In praise of thumb-operated optical trackballs with scroll wheels - and some warnings about the serious ergonomic problems of mice  . . . and how to fix a problem with the Logitech M570 trackball which results in limited cursor movement to the left

Robin Whittle Last update 14 March 2018


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2018-03-14 Fixing the focal plane problem with two M570 trackballs

I mentioned this on the Logitech forum:
The "*****" in that text there is the forum's profanity filter's replacement for "the balls".  This message also mentions how I raised the rear of the M570s body and added a rest for the first segments of my fingers.

My wife Tina and I have been using two M570 trackballs for six or more years.

During this time, at least the last few years, I noticed a problem with both of them which seemed to come and go in severity: when moving the ball to the left, especially when moving it slowly: the cursor did not move as much to the left as it should.  When this happens to a limited degree, we hardly noticed.  When it occurs to a greater degree it causes annoyance since it is harder to get the cursor to do what we want.

One test for this is rocking the ball left and right, and seeing that the cursor moves further to the right than to the left for each cycle, and so moves, on average to the right of the screen.

Eventually I figured out the cause.  If you have these problems, you can do this test too:

Establish that the erroneous behaviour is occurring when you are gently touching the ball, which is the normal mode of operation.  Then try moving the ball slowly left and slowly right - in our cases we saw the cursor move hardly to the left and reliably and substantially to the right.

Now press the ball very firmly and make the same movements.  If this improves the left movement of the cursor, then your results are the same as ours.

I concluded from this that the focal plane of the optics, which sense the granular silvery pattern below the surface of the blue ball, is too far from the surface of the ball, and needs to be moved closer - that is, towards the centre of the ball.

The optics involve an infra-red laser (perhaps a VCSEL) illuminating the ball from below, via a lens, with an image of part of the ball's surface being projected onto a sensor chip, via a very small sphere, which is above the clearly visible laser lens.  All this is mounted in a little module which clips reliably to the ABS plastic shell which holds the ball, by way of three milky-white spheres.  Earlier versions of Logitech trackballs used a red transparent ball, perhaps synthetic ruby.  These might be some other hard substance, such as sapphire.

To dismantle the trackball you need to undo five small screws, which involves removing the front, rear and right rubber feet, and using a knife to uncover the screw which is hidden behind the sticker inside the battery compartment, just below the ".5" of the "1.5V" text.

My technique for moving the optics and ball closer together is to heat the plastic of the shell in the area where it holds the rearmost (sapphire??) ball (the one closest to the optics), so the plastic becomes softer.  ABS is good for this, since it becomes rubbery and does not melt suddenly.  For the first trackball I used a narrow hot air gun, as used for surface mount electronics.  For the second one, I tried a technique which should be more accessible to most people: I heated the area behind the ball (the outside of the shell) for about 70 to 80 seconds by holding it in close proximity to, and above (2 to 3mm above, for the hot air current which rises) the heater part of a temperature-controlled soldering iron (Weller WCTP). 

In both cases, the plastic was very hot to touch, and is sufficiently soft to deform.  I can't advise in greater detail how to do this, but perhaps you could test the softness of that area of the plastic by seeing how deep a small screwdriver will go into it with moderate pressure. 

Then, with the plastic in this state, I inserted the ball and pressed firmly for a few seconds.  This is what I did with the first one, and it worked fine, as shown in the photo below.  Before doing the second one I recognised that the hot sphere might easily have caused an indentation in the ball, which would probably render the trackball useless.  So for the second one, I used 4 layers of masking tape over that part of the ball, and then two layers of alfoil from a butter container (a few layers of ordinary alfoil should do the trick), to conduct the heat away from the sphere, so it does not affect the ball.

You can see how close the ball is to the sensor end of the shell, and I think the idea is to deform the plastic sufficiently that the plastic surrounding the rear sphere is pushed out a little, sufficient to allow the surface of the ball to be, say, 0.5mm closer to the optics.

With the second one, I watched the outside part of the shell carefully as I pressed the ball into it, and did so until I could see a small bulge where the plastic was deformed by the sphere moving into it.  This was visibly the same result as I had achieved with the first one.  I think this is a better approach than trying to estimate how close the ball is to the optics.

You can see in the image above where the lamp is reflecting on the left (rear) part of the shell, the bottom of the lamp's reflection is distorted by the shell being deformed as described above, by heating and pressure on the rear sphere, so the ball now rests a fraction of a millimetre closer to the optics system (at the bottom, connected by the flexible printed "cable") and so is in better focus, so solving the problem of the cursor not moving properly when the ball is moved to the left.

I also found the same cursor movement and focal plane problem with a wired trackball T-BB18, which has a completely different ball and optical system.  The optics assembly was mounted somewhat loosely in the shell and I was able to fix the problem by placing some silicone rubber in a compressed state between the right side of the optics PCB and the main PCB, thereby pushing the optics system a little closer to the ball.

2011-05-05 No more cable-connected Logitech trackballs

Logitech no longer make a cord-connected thumb operated trackball.

I have been using their thumb-operated trackballs since 1990 - the one with a grey ball and rollers "Trackman Mouse T-PA1-9MD".  In March 2018 I found only these photos of it: . It is interesting to see that such a significant piece of technology, from pre-Internet days (for all but those in academia) is so poorly documented 28 years later.

They still make a wireless one, which requires a little USB plug receiver - and batteries, and synchronisation with the receiver.  This is the Wireless Trackball M570.

Perhaps you may like to add your thoughts to this discussion of the demise of these fine devices:

Fortunately there are plenty of the last wired model around, including on eBay: "Logitech Trackman Wheel".  Must these excellent devices go the way of airships and electronics-free cars?

Logitech stopped making wired versions of their excellent thumb-operated trackballs in 2011!

Back to the 2000 version of this page . . .

The computer mouse is an awkward, stressful, RSI-causing monster.  So is the QWERTY keyboard - which has keys laid out specifically to slow typists, in order to reduce the jamming of hammers in early mechanical typewriters.  Unfortunately, the alternatives to the QWERTY keyboard are unlikely to be widely adopted because they are either very different from a keyboard, or involve a different (Dvorak) arrangement of keys which is impractical to learn without going totally cold-turkey on QWERTY.

Fortunately, changing from a mouse to a better alternative is easy.

This page is devoted to what I believe is by far the best approach to pointing devices for general use - the Logitech TrackMan Marble Wheel. (The Marble Wheel is for PS-2 and USB interfacing, and works with the Macintosh.  I also use the TrackMan Marble + which is PS-2 and serial.  The earlier TrackMan Marble does not have the scroll wheel.)    The right hand must be used - which may be a problem for left-handers.  It may not be as good as a mouse for drawing motions - but a mouse is lousy for those anyway.  Apart from these constraints, I believe that anyone currently using a mouse would be much happier using a Trackman Marble Wheel, that their productivity would be improved and that the risk of RSI would be greatly diminished.

The problems with mice

A technical journalist friend of mine had severe shoulder pain from using his mouse (a Mac mouse) - to the point of having elaborate exercise machines in his office so he could perform the physiotherapy exercises he needed.  He had to keep working, so he learned to use the mouse in the other hand!

It seems that it is very easy to learn what a mouse does - children do it in a minute or two.  It seems that using a thumb-operated trackball takes a little longer - but it is not a hard device to use, and the RSI and productivity benefits make it well worthwhile.

Pointer devices other than optical thumb trackballs or mice


The Logitech Trackman Marble +

Logitech make a number of trackballs, not all of them using optical sensing.  See:

The one I currently use is the Trackman Marble Wheel.

The advantages of this over all other systems (apart perhaps from other Logitech optical trackballs) include: The disadvantages include:

Care and feeding of the Logitech Marble +

When the Marble is first purchased, the ball does not roll as freely as is it is meant to.  This could be a significant marketing problem, as people try it out in the shop and find the ball does not move freely.

The solution is simple:

"Oiling" the ball

The ball will run perfectly freely when it is has a bit of naturally occurring skin oil over its surface.  This is not visible, but it makes all the difference.

When the trackball is manufactured, or cleaned (for instance taken out and cleaned with soapy water or alcohol) this oil is removed, and the ball will be quite stiff, rather than running freely over its bearings.

Oiling the ball in situ:

Run the palm of your hand over the ball to move it in all directions.  There is no need to press hard – just do it for a few minutes until the ball becomes so free you can give it a flick and it will continue to spin for a fraction of a second.
Oiling the ball if you have taken it out:
Simply roll the ball around in your hands.  This puts a bit of skin oil over it very quickly, so with maybe 20 seconds of this, it will be ready to roll freely.
The ball will be so free that even if you just touch the ball with your thumb, the ball will move freely.  Without this, you may find the ball sticking a little, or that its friction may cause your thumb to slide over the ball while it does not move properly.  This is not how it is supposed to be! Make sure the ball has a bit of skin-oil on it and it will move perfectly freely.

The ball is supported by three small (~1.2mm diameter) stationary spheres of a very hard material.  Previous models appeared to use synthetic ruby, but current production uses and opaque silvery glass-like material which seems to be just as durable.  Quite why a hard plastic ball should glide smoothly over three small fixed spheres is a mystery to me, but a touch of naturally occurring skin oil is essential.

If the ball is washed in alcohol - and there is typically no need to do this - then the stiff motion appears again and it is necessary to "oil" the ball, as described above.

Cleaning.  The only cleaning which should ever be required is:

That's it.  The scroll wheel uses optical sensing and should not need cleaning unless someone actually pours coffee or glue into it. It looks robust and I don't imagine it will wear out in years of normal use.  I have been using Logitech Marble optical trackballs intensively for years and have had no trouble.  They are far superior in movement to the older sea-shell-shaped light-blue ball model, or the still older grey-ball model, both of which used rollers, rather than optical sensing.

Drivers and acceleration

The stressfulness of using a mouse, or trackball, is exacerbated by the default setting of MS Windows mouse driver software which transforms tiny mouse movements into large screen movements, whilst providing little "acceleration".  In my experience the default settings for the Macintosh are much better.  X Windows mouse drivers are, in my experience, little better than the MS Windows standard drivers.  "Acceleration" involves making slow mouse movement cause moderate pointer movement, but faster mouse movement cause much greater pointer movement.  I think the default settings on the Mac have an acceleration which is a bit too high for my liking, but I believe the standard Mac mouse driver settings are a significant reason why the system remains popular.

All Logitech pointing devices come with a good driver program for Windows.  The Marble + plugs into the PS/2 mouse port, and functions like any standard mouse (although I think the scroll wheel would not function).  To use it properly, install the supplied Logitech driver software.  This creates a "mouse" item in the Control Panel (Start > Settings > Control Panel).  The only settings I alter are for the motion - to set the "Speed" to slow and the "Acceleration" to high.  (The following illustration is for an older version of the software than the current 8.50.)


This gives me really precise cursor control when I move the ball slowly.  The result, with such slow movements, is about a 1:1 relationship between ball and cursor movement on the screen - perhaps 120 pixels for a 1.5 inch movement of my thumb.  (This was for earlier software.  The exact details may be different for the Marble Wheel and 8.50 software.)  If I move the ball quickly, the acceleration factor is applied and the ball moves much further.  Unlike the super-accelerated Mac mouse settings, this does not move the cursor to the other edge of the window, but it does move it most of the way across or up and down the screen.  Unfortunately there is a limit to how fast the optics can follow the ball, so there is no point in flicking the ball very quickly.  The ball free-wheels a little, so you can give it a flick and let it roll.  Giving the ball two flicks with the thumb is far easier and quicker than moving a mouse to the edge of the mat, and then picking it up for another trip across the mat.

Alternatives to the Logitech Marble Wheel

Logitech make a Marble FX, which looks intriguing.  I haven't used it.  Perhaps the larger ball and ability to control it with thumb and index finger provides more precise control than the Marble Wheel.  Their "Marble Mouse" is not a mouse at all, and involves finger control of the ball and the thumb for the primary mouse button.  There is no scroll wheel.  I see no benefit to this over the Marble +.

Microsoft now makes a trackball called the Intellimouse Trackball:  It uses the index finger for the ball operation, the middle finger for the scroll wheel and the thumb for the primary mouse button.  It does not use optical sensing.  They also make a jumbo-sized "EasyBall" trackball for children.  (May 2000: they also make a mouse which optically tracks the table moving underneath it.  This should solve cleaning problems, but the thing still has all the ergonomic problems of mice.)

Genius make a trackball similar in layout to the pre-scroll-wheel Marble the "EasyTrak".

Other than perhaps the Marble FX, I cannot see how any of these would be superior to the Marble Wheel.  (Unless you want to use serial connections, because your computer has neither USB or PS-2.  In that case, you need to find an older Marble +.) The Marble Wheel  retains all the switch function finger actions of the standard mouse, and simply replaces the hand-arm-shoulder motion movements of the mouse with the much simpler and easier thumb movements for the trackball.

Where to buy the Marble Wheel

Logitech's site is well organised.  There are separate sections for particular countries, and an easy-to-use system for locating the nearest retail store.  I found that this did not list every retailer which actually carries Logitech gear.  In Melbourne, I know that Software Express has them.  I bought my most recent Marble Wheels from Harris Technology: .