Artist needs help with the waving cat circuit.

[nekojita]

Hi there,

I am an artist with an electronics problem, which seems simple, but it's beyond my expertise.  I'm trying to re-create, upgrade or find a source for the the circuit and mechanism of the lucky cat – the gold, waving cats you see in Asian restaurants, so it can wave a heavier arm.  Trying to find my options and weigh out cost/time/effort.  Thank you kindly in advance

Project Goals:

- Made-in-china cats have a 2-part vacuum formed plastic arm, which is super light-weight.  My cat arms will likely be roto-cast resin, which will be at least double the weight, so I will need a slightly more robust version.

- I want the capability to make multiples and in various sizes. My waving arms may vary in weight, so ideally, the circuit can be scaled up if needed.

- Runs on AA batteries

-$10 or less per circuit, parts can be easily found

- A layman with basic electrical and soldering skills can assemble the thing
 
I disassembled a lucky cat and this is what I know:

-It runs on what I believe is called a pulse motor or pendulum motor

-the arm is on the right side, a counter-weight is on the left.

-There is a small copper-coil, 2 black magnets, 3 capacitors and 2 resistors, 2 transistors.

[Paul Price]

First you need to make a mechanical prototype, an arm balanced by a counter-weight/magnet, add a battery a switch and a coil.

I already see from the pictures that you have a large flat circular coil, two circular coin-shaped magnets that actuate the sensor beneath them in pendulum travel, the battery compartment for battery energy, and the circuit board all ready to deliver a pulse of energy to the flat coil to keep things rocking.

Now you gotta make your own arm suspended on bearings and balanced by a counter weight that might just be a strong magnet.

Once you got this balanced pendulum mechanism to look the way you want and to swing with minimal friction, you are only then ready to add the simple electronics to keep things moving.

The weight of the arm is not so important as you might think. If a counter weight balances the weight of the arm it is just a matter of  pulsing a little energy into a already balanced moving system (that was hand-started to oscillate) and then, the you need to just  replace the tiny amount of energy lost to friction (friction in the supporting bearings and air friction) every pendulum cycle.

Step one: Read up on pendulums.

Step two: Read up on magnets.

Step three: Read up on coils and magnets and how to connect a switch and a coil to a battery to create a magnetic field.

You need to add energy to the system at some point in it's pendulum cycle. If you have a magnetic material making up a counter weight, then you want this magnetic piece of metal to receive a "helping" magnetic pulse of energy from a coil as it passes near or through the coil supplying the boost energy. Some sort of electrical trigger must sense the position of the moving magnetic weight attached to the pendulum as it passes near or through a coil. This sensor for the trigger pulse could be a tiny sensitive mechanical switch, a photo-interruptor,  a hall-effect sensor, of even using the boost pulse coil itself to sense the right point in pendulum travel.  You already have a coin-shaped magnet triggering a small sensor and all properly connect to the existing circuit board.

Chances are you already have everything you need with the working  circuit from the one you have disassembled  and  this is all you you will require to get any larger arm to continue to oscillate once started by human hands.

The operation is simple, the coil is energized by a battery at some point in the arm's travel when the magnet material's (the counter weight) position of the moving arm is near or inside the coil  and at point optimal for delivering a boost of energy.

Send a short pulse of current by connecting a coil to a battery through a momentary switch and then you will see that a coil creates a magnetic field, the magnet field interacts with the magnetic poles of the metal on the pendulum arm and pushes or pulls  on the moving mechanism to add just enough energy to keep the pendulum in motion to replace the energy lost to friction.

Hint: if you need bearings and other neato-keeno mechanical parts to play with, take apart a discarded computer printer. If you want very powerful super magnets to play with take apart a discarded harddrive from a junk desktop computer. If you want wire to make a coil from, take apart a desktop PC power supply and you will find plenty.

[TerraHertz]

-There is a small copper-coil, 2 black magnets, 3 capacitors and 2 resistors.

In that line, are you referring to the parts on the circuit board?
And the 'two black magnets' are the things with 3 wire legs?

Actually those are transistors. You don't mention them otherwise, which is why I think you might be calling them magnets.

Looks like a very simple circuit, easily duplicated.
Where are you in the world? (You can set your profile to show that, which helps others tell if they'd be able to assist.)

If you can take board out, take clear pics of the front and back, and pics of the lettering on the caps and transistors, I (or almost anyone here) can give you a circuit diagram for it.

Do you want the arm movement to be in the same style, or more random?

Sources for free solenoid coils:
  small: photocopiers, printers, etc. Typically wound for 12VDC.)
  medium: The electrically operated water valves of washing machines, dishwashers, etc. (usually 240V coils)
  Big: Large mains power electrical contactors. (usually 240V coils)

If you want to wind your own coils, a free bulk source of clean enamelled wire is the degausing coils around the picture tube of glass CRT TV sets. These coils are a large loop coil, right around the face of the picture tube. Many turns, then bound in electrical tape. Carefully slit the tape off.

Heh. If you are planning to build a group of giant 'lucky cats', it would look pretty cool.

[nekojita]

Wow, thank you for the responses!  I have a lot of work and research to do now.  As I'm learning all of this, I many more questions.  As suggested by Paul, I'll make a prototype mechanism first.  If that fails in terms of function, cost or time, I will attempt to source them from China and upscale the existing mechanism and circuit.

Images of the circuit are below if anyone is willing to translate it into a diagram.  The copper coil looks like it's doing something particularly confusing.  If the photos are unclear, these are the parts I've identified:

2 Transistors with the same markings: S9014 C331
2 Small capacitors: 6.3v 47mF
1 larger capacitor: 0.47mF 50v
2 Resistors with same markings: Gold, Yellow, Purple, Red

@Paul Price:

“First you need to make a mechanical prototype, an arm balanced by a counter-weight/magnet, add a battery a switch and a coil.”

This seems to be my next bottleneck.  I will be working on this asap.  My limitations as a mechanical engineer might mean I'll succumb to buying the mechanisms from China. 

“I already see from the pictures that you have a large flat circular coil, two circular coin-shaped magnets that actuate the sensor beneath them in pendulum travel, the battery compartment for battery energy, and the circuit board all ready to deliver a pulse of energy to the flat coil to keep things rocking.”

Yes, this seems right.  I see the same thing you see with my layman eyeball.

“Now you gotta make your own arm suspended on bearings and balanced by a counter weight that might just be a strong magnet.”

In the cat I dissected, there were 2, black, donut-shaped magnets stacked on top of each other, on the end of the pendulum, which passes by the coil. 

The arm counterweight (the side opposite the waving arm end, shaped like a tombstone) seems to just be a weight sealed in plastic.  I could be wrong, but I don't believe it's a magnet. 

For my own creation: do I need to insert magnets into the arm-counterweight (tombstone shaped thing)?

Will there be any advantage to using rare-earth magnets vs regular black magnets?

"Once you got this balanced pendulum mechanism to look the way you want and to swing with minimal friction, you are only then ready to add the simple electronics to keep things moving."

Ok.  This is what I will be doing: creating the mechanism before sculpting the cat.

“Chances are you already have everything you need with the working  circuit from the one you have disassembled  and  this is all you you will require to get any larger arm to continue to oscillate once started by human hands.”

Can I unsolder and replace some parts to upscale the cat I've already disassembled?  I understand that you need to give it a bit of a push first.  Maybe my concern is unnecessary, but I'm worried it will lose momentum because of the arm weight, but as you say, the arm weight might not be a big deal. 

@ TerraHertz

“In that line, are you referring to the parts on the circuit board?  And the 'two black magnets' are the things with 3 wire legs?”

You are right.  There are 2 transistors AND 2 black magnets.  My bad.  We're on the same page.

“Where are you in the world? (You can set your profile to show that, which helps others tell if they'd be able to assist.)”

I'm in Vancouver, BC Canada. 

“If you can take board out, take clear pics of the front and back, and pics of the lettering on the caps and transistors, I (or almost anyone here) can give you a circuit diagram for it.”

Photos will be posted below.

“Do you want the arm movement to be in the same style, or more random?”

I want the same rocking motion, but am dreaming up a versions of the cat that has 2 waving arms, or single arms with different arm-poses. 

“If you want to wind your own coils... “

So that coiled bit is called a solenoid?  Good to know!  How do I know what size solenoid to get if I'm buying them, or if I'm winding my own, what length and gauge of copper to use?  Is there an advantage to having say, a larger coil?

“Heh. If you are planning to build a group of giant 'lucky cats', it would look pretty cool.”

That's the plan.  If all goes well, I will have a swarm of custom lucky cats in various sizes....but all in due time.

[Paul Price]

The two fat coin-shaped magnets generate a pulse while passing over the coil(or is it a hall-effect transistor?) underneath them to signal the PCB to add energy to the swinging pendulum arm at just the right position in travel.

You will need  only very cheap magnets to work with the magnetic sensor under them.

You don't lose momentum because of an increase in arm weight, you gain it. You only lose momentum due to friction.

It is not hard to keep friction low while supporting a heavy, massive arm.

You should know by now that it is very easy to determine if something is a magnet.

You may be able to use the control mechanism as it is to work with a much more massive arm.

Part of the original design's goal was to maximize battery life..that goal may be not so important to you as keeping a large mass pendulum swinging. You can so easily make a change to larger size batteries.

The resistors are 270k ohm resistors 5% tolerance,  according to the markings, although you are reading the value in a reversed order or color code.

[TerraHertz]

Sorry for the delay in giving you a circuit diagram for it. I've been too busy. But have all the pics saved, and hopefully can look at it this weekend.
One slight complication is the coil. Apparently two windings, and unless you have a multimeter and a soldering iron, and can lift the 4 wire ends from the PCB and tell me the resistances between each pair, I'll just be (slightly informed) guessing about the arrangement. Also won't know the ratio of turns between the (presumably) two separate windings.

I'm guessing it will be using one winding to sense the approaching magnet, triggering a current pulse in the other - which also acts to feedback gain via the sense coil for a stronger drive pulse.

If you're planning 'man sized' (or bigger) replicas, I think the drive would need to be scaled up too. That little thing wouldn't be able to overcome friction of large bearings carrying a lot of mass in the arm.

I expect you've read up on pendulums: http://en.wikipedia.org/wiki/Pendulum

How many is a 'swarm'? Around 10? Or is it a baker's swarm?

And is there possibility of wiring to the cats or must they still be battery powered?
Mainly asking because I'm wondering if a common power supply, like say 24VDC, would be better. Especially for driving more beefy solenoids. Also because if so, maybe a slightly more complex circuit could use a single coil (acting as both sensor and drive.) For larger coils, only requiring one winding means you have a lot more options in sources of ready-made (and free) ones.

Those lucky cats always struck me as having a lot of comic potential. The idea of something like a Roomba (small randomly mobile puck-like robot) except instead of vacuuming dust or whatever, it just takes a ridiculous looking arm-waving lucky cat for a wander around the place... ha ha!  Now I expect to see someone produce this, and make a pile of money. 

[vk6zgo]

Cat,Roomba,Blu-Tac-------Done!

[lowimpedance]

This article at Elliot Sound pages describes pulsed clock motors which might give some good info for you. Also in the same section is more info in relation to a free pendulum clock which I recommend you also read.
http://sound.westhost.com/clocks/motors.html#impulse

[TerraHertz]

So, here's the schematic, derived from the PCB.



It looks like the coil has two windings, with identical number of turns. Probably the wire pair is wound together. One wire has a red enamel, the other a clear enamel. The red dots on the PCB overlay are just 'same winding end'.

You wrote the transistors are printed with "S9014 C331', but I can't really make that out clearly in the pics.
If that's right they would be '2SC331' - but a quick search didn't find such a thing in that package.
I doubt it's very critical what transistor is used.

Some interesting things in the circuit. It's like a simple multivibrator, except that due to the two collector loads being a coupled transformer, and with a swinging magnet next to it, it totally isn't.
Also C3 is acting as a Miller slew rate limiter.
Amusingly, this 'simple' thing exceeds my ability to model circuit behavior in my head.
Don't have time to prototype it now and play with it. Anyone?

[Richard Crowley]

The timing of the multivibrator oscillation may need tweaking depending on the "frequency" of the waving action.  While this is a brilliant scheme for very low-cost mass production, it seems particularly fiddly for reproduction by someone with no electronics experience.

I am not sure that nekojita appreciates how critically dependent this scheme is on perfect balance and very low friction.  These are easy to achieve in mass production (after working out the initial design, of course).  But not obvious or necessarily intuitive to someone who hasn't worked on mechanical systems before.

Since this scheme requires counter-balance AND magnets of significant mass, it is not unusual to COMBINE these together so that the mass of the magnets forms part or all of the counterweight mass.

If I wanted to make a collection of this kind of thing, especially in various sizes, etc. I would strongly consider a more conventional approach like a cheap gear-motor and a cam.  Certainly a trade-off would be battery life, but in larger sizes, one could use C or even D cells, etc.  Or, if this is a "fixed" installation, a cheap wall-wart could power many of these.

[amyk]

That would likely be the SS9014 or equivalent, although it looks like the C/E are reversed...

[Rerouter]

This is a similar circuit used in some of the fancier European car clocks, when the magnet swings overhead it injects a voltage into the inductor this then turns the circuit on and makes it repel the magnet swinging it through the next half arc

these circuits are a painful bugger if your component tolerance is too wide, even tweaking the transistor gain can make it inert,

a better varient is a 555 based one, where after getting the sense pulse the first delays for however many milliseconds for the magnet to clear half way then output a monostable pulse to drive the magnet past, as this lets you adjust the clearance time, giving you and adjustable circuit,

I haven't seen this variant in some time so i dont think i could get a schematic, but it should be easy enough to simulate to work it out,

[Eheran]

I have the same circuit in my lucky cat, except with 220k resistors and C1 and C2 up to 16V. However I would like to reduce the amplitude of the swing. That way I want to reduce noise (at peak amplitude due to wiggle in the bearings), future wear of the bearings and longer runtime on two AA batterys. I probed around the circuit with my osmelloscope but im still unable to really understand how its working - even when the arm is not in place/still and it just pulses around, trying to start the pendulum. Since the only energy storage is in the capacitors (so mainly C1 and C2) and the movement of the arms... im guessing that I could reduce their capacity.
Would that work? Replacing C1 and C2 with 33 or 22µF caps?
Or would that change the frequency...? 

[Zero999]

I have the same circuit in my lucky cat, except with 220k resistors and C1 and C2 up to 16V. However I would like to reduce the amplitude of the swing. That way I want to reduce noise (at peak amplitude due to wiggle in the bearings), future wear of the bearings and longer runtime on two AA batterys. I probed around the circuit with my osmelloscope but im still unable to really understand how its working - even when the arm is not in place/still and it just pulses around, trying to start the pendulum. Since the only energy storage is in the capacitors (so mainly C1 and C2) and the movement of the arms... im guessing that I could reduce their capacity.
Would that work? Replacing C1 and C2 with 33 or 22µF caps?
Or would that change the frequency...? 

You've got it backwards. The capacitance needs to be increased, to reduce the frequency.

[Eheran]

I want to lower the amplitude...? 

[Zero999]

I want to lower the amplitude...? 

Oh I see. Increasing the frequency might do that. The oscillator is probably designed to match the resonant frequency of the pendulum so reducing the frequency may also work too.

Failing that, reduce the voltage or put resistors in series with the coils.

[Eheran]

Its not matched. By lowering or increasing the mass of the pendulum its still no problem to get resonance. I tested between 1.25Hz and 2.5Hz. So the induced voltages are a trigger. The resistors only seem to affect the start-up phase (trigger pulse) and as soon as the pendulum is moving they dont do much. I tested this with one 30k resistor, seemed to have no effect so I didnt do both. Tell me if that is foolish.

I also tested a resistor in series with the batterys and it seems to work, around 40 Ohm keep the amplitudes at a decent level.
But I would like to understand the circuit. And maybe there is a more elegant way to do it?

[alsetalokin4017]

Frequency of a pendulum depends only on its length, not on mass or swing amplitude.
http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html

Meanwhile...

[Zero999]

Its not matched. By lowering or increasing the mass of the pendulum its still no problem to get resonance. I tested between 1.25Hz and 2.5Hz. So the induced voltages are a trigger. The resistors only seem to affect the start-up phase (trigger pulse) and as soon as the pendulum is moving they dont do much. I tested this with one 30k resistor, seemed to have no effect so I didnt do both. Tell me if that is foolish.

I also tested a resistor in series with the batterys and it seems to work, around 40 Ohm keep the amplitudes at a decent level.
But I would like to understand the circuit. And maybe there is a more elegant way to do it?

It's true that changing the mass will not alter the resonant frequency but it may change the amplitude, if damping is increased or decreased.

The circuit is known as an astable multi-vibrator. A detailed description can be found on Wikipedia. If changing the resistor and capacitor values don't change the frequency, then it's most likely due to injection locking i.e. the astable locks onto the pendulum's resonant frequency, which dominates the RC time constants.
https://en.wikipedia.org/wiki/Multivibrator#Astable_multivibrator
https://en.wikipedia.org/wiki/Injection_locking

[Eheran]

Frequency of a pendulum depends only on its length, not on mass or swing amplitude.

When did I say the center of mass would be at the same distance...? I even name a frequencyrange, its not like I just make that number up.
I did pretty much this:

If changing the resistor and capacitor values don't change the frequency

I really just want to change the amplitude.
I doubt that I can change the frequency without physical changes like I did by taping coins on the waving arm. Or if I could... it would drain the batterys in no time.
Thanks for the links. I would like to know what the engineer was thinking when he applied this to the waving cat with 2 coils. Brilliant.
And I really didnt change the capacitors or both resistors. But it feels like that is only going to affect the RC time constants / start up...
I might test that tomorrow.