A colour wheel is used in physics lessons to show that white light is made of individual colours. This model can be used with various colour segmented disks to show this and also how colour mixing works.
Traditionally hand or electric drills were used with a disk of card spinning where the drill bit usually goes. These may be cumbersome and potentially dangerous. The other alternative is a hand cranked device, usually including a gear or belt mechanism which allows the operator to spin the disc at high speed.
This 'Workshop' model is both safe and easily constructed, allows a number of different wheels to be used and is very cheap to produce. It is powered by an external electrical source such as a labpack or battery by connecting standard 4mm leads.
Fig 1: Dimensions of base
Fig 1 shows the size of the base required. This should be measured and cut with a tenon saw and then any sharp edges sanded. This base should be made from 10 or 12mm thick MDF and PPE should always be used when cutting and sanding. The exact size of the base is not important, as long as it is big enough to be stable. The measurements given in the diagram are approximate.
A piece of the timber batten should be cut at around the 175mm mark, again the dimensions of the batten are not that important as long as the cross section is large enough to support the mini motor. Ensure that the cut end of the batten is as level as possible so that when stood up on end, it stands straight. Use PVA glue to stick the upright batten in the centre but closer to one side of the base as in the diagram. Hammer a few nails from the bottom to secure the post into place. Ensure the glue has set before moving on to the next stages.
Fig 2 and 3: 4mm sockets in place
Fig 2 shows the 4mm sockets in place. These are sunk into holes which are drilled into the base. Ensure the drill bit goes right through the base so that wires can be attached. The external parts of 4mm sockets vary in size and shape so you may need a drill bit from 4mm-6mm to ensure a snug fit for the socket.
You may want to solder a 50mm length of insulated copper wire to each before placing the sockets onto the drilled holes because it may be easier depending on the type of socket used. Alternatively you may solder the wire onto the terminals of the sockets once they are set in place. The sockets should fit into the holes tightly and may need to be lightly hammered in place to achieve this.
The diagram also shows the 3V mini motor in place at the top of the upright. This should be secured using a hot glue gun. Make sure none of the air vents (little holes) on the case of the motor are obstructed with glue.
A hole should be drilled in the base behind the upright batten to house the wires (see fig 2). One end of each wire should be soldered to a 4mm socket terminal and the other to a terminal of the motor. Make sure the wire is fairly taught before soldering in place. A blob of glue from a glue gun may be required to keep the wires in place on the upright batten.
Fig 4: Underside of the unit
Fig 4 shows the underside of the unit and the position of the wires. It also shows the position of four feet made from squares of plywood. These may be secured using PVA glue. A small 'G' clamp can be used to hold the feet in place while the glue dries. The depth of the feet needs to be enough so that the terminals of the 4mm sockets are not resting of the work surface.
Fig 5: Spindle attached to the motor shaft
Fig 5 shows a spindle attached to the motor shaft. These can be purchased from lab suppliers such as Timstar. They may be cut in half using a hacksaw and threaded on the shaft with the card disk between, which may grip better than a single spindle. A bit of trial and error (and maybe a bit of Blu-Tak) may help when trying to find the best way to attach the colour wheel.
Fig 6: Colour wheel disk in place
Fig 6 shows the colour wheel disk in place. A circle may be cut in a sheet of white car d using drawing compasses. The diameter of the wheel will depend on the clearance between the motor shaft and the base of the model. Use a ruler to divide the circle of card into four equal segments which then may be coloured in using pens or paints. To create white when the wheel is spun, a combination of green, red and blue should be used. Cyan can be created by using green and blue, magenta by using red and blue and yellow by using red and green. Paints and pens will have slightly different colour hues so you may need to experiment. Alternatively use a PC to draw and print the colour wheels.
The model should be connected to either a power pack at 3V D.C (never use AC with these motors) or 2 x 1.5V batteries in series. A switch may be included in the circuit to easily turn the unit on and off.
The benefit of this model is that the teacher can have the wheel spinning without having to hold or turn anything. Also the wheel will spin at a constant speed.
Why not construct several for the class to use?