Robotics-Hacking Kiddie Car Motors

Doing the same thing for over a decade can get a little monotonous.  So I mix up the rules and the available supplies for my middle school level combat robotics class every few years.  This year I am banning four wheel drive in hopes of encouraging more creative weaponry.  And I am supplying them with modified gearbox/motor combinations from de-commissioned kiddie cars.  I have lots of these, we keep getting various Barby Jeeps and such donated when we do our Advanced Robotics class.

To test the theory that a modified Jeep gearbox could be made into an effective weapon, still staying under the required three pounds, I built "Mr. Ouchy".

As you can see the testing was rather...vigorous.  But the weapon performed admirably.  It was just an unmodified Kiddie Car gearbox with a polycarbonate strip attached, the latter tipped with some sharpened steel bits.  It had enough power to shred opponents.  It also had enough power to shake itself to bits, but that's kind of irrelevant.

So I have a large number of this type of gearbox:

Temporarily remove the motor and crack open the gearbox and the innards look like this:

What this gearing system does is reduce the very high rpm's of the 12 volt motor, while increasing torque sufficient to move one or more chunky toddlers down their sidewalks at a sedate pace.  At the 9.6 volts we will be using for our weapon batteries that turns out to be about 72 rpm, and with the standard sized Kiddie car wheel is a theoretical top speed of 3 miles per hour.  (OK, I realize that under load it goes slower, but also that it normally runs on 12 volts, so it is still a ball park estimate).

Of course we want more rpm's, and also need to trim weight.  So get out the band saw...

Note the icky yellow grease that fills these gearboxes.  You have to wipe all this stuff out.  So, by trimming the plastic housing down and removing the final gear in the system we get this:

It should be possible to hub a weapon arm or disc onto this, although the linkage is going to be a tricky thing for middle school level technology.  Final weight is right around a pound once the 12 volt motor is re-attached.  It now spins at an rpm rate of 240 and should still have enough torque to knock other robots around.

On the right is a variant, a Kiddie Car gearbox with the final two gears removed.  Lighter, less torque.  I estimate it runs at 900 rpm.

Will this work?  We shall see....

All of this is the sort of thing that I could have the kids do themselves, but as it involves some deft work with the band saw I decided it would be better for me to supply these components.  Their first assignment is to take them apart and reassemble them several times, then to explain to me how they work.