RC Lego Missile Launcher

Chasing the kids around with Nerf guns is tiring. If only there were some way to shoot at them without needing to get up...

Now, there is. Presenting the remote-controlled Lego Missile Launcher:

It both steers and fires remotely, using two IR remote-control sets (one for left and right wheels, one for the launcher). There's another motor channel still left, which could be used to control the elevation of the launchers, or for a second launcher.

Here's a front view of the launcher, showing one of the IR receivers and the gearing for the wheel motors:

Here's a picture of just the launcher assembly. When the motor turns the worm gear, it slowly rotates the camshaft. Each of the cams triggers one of the missile launchers.

Since the cams can be positioned in four different ways on the axle, it's possible to add two more launchers outside the adjustable angle supports, firing out of phase with the two interior launchers.

Next, I'm tempted to rebuild it using Lego Mindstorms, and program it to seek and destroy targets on its own...

Open Source Projects

This has been a very open-source year for me at Google. In addition to working on some major projects (Chrome and now Chrome OS), I've also released the following:

Software Construction Toolkit - A set of extensions to the open-source SCons build tool, to make it easier to build and test cross-platform applications. Written in Python.

Mini Golf Score - My first Android app. I was inspired to write this by my two boys, who haven't yet figured out how to take turns at mini golf, and who often play the game more like hockey than golf. I designed Mini Golf Score so that I can just tap on their names as they hit the ball, and each tap adds a stroke to their score for the current hole. It's a free app at the Android Market (note: that link only works if you're on an Android phone). Written in Java.

Nerf Vulcan Machine Gun Rechargeable Battery Mod

Nerf has made the Best Gun Ever - the Vulcan Machine Gun. It fires 25-round belts at several rounds per second.

Only one problem. It needs 6 brand new D batteries to get anywhere close to the claimed 3 shots/sec. Those aren't cheap, and need to be recycled.

Fortunaately, there's an easy fix. 6 x 1.5V batteries is not too far off from a 9.6V rechargeable racing pack.

Parts:

• 9.6V racing pack. You can get a decent one with a charger for $15. Try to get a charger which shuts off automatically when the battery's charged; the cheap ones don't, which will fry your battery if you forget and leave it plugged in too long.
  
• Extra connector for racing pack. I chopped mine off one of those cheap chargers, which came with a remote control missile launching tank.
• Alligator clips.

Tools:

• Wire cutters
• Soldering iron

Use the wire cutters to chop down the center divider of the Vulcan's removeable battery box so that the racing pack will fit. Then strip 1/2" of insulation off the extra connector and attach the alligator clips. Solder them on, so you get a good connection; the Vulcan wants to draw lots of juice. Charge and attach the battery pack.

One end of the battery box has metal pads on it. If you hold the box so those are on the left, that matches my picture. Clip the - (black) wire from the battery pack onto the spring closest to you. Clip the + (red) wire from the battery pack down into the far right connector. It should look like this:
Now, put the rechargeable battery in the battery box and slide it all into your Nerf Vulcan gun. Add darts, and fire away! It doesn't fire any farther (since that's dependent on the spring action in the gun), but it will fire a lot faster. You should get about 3.5 shots/sec on a fresh charge. And you can always switch back to those D batteries in a pinch.

Disclamer: Use this mod at your own risk. I'm sure this voids the warranty. While I haven't seen the slight over-voltage burn out the motor of my Vulcan or break the internal action yet, that doesn't mean it won't happen eventually. This mod is not endorsed by Hasbro.

Termites and doors

Thursday I opened the side door to our garage and discovered a pile of termite droppings under the door. The bottom of the door and its frame have been a little rotted for years, so I guess it's not completely a surprise. Still, it's never a good thing to find termite droppings.

Took the door off the frame and prodded it and the frame with a screwdriver. Frame is fine. Bottom of the door disintegrates into paint flakes and a huge pile of termite droppings. Ok, it could be worse. The termites are in one of the few parts of the house that I can replace myself.

Carefully measured the doorframe. 32" wide by 81" tall. About half an inch of space between the frame and the studs. Then, off to Home Depot to buy a new door. Lots to choose from. Found a nice steel-lined door with a window. They come in 32" and 36" widths. Great, 32" is what I need. Steel-lined doors are heavy, but managed to get it into the mini-van.

Got home and ripped out the old doorframe. Broke the handle of my favorite framing hammer in the process. Finished the demolition with my favorite 3' crowbar; in retrospect I should have started with the big guns.

Now, all I need to do is prop up the new door, shim it and align it, and screw it in.

Except the new doorframe doesn't fit.

Measured the doorframe. Aha, when you buy a 32" door, they mean the door is 32" wide. The frame adds another inch on each side. So I had a 34" doorframe and a 33" hole to put it in.

But with a 3' crowbar and a 16-pound sledgehammer, all things are possible (0r at least, removable). Widened the opening a couple inches, including shifting a stud and pounding back the stucco and concrete. Not quite how I'd envisioned my afternoon. On the bright side, hitting things with a sledgehammer is a good way to get out the frustration, um, of needing to hit things with a sledgehammer.

Several hours of pounding and shimming later, the door is in place. Now, all I needed to do was screw it in with the included 2.5" screws. Which are all apparently made of cheap steel, or the studs in the garage are really hard, or both. The screws snapped off or strip partway into the frame. Not only does this remove support from the door hinges, but it bows the frame inwards so that the door doesn't close.

Gpt out hacksaw. Removed blade from hacksaw. Slid blade in between shim and now-bowed-inward doorframe. Cut screws. Repeated on other side of shim. Door frame is now unbowed.

Found 4 nice sturdier 3" screws in my box-o-parts. Now we're back in business. Never throw out good screws. Added deadbold and doorknob from old door. And at the early hour of 10:30pm, the door is in!

Did the stucco-ing over the next day and a half. Stucco is great stuff - like wet sand. Takes an hour or so to set. I bet it's possible to build a great (and permanent) sandcastle out of it. Must bring a couple of bags of stucco to the beach next time. If I build at low tide, the stucco should be hard by the time the tide comes back in. And woe to the teenagers who try to kick over my sandcastle...

Lego spider

It's spring, and the black widow spiders are coming out. Here's an enormous one I "found" in our shed out back...

It was quite upset when I brought it in the house for some pictures...

So I squashed it...

600 pieces of Lego, build time about 8 hours.

Lego chainsaw

When you're running low on ammo, here's what you need to fight off the Lego hordes - a chainsaw with working motor.

I wonder if I should pack this on my upcoming family trip to Legoland...

Lens cap gray card

Getting the white balance (color cast) correct when shooting with a digital camera is sometimes a challenge. Here's a quick project which can solve this problem.

Buy a cheap gray card from any photo shop (online, I've had good luck from Adorama and B&H). Cheap cards actually work better than expensive ones, because they're usually printed on thinner cardstock. Cut out circles to fit inside your lens caps. Stick to the lens cap with double-stick tape.

Do a quick check to make sure the card isn't touching the lens when the cap is on; some lens caps work better for this than others. You can also buy replacement lens caps which may work better than the one that came with your lenses.

Now you're never without a gray card, and it's right at hand when you need it. You can either zoom in on the gray card and use the "custom white balance" feature of your camera, or correct the images to match later in your photo editing software. The latter works better if you shoot RAW (which lets you change white balance after the fact), or if you set your camera to a white balance which is "pretty close" (for example, set it to daylight or cloudy outdoors). For this trick to work, it's important not to use in-camera auto white balance; you want the white balance to be the same in your keeper shots as it is in the throwaway shot which shows the lens cap.

Here's an example of where auto white balance can go horribly wrong, and the result with the gray card.

The first shot is straight out of the camera (Canon 30D), using in-camera auto white balance. Not bad, but the image has a blue cast. Still, it's much better that what Photoshop did with it (middle image). The last image is using click-neutral on the lens cap; this is the color the bouncy house actually is.