Lumigraph
Inspired by kinetic sand tables and roulette curves*, I was looking for a way to remove the sand which would enable the project to be mounted in any position and not limited to the horizontal but still have an erasable display. This would be acomplished by using UV sensitve paper and a UV LED.
In addition part of the process was to use a minimum of elements to simplify construction which also negated a microcontroller.
The roulette curves* would be generated in a similar way to the manual method but controlled by an electric motor.
*Most people are familiar with roulette curves from the Spirograph toy.
Supplies
3D Printer Filament PLA (colours to suit personal taste).
Acrylic White 5mm thick (sufficient for 220(L) x 220(W) mm square).
Acrylic Clear 5mm thick (sufficient for 78(dia) mm circle).
Micro Metal gear Motor 1006:1 gear ratio
M2 Self tapping screws 10mm - Qty 4
M2 Self tapping screws 8mm - Qty 4
M3 Threaded standoff 25mm - Qty 8
M3 machine screws 8mm - Qty 4
M3 machine screws 10mm - Qty 4
M3 machine screws 12mm - Qty 8
M3 machine screw 25mm
M3 machine screw 10mm
M3 locking nut
M3 plain nuts - Qty 4
Brass tubing 3.5(dia) x 0.2(wall) mm
Resistor 1K
Insulated copper wire.
Brass flat washers (M6), 13(outer dia) x 6(inner dia) mm - Qty 4
Rubber Feet (M3 fixing) - Qty 4
May prove more cost effective to buy a range of values rather than individual values unless you already have them available. Some components may also have a MOL greater than the quantity specified in the component list.
No affiliation to any of the suppliers, feel free to obtain the supplies from your preferred supplier if applicatble.
Links valid at the time of publication.
Tools
3D Printer
Saw
Needle files
Sanding paper
Craft knife
Scissors
Soldering Iron
Solder
Wire cutters
Screwdriver
Pencil
Marker
Awl
Drawing compass
Ruler
Drill
Drill bit 6mm
Drill bit 3.2mm
Drill bit 3mm
Drill bit 2mm
Drill bit 1.5mm
Masking Tape
Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.
CAD Design
The 3D printed elements were designed using BlocksCAD, sliced using Cura 5.8.1 and printed on a Elegoo Neptune 4 Pro.
1: Back. Size: 28(W) x 20(D) x 8(H) mm, Weight: 4g
2: Support. Size: 28(W) x 50(D) x 17(H) mm, Weight: 10g
3: Top. Size: 28(W) x 20(D) x 4(H) mm, Weight: 2g
4: Arm. 52.5(W) x 14.5(D) x 7.5(H) mm, Weight: 3g
5: Cog. 46.4(dia) x 14(H) mm, Weight: 10g
6: Hoop. 164.4(dia) x 15(H) mm, Weight: 64g
7: Support Template. 18(W) x 50(D) x 5(H) mm, Weight: 5g
Printing
Filament: PLA (uppermost elements grey, lower elements white), although any colour that suits personal taste will do.)
Layer Height: 0.2mm
Infill: 100%
Wall Thickness: 0.84mm
Wall line count: 4
Bed Adhesion: Skirt
No supports
All parts are correctly orientated within the files for printing directly.
A combination of individual and multiple elements are required which subject to size can be printed individually or in groups on the print bed.
Post Processing
Some post processing may be required to remove aberrations in the cavities and around the edges with sanding paper and needle files in addition to opening and smoothing the holes with a drill bit.
Particular attention being applied to the teeth of the hoop and the cog to ensure free running.
Use a needle file and/or sanding paper to smooth the parts in areas were they meet.
Circuit
The circuit consists of five elements. (Fuse, switch, motor, UV LED & resistor).
As it will be directly powered from USB (alternatively, 4 x 1.5V cells = 6V), and in the event that the motor stalls resulting in the maximum motor current and overheating a fuse is included. This may be considered excessive but given that operation is without electronic monitoring or control and the quality of USB adapters vary it offers a simple protective solution during testing and use.
The datasheet maximum for the motor in stall mode is 380mA and the nearest fuse value greater than this is 400mA.
A typical rule of thumb is for the fuse rating to be 25% greater to accomodate current surges.
This equates to (0.38*0.25)+0.38=.475 the nearest fuse value being 500mA.
The switch is a SPDT in series with the fuse connected to the motor.
In parrallel with the motor is connected a UV LED in series with a 1k resistor.
The resistor for the LED is calculated as 5V - VLED/1.65mA, where VLED = ~3.35V thus R = 1kR.
If the luminous paper and LED illumination combination is not sufficiently bright a lower value resistor that keeps the current within the component ratings can be used.
Luminous Display
On the luminous paper draw a circle with a radius of 78mm.
Optionally, for added protection the paper can be laminated or covered with sticky back plastic film.
Cut out the circle disc with scissors or a craft knife.
Clear Cover
Whether protected or not the paper may have a tendency to lift on the hoop.
In order to combat the tendency of the paper to lift a clear cover is placed over it to force it flat.
The cover is made from a clear 5mm Acrylic sheet.
With a drawing compass create a circle with a radius of 78mm.
Cut out the circular disc with a saw and smooth the edges with a file and/or sandpaper.
Not having a circular saw with a radius of 78mm, I simply cut tangents to the circumference until most of the excess material had been removed.
Main Support Panel
This is the panel to which all the elements are attached.
Referring to the template.
Cut a piece of 5mm(H), Acrylic* to create a square with dimensions of 220(W) x 220(L).
*Alternatively, 5mm(H), Plywood could be used.
Find the centre of the panel at the intersection of lines drawn between two pairs of diagonally opposing sides.
At each corner measure 10mm vertically and draw a line and 10mm horizontally draw another line. Where they cross drill a 3mm hole. These holes are used to fit the standoffs that act as feet.
With a drawing compass set to a width of 71mm, place the point at the intersection of the cross and draw a circle.
Check the alignment of the intersections against the holes in the hoop for centricity prior to drilling holes.
At the intersection of the circle with each of the 4 lines drill a 3mm hole these holes are used to attach the hoop.
A duplicate of the main support panel with holes aligned for the standoff feet can be used as a base support panel which can be used to protect the wiring and to which nonslip feet can be screwed through the holes into the standoffs.
At the intersection of the 4 lines that form a cross drill a 3.2mm hole.
Align the support template centre hole with the hole in the centre of the panel and fit a M3 x 16mm machine screw and nut to hold the template in place.
With the templates horizontal and vertical sides aligned with the sides of the panel mark the 4 x 3mm and 4 x 2mm holes. Drill out the holes with 3mm and 2mm drill bits.
Prior to fitting the motor support ensure the motor can be slip in and out of the motor support cavity, it should be a snug fit and not loose.
Remove the template and fit the Motor support with 4 x M3 x 12mm machine screws & nuts and mark the interior perimeter of the rectangular cutout.
Push the motor into the support and ensure the motor spindle fits through the hole in the Main support panel. If the spindle does not pass through the hole widen the Motor support fixing holes in the support panel to recentre the spindle.
Remove the Motor support and cut out the marked area. (10(D) x 12(W) mm), ensuring the front of the motor fits through the cut out.
Then refit the Motor support.
Top Plate
With the Motor support in place push the motor in all the way until it is flush with the surface of the Main support panel.
Use a 3.2mm drill to widen the hole in the centre of the Top plate to enable the shaft of the motor to move freely.
Secure the Top plate to the panel with 4 x M2 x 8mm self tapping screws.
With a 3mm drill open up the hole close to the centre to a depth of ~1mm.
Drill a 1.5mm hole in the panel by the side of the notch in the Top plate.
Solder a length of wire horizontally to a brass washer ensuring the solder is flat and confined to a small area.
Test fit the washer in the circular recess in the Top plate to ensure it fits flat, it may be necessary to remove excess solder with a file.
Run the wire in the notch and down through the 1.5mm hole.
Motor Install
Cut and solder three lengths of wire to the motor that will reach the switch and USB socket.
One for positive & one for negative to power the motor and one to the body of the motor which is the negative connection to the LED.
Slide the motor into the support.
Feed the 3 wires through the support back and fix in place with 4 x M2 x 10mm self tapping screws.
Rotating Cog
The cog with 45 teeth rotates around the inside edge of the hoop whilst spinning on its axis.
Set within the cog are 6 x 5mm holes that radiate out on an arc.
These serve a dual purpose either to position a LED or a magnet.
If using a LED, further additions are required to enable power to be transferred.
Cut a 3.5(dia)mm brass tube with a saw to a length of 11mm and deburr the edges.
With a 3.5mm drill clear out the centre of the cog.
Cut two lengths of wire that will enable the LED to the repositioned under any of the 6 x 5mm holes.
Solder a length of insulated copper wire to the outer at one end of the tube.
Place the small part of the cog on a flat surface and with a flat firm piece of wood or plastic, push the brass tube (wire uppermost), down into the centre of the cog. Alternatively, press between the jaws of a vice or use a pillar drill to push the tube down.
Solder a length of wire vertically to a brass washer ensuring the solder is confined to a small area.
Test fit the washer in the circular recess in the column to ensure it fits flat, it may be necessary to remove excess solder with a file.
With a 3mm drill open up the hole close to the centre of the column to a depth of ~1mm.
Push the wire through the small hole close to the centre of the column and out through the top.
Ensure the washer sits flat and level on the column.
Feed both wires down through the small hole between the 3rd and 4th, 5mm holes.
Tin the wires in preparation for the LED and resistor.
Rotating Arm
With a 3mm drill clear out the centre of the short column.
With a 3.5mm drill clear out the centre of the tall column.
Cut a 3.5(dia)mm brass tube to a length of 8.5mm and deburr the ends.
Solder a length of wire to the end of the brass tube.
Place the tall column of the arm on a flat surface and with a flat firm piece of wood or plastic, push the brass tube down into the centre of the tall column aligning the wire with the slot.. Alternatively, press between the jaws of a vice or use a pillar drill to push the tube down.
Push the wire up through the second hole along in the channel.
Trim and tin the wire to enable a M3 solder tag to be soldered horizontally on the end with the centre of the tag coincident with the centre of the short column.
Solder a length of wire vertically to a brass washer ensuring the solder is confined to a small area.
Test fit the washer in the circular recess in the column to ensure it fits flat, it may be necessary to remove excess solder with a file.
With a 3mm drill open up the hole close to the centre of the column to a depth of ~1mm.
Push the wire through the small hole close to the centre of the column and out through the top.
Ensure the washer sits flat and level on the column.
Bend the wire along the channel and solder a brass washer horizontally on the end such that it sits on the short column with the centre aligned with the 3mm hole.
To prevent the washer shifting either glue the washer down or lightly heat with a soldering iron melting a thin layer of plastic which when it hardens will hold the washer in place.
Fix the rotating cog to the rotating arm at the short column with both washers in contact using a M3 x 25mm screw and a M3 self locking nut such that the cog and arm both rotate without binding.
Solder a UV LED and resistor in series.
Before connecting the LED/resistor to the free wires determine the correct connections and any continuity issues with a DMM.
In this case the negative (-Ve), connection is from the motor spindle sleeve to the rotating cog sleeve via the M3 screw.
The positive (+Ve), connection via the slip rings.
Apply, 5V at the tall column end being sure to observe the correct polarity and ensure the LED is illuminated.
Feed the LED up through one of the 5mm holes, which should sit level or just below the plane of the cog upper surface.
Power
Align the USB socket on a suitable side of the panel and mark the two fixing holes.
Drill 2 x 2mm holes for the socket in the panel.
Fit 2 x M2 X 18mm machine screws held in place with 2 x M2 x 5mm threaded spacers.
Mount the socket on the screws and hold in place with 2 x M2 nuts.
Drill a 6mm hole for the switch and insert and secure in place.
Bend the solder pins of the fuse holder out to the side.
Position the fuse holder under one of the holes to a threaded standoff used to hold the hoop in place and secure with a M3 X 12mm machine screws.
Solder a wire from VBUS on the USB socket to one side of the fuse holder.
Solder a wire from the other side of the fuse holder and connect to one side of the switch.
On the other side of the switch connect the positive wires of the motor and LED/resistor.
Connect the negative wires of the motor and LED to GND on the USB socket.
Hoop
The hoop with 120 teeth serves a dual purpose, supporting the display element (luminous paper or sand), and one half of the two toothed wheels.
Attach the hoop to the panel with 4 x M3 x 25mm threaded standoffs and secure with 8 x M3 x 12mm machine screws.
Rotator Assembly
Attach the tall column of the rotating arm to the spindle of the motor applying downward force. Align the flat of the spindle with the hole in the side of the tall column, into which is fitted a M3 x 8mm machine screw to secure the arm in place.
Ensure the arm is horizontal to the panel and concentric with the teeth of the cog mating with the hoop, if not adjust accordingly.
The cog should sit level or just below the plane of the hoop to prevent it rubbing on the underside of the luminous paper.
Testing
Double check all the connections for correct assembly prior to applying power.
With the switch in the off position and a valid fuse inplace insert the USB socket connected to a suitable power adapter.
Switch on and planetary rotation will take place with the LED simultaneously illuminating.
If the LED fails to illuminate or illuminates inconsistently adjust the locking nut and/or the screw securing the rotating arm.
The application of silicone lubricant to overcome binding which may result in skipping of the cog or inconsistent illumination of the LED can help.
Finally sit the luminous paper (correctly orientated to ensure maximum luminousity), in the hoop and place the clear Acrylic disc over the top.
Operation
Place the unit on a level surface in a dimly lit or dark area.
With power applied, switch the unit on.
In operation the roulette curve should be clearly visible as a glowing pattern where the LED illuminates the luminous paper.
The pattern will be retraced and displayed continually as long as the power is applied.
Once power is removed the image will remain for a period of time subject to the intensity of the UV light, thickness of the paper and decay rate for the luminous material.
The image can also be erased by subjecting the paper to a bright light source or simply leaving for a length of time.
The pattern can be changed by manually moving the position of the LED between the holes or fitting multiple LED's in the rotating cog.
Luminous paper in different colours are available as suits personal preference.
Alternative Use
This project can quickly be converted to a sand table by doing the following:
1: Replacing the LED with a 5mm cylindrical magnet.
2: Remove the luminous paper.
3: Sit the clear Acrylic disc in the bottom of the hoop and secure on place with tacky to enable easy removal whilst sealing any gaps.
4: Fill with fine sand.
5: A steel ball bearing that can be pulled by the magnet.