This Dynamo Rover is a wired remote control toy that does not require any batteries, but uses the renewable energy source of kids’ muscle power (or the muscle power of adults addressing their inner child).

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.

If you like this Ible, please give it your vote.

Step 1: What you need

2 standard servos, the cheapest you can get are suitable
I used these from Modelcraft, which look to be the same as the Tower Hobbies STD TS-53.
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 and 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) 
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 saw
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
safety goggles/glasses
some clear plastic sheet
<p>is there any way to make this at home???</p>
Of course, that is what this Instructable is about.<br><br>You can buy a kit based on my concept: http://be.opitec.com/opitec-web/articleNumber/114848/zz/cID/c3I6RHluYW1vNg==<br>(Not available in English yet, it seems. Sorry)<br><br>Or you you can build the version shown in this Instructable. The parts needed and what to do is described in the Instructable. Please let me know what gives you any trouble.<br><br>Beste Regards,<br><br>Yvon
Great idea! <br /> <br />Did you know it had made the Makezine blog? <br /> <br />http://blog.makezine.com/page/2/ <br /> <br />Nice way to demonstrate energy conversion and also the inefficiencies in those conversions - I bet it takes quite a bit of cranking to get the 'bot to go one turn forward. Could lead easily to a discussion of conservation of energy etc. As well as just being fun!
Thanks! <br /> <br />It takes about two turns of the crank to make the powered wheel make one turn. <br /> <br />That is playable, but does indeed clearly show the influence of conversion in efficiencies. <br /> <br />Of course a true comparison and determination of the efficiency would mean measuring the torque. The torque manually applied on the dynamo servo is not high, but clearly higher than needed to push forward the rover. <br /> <br />Actually an efficiency of 50% is the maximum with the nominal efficiency of the little DC motor in each servo probably in the range of 70% (and 70% x 70% = 49%). <br /> <br />What is interesting to see is that when you try and speed up the crank, the resistance drops and the rover slows down. In that case you make the motor of the dynamo servo turn faster than the rpm range where it works well. <br /> <br />What is also interesting to see is that when I add a LED in parallel to the motors it obviously lights up when cranking in one direction, but also lights up faintly when cranking in the opposite direction. When I power the LED with the dynamo servo, without the second hacked servo attached, the LED only lights up when turning the crank in one direction. So it is the combination of the two motors that causes spikes with reversed polarity. <br /> <br />I was also thinking of using a stepper motor as generator. The electrical efficiency of a stepper motor isn&acirc;€™t very good either, in particular at high rpm. But we&acirc;€™re talking about low rpm&acirc;€™s here and the mechanical efficiency is much better as you can drop the gears. But then of course the output needs rectifying to power a DC motor, which looses the simple reversing function. Obviously one can always add a reversing switch. Actually, I&acirc;€™m wondering what connecting a stepper motor to a stepper motor would give. Will one &acirc;€œfollow&acirc;€ the other step by step as long as the load is low?
Update: after not finding any info on connecting a stepper motor to another stepper motor, I picked up two bipolar stepper motors and tested if one can drive the other by connecting them directly: it does not work. No movement in the second stepper motor at all.
Clever! I like this one a lot.

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