Cycle Clock V3
In a previous project Against the Clock that utilized a Microbit and Servo motors. i have for some time wished to revisit this again for several reasons and set myself a number of challenges.
Creating Racing Cyclist Whirligig afforded me the opportunity to fine tune the mechanics of the rider and simplify the bearings which would be applied in the current project.
The following challenges needed to be overcome to compete the project.
1: Remove the vertical back support board to create a more realistic support.
2: Mount the electronics out of sight below the cyclist.
3: Change the servo motors for stepper motors.
4: Remove the need for a 3rd motor to drive the pedalling action.
5: Replace the Microbit with a different microcontroller.
6: Change the drive method for the wheels.
7: Combine a number of the smaller PCB's into one.
8: Adopt an enclosure method not previously tried.
Read on to find out how it went.
Supplies
Opaque Filament PLA (Silver, White, Yellow and Red) or to suit personal taste.
Neodynium ball or cylinder magnets 3mm (dia) - Qty 2
M2 x 20mm machine screws - Qty 2
M2 x 5mm threaded standoffs - Qty 2
M2 x 10mm threaded standoffs - Qty 6
M2 nuts - Qty 2
M3 washers - Qty 24
M3 x 5mm machine screws - Qty 4
M3 x 10mm machine screws - Qty 4
M3 x 16mm machine screws - Qty 12
M3 x 10mm threaded standoff - Qty 8
M3 x 20mm threaded standoff - Qty 4
Threaded M4 rod, sufficient to make 4 x 88mm lengths
M4 nuts - Qty 8
M4 metal washers - Qty 8
M4 plastic washers - Qty 4
Capped nuts M4 - Qty 4
Acrylic Sheet 5mm thick - clear
Acylic Sheet 5mm thick - black
Acylic Sheet 5mm thick - White
28BYJ-48 5V Stepper Motor - Qty 2
ULN2003 - Qty 2
Pico Display Pack 1.14 IPS LCD 240 x 135
Hall effect (omnipolar) switch - Qty 2
Toggle Switch (on/off) SPST
Push button (push to make, release to break)
Jumper strips Socket to Socket short
Jumper strip Socket to Socket long
Jumper strip Socket to Pin short
Pin headers - Straight through hole single row
Pin headers - Straight through hole double row
Pin headers - Right angle through hole single row
Heat shrink tubing
Stripboard
74HC08 (Quad 2 I/p AND) - Qty 2
100n capacitor MLCC 1206 - Qty 7
LED red 3 or 5mm - Qty 8
1kR resistor SMD 1206 - Qty 8
Lego 12T double bevel gear
JST-XH 2, 3, 4 & 5pin (if using these connectors a suitable crimping tool will be required unless pre-terminated leads are used).
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
Drill
Drill bit 10mm
Drill bit 7mm
Drill bit 6mm
Drill bit 4mm
Drill bit 3.5mm
Drill bit 3mm
Drill bit 2mm
Masking Tape
Self adhesive non slip feet - Qty 4
Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.
Description
This is clock project in the form of a freestanding cyclist were the time elements representing hours and minutes are via the wheels.
Two separate and identical elements are used which consist of a stepper motor driven gear that drives a larger gear that represents a bicycle wheel arranged such that the drive gear is below the surface.
The reference start (home), position for the wheels are verified by hall sensors and magnets.
All this is controlled by a Raspberry Pi Pico with RTC and LCD used for both time setting and display.
The specific LCD display was chosen due to its small size and integrated push buttons negating the requirement for separate buttons and it had been used on a previous project.
The LCD displays the time in 24 hour mode whilst the wheels display the time in 12 hour mode.
All this housed in an acrylic case.
Size: 207(H) x 218(L) x 118(D) mm
Weight: 1.33kg
Supply current at 5V (static typ. 33mA), (active typ. 243mA).
Calculations
In order to move the wheels to display the correct time a few calculations are required.
Each of the wheels has a circular rotation of 360 degrees but is also a gear with 65 teeth.
However, the wheel is not directly connected to the motor but via a gear with 29 teeth.
Motor steps per rotation = (4096/8) = 512 for an 8 step beat pattern.
This allows us to create a unified calculation irrespective of the beat pattern.
Steps per degree (spd) = 512/360 = 1.422222
Gear_ratio = 65/29 = 2.241379
Hours
Total degrees for hour wheel = 360
deg_hr (12 mode) = (360*Gear_ratio)/12 = 67.24137
step_hrs = int((hrs*deg_hr)*spd)
Therefore
1 Hr = 95 steps
6 Hr = 573 steps
12Hr = 1147 steps = (512*Gear_ratio)
Minutes
Total degrees for minute wheel = 360
deg_min = (360*Gear_ratio)/60 = 13.44827
step_min = int((min*deg_min)*spd)
Therefore
1 Min = 19 steps
30 Min = 573 steps
60 Min = 1147 steps = (512*Gear_ratio)
The specific motor used an 8 step beat pattern and the calculated steps are passed to a loop which repeats the beat pattern for each calculated step.
Software
Programmed on Thonny 3.3.13 utilising Pimoroni Pirate Brand MicroPython v1.20.6
Downloads
CAD Design
The 3D printed elements were designed using BlocksCAD, sliced using Cura 4.5.0 and printed on a Labists ET4.
1: Cycle and cyclist upper body. Size:197(L) x 168.5(D) x 7(H) mm, Weight: 73g
2: Cyclist torso. Size: 59.1(L) x 33.4(D) x 5(H) mm, Weight: 7g - Qty 4
3: Cyclist arms. Size: 39(L) x 30(D) x 5(H) mm,Weight: 3g - Qty 2
4: Cyclist thighs. Size: 36.3(L) x 48.4(D) x 5(H) mm, Weight: 3g - Qty 2
5: Cyclist lower legs. Size: 25.7(L) x 46.7(D) x 5(H) mm, Weight: 2g - Qty 2
6: Pedals/Crank. Size: 28(L) x 12(D) x 6.5(H) mm, Weight: 1g - Qty 2
7: Hip spacers. Size: 20(dia) x 6.5(H) mm, Weight: 2g - Qty 2
8: Chainring spacer. Size: 20(dia) x 2(H) mm, Weight: 1g
9: Hall Sensor back. Size: 18(W) x 15.5(D) x 3.5(h) mm, Weight: 1g
10: Wheels (65 teeth gear). Size: 67.6(dia) x 7(H) mm, Weight: 15g - Qty 2
11: Front Tyre. Size: 118.5(L) x 79(W) x 11.9(H) mm, Weight: 17g
12: Rear Tyre. Size: 118.5(L) x 78.3(W) x 11.9(H) mm, Weight: 16g
13: Drive gear (29 teeth). Size: 31.6(dia) x 7(H) mm, Weight: 4g - Qty 2
14: Motor Bracket. Size: 21.5(W) x 50(L) x 20(H) mm, Weight: 6g - Qty 2
15: Pointer. Size: 24.4(L) x 4.6(W) x 9.5(H) mm, Weight: <1g - Qty 2
16: Nut Foot. Size: 12(dia) x 5(H) mm, Weight 1g - Qty 4
17: RTC box: Size: 22(H) x 32(W) x 7(D) mm, Weight 3g
18: Display Retainer: Size: 53(L) x 24.4(D) x 1.5(H) mm, Weight: 1g
Downloads
Printing
Filament: PLA
Layer Height: 0.15mm
Infill: 100%
Wall Thickness: 2mm
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.
Use a needle file and/or sanding paper to smooth the parts in areas were they come together.
Circuit
The circuit is the same as that employed in the Dual Spiral Marble Clock with suitable software modifications.
Utilising a Raspberry Pi Pico plus RTC to contol two stepper motors.
However, the physical, visual and mechanical time display methods are totally different.
PCB Design
In order to reduce the number of separate PCB's, interconnects and hand wiring I replaced all the following (2 x motor drivers, multiplexer and GPIO expander), with one custom designed PCB.
An additional PCB was designed to allow connection to the display.
The PCB's were designed using Eagle and fabricated at OSHpark.
PCB Assembly
The PCB contains a combination of surface and through hole mounted components.
The connections (2,3,4 & 5pin), to external elements are on a 2.54mm/0.1inch pitch which will accomodate pin headers, screw terminals or JST-XH connectors.
The stepper motors used are terminated in JST-XH 5pin connectors therefore matching connectors will ease construction.
The through hole components being a combination of pins, sockets and LED's.
With the surface mounted components being capacitors, resistors and 2 IC''s.
The motor driver IC's (ULN2003), are mounted in sockets to enable easy removal in the event of a fault.
Mount the components according to height with the lowest first (SMD), and the tallest last this enables the board to sit at the same level when inverted to mount the through hole components.
The links on the board can be used to enable or disable the LED's. [Linked LED's enabled, No links LED's disabled]
Prior to applying power.
Visually check the board for short circuits particularly between the SMD IC's were the leads are closely spaced.
Check with a DMM in continuity mode between the supply input to ensure there are no short circuit.
Support Rods
Cut 4 x M4 x 88mm threaded rods and round the ends to remove the burr with a file.
Each rod will require 2 x plain nuts and washers a plastic washer and a capped nut in addition to a printed foot.
Enclosure Top
The top is a single layer (218(L) x 118(W) x 5(H) mm), of white acrylic on which the cyclist sits.
Two cut outs and mounting holes are required for the drive elements and wheels. (See attached template)
For the mounting holes in the corners measure in from the corners along the horizontal 14mm and vertical 14mm and at the intersection drill a 4mm hole. Perform this operation in all 4 corners.
Enclosure Back
The back is a double layer (198(L) x 60(W) x 5(H) mm), of black and clear to which are attached the reset button, set switch, RTC and the USB_C slot.
With the two layers sandwiched together drill a series of 3mm holes.
1: Reset switch
2: Set switch
3: USB_C - Sufficient holes to allow access for a needle file. Open the hole to allow the USB_C plug to pass through.
4: RTC box - using the box as a template, 6 holes plus sufficient holes to enable access for a needle file to widen the slot for the connector.
The RTC is fitted externally to negate the need to open the enclosure to replace a battery, keeping the process quick and easy.
Once the holes have been drill and the USB slot has been opened, separate the two layers.
Reset switch.
In the black rectangle widen the hole for the reset switch with a 7mm* dril
In the clear rectangle widen the hole to accept the nut.
Set Switch
In the black rectangle widen the hole for the reset switch with a 6mm* dril
In the clear rectangle widen the hole to accept the nut.
Realign the two layers and push (it may be necessary to apply some glue), the M2 x 10mm threaded standoffs into the holes for the RTC.
*(Adjust the hole sizes accordingly if different size switches are used)
Enclosure Base
The base is a double layer (218(L) x 118(W) x 5(H) mm), of white and clear acrylic on which the control PCB sits.
Using the enclosure top as a template for the corner holes mark and drill 4 x 4mm holes.
On an M4 threaded rod (previously cut), fit a nut and beneath it a plain washer and push the rod down through the hole, fit a plain washer and a fit a foot into which a nut has been inserted.
Adjust the nuts top and bottom to tighten the rod in place leaving sufficient length to enable the top to be held in place.
Repeat the process on the remaining three rods.
The short side of the control PCB is centred (59mm), with the short side of the box, whilst the long side of the PCB is aligned such that the display connectors are aligned with the connectors on the display.
In this position mark and drill out the four corner support holes with a 3mm drill.
Attach 4 x M3 x 10mm threaded standoffs up through the base with 4 x M3 x 16mm machine screws.
Sit the control PCB on the standoffs and secure with 4 x M3 x 5mm machine screws.
USB socket
An off board USB socket is used as this allows simple replacement should it be damaged by excessive force during insertions and/or cable snagging.
Mounting holes are required for the USB_C socket.
Centred with the long side of the base (109mm), and set back 19mm drill 2 x 2mm holes separated by 12mm.
Display
A sandwich of two perspex rectangles of size (198(L) x 60(W) x 5(H) mm) black and clear are used to house the display.
In the centre of the clear rectangle measure and mark a rectangle of 24.4(H) x 52(L) mm.
Cut out the area of the measured rectangle using a saw, drill and file to accomodate the display.
In the centre of black rectangle and within the cutout in the clear rectangle measure and mark two slots of 2(H) x 52(L) mm spaced 17.78mm apart to accomodate the socket strips in the display.
Fit the display into the cavity in the box.
A 3D printed spacer surrounds the edge of the display glass and the buttons to fill the gaps, creating a uniform contrast and a firm support for the transparent film. Orientate it such that the small hole aligns with the LED. Press this over the front of the display.
The display is held in place by a brass surround and additional protection is provided by a plastic shield.
The plastic shield provides some protection to the LCD glass front whilst still enabling the buttons to be activated.
Cut a brass sheet to the following dimensions 65(L) x 38(W) mm and in the centre cut an opening 38(L) x 18(W) mm
Drill a 3mm (dia), hole coincident with the RGB LED on the display.
In the corners of the brass surround drill 4 x 2(dia)mm holes to accomodate self tapping screws.
Cut a piece of transparent film (PET or similar), from a blister pack the same size as the brass surround and attach with masking tape. Drill through the corner holes and attach the retainer to the box, using it as a template mark the positions of the buttons.
Drill 4 x 3(dia)mm holes coincident with the buttons in the transparent film and widen with a round needle file.
Fit the display retainer with the corner screws and carefully peel off the masking tape.
Enclosure Sides
The enclosure sides made of acrylic using three shades (black, white and clear), with each of the sides consisting of two layers.
Assembly is such that two ends (118(W) x 60(W) x 5(H) mm), and the base (218(L) x 118(W) x 5(H) mm), consist of a clear and white layer with clear on the inside with the edges visible.
The front consisting of a clear and black layer with clear on the outside in which resides the display (198(L) x 60(W x 5(H)) mm).
The back consists of a clear and black layer with the clear on the outside in which resides the reset & set enable switches, the USB_C opening and the RTC.
The sides are glued together to form an open rectangle.
The top is a single layer (218(L) x 118(W) x 5(H) mm), of white acrylic on which the cyclist sits.
The enclosed box is held together with 4 x M4 x 88mm threaded rods and bolts.
Box size 218(L) x 118(W) x 75(H) mm
Cyclist Preparation
Prepare the thighs
The rotating parts of the thigh occur at the hips and the knees for which some type of bearing is required to enable smooth movement. For simplicity this would be a plain bearing (bushing), press fitted into the hole as the load is light with a small degree of movement and low rotating speeds.
The bushing will be made of brass due to the following properties; self lubricating, corrosive resistance and resistance to bonding to steel (hip and knee shafts).
With a 6.5mm drill bit clear out the hole for the hip.
Cut a level length of 6.5mm brass tube greater than 5mm in length and ensure the end to be inserted is burr free and smooth.
Place the thigh on a level firm surface and using a piece of wood or plastic to protect your fingers apply firm level and even pressure to position the brass tube into the hole at this point it needs to be free standing and level. If it is not level press it out from the other side with a length of 6.5mm tubing and reseat.
Once confirmed level use a smooth face vice or parallel pliers to press the tube fully into the thigh.
Using a file remove the protruding tubing flush with the surface of the thigh.
Clear out any burr from within the tube with a round needle file/ roll of fine sanding paper and check for smoothness with the shaft of a cotton bud which should not catch/drag.
Repeat the process at the knee with 3.5mm drill and tubing.
Prepare the Legs
The rotating parts of the leg occur at the knees and the feet which will be using bushings as with the thighs.
Repeat the process as applied to the thigh at the leg with a 3.5mm drill and tubing appliying this both to the knee and foot.
Wheels
The cycle wheel is actually a gear with 65 teeth.
Rather than ball bearings a plain bearing (bushing), is created using a brass tube and rod.
Cut a 3.5(dia)mm tube to a length of >8mm and round the outer edge with a file.
Place the wheel on a firm flat surface with the back facing uppermost, orientate the tube with the rounded end placed in to the hole and with a piece of wood between the hammer lightly tap the tube in (alternatively, use a pillar drill with a similar protective separation).
With a file remove the remainder of the tube such that it is flush with the surface of the wheel.
Deburr the tube with a 3.5mm drill bit and/or round needle file.
Pointer
With a file smooth off the sides and edges of the pointer and pointer cavity in the wheel to enable it to be pressed into the opening.
Magnet
A hole is created at the opposite end of the pointer to house a 3mm diameter magnet.
Widen the hole as necessary and into the hole insert glue or epoxy putty and press the magnet in place.
The magnet is used in conjunction with the hall sensor to determine the homing position for the wheel.
Cycle Preparation
Cut three 3mm (dia), brass rods to a length of 17mm.
Round off the edges of the cut with a file.
With a 3mm drill bit open up the hole for the wheel axle in the cycle.
Place the cycle on a firm flat surface, orientate a rod with the rounded end placed in to the hole and lightly tap in with a hammer (alternatively, using a pillar drill align the rod with the hole and in line with the drill chuck (without applying power), bring the chuck down on the head of the rod and press it into the hole.
Repeat the process for the other wheel axle.
Repeat the process for the intermediate gear.
For the chain ring gear open up the hole with a 3.5mm drill bit.
Cut a 3.5mm brass tube to a length of 8mm and round off the outer edge with a file.
Place the cycle on a firm flat surface, orientate the tube with the rounded end placed in to the hole and with a piece of wood between the hammer lightly tap the tube in (alternatively, use a pillar drill with a similar protective separation).
With a file remove the remainder of the tube such that it is flush with the surface of the cycle.
Deburr the tube with a 3.5mm drill bit and/or round needle file.
Hall Sensors
The sensors sit on the inner circumference at the lower part of the wheel in the integrated holder.
Solder 3 x 20cm lengths of wire to the leads of the sensors.
Pass the wires through the front of the holder and out the back.
Bend the leads at 90 degrees close to the body of the package such that the package fits in the cavity with the front facing forwards.
Bend the leads at the back 90 degrees downwards.
Screw the covers to the back of the holders with 2 x M2 x 6mm self tapping screws.
Cut a small piece of stripboard 7 x 3 visible holes with the copper strip running the long length and drill a 3mm hole at 2 x 2 holes.
Fit a right angle 3 pin header at the extreme end from the 3mm hole and a vertical 3 pin header next to this.
Connect the wires from the hall sensor to the vertical pins by soldering or wire wrapping.
Be sure to enable identification of the correct pins either by labelling or colour coding.
Cyclist Assembly
Pelvic Rod
Cut a length of 6mm diameter tube to ~48mm (such that it is slightly longer than the width of the hips to prevent the thighs binding when the screws are tightened), and deburr and smooth the interior and external ends.
Subject to the tolerance of the standoff and the tube it may be necessary with a reamer or 5mm drill bit to open out the ends on the tube to accept the standoff.
Apply a suitable adhesive or epoxy putty into the end of the tube and push in the standoffs until its flush with the ends and set aside to cure.
Alternatively by tapping in the standoff with a mallet or press fit between a vice. Be sure to protect the open tube end with a wooden block or other soft material to prevent damage. Reducing the circumference at one end of the standoff with a file will help with insertion.
Clear the hip hole in the main cyclist body with a 6mm drill bit and Insert the rod to half its length.
Build the body
Clear out the 6mm holes at the hip of each of the 4 torso elements and slide 2 on each side of the main cyclist body ensuring they are all aligned with the central 3mm hole aligned. Clear out the 3mm hole with a 3mm drill bit and pass through a M3 x 25mm machine screw then fit a M3 nut and tighten.
Fit a 6.5mm spacer over each end of the pelvic rod.
Attach the arms
Feed a M3 X 25mm machine screw through the hand hole on one of the arms and thread a 10mm spacer onto the screw. Hex spacers were used but cylindrical spacers are equally suitable.
Feed the free end of the screw through the hole in the handle bar and screw a 10mm spacer on the other end.
Align the remaining arm with the open end of the spacer and attach with an M3 x 8mm machine screw.
Align the holes of the shoulders for the arms and the torso and fix in place with M3 X 12mm machine screws.
Assemble lower limbs
The lower limbs consist of the thigh and the leg which are attached together at the knee.
Thread a plain washer onto a M3 x 10mm machine screw and pass the screw through the thigh at the knee then place another plain washer over the screw.
Pass the screw through the knee of the leg and place a plane washer over the screw and fix in place with a self locking nut.
Tighten the nut to reduce side to side play to a minimum but still allowing the leg and thigh to rotate about the knee with low friction.
Hold the top of the thigh between thumb and finger letting the leg hang down and swing the leg in line with its plane of movement. The leg should swing freely.
If leg does not swing freely, check for over tightening of the nut, missing central washer.
Fit Pedal/Crank
Open the hole in the pedal with a 3mm drill bit to allow a M3 screw to spin freely.
The pedal is orientated such that the recess faces into the centre of the cycle and is attached on the inside of the foot.
Thread a plain washer onto a M3 x 12mm machine screw and pass the screw through the pedal and then place another plain washer over the screw.
Pass the screw through the foot of the leg and place a plane washer over the screw and fix in place with a self locking nut.
Tighten the nut to reduce side to side play to a minimum but still allowing the foot and leg to rotate about the pedal with low friction.
Hold the top of the thigh between thumb and finger letting the leg hang down and swing the leg in line with its plane of movement. The crank/pedal should swing freely.
If leg does not swing freely, check for over tightening of the nut, missing central washer.
With a 3mm drill open up the holes in the cranks.
Attach legs to body
Attaching the drive gear to the right leg.
Cut the 3mm(dia), axle to a length of ~38mm.
On the drive side feed the axle through the crank then feed on the 24T gear and a M3 washer.
Feed the hole in the thigh over the pelvic rod and the axle through the hole in the vertical frame support.
Push on a M3 washer then a 8mm spacer on the axle and non drive side crank/pedal onto the axle.
Ensure that the cranks are aligned in opposing directions (180 degrees apart).
In the event that the crank/pedal does not sit snugly on the axle provision is made to fix this using 2 x M2 x 6mm machine screws.
Feed the hole in the thigh over the pelvic rod.
Check the movement of the lower limbs and drive assembly by rotating the gear by hand resolve any binding that may occur.
Secure the legs to the pelvic rod with a 2 x M3 x 10mm machine screws and plain washers.
The leg should rotate freely about the hip with ~1mm side to side play, without this play the hips can bind when the hip screws are tightened.
If not rotating freely and assuming the internal surfaces of the plain bearing are burr free and likewise with the exterior surface of the pelvic rod a tolerance or alignment issue may exist.
Rotating the thigh about the hip a number of times from left to right will likely smooth out the issue.
Intermediate gear
Fit a M3 washer followed by the intermediate gear (12T), and a M3 washer onto the 3mm rod beside the chain wheel gear (20T).
Wheels
Fit a M3 washer over the wheel axle then fit the wheels over the axles.
Fit the tyres over the wheels.
The rear tyre is differentiated from the front wheel with a cut out coincident with the intermediate gear.
Attaching the Cyclist
Fit the motor brackets under the enclosure top with M3 x 16mm machine screws and nuts.
Pass the wheel extensions with attached tyres down through the cutouts in the enclosure top and loosely attach to the motor brackets with M3 x 16mm machine screws and nuts. Loosely attached to enable adjustment.
Insert the drive gear between the wheel and tyre extension.
Insert the axle of the motor down through the tyre extension and into the centre opening in the gear.
Align the teeth of the drive gear and wheel and fix the motor in place with 4 x M3 X 8mm machine screws and 2 x M3 x 20mm threaded standoff.
Fix 2 x M3 x 10mm standoffs between the wheel and tyre extensions in the holes at the extreme ends and fix in place with 4 x M3 x 8mm machine screws, ensuring that the small stripboard is held in place with one of the screws.
Repeat the same procedure with the other wheel.
The hall sensor supply pins are powered from the 3V3.
Each output is taken separately to GP27(X9, hours) and GP28 (X10, miniutes) accessible at separate connectors.
The motors are separately connected to X1(hours) and X2(minutes).
Final Assembly
The enclosure sides are placed over the enclosure base prior to connecting the required wires.
This will be held in place by the threaded rods and the pressure applied between the top abd based when the capped nuts are tightened.
Ensure that the leads connected between the lower part of the box and the underside of the top panel are long enough to enable work to be carried out with the top panel removed.
The USB_C board is connected to X11 (ensure to connect the right polarity to the pins).
The two switches are simply screwed into the holes drilled in the back of the box.
Reset is connected to X7.
Set enable is connected to X6.
The stepper motors are connected to X1(Hours) and X2(Minutes).
Due to limited GPIO lines a multiplexer made up of two IC's (74HC08), sit between the Pico and the motor drivers to switch the same 4 driver lines to the required motor by selection of one of the two appropriate select lines.
The LCD display sits at the front of the box connected to a sub PCB enabling jumper wires to be used to connect this to the controller board.
The RTC is connected to X5
The buzzer is connected to X8
The hall sensors are connected to X9(Hours) and X10(Minutes) at pins 3V3, 0V and OP(output)
Double check the wiring prior to completing the enclosure and applying power.
Sit the enclosure top over the four threaded rods making sure there are no wires trapped under the edge of the sides.
Fit a M4 plastic plain washer over each rod followed by capped nut.
Hand tightening should be sufficient to retain everything in place.
To carry out work inside the box
Lift the top panel and position it with the front sitting on the two rear threaded rods and hold in place with nuts. Two threaded rods can then be inserted into the holes at the back of the top panel, adjusted for height with a nut on either side of the top panel for stability.
To carry out work on the underside of the top panel.
A box or container (LEGO works well), that will allow the cyclist to be inverted and supported at the edges of the top panel.
Operation
Power (5V), from a suitable supply is provided by a USB-C lead connect to a socket at the back.
At power on or after a reset.
The homing process will begin, displaying "Please Wait ... Homing"; this ensures that the wheels are in the starting (home), position with the pointer at the top.
First the hours then minutes.
If the pointer is already at the top the wheel is homed.
If the pointer is part way around, the wheel will rotate until the pointer is at the top.
There is a 60 second timeout on the homing process for each wheel. If the timeout expires the display will show "Homing Failed"; in red text which will be reflected in the time display also in red.
With both wheels aligned the display will show "Homing Passed", in green text which will be reflected in the time display also in green.
The current time from the RTC will be displayed.
The hour wheel will rotate to indicate the hour.
The minute wheel will rotate to indicate the minute.
The wheels operate on a 12 hour cycle whilst the digital clock will operate on a 24 hour cycle.
A reset can be initiated by momentarily pressing the push button on the lower left on the back and this will start the homing process.
To set the time.
Flip the switch located on the lower right at the back.
The display will turn blue.
Press the top left button next to the display showing a "H", for each hour to be set 0 to 23.
Press the top right button next to the display showing a "M", for each minute to be set 0 to 59.
Press the bottom right button next to the display showing a "U", to update the new time.
If you wish to blank the digital display.
Press the bottom left button next to the display showing a "B".
Once complete, flip the switch on the lower right back the display will turn green and show the updated time assuming the display has not been blanked, in which case nothing will be displayed.
The time will be updated on the wheels.
RTC battery replacement.
The RTC battery is accessible externally by removing the Allen screws from the 3D printed case at the back of the box.
Troubleshooting
Problems are likely to occur with the mechanical elements during the course of the build but with patience and care these can be avoided or resolved.
The wheel fails to rotate or judders.
1: Do not apply excessive force when pressing the gear onto the motor spindle such that it locks, a little movement is desirable.
2: The wheel is rubbing on the tyre possible due to inconsistancies with the internal surface of the tyre.
3: The wheel is rubbing as the wheel extension is not equally distanced around the circumference.
Homing fails
1: Check the function of the Hall sensor.
2: Check the connections are correct and sound.
3: Magnet missing from the wheel.
Pedals not rotating
Rear tyre pressing on the intermediate gear.
The cranks and chain gear should be a tight fit on the rod, lubrication should not be applied to these areas as it could cause slippage.
Review
All challenges met with satisfaction.
1: The vertical back support board removed giving the cyclist a more realist horizontal support.
2: All the electronics housed beneath the cyclist.
3: Stepper motors installed to replace servo motors.
4: The pedalling action is driven by the rear wheel negating a 3rd motor.
5: Microbit replaced with Raspberry Pi Pico.
6: Wheels designed as large gears driven at the circumference by a smaller gear mounted out of sight below the surface.
7: Single custom PCB designed and implemented to replace multiple PCB's for 2 x motor drivers, multiplexer and GPIO expander.
8: Multi layer acrylic sandwich box implemented.
Finally
Thanks for reading this latest project.