Introduction: Chain Clock

Hello

My name is Constant and this will be my first Instructable where in the end I hope you will able to make your own clock

My brother is fond of Bycicle and me feeling creative, i wanted to make a nice cool present.

So this clock will be showing true time by numbers of each hours attach at equal interval around a chain hanging onto a rotating shaft indicating the time where the appropriate number of the hour is at the top.

Yes, unfortunatly if you want to replicate this project as identical as possible you will require various equipement and machinery but don't hesitate to let your creativity enroll and just use this tutorial as a guideline.

Step 1: Pre Design Specification

In order to make a clock, it is very important to respect the specification

TIMEKEEPING ACCURACY

In order to keep the timing right, there is tons of way to make this happens using a reliable oscilation device.

Since I wanted to develop my electronics skills I then decided to use the constant reliable frequency of the main power supply know as 50Hz to then drive a stepper motor driving itself a gear box and at the end the chain.

To make this design neat and compact, I decided to fit all the mechanical components and PCB inside a rounded stainless steel bowl which can be hang from a wall.

Step 2: 50 HZ

Everyone should know that the power electricity delivered to our home is running at 50Hz (In UK).

This frequency is what stop your light from constantly flickering

This frequency is due to to the fact that coal, oil, gas and nuclear stations are basically just giant boilers that steam water through a massive inertia turbine which rotates and generate power.

It is not perfectly stable, due to the continuously changing load of the power grid and the generator's reaction to load changes but Power companies ensure that the frequency is averaging aroud 50Hz and that the number of cycles in one entire day is always correct

Many electric and electronic clocks use this not just for power, but also as the reference frequency for keeping track of the time.

Visit your government website to look at the current grid frequency, you will be impress of the accuracy

Step 3: The Math

Suppose we want to drive the hanged chain with a motor, the torque required is very small as the weight of the chain we want to pull up is the same as the weight of the chain pulling down.

Knowing that, I decided to use a small and compact stepper motor running on 5volt

This stepper motor has the particularity to have a built in reduction gear box on the end of the shaft (2048:1), very useful has it will become handy to gain more torque.

To make thing simpler for the electronic design, I have decided to send one pulse to the stepper motor every one second. This will also sound cool when we’ll here the small clics* coming from the gear box engaging the gear teeth every second, it feels reliable.

It now become clear that to make the motor produce 1 turn at the end of the shaft, we will need to send 2048 signal.

1 hour is defined by the gear total ratio between how much link of the chain there is between two numbers, the gear on the shaft driving the chain and the gear ratio of the stepper motor.

1hour = total ratio x 2048

1 hour is 3600 seconds

Now then

1 hz x 3600 = total ratio x 2048

Total ratio = (1 x 3600) / 2048

Total ratio = 225/128

Total ratio of a train gear is describe by the equation as follow:

Gear ratio = (nbr of teeth driven) / (nbr of teeth driving)

Knowing this ratio, I then came up with defined number of teeth for each gear

225=25X9

128=16x8

16 teeth mounted on the stepper motor

Driving a 25 teeth gear mounted on the chain shaft

Driving a 8 teeth gear

Driving the chain with 9 links between each numbers.

Step 4: Mechanical Design

As mention earlier, the idea is to compact all the design into a stainless steel bowl where I could weld some fixture inside to assemble all the componants

Using a laser cutter, I planned to cut a ring with some feature tapped holle and a bracket fitted to it to mount the stepper motor.

The gear ratio being defined I decided to 3D print the two gears as the Torque applied on each teeth is very low, the friction won’t worn the parts and it is very easy to adapt the bore to suit the mechanical parts.

A couple of turned parts on the lathe need to be manufactured.

The Numbers attached to the chain will be latter described.

And the PCB, I manufactured it on my homemade CNC as well as latter described process.

Step 5: BOWL ASSEMBLY

After designing the clock, I then started the mechanical build of the clock

while waiting to receive the laser cut part, and bought out item, like the bearing, i started by manufacturing the turned part and 3D printed gear.

The bowl was drilled thru on the lathe to let the shaft go thru and then assemble the ring and bush bearing inside it for TIG welding the components together. Obviously being careful to not weld where the bracket for the motor is going to sit as this one is going to be bolted from the back.

All is left to do is to progress on the PCB design and to start manufacturing the numbers to accomodate the chain link.

Step 6: Electronics Design

As you saw on the previous step, I mock up a prototype electronic board where i used a pcb size transformer,

I then decided to get rid of it as it will potentially generate some heat inside the bowl as well as perturbing the other electronics components due to its high electromagnetism field.

So a socket type power transformer 6V AC converter will be used to run the clock.

I then reduce the voltage to 5V in order to pilot the motor at he right voltage with a voltage regulator LM7805

The idea then is to use the peak of the 50Hz coming from the outlet power supply going thru a Schmitt trigger in order to generate a nice Square 50 hz signal. Then this signal is fed thru a first 4017 IC divider stage to divide it by 10 which give me a 5Hz signal and then feeding thru this signal to another 4017IC divider in order to generate a pulse every second by dividing it by 5 (1Hz)

A switch is mounted on the second 4017IC divider to choose the frequency that the clock is running at 50 or 60HZ, either by dividing the signal by 5 or 6. which makes the clock to be accomodated all around the world.

Then every second a coil of the stepper motor is powered simulated by 4 LED for each coil.

Also using some back reverse diode as the inductance of the motor coil could induce current back into the electronic.

Here find attach the schematics

Step 7: PCB PROTOTYPE

Before i start going any further on the electronics schematics and to prove the concept, I needed to assemble a pcb prototype in order to correct eventual mistake and have visual idea on the size of each components.

Using the cnc router i milled the traces outline and then added a UV curable coat on top of the copper to make the soldering lot easier.

Step 8: CHAIN ASSEMBLY

The type of chain i decided to use is an industrial conveyor type chain (08B)

9Links must be use in between two numbers, Then multiply this number by 12 which adds up to 108 links.

In order to create the attachment number adaptor link, i first thought of using 3D Printed parts with bespoke chain clips to adapt onto the link. It was convenient, but the look of those numbers were not very satisfying with the look of the whole metal clock.

So i then decided to manufacture theses numbers with stainless steel 1.5mm thick on a laser cutter.

To install the new laser cut number, we need to count 9 links gap between each number and then use a grinder to remove the link attachment and push the pin thru with care. Then replace it with a number and pushing the pin back inside it.

Step 9: UNDER CONSTRUCTION

Here we are

The clock chassis is assembled

The numbers are fitted

And the PCB prototype is running