Member postings for John Purdy

SK
I had originally planned to use opto interrupters as I had them (Harris H2182 ) but after playing with the pendulum when first made it I found it was very easy to impart some sideways motion when moving it off to one side and releasing it to set it going. As the slots in my sensors are only 3mm wide, and there would be 4 of them spaced over about 2-2 1/2", I felt there was too much chance of the interrupting vane on the pendulum impacting the side of one of the sensors, hence the decision to use Hall devices. There were two other potential problems with with these devices: stray light activating them and they are quasi linear devices were the output doesn't switch rapidly when the beam is interrupted. John Haine has got around these drawbacks by using Sharp optos which have a 10mm wide gap and a built in Schmitt trigger output, which still leaves the possible stray light problem.

As to the temperature effects on the Hall effect devices, the data sheet I have shows that there is a maximum 10 Gauss change in the actuating or release flux between 0 and 25 deg C. Since the magnet I am using (.125" dia x .125" long neodymium ) has a magnetic flux of ~1200 Gauss at a distance of 1/16", the spacing between the magnet and the sensor I'm using, (according to info from the web site linked to by John Haine in another post here ) the difference in the position that the device would be activated for a 10 Gauss difference, I feel would be insignificant.
I don't think it would make any difference anyway as the time keeping is a function of the pendulum period and exactly when the impulse is sent to the clock would make no difference, only that the spacing between seconds might not be equal, but averaged over time would be correct.

Dave

About your comment about the "twang" I think you are correct in saying the the impulse is more powerful than needed. I am going to try and put some resistance in series with the coils and see how far I can lower the voltage and still get sufficient impulse to keep the pendulum going. Or I could also just lower the coils to increase the distance from the coils to the armature on the pendulum rod to decrease the magnetic flux.

I don't think there is a problem with the timing as the coils are de-energized just as the leading edge of the armature reaches the centre line of the coils.

John

Edited By John Purdy on 31/01/2023 22:39:23

SK
Thanks. The coils are 1.875" between cheeks and consist of 12 layers, 100 turns per layer of .45mm (.0177 ) wire wound on a soft iron core .460" dia. ending up just under 1"dia. The two coils are spaced 1.000" apart bolted to a soft iron yoke at the bottom, and spaced out from the backboard so that the centre of the two coils is on the centre line of the bob when at rest and spaced off to the left so that the left edge of the 3/4" wide armature on the bottom of the rod is on the centre line of the coils. The coils are activated as the pendulum is 11mm from the vert position in its swing right to left and are deactivated as it reaches the vertical postion . The two coils are connected in series with the start of each winding connected together and the end windings connected to the voltage source. This gives the max mag flux.
As far as positioning them horiz or vert, all the pics I've seen have them where I have them. If horiz they would have to be out to one side beyond the max swing with the impulse given just before max swing rather than at the centre of the swing. How this might affect the timing I don't know. It would have one positive effect though, it would eliminate the downward pull on the pendulum every time they are actuated that exist with them underneath as I have them. The effect is quite obvious in mine as I don't even have to look at the indicator LED on the logic board to know when the coils are driven as there is a very audible "sprong" (for lack of a better description ) sound from the pendulum rod. I put it down to one of two possible things, the rod, suddenly being put in tension vibrates like it has been plucked, or the rod has a very slight bend it it and when put under tension straitens slightly again vibrating like it has been plucked.
John

Dave
Thanks for your reply.

My thoughts are along your lines in that I plan on just logging the time difference over a number of days and see how consistent it is. The large difference between day one and two might be that on day one I had the heater on for about 2 hours bringing the temp up from its normal ~8deg to 22 for about 2 hours whereas on day 2 there was no heat on. When logging the daily difference I'll have to note whether the heat has been on to see what difference that makes.

As far as driving the magnets from the logic power supply I haven't noticed any problems, there are Schottky snubbing diodes on the output of the L298 module that should take care of any back EMF from the coils.

Your comment about being opposites in the software/hardware debate is quite correct. The last programming I did was in the '80s, and that was in Fortran and Assembler and a small amount of "C" ( still have Kernighan and Ritchies book on programming in "C", they were the ones that developed "C" at Bell Labs for the UNIX operating system ). I've been making PCB since the late '50s, first ones with model airplane dope and a paint brush! Got more sophisticated over the years graduating in the '70s to artwork/cameras,litho film/photo resist. Currently it's software/laser printer/iron on resist, much less hassle. Gave up on ferric chloride quite a few years ago, one time use, disposal problems and corrodes everything in sight. Now use cupric chloride. While not as fast as ferric can be regenerated indefinitely by  bubbling air through it and periodically adjusting the pH and SG with HCl and water . I started out with 500 ml, now have over 2L.
John

Edited By John Purdy on 30/01/2023 19:15:12

Edited By John Purdy on 30/01/2023 19:16:59

An update. After 48 hours it is now 1:48 minutes slow, so in the last 24 hours it has only lost 17 seconds (had been 1:31 after 24 ) so seems to have stabilized. The pendulum is currently swinging through an arc of 5.67 deg. right after it has been given an impulse. Just from measurements the pulse of current to the magnets lasts 96ms. At the moment I'm not about to lug my scope into the workshop to confirm that! The coils for the magnets measure 6.82 and 6.69 ohms and when connected in series draw ~370ma @ 5 volts.Too keep things simple for a start I decided to drive the coils with 5 volts from the logic board power supply. I removed the 5 volt jumper on the L298 module and connected the 5 volts from the logic board to both the 12 and 5 volt input and ground on the L298 module. I wasn't sure if this would be enough to give sufficient impulse to the pendulum as the output from the L298 to the coils is probably in the neighborhood of 4 volts, but it seems to be fine as it is impulsing only once every 3 1/2 minutes to keep the pendulum swinging.

Here's a couple of pics of the logic boards.

My first attempt at making an electronic "Hipp" toggle clock. Definitely a proof of concept. Over the last 24 hours it has lost 1 1/2 minutes compared to the quartz clock in the workshop. I don't expect it to keep very accurate time as the pendulum rod is just a length of 1/4" 303SS and it is in the workshop whose temperature currently fluctuates from 6-7 to 20-22 deg. depending on whether I'm working in there or not. The bob is a 2" x 8" brass tube filled with lead and weighs 4.123 kgms. The electronics are similar to those of Carl Wilson (ME 4694 et al ) with a number of modifications and additions. Rather than optos I'm using Hall effect devices to sense pendulum position. Currently the pendulum is receiving an impulse every 3 min. 30 secs. plus or minus a few seconds. The clock is a standard quartz movement with the Lavet stepper isolated and driven by the pendulum clock electronics. Before anyone says " why didn't you use a micro computer ? (Arduino, BBC microbit )" its because I have a whole box of TTL and CMOS chips collected over the years and its been 35+ years since I did any "C" programming!

It's time now to start on Mk2, carbon fiber tube, revised upper suspension, micro processor controlled and to try John Haines Helmholtz coils idea for supplying the impulse for the pendulum.

John

John

I have also used Eagle but the one I have used the most for many years and like the best is "ExpressPCB". Its free and also includes a schematic drawing program. It has an extensive library of components and footprints and it is relatively easy to make up your own if not in the library. The schematics and pictures of boards i have sent you were done with it.

John

Martin

Here are copies of the ST parts and fasteners list, at least those valid in 1975.

John

On a second thought I think that is the valve rod gland, the one for the piston rod would be bigger. The valve rod one is 1 3/32" across the ears and the piston rod one is 1 1/4" across the ears. Also missing is all the fixings (nuts,bolts, studs etc, )

John

Jason, I believe the item just to the left of the crosshead casting is the piston rod gland. Yes, the crank shaft is also missing (missed that ). The one in mine was a malleable iron casting. ( My castings were "original" Stuart from the '70s and were second or third hand ) I couldn't get a good finish on it so I fabricated one (loctite and pinned).

John

Martin

Having built one, as previously said it is a #9 but the front and rear cylinder covers appear to be missing from your photo. (available from Stuarts)

John

This is a snippet out of the 1972 catalogue of Northwest Cycle Co. Ltd. (Est.1912) in Winnipeg Manitoba.

John

A valve spring compressor. I have one identical which I bought in 1970 at a bike shop in Winnipeg to remove and install the valves on my Norton 750 Atlas bike.

John

Andrew

According to my old Electro- Sonic cat. your picture looks like a Weller model W60P-3 controlled temp. iron. Replacement tips were # CT5A6- , CT5A7-, and CT5A8-, for 600, 700, and 800 degree temps respectfully. The dash in each case replaced by a further number/letter to denote the tip size and shape.

John

Further to my last and to elaborate on Lathejack's post my quill is a constant 80 mm in diameter. The top two bearings supporting the pulley are 6208 radial ball bearings. The spindle runs in two 6206 radial ball bearings at the top and two 7207B annular contact bearings at the bottom preloaded by the ring "M108" in the diagram. Although the diagram and parts list shows three 6007 radial ball bearings at the bottom, when I disassembled the spindle I found that the design had been changed to the two annular contact bearings. You will see that I have hatched out the top of thee bearings at the bottom of the spindle and amended the parts list.

John

Edited By John Purdy on 14/11/2022 18:14:40

John

I don't know if it will be any use to you but you haven't said whether you have a diagram of the headstock/spindle but here is the one for mine. As I said earlier mine was made in Taiwan same as the Myford so may be of some use.

John

John

I have just measured the run out of the inside of the R8 taper on my VMC type mill and it is .0003" (.00762 mm ) The mill was bought in 1983 and is not a Myford or Warco but one imported from Taiwan by an Canadian company, and has been in regular use since then.

John

In all the free pendulum articles I have seen the material called for for the magnet assembly has been pure iron or mild steel with pure iron preferred. I know that pure iron has better magnetic properties in that when the external magnetic field is removed it decays quicker and doesn't retain a magnetic field. But in the case of the application in the free pendulum clock is there any significant advantage? We're not dealing with magnetic fields that have to switch polarity or turn off in milli seconds, (as in a transformer or solenoid ) the pendulum is slow moving (relatively ). The one disadvantage of mild steel I can see is the possibility of pole pieces and armature becoming slowly magnetized permanently over time which would tend to slow the pendulum down on each swing. What are peoples experiences?

John

John
Thank you for the conformation and the dates of the articles. Now to find the articles. My MEs only go back to '79 but my club library has a pretty complete set, but that's 250 km away. I'll have to check next time I'm down there, probably next summer.
John

John
Many years ago I came by some boxes of assorted locomotive castings including a part built duplex steam pump. I have often wondered whose design it was with the thought of finishing it. Now looking at the link provided by Paul it looks like it might be Austen-Walton's from Twin Sisters. Which issues of ME was it described in? If you could check, some dimensions of the pieces I have are: top and bottom plates: 3" x 1 3/8", Cylinders (steam and pump ) 1" dia x 1" long, overall height of cylinders and spacer less top and bottom covers 3 1/4", valve chest 1 1/4" x 1.175".
John

John, the HEDs I'm planning on using are unipolar devices with a built in trigger circuit, so the OC output transistor should switch cleanly. (If not satisfactory I have a drawer full of optos to try ).

Duncan, the reason I'm going to try the discrete route is I have a box full of 74XX, 40XX and 45XX chips so I though I might as well use them. If I get fed up with that route I can always go the micro route as I have a spare Arduino to try.
John