The Flitter

For some time I have had a display dome without a specific function sitting in my workspace and finally this project has given it a purpose.

The following kinetic project is based on an elastic pendulum with a Hall sensor controlled magnetic weight.

Were most pendulums would be required to have a repetitive swing in this particular application we require a chaotic swing.

This chaotic swing would be utilised to simulate the effect of a flying insect.

All this will be housed in a display dome with 3D printed, hand crafted and electronic elements.

Supply current at 5V: ~170mA when active.

Size: 19(H) x 10(dia) cm

Weight: 470g

3D Printing Filament PLA (White, Yellow, Brown, Green)

Glass dome with base 19(H) x 10(dia) cm*

*This project uses a glass dome but for greater protection an acrylic dome display case could be substituted although this may impact the build due to dimensional and base design differences. Alternatively, a compatible acrylic dome and a custom 3D printed base could be realised.

Enamelled Copper Wire (ECW), 16AWG/1.29(dia) mm

Enamelled Copper Wire 35AWG/0.15(dia) mm

Stainless Steel tube 65(L) x 6(dia) mm

Machine Screws M2 x 6mm - Qty 5

Machine Screws M2 x 10mm - Qty 2

Machine screws M2.5 x 6mm - Qty 2

Self tapping screws M2 x 8mm - Qty 2

Neodymium magnet cylindrical 10(dia) x 1.5 mm

Hookup Wire 30AWG 1/0.2mm (multiple colours to aid connection identification)

Hall effect (omnipolar) switch

Transistor ZTX751 PNP

Transistor BS270 NFET

Resistor 1k2 - Qty 2

Capacitor 100nF

USB-C Breakout board

Masking Tape

Clear Laquer

Strip Board

Right angle pin headers

Straight through PCB socket 2pin - Qty 2

Rolling barrel swivel #10

Multi strand wire (red & black)

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

Soldering Iron

Solder

Wire cutters

Screwdriver

Pencil

Marker

Awl

Drawing Compass

Drill

Drill 1.5mm

Drill bit 1.8mm

Drill bit 2mm

Drill bit 2.3mm

Drill bit 2.5mm

Drill bit 3mm

Drill bit 6mm

Long nose pliers

Tacky

Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.

A simple pendulum is a tether fixed at one end to a point that pivots in one plane and a weight that can be fixed or moveable to adjust the swing period.

This project uses an elastic pendulum which differs from the simple pendulum in the following manner.

1: The pivot point is not fixed in one plane but is free to spin and swing in both the X and Y planes with some small vertical movement in the Z plane.

This is accomplished by attaching the pivot point to a semi rigid wire which will flex (effectively a spring), causing the pendulum to bounce and a rolling barrel swivel to enable spin, all which impacts the swing.

2: A rigid tether is replaced with a flexible thin wire.

This allows the tension [influenced by 1], in the wire to vary which effects the radius of the swing arc.

3: The weight is fixed at the end of this elastic pendulum but the additional large surface area of the wings creates drag and inbalance which in conjunction with 1 & 2 also impacts the swing.

All these continual variations create a chaotic swing which like the typical pendulum would stop if an impulse was not applied to keep it moving.

In this case the impulse is a magnetic pulse which in conjunction with a permanent magnet (fixed at the end of the elastic pendulum), interacts with the magnetic pulse (either attracted a repelled depending in the polarities of the magnetic forces at play).

This impulse is applied when the permanent magnet passes a Hall sensor resulting in the pendulum being pushed or pulled continuing the swing.

The 3D printed elements were designed using BlocksCAD, sliced using Cura 4.5.0 and printed on a Labists ET4.

Flitter (body) 12(W) x 8.8(H) x 41.9(L) mm, weight 2g (2 parts)

Base - 92(dia) x 12(H) mm, weight 39g

Coil holder - 41(dia) x 19(H) mm, weight 9g

Coil Former - 26(dia) x 2.5(H) mm, weight 2g (2 parts)

Petals - 70(dia) x 2.4(H) mm, weight 5g

Flower centre (pistil) - 17.3(dia) x 4.3(H) mm, weight 1g

Print details for Flitter body*; flower centre, petals, coil former and coil holder:

Layer Height: 0.15mm

Infill Density: 100%

Shell, Wall thickness 1mm

Build Adhesion: Skirt

Print details for base.

Layer Height: 0.15mm

Infill Density: 50%

Shell, Wall thickness 2mm

Build Adhesion: Skirt

*Printed in PLA the body is relatively hard and will tap on the dome which may be an irritation to some individuals. Therefore, for a quiter experience a softer material such as TPU may be used.

Alternatively, you can dispense with the display dome entirely but this will open the elements up to possible tampering and the collection of dust. Tampering or the removal of dust will likely upset the delicate setup of the support wire.

Some post processing may be required to remove aberrations in the cavities and around the edges in addition to widening the holes for the screws in the coil holder and the petals.

Use a needle file and/or sanding paper to smooth the edge of the parts and the cavity in the coil holder.

With a 1.8mm drill bit open up the screw holes in the coil holder and petals.*

With the 6mm drill open up the centre hole in the coil holder and the base.

In the base ensure the hole to hold the wire support is clear with a 1.5mm dril bit.

The wire retaining screw holes are opened with a 2 or 2.3mm drill bit.*

*The holes need to be marginally smaller than the screw to self tap into the plastic and hold the parts in place. If you only have full or half size drill bits use the smaller size and if necessary use a round needle file to adjust the hole size.

The stem is made from a 6 mm diameter stainless steel tube.

Measure and mark a length of 65 mm.

Cut the tube with a saw or pipe cutter and deburr the internal and external edges with needle files.

The coil is made of ~500 turns of 35AWG wire wound on to the coil former.

Stick the two halves of the coil former together and once stuck together, file off any excess ensuring the centre hole is smooth and clear of aberrations.

Measure a length of ~120mm of wire and tape the opposite of the free end to the outside of the former.

Slide the centre of the former on to a dowel or rod that creates a snug fit to prevent it sliding or spinning (a Sharpie pen works well).

Wrap the wire around the former keeping the coils tights but not so tight at to snap the wire or separate the two halves of the coil former, keep winding until the coil diameter is just short of the coil former diameter. Keeping the coil within the diameter of the former help prevents the windings being scuffed during insertion into the coil holder which may result in shorted windings.

Hold down the tail end of the winding to the side of the coil former with tape and measure a free length of ~120mm and cut the wire.

Apply clear laquer to the windings around the circumference and let it dry.

Carefully remove the tape holding the wire to the side of the coil former.

Tin the ends of the two free wires with a soldering iron.

You may find that after printing the surface of the petals are not entirely smooth, if this is the case then lightly sand the surface. A smooth surface will ensure that the Flitter wings do not catch due to the close proximity of the petals as it swings across the flower.

Stick the small domed centre (pistil), into the centre of the petals and set to one side.

Solder 3 long (~120mm), 30AWG wires to the Hall sensor.

Apply clear laquer to the leads of the sensor to act as insulation and to prevent the leads shorting.

With the Hall sensor correctly orientated with the active area facing the petals.

Bend the leads down at a right angle close to the body.

Form a second right angle bend to the right in the remaining length.

The sensor should fit into the small recess at the edge with the leads pointing down into the coil holder cavity.

The remaining lead length and the point were the last right angle is formed should extend down and under the coil.

Bend the wire soldered to the leads up across and down the centre hole in the coil holder.

For added protection stick a square of tape over the sensor leads that extend down and under the coil.

Feed the leads of the coil down the centre hole of the coil holder and drop the coil former into the circular recess.

The coil former should sit flush with the top of the coil holder.

Place the petal assembly over the coil holder and align the hole in the petals with those of the coil holder and attach together with 3 x M2 x 6mm brass machine screws.

Feed the wires down the stainless steel tube prepared earlier and push the tube up in to the coil holder.

Feed the wires down through the centre hole in the support base.

Push the stainless steel tube into the center hole in the support base.

The wings can be made from any light weight film, foil or paper; plain, predecorated or a pattern of your own.

Use a template or draw a small wing shaped design onto the chosen material.

Cut out with a scalpel or scissors.

Align with the lower part of the body (tape in place if required).

Using a 1.5mm drill using the holes in the body as a guide make 2 holes in the wing material.

Use a pin or needle to make the centre hole in the wing material.

Align the upper part of the body over the lower part of the body.

Insert a M2 x 6mm brass screw in one of the recessed holes and screw in place.

Insert a second M2 x 6mm brass screw in the other recessed hole but only partially screw in place.

Feed a short portion of a 100mm length of 35AWG enamelled copper wire through the centre hole and wrap it over the partially fitted M2 screw and tighten the screw.

Stick the magnet into the circular recess with tacky.

Using tacky enables the magnet to be easily removed to replace the wire or change the wings.

The base of the globe requires a number of holes drilling within it.

1: To fit the USB board and allow access for the plug.

2: Allow access for the power wires from the USB board to the circuit board.

3: Secure the Flitter base to the Dome base.

From the centre of the Dome base draw a circle with a radius of 31mm using a compass.

Additionally, from the centre of the Dome base draw a circle with a radius of 41mm using a compass.

From the centre draw a horizontal straight line that passes through the two circles.

At 90 degrees to this line draw another line from the centre that passes through the two circles.

At the 180 degree line (horizontally on the left), drill all the way through the base 2 x 2mm holes at the intersection of the line and the circles.

At the extreme edge of the Dome base in line with the 90 degree line, position the USB board such that it straddles this line equally with a hole either side and drill 2 x 1.5mm holes.

At the 90 degree line (behind the USB board), on the 31mm radius drill all the way through the base a 2.5mm hole.

Mark the position of the USB socket opening and drill in from the edge with a 2.5 mm drill a number of holes to allow assess to a needle file to open the hole up to enable the plug to fit in the socket.

Periodically, check the access of the plug in the hole and that it fits in the socket.

Shape the hole and remove any sharp edges.

Solder a right angle 2 pin header to the USB board.

Using 2 x M2 x 8mm self tapping screws fit the USB board in place.

Cut two multistrand insulated wires to 150mm in length, strip and with a soldering iron and solder tin the ends of the wires.

Solder a two pin socket to one end and attached this to the two pin header on the USB board.

Feed the free end through the 2.5mm hole behind the USB board.

Motion of the Flitter is created by the interaction of the magnetic attached to the body and a pulsed magnetic field generated in the coil when the magnet passes the Hall sensor.

The Hall sensor (will detect a magnetic field of either polarity), in the presence of a magnetic field it will have a low output and a high output in the absence of a magnetic field.

The output is connected to the base of a PNP transistor which is switched off when the sensor output is high and switched on when the sensor output is low.

The PNP transistor is used as an inverter between the sensor and the NFET.

As its required to energise the coil when the sensor detects a suitable magnetic field the gate of the NFET requires a positive voltage. However, in the presence of a magnetic field the sensor output is low. Thus the requirement for the inverter.

The coil is mounted close to the sensor such that when the magnet passes the sensor the coil is switched on.

Assuming the magnet is orientated to be attracted to the coil.

This immediately attracts the magnet towards the coil but in doing so it moves away from the sensor. The deminishing magnetic field to the sensor results in the coil being switched off. The magnet then swings back towards the sensor re-energising the coil and repeating the process.

The circuit is assembled on stripboard measuring 7 holes x 7 holes and with only one track cut at hole co-ordinates (5, 5).

Make the track cut with a 3mm drill bit.

Assemble the circuit such that the components are mounted horizontally to the board and as low profile as possible.

Fit shorting links followed by the resistors, right angle connectors, capacitors then the transistors.

This assembly flow fits components of increasing vertical height with the lowest profile first which makes soldering easier.

Connections are made to the stripboard via right angle pin headers with the leads soldered to the pins.

Check if any shorts or opens exist were they should not with an DMM prior to the application of power.

Remedy any faults found before applying power.

Solder the free end of the leads from the USB board to the appropriate pins (+V & 0V), on the circuit board and check there are no issues when power is applied. Correct any issues before proceeding.

Solder the connections for the sensor (+V, output & 0V) and the coil (+V and FET drain), to the pins on the circuit board, taking care to ensure that sensor connections are correctly orientated. The coil is not polarised and therefore can be connected either way round.

The board is pressed into the space under the support base, if it will not stay in place apply a dab of flexible glue or a double sided sticky pad.

In either case stick a length of tape under the area where the stripboard sits to prevent contact with the metal dome base.

The support wire is made from a length of 16AWG enamelled copper wire (EWC), shaped to support the Flitter over the flower. This was available in my workspace but other wire materials & colours are available to suit personal preference.

Cut a length of this wire 280mm long.

Measure 20mm in from one of the free ends and bend the wire to form a right angle

Curve the other end of the wire to fit the inner contour of the display dome.

At ~10mm beyond mid point of the dome curl a loop in the wire with long nose pliers and trim off any excess.

Push the short end of the support wire in the 1.5mm hole in the side of the 3d printed base.

Hold the wire in place with 2 x M2.5 x 6mm screws.

Make sure the wire on the Flitter is straight and kink free by pressing between a flat firm surface and the body of a dowel or rod and pulling the wire through. If there are no kinks just pulling between fingers and thumb should suffice.

Feed the free end of the wire attached to the Flitter through the loop in the rolling barrel swivel* to form a loop and twist the wire down part of the hanging wire cut off the excess.

Hook the other end of the rolling barrel swivel* over the loop in the support wire with the Flitter hanging down and just over and not touching the flower.

*The absence of a rolling barrel swivel will not prevent the operation of this project, it will just reduce the variability by removing the spin. However, the Flitter will twist back and forth as the suspension wire will behave as a torsion spring by twisting about its axis at a fixed point.

The twist can be influenced to a greater or lesser degree by the type of loop attached to the support wire with or without the rolling barrel swivel.

1: Loose loop - allows greater freedom to twist and swing as the loop in the tether is not rigidly fixed and not relient on flex in the wire.

2: Tight loop - restricts the freedom to twist and swing as the loop is fixed relying on the flex in the wire to move.

Coarse Adjustment

Adjust the support wire such that the Flitter hangs off centre to the flower with the magnet between the outer circumference of the coil and the sensor.

To determine the position of the sensor, identify the hole in the tube retainer of the coil holder. The sensor is in line with this hole at the upper edge of the coil holder.

Ensure the USB lead is plugged into the dome base.

Optimum Adjustment

Let the Flitter hang free and stationary then apply the power and the Flitter should start to swing.

If there is zero movement or it just quivers inplace adjust the position of the support wire until a pronounced swing is initiated.

Remove the power.

Let the Flitter hang free and stationary.

Repeat the Optimum Adjustment as required to ensure the Flitter will always start at power up from a stationary position.

The ultimate aim is for the Flitter to reside within a display dome and to negate having to remove the display dome to start it, therefore we require it to be self starting.

That's all for my latest project, until the next time.