How to Mod the Green CHM

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Re: How to Mod the Green CHM

Postby Xamindar » February 14th, 2011, 3:49 pm

Yeah, I have three CHMs from back when the Roomba was still under warranty. I have been swapping them out at least once a month then cleaning them out and re-greasing with lithium grease. It seems the cat hair clogs the gears a lot faster when mixed with the lithium grease than it did with the original. But then again, the brush gears have worn out a little so there is a bigger gap between the housing and the gear so that hair can get in easier.

I ordered two sets of the three bearings from a place online which only cost me a total of $25. I will pick two of my CHMs to modify. That way I will have a backup for when the motor gets clogged with hair/dust and stops working. I can just swap it out with the other one instead of having to blast the hair inside with a torch and test until the motor works again.
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Re: How to Mod the Green CHM

Postby iMayne » February 14th, 2011, 3:52 pm

Nice!
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Re: How to Mod the Green CHM

Postby Xamindar » February 14th, 2011, 4:01 pm

Here is the place I bought the bearings:
rc-bearings.com
The site is a little weird. You will find the two larger bearings under the "10mm and larger" section and the small one under the "less than 10mm" section. They have a great choice though. You can get rubber or steel seals. I chose one side rubber and one side steel for all my bearings.
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Re: How to Mod the Green CHM

Postby TechGuy » February 14th, 2011, 5:20 pm

Xamindar wrote:Here is the place I bought the bearings:
rc-bearings.com
The site is a little weird. You will find the two larger bearings under the "10mm and larger" section and the small one under the "less than 10mm" section. They have a great choice though. You can get rubber or steel seals. I chose one side rubber and one side steel for all my bearings.

Why you pick the one side rubber (sealed) and the other side steel (shielded)?
The reasons that I can think of:
1. Since only the external side needed to be sealed, the inner side can be shielded. Clean lithium grease getting into the race is not a bad thing.
2. The rubber seal actually touching the ball bearings. The steel shield is not touching the ball bearings. Therefore, with one side steel will have less drag on the ball bearings.
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Re: How to Mod the Green CHM

Postby Xamindar » February 14th, 2011, 7:01 pm

Well, I just did a small amount of research on these bearings before deciding so my reason may be flawed. There was a post in some RC forum explaining that the rubber sealed ones have a better seal so less dust/dirt will get in but they cause a little more drag on the bearings than the steel seals do. I figured I'd get half and half on them and have the rubber seal face the outside and the steel on the inside where there should be no dirt to get in them.

Just received them in the mail today by the way. That was fast, only 2 business days.
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Re: How to Mod the Green CHM

Postby TechGuy » February 14th, 2011, 8:37 pm

Good thinking... I don't know that they make them half and half.
Keep us updated in a few month on how these ball bearings perform.
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Re: How to Mod the Green CHM

Postby iMayne » February 15th, 2011, 3:14 am

More drag yes but I have the seals without drag; I got them from Florida. My brother knows a company to who sell these bearings; that's why I sell mine a bit expensive.
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Re: How to Mod the Green CHM

Postby Xamindar » February 16th, 2011, 11:34 am

By the way. What are the differences between the red and green chm's? As far as I can tell, one of the gear box screws is in a better location on the green one, is that it? It's strange that they would change the whole color (hence make support call identification easier) for just one screw location. Anyone know what else might be different?
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Re: How to Mod the Green CHM

Postby Gordon » February 16th, 2011, 9:09 pm

Xamindar wrote:By the way. What are the differences between the red and green chm's? ... Anyone know what else might be different?
An important addition to the green deck assembly is the thick polyethylene foam shaft-seal fitted between the motor gear-head's casing and green deck casting where brush turning power enters the end-gears' casing to rotate gear#1.

That debris blocker was discussed in this old post: viewtopic.php?p=64644#p64644 , and you can see it in a couple images that vic7767 posted on page one of this modding thread.

The seal is very effective, so much so that it replaces the task of mounting a ball-bearing on gear#1's hub just to obtain a shaft seal in the gear-case wall. Bear in mind that the foam seal suffers only one fourth turn of rotation (whenever transient brush loading causes the motor to climb up its "elevator" cable), and does that very slowly when compared to the rotational rate of gear#1.

Another nice thing about the foam seal is: almost anyone can use a sharp blade to hack one out of a block of polyethylene (closed-cell) foam. Nominal dimensions are: a) thickness = 0.28", (7 mm), b) central hole (circular, or polygonal) = 0.25", (6 mm), and c) outer dimension(s) (circular or polygonal) = 0.8", (20 mm).

It can be added to any CHM that lacks one. The most difficult part of the task is locating a piece of proper material. It often arrives in a shipping carton, that subsequently gets binned. Its not the rigid & friable polystyrene foam you want, it is the squishy, springy foam than smells like fused candle wax when you momentarily touch a hot soldering (or clothes (heaven forbid)) iron to the foam.

Of course, reverse and forward assembly of the recipient CHM is required to install this shaft seal.
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Re: How to Mod the Green CHM

Postby Xamindar » March 1st, 2011, 12:16 am

I now have one of the bearing modified green CHMs. It came with a roomba I bought off craigslist today. I also noticed that the motor does not have any air holes like the motors on the red ones have. So they also solved the problem of dust and hair getting in the motor on the red ones and causing it to stop working. My red ones have done that at least 6 times in the last two years.

TechGuy wrote:Good thinking... I don't know that they make them half and half.
Keep us updated in a few month on how these ball bearings perform.


So far so good with my two red CHMs. The bearings seem to be working great.
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Re: How to Mod the Green CHM

Postby roboroomba » March 2nd, 2011, 9:44 pm

I just bought thees for my 440, i have installed them and they work very well, I did not get the one for the brush motor gear because it is hard to put in, but the small bearing has a yellow seal, and the large one has a red seal, and on the back they both have a shielded thing
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Re: How to Mod the Green CHM

Postby vic7767 » March 10th, 2011, 3:30 pm

Depending upon the supplier you can get Sealed bearings in both teflon seals or rubber seals. The choice in rubber seals are Green, Yellow, Blue and Black. I have not been able to determine what color seal is better than the other.
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Re: How to Mod the Green CHM

Postby roboroomba » April 17th, 2011, 9:12 am

well, today I opens up the brush deck on my 440 to see how it was doing, and there was not a speck of dirt in it. The bearings are still turning well and no dirt has gotten into them.

I would say that these bearings are a good choice.
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Re: How to Mod the Green CHM

Postby roboroomba » May 18th, 2011, 7:03 pm

rc bearings has added a different kind of sealed bearing to there thing, it is a polymide or something like that sealed bearing, it is supposed to be the best kind of seal, as it seals very well, and is non contact, and it is quit cheep to. although at the moment they only have one for the small brush gear.

here is the link to the small brush gear bearing of that type.

http://www.rc-bearings.com/catalog/product_info.php?cPath=30_31&products_id=868

also, I have ordered the small brush bearing for my 510, because the seal came off of its bearing (not an RC bearing one), I will report back in a month or so on how well it has held up.
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Re: How to Mod the Green CHM

Postby Gordon » May 18th, 2011, 8:36 pm

roboroomba wrote:rc bearings has added a different kind of sealed bearing to there thing, it is a polymide or something like that...
Yes, "something like that", but not that. The material is polyamide, not ..imide. The two names sound so much alike, that careful listening is required to distinguish which one is being referenced. However, physical characteristics of the two plastics widely differ.

You may be familiar with the phrase "acetal resin" or the brand name Delrin (trademarked) for the chemical compound "polyamide". Google it.
roboroomba also wrote:... sealed bearing, it is supposed to be the best kind of seal, as it seals very well, and is non contact, ...
Well, with regard to those two concepts:

1) Since the Delrin does not contact the inner race, the bearing is a shielded bearing, not sealed. However, I would readily agree that a Delrin shield could be spaced very much closer to the bearing's inner race than can a steel shield; and if the spacing can be maintained less than about 0.0005 inch there might be fewer hairs migrating into where the balls spin around than would be found in a steel-shielded bearing.

2) I suppose the people selling these bearings are the ones claiming: "... it is supposed to be the best kind of seal, as it seals very well ...", 'step right up here folks, and buy them before we run out of stock!'. Fact is: A shielded bearing works because its rubber lips slightly grip the bearing's inner race, and that means there is zero inches of clearance for stuff to pass through.
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Re: How to Mod the Green CHM

Postby vic7767 » May 18th, 2011, 9:38 pm

Since the rpm is much slower on the brush deck gears and brushes than the hobby car RC environment I've found some Teflon sealed bearings that hold up better than the blue rubber seals on the 10x15x4mm bearing. You can find them at vxb.com Just remember that no matter what seal material is used the seals may fail if allowed to stay in contact with built up debris long enough to generate excessive heat.
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Re: How to Mod the Green CHM

Postby iMayne » May 27th, 2011, 7:50 am

Most of my customers are wondering if my mods are "up to standard". Well yes. My mods pull about 0.1A - 0.3A. See attached picture.
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chm_testing.jpg
Voltage at 15 - 16 with an Ampere between 0.1 to 0.3. In this picture it's about 0.2A.
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Re: How to Mod the Green CHM

Postby TechGuy » May 27th, 2011, 11:22 pm

Using a 30A ammeter to measure 0.1A - 0.3A!!
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Re: How to Mod the Green CHM

Postby iMayne » May 28th, 2011, 2:19 am

TechGuy wrote:Using a 30A ammeter to measure 0.1A - 0.3A!!

I see nothing wrong with that. This meter has a section for 3A only.
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Re: How to Mod the Green CHM

Postby Gordon » July 1st, 2011, 9:28 pm

I don't drift through this thread very often, but as I did so today this post caught my eye.
iMayne wrote:
TechGuy wrote:Using a 30A ammeter to measure 0.1A - 0.3A!!

I see nothing wrong with that.
That response tells me that you are not concerned with accuracy of measured values. Attempting to measure current the way you have shown with your power supply meters is, ahem, ridiculous.

Reporting such measurements to customers borders on the untruth. Surely you are aware that galvanometer meter movements are typically calibrated only at the full-scale reading. Readings at all lower parts of the scale are subject to progressively increasing inaccuracy. If trying to read a value between the zero point and first minor division marker your interpolated number could be far from the actual value of the quantity being observed.
This meter has a section for 3A only.
Why not use that 3A-F.S. range? If doing so, a 0.20A current would be at least resolved by two minor divisions of scale!

IMO, those cheapo PSU meters are only useful for indication, and should be backed up by DMMs monitoring voltage and current when data are to be published.
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