Public Lab Research note

  • 2

Hand-crank powered flashlights

by pazb |

pazb was awarded the Basic Barnstar by warren for their work in this research note.

¿Or "crankable flashlight"? Have no idea what sounds better

-Check videos we made here:

This design can be modified/hacked a lot. As we did it, they are LED and dynamo powered lights/lanterns/flashlights that use hand crank to make the DC motor work. So, for example, something could be done to ensure the lights say on, at least for a bit after some cranking, so the user wouldn't have to use both hands at all times to make use of the light. A capacitor would be needed (but no idea where to get them from, cheaply or freely)... the latest news is that it seems I've found someone who knows how to create a capacitor with old phone batteries :) (will update this guide when and if that works out).

What is needed?

1) A low voltage and low rpm (revolutions per minute) motor. New motors like this can be very expensive (around 20USD), so we used the ones found in discharged printers (yes, we went into a rampage destroying like 50 machines ourselves). They might also be found in other household electronic equipment, which have opening and closing mechanisms. This type of printer often has very nice motors:

image description2) LED lights, we used 1,5v white ones. They are quite cheap.
3) Board for soldering.

image description4) Gears that fit the motors, to multiply torque (see more here or here). Gears can likely be found in the same printers or other machines where you find the motors.

image description5) Screws, you can also take them from the same printers/machines. It is important the ones you use have a washer and a nut so the screws (and therefore whatever they are fixing with them) don't get loose.
6) Materials for the body structure. We used discharged plastic bottles and cans. Thin-plastic bottles almost never work well.

image description7) Lids to attach the gears to the handle and to the structure. (In this photo is clear the lid wasn't properly glued to the handle, but it did work well in other occasions. We believe the quality of glue is key).

image description8) Strong galvanized wire for the crank. These come in different thickness(See previous photo).
9) Aluminum foil or anything that can replace it (like the interior of juice boxes)
10) Tools like: drill, soldering gun or soldering iron, glue gun, wire cutter, tangs, 60/40 thin/lead with rosin core, nose pliers, safety glasses, wire strippers, face masks with exhalation valve, electric tape, duck tape, etc.

About the motors

These motors can have different shapes and sizes. It is easier when they come with the cables, so you don't have to attach them. It is important to try out the motor of your liking before starting building the structure around the motor.

How the motors work

A small dynamo (generator or motor) supplies electric current to the LED lights. The flashlight must be pumped continuously during use. Because electrical power is produced only when the crank ("manivela") is cranked, a switch is not needed (Source: Wikipedia)

The difference between a dynamo flashlight and a battery-operated one is that the power is generated from the user's manual cranking instead of drawing energy directly from an alkaline, lithium or other type of battery.

The electric dynamo uses rotating coils of wire and magnetic fields to convert mechanical rotation into a pulsing direct electric current through Faraday's law of induction. A dynamo machine consists of a stationary structure, called the stator, which provides a constantmagnetic field, and a set of rotating windings called the armature, which turn within that field. Due to Faraday's law of induction the motion of the wire within the magnetic field creates an electromotive force, which pushes on the electrons in the metal, creating an electric current in the wire (source: Wikipedia).

How we did it

We did not provide a written or image based guide to the participants. We just quickly explained what materials they had at their disposal and let them try out. Some copied others' finished lights while others experimented with sizes and shapes and mechanisms to turn on the lights. Ww thought diversity of design was way nicer than having everyone creating the same type of light.

The basic instructions were:

  1. Choose a motor (not all of them had the same size or look)
  2. Check if the motor works by attaching one LED to the wires
  3. Choose the gear(s) that can be attached to the motor (finding the many gears we needed was one of the hardest things).
  4. Look for the structure material(s), considering strength (if the motor is heavy then a thin plastic bottle won't work) and checking where to place the gears and the strong-wire for the crank.
  5. If there are more of two wires coming out of the motor check which ones work with the LEDs, put the others aside (don't cut them, in case you need them later).
  6. Adapt the bottle/can/structure chosen (cutting, combining, gluing, etc.)
  7. Place the motor inside the structure, and the gear on the outside, check their precise position, considering the wire that will become the crank, screw or glue them.
  8. The galvanized wire can be turn into a straight stick using a stone and a hammer, and then bend (for the crank) with a tang.
  9. Connect the 3,4,5,6 (we connected up until 10 LEDs) in a soldering board, or if you don't have a soldering machine then attach the LEDs to each other using the board.
  10. Check if the LEDs connect well, and turn them on when connected to the motor's wires.
  11. Solder or connect the cables, and finish up the structure.
  12. Consider creating a light amplifying shade:
  13. image description

Have in mind

  • Using good quality glue is kind of key to make this work.
  • Silicone glue might not easily glue together cans and plastics.
  • In our experience, using screws as much as possible, instead of glue worked better. But not all the parts could be attached with screws. Sanding the plastic before using the hot glue might work.
  • The soldering iron or gun you use has to be a good one. We bought cheap ones that didn't last and the 'good' one we borrowed had some much demand it ended up collapsing/breaking.
  • Don't assume everyone knows how to safely use a drill, or cutters. Do take the time to tell everyone about basic safety measures.
  • The aluminum foil we find in the supermarket is difficult to work with, as it is very thin. But it does improve the strength of the light.

More photos as reference

Photo 1) This small motor here was nice, but attaching a gear to it was hard (one to try in another future workshop)

Photo 2) These small motors, quite cheap in the market, don't work. We would have to add a lot of gears to make them work. We tried this design first, following a youtube video we watched, but using the same exact materials would have taken the creativity part out of the equation. So we went for the bottles and cans (unfortunately so abundant everywhere).

Photo 3) The motor on the right was the easy one to use, because it came with the cables attached.

Photo 4) Some of the gears had to be diagonal to fit this special motor

Photo 5) This motor here is quite fast - so didn't work. Some people tried to make it work, and one 'sort of' succeeded: the light was very...light

Photo 6) Someone used way more than the 5 LEDs we recommended using, proving we could have used many more in each lamp :S

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@warren awards a barnstar to pazb for their awesome contribution!

Love this! Thank you, Paz!

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