Even after spending a few evenings in front of the TV sifting through LEGO parts (there's an image that says "mature"), I realized I wasn't able to assemble all the elements needed. After contacting the publisher, who put me in touch with the authors, I found out that the five projects in Forbidden LEGO were made up of parts from a wide variety of LEGO kits, including some that have been off the market since 2001.

That's the first strike against the book. If you want to build the projects, you're going to have to forage, have a large collection of LEGO parts already, or spend a surprisingly large amount of money on eBay. There is a thriving LEGO aftermarket on eBay and you'd be shocked at the prices and variety.

I placed another order on eBay for another lot of gears and cogs and such, and although I didn't get all the parts I needed, I did find enough to let me substitute some parts for other parts.

You readers out there who are engineers are welcome to cringe right now. Yep, substituting parts in an engineering design is about as reliable as substituting barbeque sauce for just about any other sauce in cooking. You'll get food, but not necessary food anyone will enjoy.

Anyway, I substituted a motor that came in one of the eBay lots for the one specified by the authors. Buying the specified motor online would have cost fifty bucks or so, and this project had already way exceeding both its time and dollar budget.

And yet, I wanted to build a ping-pong cannon and I could not resist the lure of shooting projectiles. After a few nights of very embarrassed futzing, I built the device, as you can see in Figure B.

FIGURE B

This is the ping-pong cannon, modified to use available parts. Click picture for a larger image.

OK, time for the first confession. This thing was amazingly fun to build. With the combination of parts, including things like gear reductions, the LEGO system has actually become an engineering prototyping system of rather astounding proportions.

The frustration
It was also a bit frustrating. The parts problem haunted the project throughout. In addition to having no indication within the book of either part numbers or where to find the parts, the bill-of-materials for the ping-pong cannon was missing mention of some parts: the long tubes needed to support the projectile balls.

And, sadly, the device didn't work well when finished. I had to tweak it a lot to get it to thwack the ball at all, and when it did, the ball just fell out of the launcher. There was no satisfying fling across the room, as I had hoped.

It could be that had I used all the original parts, the thwacker would have thwacked better. I could be that had I used ping-pong balls instead of the slightly heavier golf whiffle balls, the thwacker would have thwacked better. It could be I missed something in construction. Anything's possible.

I can't completely blame the authors for a failed design. Especially after I had so much fun tinkering with it.

But I couldn't leave it there.

More power
To the continued terror of my wife, I'm a student of both Tim Allen's "more power" mantra and the Mythbusters "well what would it take?" approach to project design.