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Beginner's Guide (Inputs)

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DaOld Man:
Basically what you need:
Motor to turn your monitor rig (I call the disc, bearings, whatever that is used to allow the monitor to turn, "the rig")
A drive that switches the high current of the motor and basically controls it.
A drive can be a simple DPDT switch, or an electronic circuit containing transistor switches.
As far as automatically rotating, an electronic drive is necessary.
A printer port on the computer, or an add-on PCI printer port card. (USB to printer port adapter will not work, however I am working on a USB version of MRotate.)
A program to control the drive such as MRotate.

MRotate offers several outputs and inputs as options that you probably wont need.

Things you will need:
2 outputs to instruct the drive to go forward (or CW) or reverse (or CCW)
2 inputs that attach to limit switches, which when the switch is made, tells the computer that the monitor is fully CW or fully CCW.

The other outputs are:
Drive enable: May be necessary. depends on what type of drive you use.
Degauss: you wont need this for your LCD monitor. (requires a relay)
Turn monitor off while rotating: This is truly a preference. (requires a relay and extra hard wiring).
Parking brake: This is something I have not seen done yet, but you could rig up a solenoid activated locking pin to lock the monitor still while it is not turning. (requires additional circuitry). Also some motors have friction type brakes installed on them. (MRotate3 is the first version to have this option.)

Mrotate is a command line program. This means to rotate the monitor, a command must be given to MRotate from the front end or another program. Example form Windows DOS (or CMD) box would be "C:\Mrotate\Mrotate3 0" to command the monitor to turn to horizontal position. When the horizontal position is reached, mrotate senses the switch being made and it turns off the motor and ends (if no other options such as degauss are selected).

Mala is a super cool frontend and it has a plugin available that was crafted for MRotate.
Mala knows the intended monitor position of each game in it's list, and the Mala plugin (startcom) sends a command to MRotate based on that position.
Mrotate is waiting for other frontend programmers to install this option. (hint hint)

I suggest you read the mrotate3 readme.txt file that is posted on here. It is much more detailed about what you can do with MRotate3.

And BTW, good luck with your project. I am always excited to see how others do the rotating monitor trick.
It is a lot of work, but well worth it, IMHO.

Feel free to download MRotate3 and play around with it. A program called pportreader is included, which will allow you to watch the activity on your printer port. (Just cant activate any inputs with it).

DaOld Man:
What motor to use?

Well, motors come in a variety of flavors. I wont get into the guts of motors, you can find out plenty of info on the web.

There are D.C. (Direct Current) motors. These work on direct current (like your car battery's current).
They usually have very high torque even at low speeds.
These motors are fairly easy to control. All DC motors have a field, which is either an electric magnet or a permanent magnet. The armature rotates in the field's magnetic field.
Simplest DC motors have permanent magnet fields and have only two wires to attach the power to.
To reverse rotation of the armature, just reverse the polarity on the two wires.
Speed can also be controlled by varying the voltage to the motor. You can also pulse the current to it.

A.C. (Alternating Current) motors are little more complex to use for what we want. They require alternating current (like the kind that comes out of the socket in your wall). Most AC motors have a Field winding (called the Stator) that creates a rotating magnet field. The part that transfers rotation out into the shaft is called the Rotor, and it has bars in it that are excited by the rotating field, inducing a current in them, which basically become electro-magnets. The rotor is pushed (or pulled) by the two magnetic fields, the rotors magnets try to match the rotating one of the stator.
Most AC motors are difficult to change rotation, unless they were designed to.
AC motors have good torque at high speeds.
AC motors do not have easy speed control. The speed can be controlled by drives that vary the voltage and frequency to the motor. Some AC motors have multiple windings, that when energized, changes the motor's speed in steps (such as a ceiling fan).

Stepper Motors. Steppers run by coils being energized in steps. The magnet (most commonly a permanent magnet) is mounted to the shaft. The magnet tries to align itself with the energized coils. As the coils are stepped, the shaft also turns in steps.
These motors can go X amount of steps and stop precisely on a degree of rotation.
The big disadvantage to steppers is that they require a controller that can control the coils to get proper rotation.
I was working on one of these to use with a rotating monitor. I even created a version of Mrotate (called MRotateStep) that controlled the motor through the printer port.
I could not find a strong enough motor (without spending my pension) that would rotate the monitor completely without losing steps in the process. Unless you have some sort of encoder feedback, if the motor misses a step it can get way out in the weeds. These motors are very common on CNCs.

Servo motors. Servos move to a precise spot based on a frequency from a controller. These motors are very common among hobbyists for car steering and model airplanes. I doubt you could get one strong enough to turn the monitor, unless you want to pay dearly for it.
We use servos at work that turn grinding rolls that weigh 60,000 lbs, but these are very expensive, and have very expensive drives and run on 480 VAC 3 phase current.

So out of these motors, the winner is: DC motor.
And a very popular motor on here is a windshield wiper motor from an automobile.
These motors are fairly cheap and easy to find on ebay. They run on 12 volts dc, which is a common voltage. (Your computer has it already, but be careful not to overload that source.)
These windshield wiper motors also have a gearbox built on, which reduce the speed and increases the torque.

I have attached two pictures. First is a dc motor very similar to a windshield wiper motor. This motor is actually a motor that was used on an 88 firebird to raise and lower the headlights. This is the motor I used to rotate my first project.

Second pic is a couple of stepper motors. I used the one on the left, which had a gearbox and a brake attached to the motor. This is what gave me the idea to add parking brake control to MRotate3.
The smaller stepper was no where near strong enough to do what I wanted, rotate a 19" LCD.
The bigger one worked, but as I said earlier, it would loose steps during rotation, which is not a good thing.

DaOld Man:
To help explain the next section I have attached the following line diagram. Please forgive the fast drawn cheesy diagram, hopefully it will lay out the basic steps in getting your monitor to rotate automatically.

DaOld Man:
Ok, after you have selected your motor, and how you are going to physically build your rig, you need to choose a drive.
I am only going to demonstrate DC motor drives, for they are no doubt the simplest motors to control.
First pic below shows how to reverse the motor rotation by reversing the power supply's polarity.
Second picture shows how a drive reverses the current flow to the motor, to control rotation.
Third picture shows a DPDT switch. This shows how the switches terminals connect to each other based on switch handle position.
fourth picture shows how you can wire the DPDT switch to control a motor's rotation.

This is probably the simplest and cheapest drive you can build.
This should show you basically how a drive works.
The major disadvantages to this drive are:
Fully manual control. Automatic control is not possible.
You must turn the switch off when the monitor has reached its full horizontal or vertical positions.

Next up I will show how to add limit switches to this drive so it will stop automatically. (So this drive can be automated just a bit.)

DaOld Man:
Ok, when you flip the above DPDT switch drive, you want the motor to stop when it has reached its full horizontal or vertical end of travel.
This can be done by installing limit switches that activate by a flag mounted to the monitor disc.
(See previously posted diagram).
The only problem is that when the drive tells the motor to turn back the other direction, it may not be able to do so because the current is broken by the previously activated limit switch.
A fix for this is to install diodes around the switches that will allow the current to flow around the switch, when current is going in opposite direction.
See drawing below.
Drawbacks of doing your rig this way:
DPDT switch must be rated for at least the maximum amount of current your motor can draw, as well as the limit switches and the diodes.
Also, speed control is nearly impossible in this setup, motor will run wide open from start until the limit is made.
And dynamic braking (more on this later) is nearly impossible with this setup.
This may not be a problem if your monitor rig turns slow already.


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