Monday, December 8, 2014

Our Roomba with a can on his head

I've posted about our iRobot Roomba before and how well engineered this little robotic vacuum is, (We call him Pierre, our little French maid.) but he lives in a pretty harsh environment down there on the raw concrete floor of our living quarters and sometimes things break down.

This time it was the bump-sensors.

He has a bumper wrapped around the front (Yes, even though he's round he does have a front!) with a pair of sensors behind it that can tell when he's run into something and whether it's center, right or left. Then he backs up a little, turns in the appropriate direction, and sets off again on his busy little way. If one of these sensors gets stuck he starts frantically backing up and spinning one way then backing up and spinning the other way, and backing up some more like a cat with it's head stuck inside a Dinty Moore stew can.

If I happened to be around when he started this weird dance a good swift kick on the nose used to sort him out again, (Otherwise he eventually gives up and parks himself wherever he happens to be and waits for us to come back home and trip over him.) but recently no amount of foot-abuse could sort him out. Clearly something has quit doing it's thing and an on-board diagnostic pointed at the left bump-sensor.

Apparently this is not unique to our Pierre because I came up with this web page that walked me step by step through the process of setting him right again.

The first step, getting the cover (Bottom) off and removing the battery is quick and simple, 4 screws and you're there.

After that it starts getting a little more complicated so I got out a small parts bin and, working from left to right, using one bin per step so the parts, mostly screws, didn't co-mingle into a mosh-pit type scenario which I'd never be able to sort out again, I carefully kept things organized.

First he's flipped right-side up and the outer covers are removed

Then the various bits that make up the controls and switches are unscrewed/lifted off 

and the main PCB unplugged, (9 connectors in all) unscrewed and removed, which exposes all the hard-wired bits, including the bump sensors tucked under the cliff sensor assembly. (Which keeps him from falling down the stairs, if we had stairs.)

One of the bump-sensors lifted out and dismantled to it's component parts

Until I got all the way down to the two bump-sensors.

What's missing in the photo above (Hey! I was up to my elbows in Pierre guts and didn't always get back to the camera!) is a little PCB (Printed Circuit Board) that has an infrared emitter on one end and receiver on the other and fits into the housing. If you look close at the bit in the top right of the photo you can see an opening in the curved end of it, a tiny window. Normally the emitter shines infrared rays through this little window and tickles the receiver. When Pierre runs into something the arm moves the window away and the receiver is no longer tickled so knows the robot has run into something bigger than itself and signals for it to back away.

The web site is focused on replacing the emitter and/or receiver on the little PCB since it's usually one of these that causes the problem. (Replacements only cost a couple bucks per set but you have to do the soldering.) Since the sensors are encased in the enclosure which has a dust-seal (The square, ribbed thingy which is rubber) the site holds out little hope that a good cleaning will solve the problem, but apparently they are unfamiliar with concrete dust which will get into everything and anything.

So, a good cleaning, some reassembly

Tiny screws are difficult for fat fingers to retrieve from those little compartments n the parts organizer, but a quick stir with a magnetic pickup solves the problem. Warning! If you lost a screw and can't find it anywhere and you wear glasses that have tiny little magnets for holding the matching sunglasses on, check them for the missing screw!  Ask me how I know this!  Go ahead! Ask!

                                                   and Pierre was back on the job again.

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