It can pay to take a Roomba apart

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It can pay to take a Roomba apart

Postby jlandahl » April 9th, 2009, 10:25 pm

Glad I found this website--it's very helpful, especially since, although I've owned Roombas for several years, I know very little about robotics! I just took apart a couple of Roombas for the first time, using a link to disassembly instructions I found here, and found that it wasn't as bad as I'd expected, at least for a blue Scheduler and a white Discovery--four screws to remove the bumper plus a cable to disconnect, then 8 screws to remove the case plus another cable to disconnect. On both I also had to remove the control button panel, just 3 more screws.

Up to now I've restricted myself to thoroughly cleaning Roombas by taking out the brushes and checking carefully for hair and thread wound around the axles, and that usually fixes the circle dance. However, that technique was inadequate for these two, both of which had been given to me by people who'd given up on fixing them after probably several years of heavy use--they're both pretty beat-up looking. The Scheduler had the "dust bin not filling problem" due to the brushes turning only sporadically and the Discovery, which had been working okay for me for a couple of months, started doing the stop-start tango--about 4 stop-start cycles with brief movements, then stopping entirely. To make life more difficult, neither had working control buttons, so I couldn't try running the diagnostics. (I was still able to run the Roombas for vacuuming using the remote, a workaround I haven't seen mentioned here.)

I took the Scheduler apart first and when I removed the bumper I found that it was full of fine hair--no big surprise because there'd also been a lot of hair on the brushes and roller and in the wheel wells when I first got it. When I took the case off I found the innards completely full of hair and a heavy layer of hair and thread wound around the brush motor drive shaft--definitely a likely cause of the dust bin not filling.

The Discovery, on the other hand, looked quite clean in the wheel wells and I had long ago cleaned the brushes and roller. With it I suspected the bumper sensors, so I took off the bumper and everything I could see at that point looked a little dusty but with no sign of hair. Now comes the surprise--when I took off the case, this Roomba had just as much hair as the Scheduler, if not more, lodged throughout the interior! In fact it had twice as much hair wound around the brush motor drive shaft! I would never have guessed that even after taking off the bumper.

If I'd had an air compressor handy, I might have been tempted to save time and effort by just blasting compressed air around the bumper sensors instead of taking the Discovery apart, a shortcut which would have turned out to be a very poor choice in this case!

I haven't finished working on either Roomba yet, so I can't say how successful I'll be in repairing their problems, but I'm much more confident of success now that I've removed all that hair from each of them! To be honest, I'm surprised that either of them ran at all after finding what I did when I took them apart.

Moral of the story: If a Roomba has unusually severe problems, it will probably pay to go the trouble of disassembling it in case, like my Discovery, outward appearances are misleading.
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Re: It can pay to take a Roomba apart

Postby Will2007 » April 9th, 2009, 11:20 pm

Thanks for sharing your findings. Very good post.

I'll do the same with my 400 series from October 2005.
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Re: It can pay to take a Roomba apart

Postby mfortuna » April 10th, 2009, 7:21 am

The next step you should take is to remove the brush deck and open up the gearbox. Clean, inspect, and lube. You may want to check the wheel assemblies but after many years of use, none of my 400 series have had drive belt or debris issues in the wheels. The only wheel issue I've had is the tach sensors.
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Re: It can pay to take a Roomba apart

Postby jlandahl » April 10th, 2009, 5:30 pm

Thank you, Will2007, for the compliment, and mfortuna for the suggestion abut taking the gearboxes apart. Haven't gotten to that yet, but after my first try at cleaning out all the hair I put both Roombas back together and found that they each had the same problem as before.

However, I'm happy to report that the instructions for cleaning the control button pad to fix unresponsive buttons worked like a charm on both machines! As a result I've now been able to run the diagnostics on the white Discovery, which is a Model 4271. It passed all the tests until it got to 9-b, where the SPOT light blinked as expected but the CLEAN light came on steady, indicating a malfunctioning right tach sensor, so I'll need to see about working on that. Perhaps more important, though, when I got to test 10, the SPOT light showed steady green when I turned the front wheel, which wasn't difficult to turn but didn't spin freely, as it's supposed to. The diagnostic test description also mentioned the "body-centered circle dance," which is probably a better description of the behavior this machine was exhibiting than what I called the "start-stop tango" in my original post.

This drew my attention to the front wheel well, which I thought I'd cleaned out before, but when I looked more closely at it I could see a little matted hair inside. It turned out to be much more than a little, and very throughly packed into the interior of the well including some at one side of the wheel. It took a long time, but I was able to gradually tease it out with a pair of bent-nose dissecting forceps. I found that after cleaning the hair out a strip of stiff paper would pass completely through the well beside the surface of the wheel, which it wouldn't do before I started.

This in itself didn't fix the body-centered circle dance problem, but it certainly can't hurt to have that wheel well cleaned out and the wheel spinning freely again! This model has a front wheel that's half white and half black, so I'm thinking that it may have an LED sensor rather than a cam. I may come back to it, but it looks like I should check the right tach sensor first, especially since mfortuna, you say you've run into problems with these in the past.
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Re: It can pay to take a Roomba apart

Postby mfortuna » April 10th, 2009, 9:18 pm

Since you have the swivel front wheel, your MCU firmware most likely will ignore left and right wheel tach issues. What you will see is the first time after you install a battery, a 400 series with a bad left/right tach sensor will go straight instead of spiraling. After a few seconds it will spiral and record the bad sensor in memory. On subsequent missions, it remembers the bad tach and ignores it when the mission starts.

I would suggest some compressed air for the front tach. The only long term robot I have with a swivel wheel was my dirt dog and the front wheel was almost completely black due to garage oil and grease. It seemed to work fine but at the time I didn't know about the diag mode find from vic7677.
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Re: It can pay to take a Roomba apart

Postby JEfromCanada » April 10th, 2009, 11:24 pm

My mother-in-law, after seeing our Discovery, decided to get one of her own. She used it once a week for about 9 months, but found that the machine was running for less and less time each mission. Finally, she got tired of it and offered to give it to me.

I verified it wasn't running properly, then took out the brushes and bin to do a cleanup. Imagine my surprise when I saw that the dirt bin was missing the filter! Somehow, she must have discarded the filter accidentally. There were months of fine dust particles wedged into the motor cavity, totally obstructing the fan blades. When I removed the outer cover of the exhaust plate and cleaned off the fan blades, everything worked like new!

After swapping my Li-Ion battery and pet brushes into her newer Roomba body, I feel like I have a brand new robot!
Current robots:
Roomba Discovery 4210 (not connected)
Roomba 560 (not connected)
Neato XV-11 SW version 3.1.17844, LDS version 2.6.15295, with Pet Brush and Vic's filter
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Re: It can pay to take a Roomba apart

Postby Gordon » April 11th, 2009, 12:23 am

jlandahl wrote:... This model has a front wheel that's half white and half black, so I'm thinking that it may have an LED sensor rather than a cam. ...
To learn more than you may care to know about the swivel-caster's rotation sensor electro-optics, do an Advanced Search, author-search for member "jasperpants", then pick out his longest thread (which ultimately drifts onto the caster-sensor topic). Its a case of broken solder-joints which can be, and were fixed.
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