Nodding Bird

The Nodding Bird continues the series of kinetic magnetic inspired projects. Previous projects being The Angler and The Flitter.

Due to the use of the same methodology some steps will be identical between the projects but for continuity and completeness each can be viewed independently.

Whereas the previous projects made use of chaotic motion this project has a more metronomic motion due to the limited plane of movement as with a simple pendulum.

This latest project taking its inspiration from the Drinking Bird but instead of using fluids uses magnetics.

Size: 186(H) x 120(dia) mm

Weight: 192g

Current Consumption at 5V: 150mA peak

Transparent plastic straw with retaining ridge 230mm(9inch)(L) x 7.5(dia) mm

M2 Self tapping screws 8mm - Qty 8

Neodymium magnet cylindrical 10(dia) x 1.5 mm

Enamelled Copper Wire 35AWG/0.15(dia) 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

Strip Board

Pin headers - Straight through hole single row

Feathers

Ball bearings 3/16 inch (4.7625 mm)

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

Pin Vice

Drill bit 1.5mm

Long nose pliers

Wire Wrapping Tool

Plastic Adhesive

Tacky

Masking Tape

Silicone Grease

Clear Laquer/Varnish

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

The 3D printed elements were designed using BlocksCAD, sliced using Cura 4.5.0 and printed on a Elegoo Neptune 4 Pro.

Head 30(L) x 30(H) x 30(W) mm, weight 5g (2 parts)

Body 60(L) x 60(H) x 60(W) mm, weight 16g (2 parts)

Pivot 104(L) x 20(W) x 10(H) mm, weight 8g

The head, body and pivot come in two versions to suit 6 & 7.5 mm tubes.

Legs 89(L) x 15.8(H) x 32(W) mm, weight 23g (2 parts)

Feet 97.6(W) x 76.9(L) x 10(H) mm, weight 8g

Coil Former 26(dia) x 2.5(H) mm, weight 1g (2 parts)

The base consists of three elements the main support and two covers to hide the electronics.

Base1 120(dia) x 22(H) mm, weight 89g (The main supporting base).

Base2 39.6(W) x 58(L) x 9 (H) mm, weight 4g (Cover for coil and sensor).

Base3 75(W) x 87.5(L) x 8(H) mm, weight 17g (Cover for electronics board).

Filament: PLA (Blue, Brown), but any colour as suits personal choice.

Layer Height: 0.15mm

Infill: 100%

Bed Adhesion: Skirt

No supports

All parts are correctly orientated within the files for printing directly.

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. This can be accomplished using sanding paper & needle files for cavities and edges and 1.5mm drill bits for the M2 screws.

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 with plastic adhesive.

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

Secure the centre of the former on to a dowel with a M2 x 10mm screw that creates a snug fit to prevent it spinning.

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.

Remove the coil former from the dowel.

Motion is created by the interaction of the magnet attached to the straw 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 straight 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 the sensor connections are correctly orientated. The coil is not polarised and therefore can be connected either way round. However, you will need to ensure that the magnet is attracted to the coil.

Fit the assembled circuit in to the base.

Position the USB C board in the cut out.

The supply wires are routed in the slot around the coil.

The coil is inserted within the circular recess behind the USB socket and the wires exit via the slot in the front.

This can be held in place with tacky or a flexible adhesive.

In front of the coil is a recess for the Hall sensor.

Insert the sensor with its active surface facing down and secure in place with a small blob of tacky, alternatively glue can be used but its recommended to use a flexible glue should it be required to remove the sensor for any reason.

The board fits into the space under the support base, to hold in place apply a dab of flexible glue or a double sided sticky pad.

Fit the small base cover over the USB socket, coil and sensor.

Secure the cover in place with 2 x M2 x 8mm self tapping screws.

Fit the larger base cover over the circuit board and secure in place with 4 x M2 x 8mm self tapping screws.

With a 1.5mm drill bit open up the two visible holes to the front of the base.

The head consists of two parts the front and back which are stuck together.

Apply a little adhesive around the edges with the exception of the hemispherical cut outs and press the two parts together. Hold in place until the adhesive has set, if necessary use tape to hold the two pieces together.

The body consists of two hemispheres each with a cross brace and central holes to aid the joining process by keeping the hemispheres aligned.

Apply adhesive to the cross braces but not around the central hole.

To aid alignment the straw can be inserted through both halves whilst the adhesive cures, hence the requirement to not apply adhesive to the central hole. allowing the straw to be removed.

The pivot is constructed in one piece with a central hole to accommodate the straw.

Where the pivot and hip contact both these surfaces are curved.

Therefore, ensure the curved surfaces of the pivot arms are pointing downwards.

The spine straw connects all the main elements of the bird together (head, pivot and body).

Using a 7.5mm straw with a ridged, cut off the short portion but retaining the ridge on the straw.

Measure and mark 160mm from the edge of the ridge and cut off with a saw.

Tidy the edges with a file and/or sanding paper.

Temporarily apply a small slither of double sided tape or tacky to the ridged end and attach a cylindrical magnet.

The nodding elements consist of the head, spine, pivot and body.

With the ridge of the straw facing downwards slide the assembled body onto the straw and down to the ridge.

Ensuring the curved surface of the pivot arms are facing downward and slide the pivot over and down the straw leaving a small gap of ~5mm. If the pivot slides or spins temporarily apply a little tacky to maintain the position.

Apply a small amount of adhesive to fix the head in place at the top of the straw.

The legs consist of two parts which are attached to the feet.

The feet are printed as one piece with an integral spacer bar.

Attach the feet (with the single heel toe facing the USB socket), to the base with 2 x M2 x 8mm self tapping screws.

The legs are inserted into slots in the feet with the flat surface of the leg facing inwards and the point (ankle), of the leg facing towards the USB socket.

The legs are a press fit but can be glued if required.

Holding the nodding elements by the pivot, lower this down into the slots in the legs.

Position the magnet on the end of the straw as close as possible to the spacer between the feet without it touching when swinging. This is accomplished by sliding the straw up or down within the pivot.

Assuming that the circuit has been correctly assembled and no faults are found.

Apply the power.

If nothing occurs, gently push the body of the bird, if it nods and then stops then further adjustment is required.

Remove power.

If it fails the above, flip the magnet on the end of the straw over.

Apply power,

If nothing occurs, gently push the body of the bird, it should start to nod.

Remove power.

Remove the temporary fixing for the magnet and glue in place.

Apply a little drop of glue into either of the holes in the pivot to secure the straw.

For the bird to auto start it needs to be in a near vertical position, if it has a forward lean this can be corrected by adding additional weight to the bottom of the body.

This can be accomplished by dropping a few ball bearings into the straw via access in the head.

To reduce friction at the pivot apply a thin layer of silicone grease.

Further embelilshment in the form of feathers can be added which if kept small and to a minimum will not impact the motion. These were added to the top of the head and the back of the body.

If the bird is optimally set up it will auto start with the application of power.