1  Roomba : What it Can and Cannot Do

Executive summary: It’s not fast, it’s not smart, and it needs your help … but it does clean the carpets.

• In many cases, it does a wonderful job of cleaning under things. It can clean under the table. It can clean under the bed and other places that would be hard to reach with an ordinary hand-held vacuum.
• The first few times you use the thing, it doesn’t save you any time at all, because you spend all your time watching it. Partly that’s because it is interesting to watch … but more importantly because you need to learn what it can handle and what it can’t. You need to learn how to use it wisely.
• It doesn’t gracefully deal with clutter. You must declutter the place before you turn the Roomba loose. See section 2.
• It can’t be trusted to deal with cords, speaker wires, et cetera. This is deceptive, because sometimes it will crawl over them or bounce off them; the problem is that sometimes it won’t, which means you can’t leave the thing on its own unless all the cords are out of the way.
• It sometimes gets stuck if there is a “blind alley” or a “funnel” where the boundaries gradually converge at a shallow angle. (It’s OK with corners where the boundaries meet at an obtuse angle.)
• It is very likely to get stuck if there is a “low bridge” that it can almost get under. If the passage is really low, it will just bounce off in the usual way. If the passage is really high, it will pass under in the usual way. But if the passage is barely too small and funnels down at a shallow angle, it will get wedged.

  In particular: The three inch high “kick space” under the front of typical cabinets forms a nasty Roomba trap, especially if the space extends more than two inches behind the front of the cabinet. This seriously reduces the usefulness of the Roomba for sweeping the kitchen floor.

• Sunlight saturates the IR detector. If bright sunlight is falling on the thing, it will not respect the virtual walls and will not respond to the handheld remote controller.
• It has a problem with hair. Although most of the hair gets wound up in easy-to-clean places, the other 10% is really nasty. It works its way into the bearings and gears and such. A significant percentage of the cost-of-ownership of a Roomba is the time spent cleaning hair out of the brushes and bearings.
• The “Discovery” model is one of the second-generation models. Compared to the first-generation models, it has 3x more dirt-holding capacity and 3x more battery autonomy per charge – both of which are very useful features. See section 3 for more about the battery.
• Current models are sold bundled with two Virtual Walls. Those are useful. I use them all the time. If I had three of them, that would be even more useful. In a pinch, a chair turned on its side does a satisfactory job of blocking a hallway or doorway.
• The idea that it will seek out its charging station when it needs a recharge is cute, but only 10% as practical as you might have hoped. That’s because there is only one charging station, but there are lots of rooms that need cleaning. I find carrying the Roomba from room to room easier than carrying the charging station from room to room and finding a place to plug it in. So I just leave the charging station in one place. In other rooms, I just let the Roomba run until it stops, then carry it back to the charging station.

2  Clutter

You need to learn how to use a Roomba. Here’s an example of what I mean.

Suppose you are vacuuming the dining room. You need to vacuum under each of the chairs.

• With an ordinary vacuum cleaner, this is straightforward; you just move the chair a couple of feet, vacuum where it was, and then move it back.
• With a Roomba, this is tricky. One laborious solution would be to carry all the chairs out of the room, run the Roomba, and then carry all the chairs back. Compared to an ordinary vacuum, this requires moving each chair much farther, and requires having someplace else to keep the chairs for an hour or so.

  A slightly cleverer solution is to flip the chairs up onto the table, as they sometimes do at the pizzeria at closing time. This allows nearly-unobstructed sweeping, and doesn’t require moving the chairs very far.

  A trickier solution involves two steps: First, leave the chairs where they are and let the Roomba clean around them. Then, move each chair a short distance, and turn the Roomba loose again. This means that most parts of the room will be cleaned twice, while areas near the chairs will only be cleaned once … but there’s nothing wrong with that. My objective is to minimize the amount of work I have to do, and if the Roomba has to do a little extra work, so be it.

3  Battery

The batteries can be recharged, but only a few hundred times. Eventually the battery becomes worn-out and useless. Then you have to buy a new battery pack.

The Roomba is remarkably stupid about this. Sometimes – not always – here’s what happens: When it is on the charger, it thinks it is fully charged, but as soon as you take it off the charger it thinks the battery is empty. Another symptom of a messed-up battery is that sometimes – not always – leaving it on the charger overnight is less helpful then using it immediately after charging. I’m not sure I understand this, but it may be related to the Roobma’s non-understanding of open/loaded issue discussed below.

Typically when the battery fails, almost all of the cells within the battery are still good; only one or two cells have died.

Therefore, keep the old battery pack whenever you buy a new one. The reason is that when the second one fails, you can repair it by clipping out the bad cell and replacing it with a good one from the other pack. This requires some soldering skills.

You usually cannot detect a bad cell by looking at its open-circuit voltage. Instead, you should load the battery pack using a 50 Ω resistor with a 5 W (or better) power rating, and look at the cell voltages under load. To say the same thing another way, typically the cell fails by developing an unacceptably large internal resistance.

Note: On the cover of the battery pack, the screws may have a funny three-cornered socket head. You could buy a special tool for dealing with these, but it is just as easy to make one. One solution is to start with a #10 machine screw and put a triangular tip on it using a file or a grinding wheel.

4  Error Codes

If the Roomba detects a problem, it will stop and play a “song” consisting of the two-tone “uh-oh” prefix followed by a number of beeps. The meaning of the beeps is:

0: Wheel drop — Either a wheel is physically dropped or one of the wheel drop switches/wires is broken. You commonly hear this when the robot is picked up.

1: Main Brush stall — Check for something wrapped around the main brush.

2: Side Brush stall — Check for something wrapped around the spinning side brush.

3: Vacuum stall — Check for something stuck in the vacuum chamber.

4: Drive Stall — Either the robot got stuck on or under something, or something got wrapped around a drive wheel. Other possible causes include internal failures of the motor, drive circuitry, encoders, or wheel belts, failure of string that raises cleaning head, failure of main brush motor (which would cause the cleaning head to not raise up).

5: Constant Cliff — Cliff sensor failure. Check for debris stuck in the cliff sensors.

6: Wheel Drop Rate — too many wheel drops within a certain period of time. This can happen if the robot is stuck on an extension cord or similar object.

7: Stasis Stuck — The stasis switch has failed. This should never happen – it has been disabled in the code – but this code remains here to avoid re-numbering the higher-numbered codes.

8: Vacuum fell out — This has also been disabled in the code.

9: Wheel Drop Failed — Hard failure of a wheel drop switch/wire. This happens when a wheel drop switch is failed at startup and stays that way for 3 minutes after startup. During this time, the robot will engage in a ‘wiggling’ behavior to try to nudge the switch into working again.

5  References

1.

Tod E. Kurt, “Roombongle! A Roomba USB dongle” http://todbot.com/blog/2006/07/19/roombongle-a-roomba-usb-dongle/

2.

Roomba Review – Roomba Robotic Vacuum reviews, news and user forums.

http://www.roombareview.com/