Friday, October 5, 2012

Electric stroboscope

• 10'' 1x2'' wood
• Matt board
• 11/2''x 3'' cardboard tube
• Hobby motor
• AA Battery
• Wide rubber band
• Wire (solid core preferred)
• Cloths pins
• Aluminum foil  
• Tape

• Hot glue gun
• Small wood saw
• Utility knife
• Wire strippers
• Compas
• Circle cutter (optional, available from cart and art supply stores )

Cut a 5-6'' matt board circle using a compass and a utility knife or a circle cutter to make your shutter disk. Make sure that you have a method of marking the center and the radial slot before cutting your circle out.  Use a nail to poke a hole in the center of your shutter disk. The nail should be slightly smaller than your motor shaft.

Cut a 1/8'' to 1/4'' slot about 1/3 of the way through the disk.  One slot will allow good viewing of most things, but if you want to look at something that moves particularly fast you may want 2 or 3 slots. This will double or triple the scopes shutter frequency.

Stick the motor shaft into the center hole of the disk and apply a generous amount of hot glue to the far side making sure it stays relatively square.  Alternatively, you can add a small matt board washer to the far side of the disk and glue on top of that for even more strength.

Heres a simple clothespin-based momentary switch. Strip your wires and wrap them around the handles ends of the clothespin, and then wrap the ends of the pin and wire with foil. Tape them in place with electrical tape.

Here you can see the basic assembly. The motor and shutter disk have been hot glued to the top of the handle (10'' of 1x2''). The eye piece tube has been placed next to them. The momentary switch has been hot glued onto the side of the handle.  A AA battery with a wide rubber band (we use inner tube)  to hold the leads has been taped onto the upper portion of the handle. The basic circuit goes from the motor to the switch to battery and back to the motor.

Using the stroboscope:
At first glance this design didn't appear to be very useful because it has no apparent speed control. Upon trying it we realized this wasn't and issue, because of the weight of the matt board the shutter disk speeds up and slows down slowly.  By bringing the shutter up to speed and then letting it coast, you can reach a wide range of shutter speeds. Once you find a speed that works you can just pulse the switch briefly to maintain it. As with the manual stroboscope, looking at things with rotating or oscillating parts usually yields the best results.  Things like scroll saws, fans, or car wheels can be made to look like they're not moving if you an match their rate of rotation or oscillation to the stroboscope shutter speed.   Just as in the manual stroboscope, this device relies on persistence of vision to string together the moments when you can see through the slot. The result is that objects appear to move more slowly when viewed through the stroboscope.

Here's a video of the stroboscope looking at a fan:

Using the stroboscope as a siren disk:
Using this setup with disks with two or three slots you can easily us it as a siren disk by blowing through the disk with a straw or a vinyl tube.  Alternatively, you can use a siren disk with a ring of hole punched holes instead of a stroboscope slot disk to achieve higher frequencies.

flat flashlight

•5mm led ( we got ours from Evil mad Scientist, their prices are good in 100+ quantity, they also sell a bright defused version   ,all electronics or goldmine electronics are also good place to start looking water clean leds)  
• 3v lithium button battery ( we got ours from item # 40919)
• copper tape (found in the gardening section of hardware stores as an anti snail/ slug product or alternatively in 1/4'' form on amazon  )
• wide popsicle stick (tongue depressor) 


The first step is to put a long strip of copper tape down the length of the popsicle stick with enough extra to wrap about 1'' to the other side like so.

Place your button battery on to the piece of copper tape you wrapped over the end of the stick with the positive side up. Take a shorter piece of copper tape and fold the end over about .75'' each side,  then glue on the copper tape. Glue is not conductive so you have to double the tape up to allow the electricity to flow.  The right side will be the battery contact and the left side will be the switch contact.

Tape the battery and battery contact in place with electrical tape.  Add a final piece of doubled up copper that runs from under the switch contact to the top of the popsicle stick. Alternatively, you can use a folded piece of aluminum foil for this part and tape it down in the middle. This may be easier for younger kid as folding the tape can be challenging.

Heres the flashlight with the switch open and the led in place.  Note that the long lead of the led, the positive lead, goes on the switch side of the flashlight. Make sure to test the test the flashlight before taping the led down with electrical tape.

Here the switch is closed and the light on. Note that for this example we ended up using a yellow led we had laying around not the recommended bright white led.

Heres the final flashlight with the battery and led taped in place.

This is a slightly modified version using an ultra bright led and a cup with wax paper as a diffuser. Adding the cup and defuser spreads out the light and makes shining it it in someone eyes less hazardous.  This version also had the folded and taped aluminum switch, and it also uses aluminum for the conductors.

Here's a video of the flashlight working during the day and in the dark:

Personal Fan

• 8'' 1x2'' pine
• Plastic cup or bottle
• Masking tape
• Aluminum foil
• Hobby motor
• 1 AA battery
• Solid core wire (we like telephone wire)
• Thumb tacks
• A broccoli rubber band, or inner tube cut off

• Small wood saw
• Scissors
• Wire strippers
• A hammer
• Hot glue gun

First take a piece of foil and fold it to make a 2" x .75'' strip and tack it loosely in place on one side of the handle.

Add a second tack under the end of the foil (not through it). Then twist two lengths of telephone wire (with ends stripped) onto each tack so the exposed copper touches the tack.

Hammer the tacks in to lock the wires in place; this completes the fan's switch.

To complete the circuit cut and add a third piece of wire and create a path that goes from the switch to the motor to the battery and back to the switch.  Stretch a broccoli rubber band or a cut off piece of inner tube around the battery, and simply stick the ends of the wires under the band to hold them in place.    

Hot glue the motor to the top of the handle and bend the foil up so the motor will remain off until pressed into the tack. Once you've made sure you circuit works and there are no loose connections, tape the battery to the handle to secure it.

To make the propeller cut an elongated oval at a diagonal out of the side of a plastic cup or bottle at an angle.

Use a tack to poke a hole in the propeller that is a little smaller than the motor shaft so it will stay on once pressed in place.  You can always add a little glue for more security.

The final fan should look something like this.

Things to do and notice: 
Despite being a simple circuit project, most of the experimentation with the project can be done with the propeller.   This type of propeller tends to work better spinning in one direction than the other, which is worth looking at and trying to explain. The diameter, width, and curvature will all effect how much air the propeller will move. Going with particularly large propellers from large bottles or very small propellers tend not to be very effective. The trade off between curvature and area can be further understood by simply making many different sizes of propellers from different containers and experimentally comparing their effectiveness.

Here's a decorated fan in action: