Silencing the Bill Smith Gearless Gravity Arm Clock

You will find details of my activity building the Bill Smith Hip Toggle Gearless Gravity Arm clock elsewhere on my site.   This was the first clock I ever made and it taught me a lot about techniques all of which were well documented by Bill in his write up and in his many other books and videos.

Let me state now that the clock design as intended by Bill works and works well.  It has one distinct disadvantage that every minute or so it gives a very loud ‘clunk’ as the pendulum amplitude diminishes, the hip toggle triggers and the solenoid resets.    Running it in the workshop was fine as I became immune to the noise but sadly the clock will never progress into the house given my wife’s sensitivity to noise.

This has been a frustration to me as the clock looks splendid and its motion work action is a fascination to behold.  It deserves to be on display in a more public arena than the workshop.

All of which lead to some head scratching and a compromise re-design.   If I accept that the clock is an electro-mechanical device then my conscience allows me to consider other electro-mechanical solutions that are significantly less noisy.   This is the fundamental premise to my re-design.

There are many clock designs that use magnetism attraction and repulsion as the driving force and my thoughts turned to this as a potential solution.

I 3D printed a magnet holder to fit on the pendulum rod.   This holds two magnets.   There is a large one facing the direction of swing and a small one perpendicular to the swing towards the backboard.  I mounted a Hall Effect Sensor (HES) on a prototype board onto the back board at the mid swing position.   The gist of my idea was to have the pendulum swinging back and forth across the HES with the HES being triggered by the small magnet.   I would count the number of swings detected by the HES and after a defined number of swings I would energize a solenoid to repel the large magnet.

There was a little bit of electronics involved.   I had a 4060 binary counter counting the swings and used the divide by 32 output to trigger a 555 in monostable mode.   This would create a delay period from the mid point to the end of swing before the solenoid was energized.   A second 555 would then define how long the solenoid repelling pulse would last.   I also added LED indicators to all key timing points so I can easy diagnose what was going on.   I also allowed selection of the 16,32 and 64 divisions from the 4060 until I established the optimum choice.

The pendulum period is 4800 beats per minute so one swing lasts for 750ms.  The first 555 must therefore provide a delay of 375ms before energizing the solenoid.   The second 555 delay would be a ‘suck it and see’ period to be determined.

The concept was lashed up and worked OK …. except that the pendulum amplitude just grew and grew until the large pendulum magnet attached itself to the solenoid core …. not a good idea .   What was needed was a maximum amplitude detector to act as feedback to inhibit the solenoid pulse action.   

A second HES was mounted at a position that represented the maximum swing position and the output from this, when triggered, would feed back to the 4060 RESET pin to stop the count until the amplitude diminished sufficiently.   This worked and the result was very repeatable.   There was one proviso that the pendulum must be started by triggering the over swing HES and releasing.   Without this the 4060 could be one count out of step and would energize the solenoid as the pendulum was swinging back from its furthest point.  This would cause a repelling and slowing of the swing.

Overview image of the new pendulum sustaining mechanism on the Bill Smith Gearless Gravity Arm clock
Overview image of the new pendulum sustaining mechanism. Top left is the timing board and lower right is the Hall Effect Sensor board. The solenoid is the original Bill Smith design. The white block on the pendulum is the magnets holder. You can see the two Hall Effect Sensors hanging below the blue prototyping board.
close up view of the sensor board
A close up view of the Hall Effect Sensor board where the two sensors can be more clearly seen along with diagnostic LEDs and interface converters to the timing board.  The pendulum magnet holder can just be seen coming into shot.
Oscilloscope display of the new timing sequence for the Bill Smith Gearless clock
Oscilloscope display showing the yellow regular negative going pulse from the centre swing HES detector, the blue delay pulse to allow the pendulum to travel to its extreme and commence its swing back and the purple pulse triggered from the back edge of the delay pulse which defines the solenoid ‘On’ time.

The prototype has proved the concept but I now need to engineer a clean solution.   First choice is perhaps an Arduino Mini but it could also be PIC based.   

More to follow.

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Tormach PathPilot G37 Update

I have my Tormach PCNC440 wired into the workshop network and as a result if a new version of PathPilot is issued my PathPilot controller warns me.   This is quite nice as there is no formal emailing warnings of new issues by Tormach.  Anyone whose machine is not Internet connected would need to check periodically with the Tormach site to see if an update was needed.

To continue the story … last week I got a warning of a new version of PathPilot (2.4.0) was available and I duly downloaded.  One of the immediately obvious changes in the new firmware was a G37 tool measurement routine which works in conjunction with a simple Normally Closed tool setter.   From my previous ramblings you will see that I had done a combiner box to allow both probing and toolsetting to share a common input to the Tormach.   In theory I was therefore ready to go ….

From my many years in industry I should know that all that glitters etc … the new routine did not work.   I thought it must be me but in the end I logged a support call with Tormach and sent them my log file.   I also logged the problem on the NYC CNC forum to see if anyone else was having the same issue.   I did get one response saying that he was not having an issue.   The plot thickened and nothing back from Tormach.

A couple of days later the same responder said there was a fix update available from the Tormach site.   It seems the software worked well in G20 Imperial mode but not in G21 Metric mode.   He was running Imperial and I was trying to run in Metric   Software update downloaded and all is well.   It is rather nice.   You tell PathPilot where the tool setter is located and then to run the auto tool measurement you put a G37 command in the GCode after a tool change.   Away the spindle goes to the tool setter location, dunks the tool and updates the Tool Table.   Magic.

Still waiting for Tormach to close off my enquiry and let me know they had fixed the problem and as a result there was a new firmware available.  But it is Christmas and maybe they had other pressing matters.

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New Microscope

Technology Upgrade

Quite some time ago I mentioned a really low cost simple microscope that I think John Saunders had recommended from Amazon.   The device has served me well even though it was quite basic.

I recently had a job to do where I needed to see and measure a very small part I was making.   The simple microscope was struggling to cope or at least I was struggling to cope with it. Looking on the net to see what the current technology could offer I spotted a device on Amazon that looked interesting.

KKMoon Microscope from Amazon

It was a bit more expensive but nowhere near a ‘proper’ professional optical product. Having taken delivery it is very impressive. 

It can act as a simple standalone viewer using the built in screen or can be externally connected via HDMI to a monitor or (and this is the impressive bit) it can be connected to a PC via a superb application that has so many bells and whistles it will take me ages to understand all the functions.  The sensor is a 16 Megapixel Sony CMOS 1/2.3″ HD device and video output can be 4K/2k/1080P.  Magnification is up to x300.

So I am well pleased with the investment and  it will certainly earn its keep.

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New Zealand trip

Springtime in New Zealand

Sorry that things have been quiet but we have been on a 6 week trip to New Zealand.  It was the only country that my wife and I both had heard so much about and both agreed we wanted to see.  So I had to bid farewell to the workshop for longer than I really wanted but you can’t go round to the other side of the world for just the weekend.

We flew Emirates from London to Dubai, Dubai to Melbourne and Melbourne to Wellington with a few hours stop over at each.  If we must fly long haul we like Emirates or Virgin whenever possible and Emirates once again was brilliant.

We had considered doing a golfing holiday through a package deal but it ended up like some sort of crazy route march with tee times booked months in advance.   Not really a holiday.  We chose instead a camper-van do your own thing style tour.   We were both a bit apprehensive about being in close confines for 6 weeks (instead of our normal me in the workshop and my wife playing golf). It took a few days to get into the swing of things and work out a routine but once we were sorted it went well.

We covered over 5,000 kms wandering around North and then South Island.  We usually booked one night’s camp site ahead.  We used the Top10 sites most of the time but also some independent ones.   Some sites were very good, some not so good.  We had one where we felt like cleaning our shoes when we came out of the toilet block …

We covered a significant part of both islands and were blown away by the scenery.   We struck lucky with the weather with the sun following us around on our journey.   We did get to play golf but rather than pay NZD200 for a round we played small town courses for NZD30 tops.   The courses were beautifully manicured, most were deserted with an honesty box for green fees and we met some interesting people.

I didn’t get to see much mechanical tech but there were a few heritage steam railways and museums that I couldn’t resist visiting.

It is a great destination and despite my reservations, the camper-van was a great way to see things and the 6 weeks flew by.   Highlight for both of us was a front seat helicopter flight from Queenstown to Milford Sound via a glacier landing and with blue skies all day.   Not many people see Milford Sound in sunshine.  We were very very lucky.

The workshop awaits and my newly installed heater will ensure a cosy winter activity session.

Great to be back and it will be even better when we have shaken off the jet lag.

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Probe and Toolsetter together on Tormach PCNC440

New Tool Setter Arrives

I recently bought a special offer price tool height setter from Banggood.   On arrival this seemed nicely made and robust and looked like a worthy addition to the armoury.   

The Tormach PathPilot control software has facilities for tool height setting using such a probe.   I also have a Wildhorse Innovations probing tool for edge and centre setting.   Both these devices can be connected to the Tormach PCNC440 external input accessories connector which is  a 5 pin 180 degree DIN.

The input to the Tormach accessory socket is a 2 wire connection.   Sensing and operation of external tools like the probe and tool setter depends on the device having a normally closed connection that goes open circuit when activated (i.e. the probe tip moved or the tool setter pushed down).   The probes are in essence a single pole normally closed switch.

Frustration Sets In

After spending time having to keep swapping these two devices in and out of the accessory connector I figured there must be a better way.

The Tormach does not care if you connect multiple probes at the same time provided they are all in series on an electrical loop to and from the two pins on the interface connector.   Any device when activated will break the loop and create an interrupt to the PathPilot software.   Because you will be in the area of PathPilot software that relates to the function you are measuring, the relevant probe will be the one you are intending to use.

The Solution

What was needed was a simple interface box that allowed the two probes to be connected in electrical series back to the two pins on the DIN connector.   I also wanted flexibility to be able to unplug either of the two probes and not affect the operation of the other.   This meant that on removal of either probe it would need an electrical short circuit across the pins of the connector from which the tool had been removed.

This could be done with a small by-pass switch, that is normally open circuit, connected across the connector.  You would manually close this switch if the probe is removed. 

This is fine so long as you remember to activate the switch when you remove the probe otherwise the sensing loop will see an open circuit and the software will get confused.

My solution was to use sockets for the connections that would automatically provide a short across their contacts when their mating plug is removed.   A good example is an audio style jack plug socket.   These come in various sizes (2.5mm, 3.5mm, 1/4″ etc).  Usually on these sockets the tip of the connector gets shorted to another contact when there is no mating plug in place.

I had some 3.5mm stereo jack plug and sockets to hand (either mono or stereo can be used as it is only a two wire connection) and these were simple to wire for this application.   

wiring two jack sockets for the probes on a tormach

I also ran a modified version of one of my standard 3D printed enclosures to mount them in and fitted a flying lead to a 5 pin DIN to plug into the Tormach interface.   A hot glued magnet onto the bottom of the enclosure allowed flexible mounting of the box somewhere on the Tormach body.  The only fiddly bit was replacing the existing connectors on the two probes with a 3.5mm jack plug.  (Don’t forget to the put the connector shell on the cable before you solder the wires in place ….. ).

finished dual probe input assembly

close up showing the wiring on the two jack sockets

A neat solution and the problem solved.   Both devices plug into the box to perform their various probing functions into PathPilot.  Unplug one of the probes and its mating socket will automatically short out the probe connections when the plug is removed.  The remaining probe plugged into the other socket will continue to function.

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