I'm a physics professor, and the last few classes I've taught I've started filming my solving physics problems and posting them to my YouTube Channel (channel: www.youtube.com/sciencejedi, ever-growing playlist of problems here: PhysicsProblemSolving) . This has many advantages:

I do it offline, so I can spend as much time as necessary solving a problem, unconstrained by the limits of a class hour
I can solve many more problems offline by video than I can during class
Students can watch solutions over and over again, or just watch the parts they are confused about
Students who don't think they need to help solving problems can skip watching problems and solve on their own
By not using 10-15 minutes to solve a problem in class, I have more time for active learning activities

The past couple of terms I've been doing this I've jury-rigged a tripod with clamps and bungee cords to suspend a video camera over my desk. But it's precarious and unstable, and hard to get lined up and illuminated well. So I resolved to make a better solution -- a gantry to hold the camera! The requirements were:

It had to be easy to take up and down (so it wasn't on my desk all the time)
It had to be resistant to cats (or me) knocking it over
It had to securely hold the camera in a good orientation

This is my solution; it took a couple of hours to build.

Step 1: Planning

The desk where I film is my writing desk in my study. It has a sturdy construction and isn't paneled on the sides, making it easy to clamp a structure onto. I had the idea late one night while writing lectures and homework solutions, and quickly sketched it out (with relevant measurements to my desk) in my Moleskine.

The final product is very close to the original sketch. The specifics for your desk will be different, but the most relevant numbers here are:

The desk width. The top of the gantry is a rail the camera can slide on, so I can position it anywhere over the desk I want
The camera height. Since I'm filming myself writing, I wanted the camera out of my way so I can see the page, but also still be able to glance up at the camera's flipout screen. The vertical height of the gantry over my desk is roughly the height of my head when I'm sitting in my chair.

Step 2: Materials

To build the gantry as it appears here, I used:

1x4 boards (3 "longish" and 4 "shortish" and 2 "really small" ones -- I just used pieces from my wood bin)
3 1/4-20 hex head bolts; 1 is 2-1/2" long, and 2 are 2" long)
3 star knob handles (fitted for hex head bolts)
1 pot knob (1/4-20 thread -- fits camera mount)
3 tee-nuts for 1/4-20 bolts
drywall screws
2 bar clamps (to secure to desk when needed)
2 clamp on area lights (for extra, even illumination)

The star knobs and the pot knob were the only things I had to buy special; you can find them at your local hardware store, usually with the specialty connectors and bolts.

Step 3: Vertical Supports -- Clamp Boards

The vertical supports hold the gantry rail but also sit directly on the surface of the desk. I put wide "feet" on them that sit on the desk, allowing the gantry to stand upright before it is clamped to the desk. It hangs lower than the desk edge, making a firm "L" that overlaps the surface and the side of the desk.

For my gantry, the dimensions of the pieces are:

Vertical: 25" long (4.5" hangs below desk surface)
Clamp Board: 7.5" long

I always predrill holes for screw to prevent splitting of my boards. I traced the outline of the clamp boards on the vertical strut, drilled guide holes, and the secured the clamp boards with drywall screws.

Step 4: Vertical Supports -- Rail Mounting

The rail that holds the camera is secured to the vertical supports with a hand knob that threads into a tee-nut.

In the middle of the top end of the board, drill a 5/16" hole (to fit the barrel of the tee-nut) 1.5" from the top edge in the center of the board.

Tee-nuts have sharp teeth that secure them to the wood they are inserted into. You can pound them in with a hammer, but I find they tend to be loose and fall out sometimes if I do that. Instead, I use my bench vise and press them into the wood slowly. The tee-nut should be on the desk-facing side of the vertical support! This insures that when the bolt is tightened into it, it pulls the tee-nut into the board and clamps the boards together.

Set aside the two vertical supports while completing the rest of the gantry.

Step 5: Top Rail -- Slide Channel

In order to make the camera positionable anywhere over the desk, I wanted it to be able to slide back and forth. To this end, the top rail has an open channel that runs almost its full length. The securing bolt for the mounting bracket will pass through this channel and can be tightened down at any location.

To make the slide channel, I used my router table and ran the rail length along the fence to make a long straight channel. I think it is too much for the bit to chew the channel out in a single pass, so I made the channel in several passes.

I started with the bit very low, and made one full length pass. Turn off the router and remove the board, raise the bit slightly, and make a second pass. Repeat this process until I work my way all the way through the board. It took 5 passes to make this channel.

Step 6: Top Rail -- End Bracket

The top rail has L-shaped end brackets that hook over and secure to the vertical supports. My brackets are 3.5" long pieces of 1x4.

Drill a hole in the center of each bracket, 1.5" up from the bottom, for the mounting knob that will secure the rail to the vertical supports.

Pre-drill holes in the top edge of the brackets, and mount them to the rail with dry-wall screws.

Insert one of the hex-head bolts (2" long) in a star knob, and pass it through the hole you drilled in the bottom of the bracket. It should match up to the hole and tee-nut you inserted into the vertical support, and tighten down, securing the rail to the vertical supports.

Step 7: Camera Mount

The camera mounts on an L-shaped bracket that slides and secures to the channel in the top rail.

These pieces are smaller than the nominal 1x4 width; I ripped them down to be the width of my camera to insure that I could reach the controls and flip the screen out without difficulty. It consists of two pieces:

Rail Slide (sits on top of the rail): 4.5" long x 2.5" wide
Camera Plate (vertical, against camera body): 4" long x 2.5" wide

Secure the two pieces together to make an L with drywall screws.

There are two holes you need to drill in this piece. First, hold the piece against the rail, and mark where the channel runs on the rail slide. In the center of that mark, drill a hole for the clamping knob that will secure the camera mount to the rail. Doing it this ways goes a long ways to making sure the camera mount slides easily along the rail!

The second hole is for your camera, and where it is located depends on where your camera's threaded mounting hole is. Mine is near the front edge of my camera, so I drilled a hole in the camera plate 1/2" from the bottom edge.

Step 8: Camera Mount Clamping Knob

The camera mount secures to the rail with a star knob, but it has to thread into something. I used a small round piece of wood that came out of my scrap bin.

I drilled a 5/16" hole in the center, and press fit a tee-nut into it with my bench vise.

After the fact, I discovered that using a round piece like this makes it possible to use the bottom as a hand knob as well; that seems like a useful observation if you wanted to make your own knobs instead of purchasing star knobs.

Step 9: Camera Mount Assembly

Insert the pot knob through the camera plate, and secure the L-bracket to the rail with a star knob and the tee-nut plate made in the last step.

Things to check at this step:

Make sure the camera mount slides easily along the entire rail
Make sure when tightened down, the camera mount does not move along the rail
Make sure the camera fastens securely to the camera plate

If the mount does not slide easily when the star knob is loosened, you may need to clean up or widen the channel in your rail with your router. If you made the rail like I did, on a router table with a fence, then the channel should be very straight and a fixed distance from the edge; I had no binding problems sliding it up and down.

If your camera does not secure well, you may need to get a shorter pot knob, saw off the pot knob you have so it is a bit shorter, or shim your camera. I had identified the camera plate board before I went looking for a pot knob, so the length I had was good.

Step 10: Securing to Desk for Use

The pieces are small enough that when it is disassembled I can lean them in the corner of my study or put them on my closet shelf when school is not in session.

The gantry is very lightweight and easy to lift and move. I found the easiest thing to do is pre-assemble it by connecting the vertical supports to the rail, and then lift the structure onto my desk. I secure it to the desk by putting a bar clamp on each end, securing the clamp board to the edge of the desk.

Step 11: Ready to Make Videos!

The gantry is ready to use! It looks like a contraption on my desk, but it is out of the way so I can write comfortably while filming without having to worry about knocking it over or something coming loose. As planned, I can easily see the camera screen, and it looks straight down on my work page.

There is good natural light from the window of my study, but if I'm filming with my desk lamp there are harsh shadows, so I added two clamp on utility lights I had in the shop to even out the illumination.

This has been a great improvement over my previous setup, and I hope to make many more videos now that I don't have to futz and fret with the video setup. I hope you found this useful, and encourage you to try this in your own classrooms or filming projects.