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Building the Helmet Cam

Posted by Tom Benedict on 19/05/2014

The biggest problem with most hat cams or helmet cams is that there’s no way to aim them accurately. A couple of posts back I mentioned a project to attach a reflex sight to a helmet camera to give me some way to keep the camera aimed at the subject. I ordered a reflex sight and a Picatinny / Weaver rail to mount it on along with a Gopro Frame mount. All the bits and pieces have arrived, so I started designing. Then I realized this is really a scrap box project: the design and build phases are really one and the same. So I started over with the bare bits I wanted to stick on the helmet: a Gopro, an A2200, and a reflex sight, and got busy.

Two Cameras and a Reflex Sight

Reflex Sight:

The reflex sight has nearly zero magnification and projects a red dot into your field of vision as if you had a laser pointed out at the landscape. The idea is that once the sight is dialed in, the center of the frame of the camera will lie where the red dot points.

Reflex Sight Dot

The dot is projected out at infinity, which explains the reason why I couldn’t get the dot and the body of the sight in focus at the same time. (Dang limited depth of field!) Even though this one was made for a firearm, reflex sights like this have been used as wide field finder scopes on amateur telescopes for decades. Adapting one to this application seemed reasonable.

Camera Mounts:

I toyed with the idea of having the two cameras share a common mount, but wound up scrapping the idea. The field of view of the Gopro is wide enough that I can get the two reasonably aligned even if the Gopro is on a separate mount. Since my Gopro came with a bunch of helmet mounts I sacrificed one to the project and stuck it to my bicycle helmet. Done.

Gopro Helmet Mount

Since I’m planning to use the A2200 zoomed in to about 35-50mm equivalent, its pointing is more critical. The reflex sight has screws for adjusting azimuth and elevation, so the mount for the A2200 is fixed – no ballhead, no adjustments, just a hard stop at the back to keep it from rotating on its tripod screw. The reflex sight and its mount need to maintain registration with the A2200 mount, so I built them as a single unit that can be mounted to my bicycle helmet.

Reflex Sight Mount:

I’m left-eye dominant. Most of the time when building aiming devices you want to use your dominant eye. But since the idea here is to also have one unobstructed eye to… well… to keep an eye on things, I also wanted to leave my dominant eye free. In short, I really wasn’t sure which eye to put the sight in front of. So I made it ambidextrous. To do this I just needed to have another rail on the other side of the camera mount so the sight can be mounted on either one. In anticipation of this I bought two lengths of rail. As it turns out each one was just over twice as long as I needed, so I cut one in half and kept the other as a spare.

Reflex Sight on Rails

Since the camera will be mounted above my eye line rather than below, I decided to mount the sight upside-down. This is the opposite of how these are typically mounted, but in this case it made sense. This keeps everything nice and compact, minimizes parallax between the sight and the camera, and simplifies attaching the sight to the camera mount.

Helmet Mount:

A quick word about the fate of my bicycle helmet: It’s doomed never to be used on a bicycle again. In order to mount all this hardware to the helmet I wound up screwing and gluing a strip of aluminum to the front of the helmet. From a crash standpoint this basically means I’ve got lots of sharp metal points aiming at my head. A crash with this thing on would be an instant frontal lobotomy. So from this day forth it’s strictly a camera mount.

Reflex Helmet Mount

The helmet has a vent hole straight down its centerline so I had to use a wider strip of aluminum than I wanted to. I wound up using a strip 1.7″ wide with screws spaced 1″ apart down the sides. The strip was bent across a form (the corner of the bandsaw table) and glued using white Gorilla Glue. It’s not coming off.

The edge of the strip that protrudes down in front of my face has  double row of holes spaced 1″ apart. The holes are spaced 0.2″ apart vertically to give me some range of height adjustment for the camera mount. I put four corresponding threaded holes in the camera mount spaced 0.3″ apart. Depending on the combination of holes I use, I can change the height of the whole camera mount in 0.1″ increments. It turned out I didn’t need this kind of adjustability, but it’s there.

Putting It All Together:

A lot of the “where should things go” decisions on this were made by standing in front of a mirror with all the various parts in hand. I know now my eyes are slightly less than 3″ apart, they’re shifty, and I’m not to be trusted. No! Wait! Disregard that. (They really are less than 3″ apart, though. Gotta love calipers.) I now know my helmet stops several inches above my eye line. So much so that I had to change my original idea for the mount to add more “drop” to it. Once I got those issues sorted out, though, it was just a matter of bolting it all together.

Whole Shebang

Of course no design choice, no machining technique, could keep this from making me look like an utter dork once I strapped it to my head.

Dork in a Headdress

But hey, if it gets good photos and video footage, it’s worth it.

– Tom


5 Responses to “Building the Helmet Cam”

  1. Dork? Not a bit! OK a little bit, but who cares. Makes you look dangerous.

  2. Tim Cole said

    How do you go about boresighting the A220 and the red-dot sight — just trial and error?

    (Spec ops toy plane? Sounds like a drone to me!)

    • Tom Benedict said

      At first I tried trial and error, but finally I got frustrated and hooked it up to a remote monitor. That way I could see in front of me, see the dot, and see the display from the camera. I picked the corner of a picture frame hanging on my wall as a target and dialed the little guy in.

      The most disconcerting part about the whole thing was bringing this tiny little allen wrench up to my eye. I found myself chanting, “Don’t… twitch… now…”

      The plane I want to use this with doesn’t even have a motor. If it is classified as a drone, we’re doomed.

  3. […] « Building the Helmet Cam […]

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