The Electric Table (Ver. 1.0)

I've only seen a couple of dinette table mount systems:  The wall hung, swing bracket type and the two-post type.  Both are non-adjustable in height, require physically lifting the table, and are either all the way up up or all the way down. And "up" is just too high for comfortable use of a laptop.  (I never have gotten use to using a laptop on my lap.) , or, as we've found with the current arrangement, too high for normal use.

Some time ago, I made a different kind of "manual" bracket that allowed intermediate height positions but it still required someone to physically lift the table.  This is difficult for the Mrs.  There had to be a better way...

The following solution seemed pretty frivolous at first but after thinking it over, something invoving a motor seemed possible. That decided, I started putting the following prototype together.

Click on picture for larger image.

Here's what the Electric Table looks like from a normal perspective.  To change the height, operate a small toggle switch just under the front edge of the table.   More on the leg, below.
This is the over all view of the hardware without the table.  The black arm is a diagonal support made from 1/2" conduit that provides cantilever support when moving the table up or down.  The table top is screwed to the "T" bar in the back and connects to the conduit near the middle.  See below for a better picture. The cable dangling near the bottom ends in a double-pole, double-throw, center-off switch that reverses the motor for "up"/"down".  This switch is mounted under the front edge of the table
A view of the right side of the motor, a 24vdc worm-drive windshield wiper unit that has  plenty of power at 12 vdc to lift the table.  Got it from a surplus outfit on-line.  All the other stuff, unless otherwise stated, is out of the hardware store or my junk box. From down in bed postition to maximum height takes 10 seconds.
Left side:  100 lb test aircraft cable winds on a drum that is set-screwed to the motor shaft.  The cable goes down, around the sheave near the bottom and up the back where it's secured to the rear rail support.  The motor thus travels with the table.  The red and black switch is the down limit and is rigged to sense the cable tension.  If the cable slackens, either because the table is down all the way or hits an obstruction (like someones lap or a cushion) the cable relaxes, the follower releases the switch and the down circuit is interrrupted.
A closeup of the down limit switch.  The white rollers reduce wear on the cable.  The brass arm bends at 90 deg and pivots at the bottom.  The upper roller contacts the cable.  It's easier to see how tension of the cable keeps the switch closed until something obstructs the downward table movement.  Not shown is an auxillary spring that keeps more tension against the cable than provided by the switch.  This keeps the cable from looping off the drum.
The up limit switch.  I forgot to take a picture of this prior to installing the assembly but it's just a Radio-Shack micro-switch with a small roller arm.  The roller rides on the edge of the left rail and drops into a shallow dip where I wanted it to stop. Shown here is one of four slotted polypropylene blocks that slide on the aluminum angle iron rails.  I chose this mostly to avoid having to mount a dozen rollers to restrict the carriage to only up-down motion.  (It was a prototype, afer all...)  As it turned out, the blocks work fine
Here's one of the two "wiggle stops" that help laterally stabilize the table. They press lightly on two aluminum strips that are screwed to the wall.
A view from beneath with the table installed.  The two legs folded up are left over from the previous manually adjusted model.  Even though the table is quite sturdy and works fine in cantilever mode, I've decided to keep one of the legs in place and drop it down when the table is being used in the up position just to protect things from someone leaning or sitting on the table.  The machinery is strong but the wall paneling is not.  (See comment, below).
Here's the schematic for the rig, a standard motor reversing circuit with limit switches.  The "NC" next to the limit switches means that the contacts are "normally closed" when the switch is not being activated, namely, when the table is not at one of the limits.  When a switch is contacted, it opens, interrupting current of that particular polarity to the motor.  Since the other limit is not contacted, reversing the switch reverses the polarity and the motor can run in the opposite direction . . . until it hits it's limit.

Actually the whole thing turned out pretty well, a rare case where a prototype works better than expected  Unfortunately, the framing needed to support the regular table isn't sufficient to handle the kind of stress that a cantilevered table can put on it.  If I decide to keep this basic design, I'll likely mount the whole thing on a piece of 3/4" cabinet grade (ie. flat) plywood and secure this to several more points on the wall.  
No matter what, a powered table is the height of convenience when you find yourself configuring your dinette for sleeping-eating-sleeping .... etc.