2 standard servos, the cheapest you can get are suitable
If you happen to have a servo with fried electronics but sound motor and gears, you can use it for this project.
If you want to use smaller servos, you can, but then the cheaper ones tend to be not strong enough to serve as dynamo.
2 servo horns (normally come with the servos)
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.
The cheapest servos often do not come with the latter two those. You can buy them separately (like this set
) or use other screws about 2.5 mm x 20 mm and a short tube loosely fitting those)
1m25 (4') of twin cable the more flexible, the better, you only need thin gauge. I used 2 wires from 0.08 mm2 (28 AWG) servo cable
You can use two single wires too, and even glue them together at intervals with some superglue (I recommend not to glue them together over all of their length, as this adds stiffness).
3 wheels 4 to 6 cm (1 5/8" to 2 3/8") diameter, of wich at least one has spokes on the inside. I used these from Opitec
and alternatively these
. They all work, but the first (the biggest) give the best speed. You can find these very same at Kelvin
too, be it at a rzther high price.
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)
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 plateImportant for safety:
a sturdy work surface, not minding scratches
some clear plastic sheet