Member postings for Tony Jeffree

Interesting! I suppose current consumption is an issue for a clock that you expect to run from an AA cell, but as I am using a 12V "wall wart" as the power source, using a conventional stepper motor with microstepping would definitely be an option.

Looking at the patent drawings that Duncan posted, it seems that he built variants with more than 2 poles, but I haven't (yet) got my head round how that works in detail.

The continuous Quartz clocks could well be using a fairly conventional 2-phase bipolar stepper - if you apply sine waves (one phase-shifted) to the two phases you get a close approximation to continuous rotation. The tricky thing then (for a pendulum clock) is generating the sine waves at the exact frequency of the pendulum.

Edited By Tony Jeffree on 26/03/2021 10:04:47

More poles would certainly help with smooth running of course.

Managed to delete one of the earlier videos - here it is again:

LINK

Of course, I had to try it...I have a crude sig gen that will give a ~1 Hz sine wave and a cheap Class D amp, so this is the motor driven from the output of the amp:

LINK

Not very smooth, some of which may be down to the quality of the signal of course, but interesting!

Edited By Tony Jeffree on 25/03/2021 16:52:33

Thanks John!

It is a short cylindrical (but diametrically magnetised) magnet sandwiched between two brass cylinders of the same dimensions, with axial 1.5mm holes to take the steel shafts. Not the easiest way to go and a pig to align, even badly - but I have found some donut shaped magnets that will do the trick and will be easier to use. I've sourced some from Ebay, some from Amazon; the donut shaped ones are these:

LINK

Supplied by Magnet Experts - haven't been delivered yet though!

Yes, getting them to work quietly is an issue - even the tiny ones in the quartz movements generate a significant "tick". With the relatively large magnet I am using the tick is very loud indeed, especially when attached to a sounding board. The smaller ring magnets should be better from that point of view.

I'm wondering what happens if you simply drive the Lavet motor using a Sine wave...? Might be worth a go.

Thanks John!

It is a short cylindrical (but diametrically magnetised) magnet sandwiched between two brass cylinders of the same dimensions, with axial 1.5mm holes to take the steel shafts. Not the easiest way to go and a pig to align, even badly - but I have found some donut shaped magnets that will do the trick and will be easier to use. I've sourced some from Ebay, some from Amazon; the donut shaped ones are these:

LINK

Supplied by Magnet Experts - haven't been delivered yet though!

A nice feature of these motors is that you don't have to worry too much about end float in the rotor shaft - the PM in the rotor centres itself on the pole pieces and holds the rotor in place with significant force.

Hard to see from the vid, but the necessary asymmetry in the magnetic circuit was achieved by making the two pole pieces moveable - they are offset slightly so the rotor's rest position is not straight across. The pole pieces started life as a 3/8" X 1/8" steel strip with an 8mm hole in it, held in slots in the ends of the armature side pieces. They are each offset by about 1/2mm to get the asymmetry. The shaft is pivoted in tiny ball races, but that is probably overkill.

I've removed the white blob and marked the rotor with red/black pen to make the movement more obvious.

Fooled me to start with too!

Thanks! Yes, it's an optical illusion - the blob of white tac is actually slipping on the shaft because the motor's acceleration from rest is quite high. I will be writing it up in due course, but it is early days!

See Youtube video here:

That's a very pleasant surprise, Neil - I had almost given up on seeing that article appearing! Of course, in keeping with pandemic regulations, Skelly (as he is affectionately known) is now wearing a mask, but unfortunately, the ravages of salt water have now fused his bottom bracket, so he has been reduced to freewheeling. The unipivot is slowly boring its way through the top tube of the bike, so I fear it won't be long before he rests in pieces...

More by luck than judgement, I seem to have adjusted the rate to less than a second a day already just by adjusting the rating nut.

John, that seems to do the NTS thing, but nothing else - the one I mentioned earlier allows you to record measurements and will calculate day rates for you. There are a couple of other similar offerings that I am trying out: WatchCheck and Toolwatch.

It was a while ago now, but we had a very pleasant day on the Waverley, steaming from Tobermory to Tiree and back. Not been possible recently, due to boiler refit and Covid 19, but hopefully soon.

https://youtu.be/BFob-kOxq7U

https://youtu.be/U8O7aXrxuaM

https://youtu.be/POMP-p_X1CI

https://youtu.be/QMW0KAAWsAw

Couldn't find clocksync on the Android app store, but I did find an app called "Atomic Clock & Watch Accuracy Tool (with NTP time)" which gives NTP time and in the unpaid version will allow you to record measurements for a single timepiece (more if you pay the sub). Pretty neat - you tap the screen when you want to take a measurement and enter the time from the clock & it records the NTP time at the moment you tapped. Nice graphs etc. and calculates a day rate from your data when you give it enough measurements.

Reducing the effective spring length to ~5mm seems to have controlled the rotational oscillation pretty well, so that will hopefully improve matters. I've been playing around with the height of the electromagnet (the gap between it and the armature on the pendulum) and it is easy enough to increase the time between impulses - up to just short of 3 minutes at one point. However, given some of the discussion above, it probably makes sense to increase the gap (reduce the force of the impulse) as that will result in a smaller variation in amplitude.

Edited By Tony Jeffree on 13/03/2021 16:09:48

Edited By Tony Jeffree on 13/03/2021 16:09:58

I'm using a single 1/2" wide spring steel strip. I think part of the problem is that I have made it longer than necessary - just made up a pair of larger cheeks that will reduce its effective length.

Agree with your comments about the other alternatives. If the larger cheeks don't improve matters, I may try a similar setup to yours, but with two 1/2" springs.