Roomba 550 Cliff Sensors -- New Fix

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Roomba 550 Cliff Sensors -- New Fix

Postby Dajiu » October 13th, 2008, 12:05 am

I was going to post this on the Roomba website but there is a problem logging in there. Anyway, I have created a website that is a walkthru on how to fix the Cliff Sensor problem on the 550's.

Roomba 550/5xx Cliff Sensor Fix Walk-thru

I hope this helps others, works very well and doesn't require cutting wires, soldering or anything other then disassembly.


Moderator Edit:
This thread contains information about modifications that can potentially cause harm. Please keep in mind that people should be very careful when tampering with the cliff sensors. We have been notified by iRobot that there is the potential for SEVERE BODILY INJURY if the robot falls over a ledge such as a flight of stairs.

PLEASE USE CAUTION, and remember that these modifications not only void your warranty, but they can be dangerous if the Roomba can potentially fall from a ledge and injure someone, especially children and pets.
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Postby vic7767 » October 13th, 2008, 10:33 am

Nice job! A very great solution and a nice step by step disassembly procedure.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby Gordon » October 13th, 2008, 12:14 pm

Dajiu wrote:... I have created a website that is a walkthru on how to fix the Cliff Sensor problem on the 550's. ...I hope this helps others, works very well and doesn't require cutting wires, soldering or anything other then disassembly.
I agree: It should help other 5XX DIY types disable cliff-sensing.

The same process applies to most other iRobot robots--once you get down to the LED & PT module.

I also think most 5XX-owner, DIY-types should bookmark your site as a source of general disassembly instructions, so far as going into the main-elex area to do work.

Now, having dispatched the kudos, :-), I want to tell you about a site-reading problem I experienced, and offer a suggestion to add a warning to one of the steps.

My eyes have degraded over the decades to the extent that I must enlarge type-face size at every site I visit. On my PC (running Firefox browser), I do that enlargement quickly, and temporarily, by depressing <Cntl><+> keys. The <+> key will usually be pressed two or three times.

When I did that at your site, the text enlarged appropriately, but I soon noticed each instruction step (paragraph) had gone out of phase wrt its image!

I don't know how to lock images to an html page in a manner that text is independent. So, I wonder why you constructed the site in that manner. To overcome the 'problem', and to read the words, I left them at default size and slipped on my binocular eye-loupe!

Do you have that effect on your machine? I gather its a Mac, and may be using the Safari browser.

Now then, regarding the "warning" I mentioned. In your step 9 you say: "Note the other half of the sensor on the top will fall off, that's fine. Now you can ...". I need to point out that it would not be "fine" if done on any other iRobot robot--but, I don't know the 5XX's details.

All the other robot assemblies, Home-Bases and VWUs too, use an optical-coupling grease between the 2nd-surface of the top-optic and the lens of the detector-IC. If the worker was to casually wipe away that grease, the performance of the receiver would be impaired.

If appropriate, that is why I suggest a little warning be added to Step-9.

Regards;
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Postby igors48 » October 13th, 2008, 2:57 pm

Nice! Thanks for that great disassembling manual. I will bookmark it. :)
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Postby Dajiu » October 14th, 2008, 12:43 am

Thanks for the positive feedback. As for the optical sensor on the top it appears to just be a plastic cover that reflects the waves into the receiver, thus it falling apart isn't a big deal; there didn't appear to have any grease on it. But I can make the note.

I am going to recode it into standard HTML instead of using iWeb; it just doesn't do a good job of changing the text size. I will look into fixing this and getting it to look better then it is now. I agree, it kinda doesn't look quite right; but it was getting late last night.

Thanks,
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Postby Gordon » October 14th, 2008, 10:34 am

Dajiu wrote:... the optical sensor on the top it appears to just be a plastic cover that ... didn't appear to have any grease on it. But I can make the note.
Dave, in that case I'd say don't bother with the caution note. Perhaps iRobot determined the coupling-gel was not all that important, so it was omitted in the 5XX models.

I don't have a 5XX to fool with, but maybe vic7767 will pipe in to say if he has taken apart his 5XX's top-optic; and, if he noticed any coupling-gel. When present, the gel is quite obvious since it fills the recess under the 'lens' to ensure no air remains between the top-optic lens and the detector's lens. Its messy, and hard to miss.
I am going to recode it into standard HTML instead of using iWeb;...
Great! Many old peepers will be appreciative!
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Postby vic7767 » October 14th, 2008, 6:47 pm

Gordon wrote:I don't have a 5XX to fool with, but maybe vic7767 will pipe in to say if he has taken apart his 5XX's top-optic; and, if he noticed any coupling-gel.


I'm amazed to say that the gel is no longer being utilized in the 5XX front bumper IR optic unit. I have looked at both the 535 and the 510 and from those observations can assume that the entire 5XX model line-up has the same design and is no longer using the optic gel.

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Postby Gordon » October 14th, 2008, 9:11 pm

Thanks for the service, vic7767!

The gel is probably the victim of some iRbt bean-counter that asked "why do we use this stuff?", as s/he embarked on examining all Roomba bits & pieces that would be carried forth into 5XX production.

Prior to committing the 5XX-Roomba to production, it was then very critical to cut down the mounting estimated-cost of mfg a 5XX, since a large number of $$$ had been expended to make all the motor assemblies modular! New castings and the like--not to mention RF comm!

Of course, at that point in time, which was five years after iRbt had probably farmed out the optics design work (for the omni-directional receiver optics on the 2XXX Roomba). it is highly likely that only one or two people at iRobot actually knew what function the gel provides, and they were working military designs (and couldn't be distracted to assist this commercial project!).

Since there was no one to defend it, the gel bit the dust.
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Roomba "Apartment" ?

Postby adam_lux » October 17th, 2008, 11:18 am

Here's an idea for iRobot. Why don't they produce a series of Roomba's without cliff sensors and call them "Roomba Apartment" or Roomba 1-floor". So they are designed for places without stairs and with black carpets!

Moving to the gel discussion, isn't it waterproof? Meaning iRobot used it in military robots but not much use in Roomba?
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Re: Roomba "Apartment" ?

Postby Gordon » October 17th, 2008, 1:26 pm

adam_lux wrote:...Moving to the gel discussion, isn't it waterproof? Meaning iRobot used it in military robots but not much use in Roomba?
The optical-gel, or optically-clear and colorless grease that I brought into this thread is an optical-component which has nothing to do with moisture control.

Generally, the goal in using the gel is to achieve improved energy transfer between lenses.

The idea is to choose a gel with an index of refraction (in the wavelength-band of interest) that has a value between indicies of the plastic from which the top-optic is molded, and the plastic lens of the detector. With the gel filling the void between those two lenses, light that exits from the top-optic passes, not into air but into a higher-index material, which then helps to keep more of the radiant energy bundle heading towards the detector's lens than would occur if air filled the gap between lenses.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby malonesean » May 16th, 2009, 7:17 am

This is by far the best method for disabling the cliff sensors. I did this with my 560 but I am sure that I have a faulty front left sensor. It still stops after about 10 minutes asking to inspect and clean the cliff sensors. I monitored the sensors via a serial connection and every time it reports the front left sensor is detecting a cliff. Could I replace the IR emitter and photo transistor with ones I could buy locally?
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby TechGuy » May 16th, 2009, 1:16 pm

The missing gel/grease may be the cause of the 5xx Roomba problem with the dark floor.

Will it fix the dark floor problem by replacing the LED and/or the light sensor with the one used in 4xx or the original silver Roomba.

The 5xx cliff sensor is a sealed unit. Will it fix the dark floor problem by removing the clear plastic cap?

Disable the cliff sensor is not a good idea. Someone may accidentally sends your Roomba on a mission in an area near stairs. Murphy's law will get you when you are least expected even you have big warning label on your Roomba. That person may read it. But doesn't quite know what it means and sends it on a mission...

This is another example that iRobot does not care about their "consumer" product. This and the gearbox problem should be fixed by now.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby Gordon » May 16th, 2009, 4:23 pm

malonesean wrote:... I am sure that I have a faulty front left sensor. ... Could I replace the IR emitter and photo transistor with ones I could buy locally?
Of course you may.

I don't have a specific part numbers to pass on, but I can offer some guidelines to go by, some of which stem from 4XXX-Roomba knowledge, but which I feel confident will also apply to the 5XXs.

You will be hunting for electro-optical components which are packaged in the traditional panel-mount, or through-hole (bullet shaped lens) T-1 case style & size. The "1" stands for 1/8th inch (diameter), and that conforms to the 3mm diameter metric references. Seeking parts with this case-size and configuration will reveal components having the electro-optical characteristics you need.

You should be more concerned about replacing the IR-Emitting Diode (IRED) than the photo-transistor, (PT), (a diode, actually, because its base terminal is not brought out of the package) detector, since the AlGaAs (940nm WL) IRED material is known to suffer performance degradation with use & time. IOW, it is probably at fault here, not its associate PT.

When choosing a replacement IRED, you may select other wavelengths (WLs) between 800nm to 1000nm. You could even use visual light emitting diodes (LEDs) for Dave's direct-coupling tactic, except those shorter WL devices all have increasing voltage drops across the device (at some specific operating current), and you will achieve a better match to Roomba's IRED driver elex by choosing an IRED that has a dV_fwd of approx. 1.2 volts. iRbt generally hooks a bunch of these IREDs in series and uses a single 'driver' ckt to power them. If you were to stick a visual LED in that series string, its higher voltage drop would current starve the other group members and those cliff-sensor positions might show marginal performance!

As I recall, the IRED applications if Scooba and 4XXX-Roomba put about 10mA through the IREDs.

Notice the photo-transistor's case/lens is blue/black color. The purpose of that is to serve as a UV-WLs filter. Behind the lens is an ordinary silicon-xstr die that serves as the detector. You don't really need the blue filter since your direct-coupled package can be taped over (say with vinyl electrician's tape) to mask the sensor from all ambient / spurious light sources. I presume you will discover that buying a UV-filtered Si-detector is as easy as finding one with a water-clear case.

If you must wait some few days to have new parts delivered to your home, you might think about testing the existing IRED/PT combo in a coaxial direct-coupling configuration, rather than the present side-by-side coupling. IOW, if you could come up with a short (1cm LG) piece of tubing with an ID that will accept the IRED & PT, you could stuff one in each end of the tube and tape parts together. Then test that arrangement. The additional IRED-emittance that the PT sees by looking directly at the IRED may make that sensor position function for a few more months.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby Gordon » May 16th, 2009, 4:39 pm

TechGuy wrote:The missing gel/grease may be the cause of the 5xx Roomba problem with the dark floor.
TechGuy, the optical coupling gel is used in 4XXX-Roombas and in Scoobas between the omni-drectional lens and the lens of the remote-signal sensing IC behind the lens. Cliff-sensors make no use of the gel.
Will it fix the dark floor problem by replacing the LED and/or the light sensor with the one used in 4xx or the original silver Roomba. ...{OR}...The 5xx cliff sensor is a sealed unit. Will it fix the dark floor problem by removing the clear plastic cap? ...
IMO, the sensitivity of a cliff-sensor position, which has been modified as you question, would temporarily be increased. I say "temporarily" because the resulting cavity surrounding the electro-optical components would either be the same as in 4XXX robots, or nearly the same -- but probably worse in a 5XX bumper assembly -- because debris trapping would occur more easily. Not many cleaning missions would pass before performance at that cliff-sensor position would be impaired by trapped debris.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby malonesean » May 18th, 2009, 5:43 pm

My 560 has run for around 90 minutes now without a cliff sensor problem. Here's what I did. I swapped the photo transistor from the front left cliff sensor with the one from the left. I didn't cut the wires. I just had to remove some of the tape holding the loom together. The wires were then long enough to allow me switch the diodes. I have no idea why this seems to have solved the problem. It still behaved exactly as it should when I placed it on a coffee table. That is the response when the left sensor detects a cliff is the same as when the left front senses a cliff. I hope that this is not just a coincidence
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby vic7767 » May 18th, 2009, 6:26 pm

malonesean wrote:I have no idea why this seems to have solved the problem. It still behaved exactly as it should when I placed it on a coffee table. That is the response when the left sensor detects a cliff is the same as when the left front senses a cliff. I hope that this is not just a coincidence


I have no clue either since the robot tests all the sensors according to the factory diagnostics:

factory-test 3 cliffs-side
wiff: cliff-right on 4092 off 1312 signal 2780 on? 0
wiff: cliff-front-right on 4092 off 1296 signal 2796 on? 0
wiff: cliff-front-left on 4092 off 1258 signal 2834 on? 0
wiff: cliff-left on 4092 off 1285 signal 2807 on? 0
wiff: lt-bumper-right on 96 off 84 signal 12 on? 0
wiff: lt-bumper-center-right on 3961 off 4001 signal -40 on? 0
wiff: lt-bumper-front-left on 107 off 66 signal 42 on? 0
wiff: lt-bumper-front-right on 174 off 59 signal 114 on? 0
wiff: lt-bumper-center-left on 120 off 75 signal 45 on? 0
wiff: lt-bumper-left on 4008 off 4002 signal 6 on? 0
(cliff-left?) PASS
(cliff-right?) PASS


factory-test 4 cliffs-front
(cliff-front-left?) PASS
(cliff-front-right?) PASS
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby mfortuna » May 19th, 2009, 6:39 am

malonesean wrote:My 560 has run for around 90 minutes now without a cliff sensor problem. Here's what I did. I swapped the photo transistor from the front left cliff sensor with the one from the left. I didn't cut the wires. I just had to remove some of the tape holding the loom together. The wires were then long enough to allow me switch the diodes. I have no idea why this seems to have solved the problem. It still behaved exactly as it should when I placed it on a coffee table. That is the response when the left sensor detects a cliff is the same as when the left front senses a cliff. I hope that this is not just a coincidence


It could be a mounting or tolerance issue. Maybe when you swapped them you improved alignment. Or the LED was weak but the PT it is now mated with is more sensitive.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby malonesean » May 20th, 2009, 6:09 pm

Back to square one again, still reporting the front left sensor. I have ordered a new cliff sensor array. While removing the one in my Roomba I noticed that there are only 10 wires going into the connector from the cliff sensors. The others come from the left and right bump sensors. This means that the emitters are connected in series, so if one fails with an open circuit they will all fail. I thought that I might have a problem with two sets of sensors in the one connector but iRobot makes it easy to remove the individual wires from the connector simply by lifting a small plasict tab with a pin or paper clip and sliding out the wire crimped to the metal receiver. By the way Roomba will not work when the cliff sensors are removed. "Please inspect and clean Roomba's cliff sensors". Patiently awaiting deliver of new sensor array.
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Re: Roomba 550 Cliff Sensors -- New Fix

Postby imnactr » May 21st, 2009, 5:59 pm

I have tried several cliff sensor "fixes". When I found this, I was leary of it working. It took me little over an hour to follow your exact tear down-put back instructions...all the while thinking it probably wouldn't work. Much to my surprise and delight, it worked like a charm. Now I don't have to restart my 560 when it runs up on the dark squares in my area rug. It just goes across them now. It cleans those areas that didn't get cleaned before. Thank you for this excellent info.

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Re: Roomba 550 Cliff Sensors -- New Fix

Postby Webentpr » September 2nd, 2009, 10:01 pm

I just wanted to thank you for a great job explaining this procedure. Worked perfectly - thanks again - great post.
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