Whenever I write in AutoSpeed about making something of the items others throw away, I am always a little surprised at the positive reader response.

That said, some stories have been more enthusiastically received than others: I now carefully preface all such stories with something like:

If you’re the sort of person who isn’t into junk, read no further. However, if you like picking up discards cheaply (or at no cost at all) and aren’t afraid of putting together some bits and pieces, this is for you!

Putting that first normally stops those people who really aren’t much interested in grubbing through others’ rubbish!

And so I am presenting here another such item. Again, it’s clearly not for everyone!

My 3½ year old son, Alexander, loves monster truck toys. Because he knows that real monster trucks can jump cars, roll over, do wheel-stands (etc, etc), he rightly expects his monster truck toys to do the same. But they’re not cut from the same cloth, and often suffer fatal results.

However, in our household, that’s no problem. Why? Because most of his monster truck toys cost nearly nothing.

What we do is this.

Where we see a second-hand monster truck toy at very low or zero cost – the tip, garage sales, second-hand stores, etc – we grab it. Because many are remote control toys that no longer work, these come up all the time. Missing remotes, rechargeable batteries that no longer charge, broken aerials – you name it.

But isn’t a remote control car that’s no longer remotely controllable not much fun?

It might be, but for a very simple trick.

Inside remote controlled cars is an electric motor – and in the better ones, a gearbox and differential as well. If the motor is driven backwards, it acts as a generator. To make the toy exciting, all I do is wire the electric motor leads straight to a big LED (eg 10mm) that is mounted on top of the vehicle. I don’t even bother using a dropping resistor, but I do make sure that the polarity is correct so that the LED lights when the vehicle is pushed forwards, not backwards.

Alexander helps me pull the toy apart, decides where he wants the LED positioned, and helps test that the circuit works by spinning the wheels with the vehicle held stationary.

Some of these toys even have existing LED headlights and tail-lights – again, easily wired to the motor. (The pictured monster truck is set up like this.)

Of course, the LEDs will not light until the generator is spinning fast enough – speed is vital. So if you want to see a little boy screaming around, monster truck being pushed as fast as possible in the dusk light, come to my house!

Alternatives to the LEDs include buzzers and sirens.

It’s not some incredible breakthrough, but it works so well that I thought I’d mention it here…