, Mint cleans using two different techniques depending on whether it’s mopping or sweeping. I took a long exposure image of each of these patterns, and the differences are pretty cool. First is sweeping; Mint finished the room in about 15 minutes:
You can easily see the linear coverage pattern of the open space, as well as the edge coverage behavior. Mint did miss a small area at the lower left which temporarily contained a cat. The cat did not suffer any permanent physical damage, but I can’t speak to potential emotional trauma.
Here’s the mopping pattern, which took Mint a little over 20 minutes to execute:
It’s essentially a similar coverage pattern, except with the addition of the back and forth scrubbing behavior and without doing the edging.
As you can see Mint has no problems navigating around corners, under furniture, and avoiding (most) rugs. We have a tangle of cords under our entertainment center, and Mint didn’t get caught or disconnect anything after multiple runs.
I mentioned that Mint was cute, and its cleaning behavior is equally adorable. I’ve always liked watching cleaning robots at work, but Mint is my favorite, because you can see it thinking… Whenever Mint updates its internal map based on new data and decides where to go next, it pauses and its little indicator lights blink for a second. To me, this small touch lends it an incredible amount of personality.
While sweeping, Mint is excellent at picking up dust and small patches of dirt and hair, which actually stick to the pad. In open areas, it’s likely more effective than you wielding a Swiffer because of Mint’s consistent, overlapping coverage. Mint does have problems with larger objects and will just push them into corners and next to walls since they don’t get trapped on the pad. For example, we have some pet rats in our living room (in a cage, obviously), and they like to toss sunflower seed shells onto the floor. Mint doesn’t pick these up. It also has problems with big clumps of cat hair and dust bunnies, since it pushes them around as well. The dry pads also aren’t great at dealing with stickiness; they’re basically just for small dry things like dust and hair.
Overall the wet pads did a better job at cleaning since they (combined with the mopping behavior) were more effective at breaking up dirt and getting stuff to stick to them. Impressively, the pad that came with Mint stayed moist, even while cleaning most of our living room. The difference was easy to notice when walking around barefoot. Mint didn’t do quite as well on grouted tile, because it was hard for it to get down into the grout lines as effectively.
When Mint finishes cleaning, it sings at you, and then returns to where it started, which is both handy and adorable. The battery is supposed to last 3 hours dry sweeping and 2 hours wet mopping, and I never had any issues with Mint running out of power. The only thing you have to do after Mint finishes (besides plugging it in) is either tossing the pad in the trash if you used a disposable one, or tossing it in the laundry if you used a reusable one. Otherwise, there’s no additional maintenance… I didn’t experience any issues with hair tangled in the wheels or anything like that.
It is slightly irksome that there’s no easy way to confine Mint to a specific area. Placing the NorthStar cube does mean that Mint will tend to not to stray to far from there, but if you don’t want it under your couch or something, you basically have to go old school and block it off by putting stuff on the floor.
Mint not having a vacuum means that it doesn’t sound like a vacuum. In fact, I would describe Mint as silent, for all practical purposes. There’s an almost imperceptible hum from the wheel motors when it moves, but otherwise, it’s just the noise of the pad moving over the ground. What this means is that you can run Mint while you’re home, like when you’re on the couch watching TV, and it won’t bother you in the least.
Many things about Mint seem, at first blush, to be compromises in functionality when compared to other cleaning robots like the Roomba or the Neato XV-11… Mint can’t be scheduled. Mint doesn’t have a charging dock. Mint can’t clean carpet. However, Mint is designed to be simple and straightforward, and you probably won’t find yourself missing those features. Realistically, even though the Neato XV-11 and Roomba dock themselves and will run on their own when you’re not around, you still have to empty their dustbins, which means that you’re spending similar amounts of time on post-cleaning maintenance for all three robots.
Another thing to keep in mind is, as Nancy Smith from iRobot told us, cleaning robots (at this point) aren’t really able to duplicate the level of cleaning that a human can accomplish with an upright vacuum or a mop. Mint is not really designed to clean a very dirty floor, but it’ll keep an already clean floor clean. You can run it every day, or every other day, and it’ll help keep dirt, dust, and pet hair under control with only minimal effort from you.
Personally, I was more than satisfied with how well Mint cleaned, although I’m not sure why I wouldn’t just have it use its wet cloth and mopping technique every time, since it seemed to clean better and it left my floors all shiny. Also, the fact that Mint is silent is a major plus, because it means I can use it whenever I need to and it doesn’t prevent me from doing other important things, like napping.
So, the big question: how does Mint compare to iRobot’s Roomba and Neato’s XV-11? Well, firstly, it’s $250, which is cheaper than either the Roomba ($300 and up for a 500 series) or the XV-11 ($400). Secondly, it doesn’t do carpet, so if you want a robot that cleans carpet… Yeah, it’s not gonna be Mint. On hardwood, Mint does as well or better than the other robot vacuums at daily maintenance of dust and pet hair, but suffers at times from the lack of a vacuum for picking up larger pieces of debris. While sweeping, Mint is similar in speed to the XV-11, and significantly faster than the Roomba. Mint’s ability to use different types of cleaning techniques (wet and dry) is also a bonus, and its lack of noise is a major distinguishing feature.
I’d recommend Mint if you’re considering a robot vacuum and don’t have a lot of carpet to deal with. Mint is smart, it’s versatile, it’s quiet, and it’s (relatively) cheap. It does have some issues picking up larger clumps of dirt and hair, but as a simple maintenance robot, it’s very effective.
Now, I realize that I may not have explicitly answered all of your questions, but fear not, I’ll be on the phone with Evolution Robotics in the next couple days for a follow-up post in which they’ll personally be answering all of the questions that I haven’t been able to, as well as whatever new comes up based on this post.
You can find out more about Mint at the Evolution Robotics website, and buy one from MintCleaner.com.
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.