Transfer Table from Flatbed Scanner ?

[jrbarney]

Okay, it's "Rube Goldberg" time. I have a flatbed scanner with a sensor that is dying. Has anyone has used a flatbed scanner mechanism as the basis for a transfer table in HO or N scale ? The mechanism would have to be mounted below the rails and table, and you would have to stop the scanner motion at
each track.
Bob
NMRA Life 0543
P. S. No, I don't need yet another project.

[Anonymous]

It's a neat idea - the scanner motor is designed for precise control (they may be stepper motors, which I know little about beyond that they are very precise) so you should be able to wire it to move in small increments (maybe put a microswitch in line with each track so that it automatically stops there, then have a pushbutton that over-rides that to move it to the next one - you'd just release the pushbutton to have it stop at the next track). Could be wired to operate with two buttons, one to move each way. This is way beyond my electronics abilities but it sounds like a really neat project!

[mecovey]

Great idea! I have an old flatbed scanner that is used to display my dust collection. A transfer table sounds like a much better use. What's needed is a SIMPLE control mechanism.

[Anonymous]

The microswitches would probably be the simplest - you'd wire it so the switch cuts off power when activated (by the moving part of the table), but pressing the pushbutton would briefly over-ride that and move it in the desired direction. I've seen a similar mechanism in a ball-bearing clock (one of those ones where ball bearings are rolled down tracks to show the time), a basic clock mechanism with a magnet activates a reed switch which gives a burst of power to the motor, when the arm moving the bearings has completed one turn it hits a microswitch and stops (until next time).

[edkowal]

Stepper motor control is not a simple matter of a push button or toggle switch. There is, first of all, more than one type of stepper motor. Each of the types has to be wired up to a power source in a specific way. Wire up yours wrong, and nothing will happen.
So you've got to find out which type of stepper motor you've got. This can be done, but before you do anything else, you've got to know that.

Secondly, rather than a level voltage like 3 volts, or 6 volts to generate a certain speed, stepper motors require a train of voltage pulses. If you want the motor to turn at a constant speed, the train of pulses has to be provided to the motor at a constant frequency. Very often, to get the motor to turn in specific directions, you've got to provide TWO sets of pulses, both at the same frequency, but separated in phase. If channel A's pulse precedes channel B's, the motor turns one way. If channel B precedes channel A, it turns in the other direction.

There are circuits called, appropriately enough, stepper motor controllers, which do most of this for you. So that may not be as difficult as it seems.

However, since this is a precise and digital method of operation, you've also got to arrange other information. Each stop on the transfer table will be at a specific number of steps from a known origin point. You've got to determine those values. You've also got to provide a method for the transfer table to be able to reset itself to that known origin point. And so forth.

All in all, this is a do-able project. But it is not a simple one. It would probably require you to program a microcontroller, similar to the processors in the DCC decoders, to do what you need doing. You'd also need to get that to interface with the stepper motor controller circuit. And then you'd need to adapt that to the mechanism which you've built around the flatbed scanner, or whatever parts you've salvaged.

Although this may not have been the answer that you were looking for, it gives you an idea of the types of details involved.

-Ed