Alternative power source... Dynamo or Stepper motor?

Thread Starter


Joined Jun 23, 2009
We have been given a project to design our own alternative energy source to power a small electric screwdriver (around 4v).. Instead of using the normal ideas of solar and wind power that other groups are trying to create we wanted to go outside the box and use a different mechanism.

Therefore we came up with an idea of using bungees attached to a drive shaft, using a handle we would turn the drive shaft to tighten the bungees and then lock them off. we would then release the bungees to release the energy and this will turn the drive shaft, the drive shaft will be connected to a series of gears which will turn the 'generator'.

We are currently thinking of using a 12v dynamo, but how would we charge a 12v battery with this?

Do you think it would be better to use a stepper motor and re-designing or using a dynamo?

We are open to any ideas you may have :)


Joined Jun 7, 2009
Let me ask you a hypothetical question in regards to your project.

Now I'm thinking a small battery operated drill opposed to a screwdriver for simplicity sake.

Would it be acceptable within the confines of your project to fashion up a steel rod into a handle that you could chuck into the drill. You would then turn on the de energized drill and spin that handle backwards like a madman. After some period of time doing this, you would release the handle and low and behold, it would spin (albiet slowly) in the forward direction.

Why, because the drill motor acts as a generator in reverse, and rather than storing your muscular energy in the bungies, your storing it into the battery. It may not look as complicated, but that's simplicity.

If you move forward with your bungie concept, make sure to explain to the evaluator that although your tensioning by hand, in reality the tensioning can come from the energy of a braking vehicle, and that your screwdriver actually accelerates the vehicle.

Unless muscular power is acceptable as an 'alternate' energy source. In which case you could just buy an old crank drill.