Noticing streaks on the Macro or SLR with Letus?

[Bob Hart]

1. Quyen suggested don't do it.

2. There is a small dropping resistor on the motor to slow it.

3. There is an adhesive blob on eccentric to slow it.


Basically I trusted the designer on this one. The subject came up some time back and the observations as I recall were no improvement in the groundglass movement and concerns over possible shorter life of motor in continous duty at higher voltages.

9v was being talked about at the time. 4.5v is probably more realistic.

The motor's original function called for intermittant duty only.

[David Delaney]

Bob,

I got the same message from Quyen. I am thinking of upgrading the motor though, but I want one that is small and light enough to work, but that will give me the "axle" so I can put a counter weight on it - any suggestions?

[Bob Hart]

There are two styles of simple DC tracker motors in junked CD/DVD players.

One is identical with the CD tray actuator motor and almost identical to the disk drive motor itself except that the shaft is much shorter. As these motors are in intermittant duty only in a CD player, they are almost always in good condition.

These are a little to large to be used in a Letus35 but are fine for a full CD-R disk sized spinning groundglass design where space or size is not an issue.

Another style, is a smaller motor with a plastic worm drive pressed onto the shaft. This is the style I used on the Letus35 mod I attempted. It got left on and forgotten long enough to flatten a battery set so longevity should not be a problem.

I think I have seen this motor style also used in 3.5" 1.44Mb floppy drives.

There is a newer brushless motor used in some DVD players. This requires a control circuit to power it. Small scale aircraft motors likewise cannot be simply powered up with a battery two wires and a switch.

The small tracker motor is a very difficult fit in the available space in the Letus35 and the motor shaft needs to be shortened a little by trimming with a small cut-off wheel on a Dremel.

When you do this, you also need to tape over the exposed area of the motor bearing to protect it from abrasive contamination from the cutting disk. It otherwise it won't last very long before becoming noisy.

I think you will find Quyen did a very thorough search for suitable motors and there may not be much else out there he has not already examined and rejected. That is not to say the search should not continue.

I have contemplated actually dismantling a DC motor, drilling out part of the laminated centres in the armature fields, on one field, filling the drilled metal with lead to deliberately set up an out of balance state in the motor and use the motor itself as the eccentric. There will be a performance hit but the motor itself will not be otherwise loaded and air resistance will be minimised.

As I do not have the camera this Letus35 works with, I have not had it on the front burner as such.