How to Mod the Green CHM

[vic7767]

The Sealed ball bearings used were 1) 6 x 10 x 3 mm bearing for the brush motor from VXB.com, 2) 10 x 15 x 4 mm bearing for the small rubber brush. 3) 15 x 21 x 4 mm bearing for the large brush. The 15 mm inside diameter ball bearing does not allow much clearance between the square portion of the brush gear and the wall of the ball bearing. If one is concerned you may substitute a larger ID sealed bearing like the 17 x 26 x 5 mm instead but you will have to cut away some of the plastic from the wire brush retainer.

This mod does not cover the actual removal of the CHM from the Roomba. The owners manual and online video at the iRobot site should help the owner with the actual removal of the CHM.

I'll mention here that I can also perform this mod on your CHM no matter which one you have.

[vic7767]

Just as a side note: If the Red DOT is not in place then after the mod is complete please use a piece of tape and place it over the deck height adjustment wire to help prevent early failure of the CHM due to a broken wire.

[vic7767]

Remove the end-plate of the blue assembly so that the complete Green brush deck can be removed from the case housing.

[vic7767]

With the blue end-piece removed, spread the plastic case apart enough to allow the deck height adjustment cable to be removed from the slit it normally sits in. You can also pull the paddle board connector out of its holding place since the screws were previously removed. Then you can pull the rest of the brush deck out of the blue plastic cage.

[vic7767]

When the two screws are removed from the brush motor and the motor is pulled back away from the gear assembly the screws can be returned to the holes they came from.

[vic7767]

Once the motor is removed it can be turned around and kept in place out of the way using some clear tape.

[vic7767]

The brush deck can now be turned up so that the six screws holding the gear access plate can be removed.

[vic7767]

With the plate removed you will be able to access the six gears and the surrounding area to wipe out the lubricant applied during assembly.

[vic7767]

Once the six gears are removed they can be cleaned of the lubricant by using liquid soap and a toothbrush.

[vic7767]

When filing down the diameter of the brush motor gear a small screw and nut can be used to hold the gear and insert the screw into the end of the drill.

[vic7767]

The two larger gears can be inserted into the drill using the metal shaft that is already installed in each. As the diameter is filed down on each gear a test fitting of the ball bearing should be done from time to time so that the bearing has a tight fit.

[vic7767]

There are three basic tools that can be used to enlarge the diameter of the holes for the gear assembly. Although two of the tools can be installed into an electric drill it is slower but safer to use them by hand.

The first tool is a "step drill", the second is a shank mounted grinding stone, and the third is a fine round file.

[vic7767]

As each hole is enlarged just enough for a tight fit of the gear with the bearing installed on it, a test fit of the gear next to it can also be done. This helps verify that the gear alignment will be true when all three bearing gears are installed. After all gears are in place the gear cover plate can be trial fitted to make sure the gears are in alignment.

[vic7767]

When installing the brush motor check that the motor is in proper alignment with the Green deck and that the deck height adjustment wire is stretched out so the end of it can be reinserted into the slit in the blue cage.

[vic7767]

After white lithium grease is applied to the gear teeth surfaces and the metal shafts, install the gear assembly access cover with the six screws. This part will be difficult for most but you might be able to at least test and verify the brush motor and gears will operate without much resistance. Try using a 9 volt battery connected to the red and black leads of the paddle board and verify that the gear assembly will spin. If you can test the amount of current being consumed by the brush motor make sure it is below .5 amps at 16 volts.

[vic7767]

Finally install the Green brush assembly back into the blue CHM cage. Make sure the paddle board is in place and the screws tightened so they are flat with the blue plastic case. Make sure the brush deck height adjustment wire is in place and the Red DOT in place or a piece of tape over the plastic slot.

[vic7767]

All comments are welcome and if additional info is needed, post it.

[Fraggboy]

Excellent work Vic!!


A small note to members needing this service performed, Vic7767 can perform this for you for a fee.

[Tearstone]

Very nice write up I just got my bearings from Vic and I'll be doing this soon

[MikeD55]

Vic, Thanks very much for posting the process and pictures! Question, is the process (or parts) different for modifying a red/blue CHM?