Here is a list of all the postings Tony Jeffree has made in our forums. Click on a thread name to jump to the thread.
|Thread: Radio controlled clocks|
That would work! Actually, the BBC Micro:bit processor that I am using in my current clock is capable of broadcasting to other Micro:bit processors so that might be a simple thing to achieve - not sure about range though, I suspect it is similar to the range of Bluetooth so may not be good for the whole house.
I have 3 wall clocks dotted around the house which used to contain "standard" Quartz clock movements, but a couple of weeks ago I remembered that I had three MSF radio controlled clock movements squirreled away doing nothing, and have replaced the "vanilla" Quartz movements with them. For the benefit of those that are not familiar, these movements use the radio time signal from Anthorn in the Lakes (broadcast at 60 KHz) to keep the clock accurate, and they revert to a conventional Quartz movement if they lose radio signal for any reason. The great advantage of these movements is that they are always accurate and automatically compensate for GMT and British Summer Time changes, so you fit and forget.
So far, so dull. However, given my recent experiments with a free pendulum clock where I used a gutted Quartz movement as a cheap means of providing motion work (see https://www.model-engineer.co.uk/forums/postings.asp?th=171748 ), it occurred to me that these movements could be useful in other projects, given that it should be possible to extract useful pulses from the drive system. The movements I have here seem to have separate drives for the minute/hour hands (pulsed every 15 seconds) and the second hand (pulsed every second), and these could be used to drive other things, for example:
- Use the 1-second pulse in place of a pendulum to drive more conventional and visually interesting motion work;
- Use the 1-second pulse to drive a hit-and-miss synchroniser to accurately synchronise a mechanical pendulum & associated motion work;
There are also receivers/decoders around that can extract the whole of the data stream transmitted by Anthorn, which includes year, month, day of the month, day of the week as well as time of day, so potentially one could produce a mechanical clock with perpetual calendar, taking the data from the radio signal.
Anyone ventured down these (or similar) paths?
|Thread: A prototype Lavet stepper motor|
You can certainly do that - apply two sinusoids, 90 degrees out of phase, to the two coils of a conventional stepper and it should give you continuous motion or near enough. In effect that is what happens in a brushless motor.
I bought the book too - makes an interesting read!
Talking of resonances, we have a long case clock that occasionally strikes a "duff" note - never the first of a strike sequence, and never more than a couple of times when (for example) striking 12. Nothing wrong with the striking mechanism as far as I can tell; I eventually concluded that sometimes the hammer strikes the bell at just the right point in its oscillation for the movement of the bell and the hammer to effectively cancel each other out.
Ugh - that one's a bit rough to say the least - some nasty resonances interacting by the look of it. Definitely in need of some damping somewhere. There's an awful lot of inertia in that drive system which isn't helping.
You could probably improve that somewhat by reducing the rotor mass and increasing the coil current...
Interesting - thanks. I had already started experimenting with magnetic gears...
|Thread: DeskCNC resurrection - USB to serial adapter|
I converted my Taig CNC mill some years ago to make use of DeskCNC as the controller software/hardware (writeups were in MEW at the time). The mill has been gathering dust since we moved to Scotland in 2014 and I have only recently been resurrecting the PC side - the original laptop that I used had a serial (COM) port, which is long gone from modern spec PCs, so a major hurdle was to find a suitable USB-to-serial adapter that would do the job. I had 2 of these lying around that I spent much time & effort on, unsuccessfully - mostly due to hardware in the adapters that was too old to have any drivers that would run on Windows 10. So, after much frustrating effort, including managing to get one of the adapters to sort-of work with an old driver, I bit the bullet and bought a new adapter, one of these:
Which seems to work nicely with the in-built driver options that Win10 provides. I thought it would be worth mentioning in case others have come across a similar problem.
Now to see if I can remember how to run the mill and cut a few parts...
|Thread: A prototype Lavet stepper motor|
There may be a short (or long!) delay while I get my Taig CNC Mill back up and running - looks like I will need to do some major surgery on the controller side as my Desk CNC software/hardware doesn't seem to want to play with a modern-spec PC. So currently looking at alternatives...
|Thread: Greenwood Tools|
That is very sad.
|Thread: A prototype Lavet stepper motor|
Ah...yes indeed. Mind you, my head tends to take me in the direction of CNC for that kind of milling, so much less of an issue.
Hmmm...still not seeing where you are going with this...
The shaft is 1.5mm diameter and is the plain part of a 1.5mm twist drill. The bearings had an ID of 1.5mm and I happened to have a pack of cheap drills to hand so that was the obvious solution.
There is certainly some flux in the hole, but I suspect it wouldn't make much difference to the peripheral flux - might actually increase it. Worth some experimentation there.
I'm also considering the solid-strip-with-holes-at-45-degrees variant for the next (final) attempt as it is potentially easier to make.
The coil is 20mm long wound on a piece of 3/8" steel bar. The OD of the winding is a gnats less than 14mm but I couldn't tell you how many turns. The wire is 38 SWG. I'm planning to try a slightly different configuration for the magnet - I have 4 plastic sewing machine bobbins that I wound with rather thinner wire (50 SWG I believe) for another project that never completed; the bobbins are around 6mm ID. One or possibly two of those may be about right to drive a rather scaled down motor. We'll see.
Edited By Tony Jeffree on 29/03/2021 18:34:50
I've made a new rotor for the motor. The original rotor looked like this:
The magnet (in the middle) is 6mm diameter 4mm long. Had to be made in 3 sections because the magnet is a solid cylinder. The new rotor:
The magnet is 6mm OD, 3mm ID, 1mm thick and the brass bobbin that it is mounted on can therefore be machined in one piece. Short video of the motor with its new rotor:
What a tease, Michael c'mon...spit it out!
The tapering is all about ensuring that the rotor's rest (un-energised) position is as shown in Fig 2. That is important so that when the next polarity reversal happens, the tapered horns are attracted to the next stator pole, and the rotor will rotate. It controls the direction of rotation of the rotor. If they weren't tapered (or bent inwards to create more clearance at the tips, which would have the same effect), the rest position would be somewhere more nearly half-way along the rotor poles, and it would be uncertain as to which direction the rotor would move on the polarity reversal.
You could achieve the same effect by keeping the thickness constant and the clearance between the rotor and stator poles constant, but making the "flying" part of the rotor poles taper to a point in the axial direction.
I found Figure 2 from the patent was the best one for visualising what is going on. You are right - the two pole pieces (10 and 11) are best visualised as being cut from a steel version of one of your plumbers' stop-ends. If you look at part 10 in fig 2 and attempt to screen out the "noise", the top surface of 10 looks very much like the profile shown in Fig 4, with the cylindrical portion of the part (which appears from the photo to be essentially rectangular if you were to cut it away and flatten it) has been thinned, so it is full thickness at the end nearest the electromagnet's pole pieces and tapers to almost nothing at the tips. The tips therefore clear the pole pieces of the electromagnet by the minimum clearance plus almost the thickness of the metal. The effect of this is that in its un-energised state (as shown in Fig 2), the permanent magnet will align the rotor so as to minimise the gap between the rotor's pole piece and the electromagnet's pole piece (which is the state shown in Fig 2). However, the thinner tail of the rotor's pole piece is near enough to the next electromagnet pole piece to ensure that when the electromagnet is next energised, with the reverse polarity, the rotor will rotate in the direction of the next pole.
No necessity to use hands, of course, you could use a digital style HH MM SS display.
Edited By Tony Jeffree on 27/03/2021 16:59:58
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