MOTOR-SPEED REDUCTION GEARING -- DRIVE-WHEELS

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INTRODUCTION

In this document we open the wheel-drive-gears box, give you a peek inside so you can see what the gear-set looks like, and to verify there are no drive-belts used to move Scooba's wheels. Information is provided which should tend to suppress any hope of being able to obtain any of these special parts, except from like assemblies.

Within the Gearbox

Having removed the motor/gear-head assembly in a prior process, along with the Wheel, entry into the gear-case is done by removing four each TFS3x1.4x10LG, #2 Phillips, pan-head screws from the case corners. Parts come out as follows:

  1. The cylindrically shaped outer-case slips off first, revealing a combination stub-axle and an internal-toothed final-gear having 31T. At the outer end of the stub-axle there is a pair of dog-clutch, type driving lugs that engage slots in the Wheel's hub-area.
  2. An intermediate bulkhead is the next item to remove. Notice it supports a static, axle-shaft from which the Wheel-gear receives much support. As this bulkhead is dismounted, the mechanic may hear a slight click as an unattended part falls to the bench. That would be the bar-magnet shown in Figure 2. Keep it safe, and remember to replace it when these steps are reversed. Replace it! Where does it fit? Oh yes! Notice in the end-view (extreme left in Figure 1) of the gear-case / motor-housing casting, there is a fifth hole, but only four screws were removed! The magnet's pocket is the largest-diameter hole in that group. Referring to this other Figure-2, the difference in diameters may be more easily detected.
  3. Next off, is the compound-gear made by forming two gears on the same axle. The smaller gear has 10-teeth which mate with the Wheel-gear; while its larger partner is a 44-tooth gear of finer pitch.
  4. Two more compounded-gears pull off in sequence, a 15T x 44T cluster; and a 15T x 30T cluster.
  5. Innermost, there is a 14T pinion gear that may be considered as permanently affixed to the motor-shaft.

The array of removed items is shown in Figure 1, with items removed in (1) at far right, and the final gear at left.

Figure 1. Motor's Speed-Reduction Gearing

In this particular gear-head, very little grease was found present, and that which was there was a colorless lubricant -- not seen in any of Roomba's Wheel or Brush drive gear-sets! That may explain why grease is not seen in the Figure-1 photo. It is there (no grease was removed, the gears were taken out and placed on a sheet of waxed paper).

Figure 2 provides a close-up of the sensor's magnet. It is probably safe to assume that this one is the same as each magnet used in at least three other places to actuate their associated reed-switch 'sensor'.

Figure 2. Magnet-Pellet for Wheel-Drop Sensing

What IF a Replacement Gear is Needed?

Finding replacement gears, made by a company other than iRobot, is highly unlikely. These gears, and gears in Roombas too, are all specially designed by, and manufactured for iRobot products. The chance of locating an equivalent part from some other commercial source has got to be poorer that winning a multi-million-dollar National lottery!

The most reasonable source of custom-parts, like these gears, is from a duff Scooba. However, that is not always possible, especially when the product is newly released, so there may be owners who begin thinking about having a damaged gear custom manufactured for them -- as has happened for Roomba-gears. A hint of what is involved in that process may be found here

Close It Up

As one might expect, the procedure for reassembling the gear-set is simply a reversal of the steps taken to pull it apart. There are just two precautions to mind, before moving too quickly:

  1. Engage the retaining-tab of the (wheel-down) leaf-spring with its slot at the top of the main-housing before mounting the intermediate flange.
  2. Be sure to insert the magnet into its receptacle, before mounting the intermediate flange.

Gear-Grease: Since there is no way to determine what grease had been applied to these gears at the factory, there is no way to make a specific replacement, or additive, recommendation.

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This page is currently maintained by G. Plews