Avi's page for iRobot Roomba 5xx / 6xx / 7xx Red CHM mod

How did I mod (modify) iRobot Roomba 560 Cleaning Head Module gearbox with bearings?

I my Roomba 560
(Well... I still do...)

This mod assumes that you already cleaned the gearbox (see this page)
and/or found that the plastic housing had started to deform due to massive friction.

With this modification dust and hair entering to the gearbox will be blocked.
Worn to the gearbox wheels, wheel holes and to brush hubs will be reduced dramatically as ball bearings will replace the plastic to plastic friction.

Doing this modification on time (when no serious damage was done to the plastic holes) will 'save' and extend Roomba CHM life and will add many hours of smooth and quieter work.

This page describes Roomba 560 but it is the same for all 5xx 6xx 7xx series models that uses Green / Red / Gray CHM though procedure might be slightly different.
For the Gray CHM mod details instructions go to this page.

This fix is ONLY for those with electronics and mechanical knowledge and skills.

This fix is NOT recommended by me
nor by iRobot and will void product warranty !
If you follow this fix, you do it on your own risk !


A. Preparing for the fix:

Suggested tools and materials:
  • Phillips head screwdriver
  • Old toothbrush or some other small cleaning brush
  • Lithium grease
  • Vacuum cleaner (to be use it in each step where you find dust and hair buildup. Be careful not to vacuum small parts as well.)
  • Electric screwdriver or drill
    (This will be used as a kind of lathe that holds the gear wheel in order to contract its diameter.)
  • Set of files, straight and round.
  • Screw and nuts 4-40 or M3 to retain the small gear wheel to the drill.
  • Step drill bits
    or any other tool that can help expand the housing holes diameter such as grinding stone, awl or a file.
  • Swivel burrs removal tool.
    (This is a great tool to help in expanding housing holes.)
  • Vise grips or a bit handle
    (This is to hold the drill bit etc. It is advised to expand the holes by hand and not with an electric drill to gain precise and more controlled process.)

  • 3 sealed ball bearings with the following dimensions:
    (in x out x thick, Metric system)
    - 6x10x3 mm (for motor gear)
    - 10x15x4 mm (for small beater brush gear)
    - 15x21x4 mm (for large bristle brush gear)

    To save you time, I have prepared a set of the 3 needed bearings that you can purchase now. Click the following Buy Now button to purchase.

Buy the bearing set now for just US$ 24.90

You'll receive:
- 3x bearings with listed size. (1x each)

* Rubber sealed type, best for dust blocking. (rubber color varies)
* Flanged 6x10x3 bearing for easy installation.
* FREE worldwide shipping included ! (Registered airmail)

CHM mod bearings


B. Disassembly of the robot and modding the gearbox
Note: since most of the screws are screwed to plastic bosses,
it is advised to use hand screwdriver for fine torque control.

1. Place the Roomba top down on a solid work surface
Remove the screw from the rotating side brush and gently pull it out
Avi's CHM mod 1

2. Remove the four screws holding the bottom plate and remove the plate
Avi's CHM mod 2

3. Take out the battery, lift it using the 2 plastic tabs.
Take out the dust bin.
Avi's CHM mod 3

4. Unscrew the CHM 4x screws and take it out by pulling it gently.
Avi's CHM mod 4

5. This is the CHM - "Cleaning Head Module"
* Arrow points to the gearbox side
Avi's CHM mod 5

6. Open the module top door and take out the bristle brush and the beater brush.
Avi's CHM mod 6

7. This is the mating area where bristle brush and beater brush mate with the gearbox.
The gap between the gear wheels cylinder to the plastic housing is seen clearly.
This is the area which this mod is dealing with.

Avi's CHM mod 7

8. Take apart the CHM module by unscrewing 3x frame screws and 2x motor PCB screws.
Take off the small round sticker that keeps the motor tension cable.
Avi's CHM mod 8

9. Grab the head of the tension cable with a small pliers/tweezers, pull it up, slide it while spreading the frame a little and push the head down through the gap in the frame
so the head and cable will go under the slot / inside the module case.
Avi's CHM mod 9

10. Start separating the CHM frame by spreading its 'wings' (one after the other)
and rotating the CHM inner case.
Be careful not to use excess force.
Avi's CHM mod 10

11. Pull up the motor's PCB. (hold the board, not the wires.)
Avi's CHM mod 11

12. You can now separate the inner CHM case (Red in this case)
from the outer frame (Blue in this case)

Avi's CHM mod 12

13. Remove the gearbox cover by unscrewing its 6x screws.
If cover does not get off easily, use a small screwdriver to help separate it.
Avi's CHM mod 13

14. Remove the 6x gearbox wheels, clean it with warm water and soap.
Avi's CHM mod 14

15. In order to get to the CHM case motor hole, move aside the motor.
First unscrew the 2x screws of the plastic bracket that holds the motor to the case.
Avi's CHM mod 15

16. Slide the motor and move it aside to clear room for case hole rework.
Pay attention to the hex shape motor shaft which meets with the motor gear wheel.
Avi's CHM mod 16

17. Now contract the gear wheel mating cylinder diameter.
Modified diameter should meet the inner diameter of the relative bearing.
Mating should be tight. All gear wheels cylinder mating diameter are contracted.

First image shows the 3 gear wheels to be modified.
Second image shows the motor gear wheel which is held with a 4-40 screw
and nut in order to attach it to an electric screwdriver chuck jaws.
If possible, prefer using table drill or a lathe for perfect centering and slignment.
Avi's CHM mod 17_2
Avi's CHM mod 17

18. Diameter contraction is done here with the help of an electric screwdriver and a file.
This is not the best method to use as it is very difficult to get perfect centering.
Use a table drill if you can or a lathe for much better results.
Pay close attention not to file too much !
Check fitting to the bearing often till you reach needed diameter.
Don't file the gear wheel, just its mating cylinder diameter !
Make sure that file's flat surface is pointing towards the gear.

Motor wheel cylinder size fits bearing inner diameter of 6.0mm. Stop modifying at 6.3mm
Beater wheel cylinder size fits bearing inner diameter of 10.0mm. Stop modifying at 10.3mm
Bristle wheel cylinder size fits bearing inner diameter of 15.0mm. Stop modifying at 15.3mm
Avi's CHM mod 18

19. Bristle and beater gear wheels attach to the electric screwdriver with its internal metal pin.
Pay close attention not to file too much !
Check fitting to the bearing often till you reach needed diameter.
Don't file the gear wheel, just its mating diameter !
Make sure that file's flat surface is pointing towards the gear.
Avi's CHM mod 19

20. Now expand the case holes to meet the outer diameter of the bearing.
Do it by hand for better control and use any of the above mentioned tools.
Mating should be tight. All mating holes diameters are expanded.
Check fitting to the bearing often till you reach needed diameter.

Hole size for motor wheel fits bearing outer diameter of 10.0mm. Stop modifying at 9.7mm
Hole size for beater wheel fits bearing outer diameter of 15.0mm. Stop modifying at 14.7mm
Hole size for bristle wheel fits bearing outer diameter of 21.0mm. Stop modifying at 20.7mm
Avi's CHM mod 20_2
Avi's CHM mod 20

21. When reaching needed diameter, insert the bearing with a little force.
Here you can see the motor bearing with the gear wheel installed.
If using a flanged bearing, the flange should be on the gearbox side.
Avi's CHM mod 21

22. In case you missed and diameter is larger than needed, don't despair ;-)
Use Epoxy glue to fill the gap but make sure the bearing is centered to the hole.
Tip: To prevent gluing the inner bearing ring, mask the bearing prior of applying the glue.
Avi's CHM mod 22

23. Assemble all gear wheels and rotate the set by hand to see it moves freely.
Lubricate the gear wheels using Lithium grease.
Assemble the gearbox cover with its 6 screws and make sure it attaches without gaps
Avi's CHM mod 23

24. Assemble the brush motor.
Pay attention to the hex mating of the shaft to the gear wheel when you slide in the motor.
Pay attention to the plastic notch that needs to fit its recess in the case.
Avi's CHM mod 24

25. Test CHM. You can use a 9V battery or a power supply if you have one.
Connect + to the Red motor wire and - to the Black motor wire.
At 16VDC, current should be less than 0.5A
If you test it without outer frame, hold the tension wire to allow it to work.
Avi's CHM mod 25

26. Assemble the CHM outer frame.
Return the tension wire round head to its place. Screw 3x case screws and 2x PCB screws.
Avi's CHM mod 26

27. Attach a new small piece of tape to cover the tension wire head recess/slot.
Avi's CHM mod 27

28. This is a view of a modded CHM with bearings from inside the case
where bristle brush and beater brush meet.
Avi's CHM mod 28

C. Assembly - assemble all parts in reverse order to what is listed above
If you have completed the assembly and left without any screw,
hit the Clean button and check if your Roomba is working...

D. Voila - you now have a working iRobot Roomba with modded CHM gearbox


Have fun and enjoy your Roomba.

Want to improve your Roomba with this mod? Buy Now the bearing set or,

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Last update: Apr 14, 2014

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