The idea of using a dynamo or generator to power a toy can be found in products like 4M’s Dynamo Robot. What I did is adding a basic mechanism for steering control and working out a simple way to build the complete rover out of two hacked servos, three wheels and just a few extra parts.
This little project demonstrates how a hacked servo with a crank becomes a pocket-sized generator. As servos are based on a DC motor, simply reversing the direction in which you rotate the crank reverses polarity and gives you forwards and backwards movement on the rover.
Inspired by toys from the times that remote control largely relied on mechanical solutions, I made the backwards movement into a steering action. By making one wheel run forwards only and cleverly positioning the other wheels, you can still go straight forwards, but moving backwards becomes turning, almost on the spot. This way you can get anywhere you want (al be it not in the fastest way).
Here's a video of the Dynamo Rover in action:
The very basic mechanism is based on the use of a spoked wheel and a simple “catch” with tape as a hinge. Here is a video in close-up:
If you can pick up two cheap servos, the cost of this project is pretty low. The wheels and the few extra parts shouldn’t set you back more than couple EUR/USD.
I'm planning on making a version with laser cut chassis, wheels and "catch", somewhat more expensive, but even simpler to assemble. I'm thinking of giving it a scorpion look, with the tail holding up the wire and the front wheels integrated in the fangs.
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Step 1: What you need
2 standard servos, the cheapest you can get are suitable
1 servo horn screw (to keep the horn on the servo output shaft)
4 servo mounting screws (the ones that usually come with a servo are suitable)
2 rubber grommets and brass inserts as common to mount servos in models susceptible to vibrations.
15 cm (6") of threaded rod with a diameter suitable as free running axle for the wheels (M4 or 8-32 with the wheels mentioned above)
10 nuts fitting the threaded rod
a 4.5 cm x 3 cm (1 3/4" by 1 3/16") piece of plywood or another stiff material that can easily be trimmed
a little duct-tape
a 200 mm (8") tie-wrap
your choice of decoration materials (keep it light). I used Play Corn. For some more information on Play Corn, see here)
a soldering iron and a little solder for electronics (desoldering gear can help, but is not really needed for the simple desoldering in this project)
sturdy cutting pliers
2 wrenches fitting the nuts (7 mm size for M4, and if I read the info on the net right: 11/32 wrench size for 8-32)
a Phillips screwdriver fitting the screws on the servo (size PH0 or close)
a metal file
for gluing the play corn: a damp piece of cloth on a plate
Important for safety:
a sturdy work surface, not minding scratches
some clear plastic sheet