# Why are balance wheels used as oscillators?

#### Mk2

##### Registered User
Sounds like a dumb question, but having read lots and lots of books and watched loads of YT videos, I can't find the obvious answer.

As an engineer, it occurred to me that there have to be many alternatives to a wheel swinging back and forth round a pivot (think see-saw or American teeter-tottor I think!). There are so many ways it is possible to design a mechanical oscillator. Sure it has be immune to movement (take Harisson's first clocks), but anything that can balance evenly (no beat error) would surely work?

And the fact that the Incabloc company came up with a popular sprung pivot bearing system because of the inherent flawed design- a relatively heavy balance wheel rim poised around the tiniest of pivots shows that there is a weakness in a rotary balance system.

Why not use the mass of a spring as a natural resonator? A bit like how quartz crystals work...?

#### Appa69

##### Registered User
Any physicists in the house today?

#### wisty

##### Registered User
Two factors to consider. Motion as you say, but also gravity. A watch needs to work the same regardless of orientation, so the mass used in the oscillator needs. to behave the same regardless of orientation to gravity. A disc fits the bill, a seesaw doesn't.
The period of a torsional oscillator depends on the square root of the moment of inertia of the mass divided by the stiffness of the spring. So for sensible (read fairly robust) springs the moment of inertia of the mass needs to be reasonably high. The best way to increase the moment of inertia of a disc is to put the mass at the edge.
Hence the balance wheel. A disc with all (most of) its mass at the edge.
At least that's my theory.

Mk2

#### Mk2

##### Registered User
Would a flat carbon steel plate work, with a spiral cut in it, where the motion would be through the centre? I'm doing too many experiments with a laser cutter... (So like a musical drum action, contact in the centre)

#### Mk2

##### Registered User
Excellent question. I hadn't thought of that. On a cheap mech watch with regular balance (not the glucydur type), how does temp compensation work? The hairspring properties and the balance wheel must change too?

But yes, spring steel softens slightly as it warms up, which would mean the oscillations would slow down. I don't think thermal expansion with regular temperatures would be that significant. I have to have a think...

#### Skutt50

##### Registered User
A long time ago I had a wall clock on my desk. It appeared to be a Swiss made clock with some resemblance to a CoCo clock but the pendelum/oscilator was actually a spiral spring and at the end was a girl on a swing. She and the swing went upp and down (not sideways) and the motion was letting the escape wheel move in steps. At first I was quite puzzeled but it turned out there was a battery that kept the "swing" motion in action and the regulation was made by shifting the girl/swing position upp and down on the spiral.

So I guess you can use a spring as a type of oscillator but not very practical on a portable movement.

Mk2

#### Raymond101

##### Registered User
interesting subject . I to have wondered why. first most arbors use the most ridiculous small pivot size to reduce friction
but a small say 0.3 mm against 1mm or larger pivot . if the point of balance is true the friction will be the same .
why not make the balance oscillate using copper disc floating between 2 magnets . The beat would be much slower
less friction & do away with the spring .
For compensating for the gravity 0.005 U.Tesla . with a wrist watch just swinging on ones arm would crate a greater G Force.
I have been playing with a magnets with aluminum disc the speed is very smooth No spring required .
on a "see saw" is also the same effects ie as a pendulum
Example . the balance wheel could rotate 360 degrees and the rotational speed controlled . doing away with the hairspring & rocker arm .

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Mk2

#### Mk2

##### Registered User
I've tried to suspend/hold a contactless shaft between magnets (project completely unrelated to watches), and I just couldn't do it. Hours of time wasted. If anyone has figured out how, please speak up... coffee, beer, cake, free company shares await!

But yes, if you could suspend a small copper disk, that'd work really well I imagine. Drawings/sketches please! -and actually could beat quite fast if made small enough. Would induced eddy currents be a problem (magnetic braking action)?

#### DeweyC

NAWCC Member
Excellent question. I hadn't thought of that. On a cheap mech watch with regular balance (not the glucydur type), how does temp compensation work? The hairspring properties and the balance wheel must change too?

But yes, spring steel softens slightly as it warms up, which would mean the oscillations would slow down. I don't think thermal expansion with regular temperatures would be that significant. I have to have a think...

OK. First, you need to understand that a 1900's RR watch was adjusted to an error rate of less than 5 seconds per day accounting for temperature and position (no less than 5 positions). They can still achieve that if properly serviced. Tighter than modern Rolex factory standards and without torque equalizing autowind and modern alloys.

It was also before modern statistics and electronic aids. Waltham had several patents for balance and spring matching that could deal with a number of units at one time. This was a serious bottleneck.

Temp compensation of the oscillator was initially accomplished by a bimetallic balance that reduced its moment of inertia as temperature increased This was to compensate for the change in elasticity of the balance spring as temp increased. The change of rate due to increased length is a minor term. There was work in mechanically changing the response of the balance and even glass balance springs. Ultimately the accepted solution was alloys.

For watches (especially pocket) the expected temp range was fairly restricted, although at night in winter the change range could be quite large. Watches were typically adjusted to have the same rate at 50 and 90 degrees F with the peak (fast) rate at 70 degrees. This is important because the distribution of mass on the bimetallic balance is used for two compensations (dynamic poise and temperature). So for pocket watches, the priority was (is) given to dynamic poising. The closer the masses are to the free end of the arm, the greater the temp response. A second factor that then came in was the change in centrifugal force with amplitude changes from fully wound to partially wound mainsprings. This variable is "eliminated" by modern solid (unsplit) balances I was told many RR'ers wound their watches at least once during their shifts.

During the 1800s and early 1900s there was considerable research into this topic. Culminating in a 1920 Nobel prize in physics to Guillaume who was the Director of the Swiss Bureau of Standards (developed Invar for dimensional standards).

Today there is research in growing balance springs as a crystal.

But in reality, smartphones make most of this a purely academic exercise funded by watch enthusiasts.

#### Raymond101

##### Registered User
I've tried to suspend/hold a contactless shaft between magnets (project completely unrelated to watches), and I just couldn't do it. Hours of time wasted. If anyone has figured out how, please speak up... coffee, beer, cake, free company shares await!

But yes, if you could suspend a small copper disk, that'd work really well I imagine. Drawings/sketches please! -and actually could beat quite fast if made small enough. Would induced eddy currents be a problem (magnetic braking action)?
rotating 2 very small magnets between 2 copper disc will work . by setting the distance of the plates the desired eddy
field force . spin via center shaft . if the rotation is 1 rpm (1hz) . Basically a squire cage powered from main spring .
speed control can be adjustable magnet on top of one plate.

No electronics require . temperature would not be a problem as the rotating eddy field will produce a small amout of heat self cooling
Raymond

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#### Mk2

##### Registered User
Raymond101 So your design is in essence, a copper disc where the escape wheel goes (instead of the toothed wheel, but still on a pivot), with a couple of tiny neodiddlyium (deliberate sp!) magnets above and below. So a regular movement, with the power running from a main spring as normal.

Not an oscillator, but a precise magnetic friction energy release. As the main spring unwound and provided reduced torque, wouldn't the copper wheel reduce RPMs a bit? So fully wound, running fast and slowing down as it exhausted the spring reserve? Or would it be self regulating (rpm)? I'm trying to think back to eddy current physics!

It'd be fairly easy to modify a spare movement to try this, and best of all, a TRUE sweeping second hand!

#### Raymond101

##### Registered User
Raymond101 So your design is in essence, a copper disc where the escape wheel goes (instead of the toothed wheel, but still on a pivot), with a couple of tiny neodiddlyium (deliberate sp!) magnets above and below. So a regular movement, with the power running from a main spring as normal.

Not an oscillator, but a precise magnetic friction energy release. As the main spring unwound and provided reduced torque, wouldn't the copper wheel reduce RPMs a bit? So fully wound, running fast and slowing down as it exhausted the spring reserve? Or would it be self regulating (rpm)? I'm trying to think back to eddy current physics!

It'd be fairly easy to modify a spare movement to try this, and best of all, a TRUE sweeping second hand!
Yes . Just a regulator brake.
Or you can oscillate it with two small magnetics 180deg . And then it will require a 3rd really small magnetic above the plate to set stop . Note the copper or aluminum will amplifie the 3rd magnet's force . So it could be a mm away.
I haven't tried the oscillator type.
Pendulum or other devices in a clock or mechanical is only to set the spring release torsion at a set rate via a gear train.
The old kitchen timer just used a Centrifugal brake.
Accuracy will be the fun part.

#### Wimberleytech

NAWCC Member
I think this is what Raymond101 is proposing: a spring power source driving train wheels to either a copper disk that is spinning (between fixed magnets), or a non-magnetic disk with magnets mounted on it spinning between copper disk(s). The copper disk and magnets 'regulate" the speed at which the disk spins because of Lenz's Law. A current is induced into the copper disk which in turn forms an opposing magnetic field.

This idea is not foreign to horology. Seth Thomas was clever by half when they replaced both FLY with a copper disk in one of their Westminster clocks. The 'regulation' function that the FLY performs was instead done by the copper disk and associated magnet. The magnet position was adjustable in order to get the right regulation. Moreover, back in the 50's or whenever these were made, neodoowahdiddy magnets were no used (maybe not even invented...I don't know). The magnets they used lost their strength over time with obvious results. I recently repaired one where I added a couple of tiny neodoowahdiddy magnets to get better regulation.

I think it was a cute but dumb idea. The FLY has survived the test of time.

Using this concept is a bad idea because you would have to have a huge mainspring to last the time needed, or a very long train of wheels.

I guess it is fun to think about.

#### Raymond101

##### Registered User
@ Wimberleytech Thanks for the better explanation .

#### jagrieff

##### Registered User
A little over ten years ago TAG Heuer was experimenting with some of the concepts described in this thread. They produced a number of chronographs that vibrated at extremely fast speeds (the Micrograph at 360,000 BPH, the Mikrotimer at 3,600,000 BPH and the Mikrogirder at 7,200,000 BPH). To do this they had to create a number of different oscillators. The Mikrotimer used a small perforated disc with a stiff hairspring as the oscillator. The Mikrogirder did away with a balance completely and relied on the vibration of a metal blade. At that time they were also working on a magnetic oscillator which was used in the Mikropendulum. In 2015 they had a change of leadership and moved away from this kind of high tech development but for a while produced some interesting variations on the standard oscillator.

Jeff Grieff

#### Mk2

##### Registered User
Ah, of course you mean a RAILWAY watch. I understand now.

Actually, sarcasm aside, I heard and read that US Rail Road watches are what made Waltham the company it is/was. Better than many swiss things when it came to accuracy. Explains why so many of us Brits want at least one in their collection i guess. I don't have, but mainly because I can't justify the £s.

#### roughbarked

##### Registered User
It would be nice to have one but it is likely way outside my means. Even the postage is.

#### Mk2

##### Registered User
jagrieff The metal blade vibration concept was exactly what I was thinking- and sounds like how a piezo quartz crystal works. Thanks for the info. Never heard of this TAG Heuer thing. Shall research it... kinda like my musical drum visualisation.

There are some really smart people on this forum. i just love it! Continuously learning new stuff here.

#### Mk2

##### Registered User
I have searched and looked and looked...

Anyone got a link how the Mikrogirder thing works? Like a diagram or animation? All i can find is promotional stuff and how amazing it all is, bla bla bla.

#### Al J

##### Registered User
You could always look into Grand Seiko's Spring Drive...but it uses a quartz crystal for the timing...

Mk2

#### Raymond101

##### Registered User
Ah, of course you mean a RAILWAY watch. I understand now.

Actually, sarcasm aside, I heard and read that US Rail Road watches are what made Waltham the company it is/was. Better than many swiss things when it came to accuracy. Explains why so many of us Brits want at least one in their collection i guess. I don't have, but mainly because I can't justify the £s.
If British Rail had ever had an accurate watch the union would not have had any excuse to strike.

Mk2

#### Mk2

##### Registered User
If British Rail had ever had an accurate watch, the union would not have had any excuse to strike.
If you're reading this comment and are a brit; this is the best comment ever...!

#### jagrieff

##### Registered User
Mk2,

There are some great pictures of the TAG Mikrogirder online - check out the Hodinkee article on this watch. Unfortunately the more detailed article that was posted on the Caliber 11 website years ago does not seem to be available any more. I have pictures from that article but, because of possible copyright issues, I will send them to you in a PM.

Jeff Grieff

#### Mk2

##### Registered User
Mk2,

There are some great pictures of the TAG Mikrogirder online - check out the Hodinkee article on this watch. Unfortunately the more detailed article that was posted on the Caliber 11 website years ago does not seem to be available any more. I have pictures from that article but, because of possible copyright issues, I will send them to you in a PM.

Jeff Grieff
You could always look into Grand Seiko's Spring Drive...but it uses a quartz crystal for the timing...
Yeah, the spring drive thing simply uses mechanical induction to generate a tiny bit of electrical power, which in turn is used to run a quartz oscillator circuit (think standard LCD watch chip). Like a shaking a magnet flashlight. That bit works like a difference engine, where the amount induced voltage is proportional to the tick rate. If it's too fast, magnetic braking slows it down (but still generates some voltage). If too slow, the induction is reduced allowing it to speed up.

So fundamentally like an inductrial syncronous motor/generator setup. Like how the power grid works too- means all the power stations' generators spin in exact lock step with each other. If one power station tries to speed up, it has to overcome the power being produced by all the others until it can generate no more power...

Thanks for the PM with girder pics jagrieff The girder thing must have some sort of crank or ratcheting mechanism to generate rotary motion from the sideways vibration (think guitar string I suppose?) But how is it shaken, or excited. No working diagrams anywhere... A hand sketch is more than sufficient. Anyone?

#### Al J

##### Registered User
Yeah, the spring drive thing simply uses mechanical induction to generate a tiny bit of electrical power, which in turn is used to run a quartz oscillator circuit (think standard LCD watch chip). Like a shaking a magnet flashlight. That bit works like a difference engine, where the amount induced voltage is proportional to the tick rate. If it's too fast, magnetic braking slows it down (but still generates some voltage). If too slow, the induction is reduced allowing it to speed up.

Yes - the "glide wheel" instead of a balance wheel was the part I thought you might be interested in. The design is interesting, not from a mechanical perspective, because there's nothing special there. It's the very low power needed to run the circuit that is the real achievement in that movement.

They had to make it consume so little power that when the mainspring winds down it can still function, otherwise you end up with a prolonged period of the spring unwinding out of control. If you watch one near the very end of its power reserve, you can see it cycle in and out of control...

#### Mk2

##### Registered User
I'm starting to think that the mikrogirder thing is fake or gimmick. A marketing exercise, taking advantage of mechanical ignorance. Nothing more than a motion multiplier -up- from the standard 28 balance that runs the movement. Please will someone prove me wrong...!

I've seen the same thing many times in the electronics world which upsets me. Electronics is magic to many people, just because they don't understand how it works. And once they understand, the magic is no more. Maybe it's good to think it's magic...

#### Raymond101

##### Registered User
I'm starting to think that the mikrogirder thing is fake or gimmick. A marketing exercise, taking advantage of mechanical ignorance. Nothing more than a motion multiplier -up- from the standard 28 balance that runs the movement. Please will someone prove me wrong...!

I've seen the same thing many times in the electronics world which upsets me. Electronics is magic to many people, just because they don't understand how it works. And once they understand, the magic is no more. Maybe it's good to think it's magic...
I watched the demo the microseconds hand spins ridiculous fast. That has to be a weak link . Way too complicated to be practical. Does any one really need that sort of accuracy. & the price .
I would rather have a Ferrari.

Mk2

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