cheap artificial pseudo-muscles here
Well, lazy me soldered high side MOSFET driver yesterday, in replace of strange IR2117 (probably, burned)
Now it use three transistors instead of IC, it gives bug-fix freedom. Happily, it worked "right from the box", transistor opens as needed, as bootstrap capacitor sends needed amount of voltage to drain.
Yes, I cannot feel any heat, so I would return to surface-mount housings instead of heavy-lifters like TO-247 (however I like them, ahaha) - but it's not the interesting part!
Now I have fully-working electromagnet driver, and I've made some test. Results were kind of intriguing. First of all, I found, that you can maintain semi-constant current on coil, it wouldn't affect efficiency.
As you can see, current is quite stable. I'm not sure if I can achieve greater efficiency by increasing amount of withdrawn energy. So we can forget about kind of PWMed magnetic field! Hooray!
But question of efficiency remains unsolved for now:
I wasn't there for long, but that's for reason! I made a small vacation for myself, also - 3d printer arrived. So I've been working onto fixing some printing issues, caused by troublesome Z-axis mechanics. Now everything seems to be fixed, I regained access to 3d printing stuff, hooray! :)
Of course, I tested modular electromagnets
It seems, that I failed to produce reasonable design of winding, ahaha
And I want to say, that it performs very well! Self-proclaimed "modular" electromagnets are pretty small and light, use a little amount of cooper wire and also pretty strong compared to beefy convenient electromagnets, even with nails used as a core material. So I can say, that with nice core material or control circuit, which can sustain powerful magnetic field, it's a win : )
Now about core material, I thought a lot about using induction heater and I already have one, of course, but this method requires deep vacuum pump, I think I can do it without low pressures.
On last week I played with coils, and played a lot
Now I have 18 coils, all what's needed to complete one modular electromagnet:
As I'm too lazy to wind them by hands, I had some extreme prototyping experience ->
Yeah, it's winding machine made from a building kit! Works surprisingly well!
I would design something more reliable later, of course, )
Since I have some troubles with accessing 3d printer and drilling machine for now, I haven't completed modular electromagnet yet, however I fixed problem with transistor's opening!
It seems what I've figured out what's gone wrong with new PCB
For the reason, I use transistor to cut off connection between coil and power supply, ground is connected permanently and control circuit tracks current on electromagnet to choose duty cycle properly.
That's why transistor works like common-drain-amplifier.
Drain current derives from difference between gate-voltage and drain-voltage multiplied by forward transconductance of a transistor, so drain voltage cannot be greater than gate voltage minus voltage drop on gate-drain junction, that's why you can see something like this:
Hello everyone. After a couple weeks I've got my PCB's and assembled first one.
Big thanks to PCBway, never seen so much enthusiasm from a PCB manufacturer
Quote: "power of chaos" - such a pearl! It was a fun time talking with you, guys : )
^ wire here - bridges VCC and V_TRG, leaving possibility to use high voltages in coil circuit
without bad outcomes for the little 5V linear stabilizer, used to power up logic circuitry!
I was able to control it via MCU (Arduino) directly, hooray!
First of all - never trust PWM->Voltage article on Instructables. It's totally wrong - instead of using 0.1uF capacitor in Low-Pass filter, I highly recommend 10uF, it is fixed in project files which I gonna upload in future, however, I think I should mention it
Well, not that simple! All circuitry, responsible for a giveaway-reserve energy cycle works fine - it generates control signal in right time and then sends it to the gate of MOSFET
And then strange thing happened - IRLZ44NS (that mosfet) fails to output more than 5V:
- source voltage - is OK, much greater than 5V
- it obviously not from logic elements, how they can output half-amp currents? no way!
- stabilizer heats? not at all, but MOSFET does
FETs were connected similarly back in the days, then I tested previous version. If anyone has a theory why that can happen - would be happy to hear, because I have no idea at the moment
Here is schematics again, if needed:
In previous log I've posted an idea - how to improve current->field transformation efficiency via something except of a good core material. So I experimented with that for a while and it seems to work.
So, what I've got for now:
First of all - I've wrote a code, which calculates magnetic field in a core, corresponding to shape of a wire.
Because most of calculators have no idea about shape and it's crucial in that case : )
Also, thanks to Florian Festi, who shared a nice way how to think about coils, you can check it in comments under previous update, it's really very helpful!
Results (coil performance, one layer, same voltage, different wire diameter):
That is very interesting here - how better distribution of area (through which current flows) in case of small wire diameter increases efficiency drastically. Overall, wire is closer to the core and it almost reduces effect of current drop, in case of supplying with the same voltage:
75% current drop leads only to 35% magnetic field drop!
It means, that by using greater voltages (like 100V except of 30V) we can achieve amazing performance even with a bad core material, in case of single-layer coil! Of course, there still a question about heat dissipation, however, all experiments shown, that this stuff not likely to be heating much with such amazing control method, ahaha :)
And of course I experimented with that a lot, experiments show almost similar results.
2. Electromagnet design
Of course, I'm on my way to build one of this magnets. I made 18 cores (from nails this time, but who cares, if it would work with bad core material, it should do it best with nice pure-Fe cores later, obviously)
So now I'm on stage of wire-winding. Here is final design comparing to previous one:
Yesterday I told, that I haven't found an another way how to improve electromagnets,
It was partly true - I found one way, but I thought that it was impossible due to some reasons. Then I realized, that I might know a solution! And it seems possible to me now.
In previous logs was the idea - closer you place wire to a core, more efficiently it use current to induce magnetic field into core. So how we can maximize surface area of a core to place as much coil on the first layer as we can?
Solution for that was something similar to radiators which dissipate heat. However there was one problem - on the different sides of wire you have field with opposite direction, it weakens nearby electromagnets.
And today epic idea came to my head - it's right for straight wires, but around curved ones much more dense field is on the internal side of a curve, while outside it's kind of a weaker field!
Hello everyone! This log gonna be long-term one (not long)
Why? Well, of course there would be an update about new version of control circuit, which should arrive .. in some period of time (says "Export of international mail" since 20th of May), but periodic logs about how things going are gonna be less periodic, because almost everything what can be done to make first version of an actuator a reality was done, really:
- control circuit is fully tested, it retains energy well and controls everything what needed, as beta-version it works amazingly well and I hope it gonna work even greater with a new PCB : )
- technology of stripe manufacturing is fully developed, reliable and easy, all problems were fixed, I like current design of stripes too, as it provides great pulling force
^ this picture represents duel with fluid dynamics and glorious victory (thanx, corn syrup!)
Of course, I've measured a pulling force, now I have a nice equipment for that!
Everything there is measured with 20kg magnets on each side and 10x10x4mm inside:
- stripe can reduce it's length at least on 60%. more? possible, but with different proportions
- stripe provides from 500 to 660 grams of pulling force on it's own, I found that pretty persistent!
- attraction force between big magnets (or electromagnets) increases pulling force - 1kg to 1.5kg
Only one thing is not ready - electromagnets. Of course, I've done one and showed it in previous log, but it still can't provide significant attraction forces - it has flaws. About them:
First of all we need to have a look at coil itself. Wire here (along with current) works as a source of electromagnetic field, shown on the left side, and further we place core from wire - weaker field becomes. We need this field to orient magnetic field of our core's material atoms, which works as an "amplifier".
That means: less layers of wire we have in our magnet - more efficient use of current we get.
Also, material of core really matters, parameter called permeability is significant - so we need to get best material we can. That's why I want to use hydrogen chamber, to make Fe annealed in it. As I told in previous logs - such a material has one of greatest characteristics which is possible to get, so it's quite helpful in that project, but requires some time and additional equipment.
Well, everyone knows what syrup is. Sweet thing!
Probably it isn't on your kitchen, wide-spread in cakes.
As you may remember from previous update, I faced with capillary effect problems another time - oil just runs away from epoxy. One approach was to change mold some way or to pour more oil. But you know - more oil isn't good for health of an actuator, so I decided to find a way how to prevent runaway with same mold and same amount of oil.
And I gracefully present you this -> !!!I thought that problem was in viscosity... And it surely was!
I bought a bottle of magnificent corn syrup and water-thinned it (10 syrup per 1 water) to get epoxy-like viscosity. It's dirt cheap and yes, it has pretty high viscosity, without water-thinning it outperforms epoxy drastically.
Main thing: as a syrup it's just a high-concentration solute, so reducing concentration by water-thinning is a reasonable process. And as you may guess - it's possible to dissolve it in water after hardening of epoxy!
How great! Results are incomparable to results with oil, stripes are bending perfection : )
P.S. I love that it doesn't requires any noxious solvent.
Secondary part about electromagnet, as I've one completed:
Of course it still has somewhat illogical design, but as experimental equipment it should work. One thing with which I faced - compromise between voltage and current, to reduce heat dissipation on control circuit's semiconductors.
This electromagnet has a resistance of 2.2 ohms, well... :D
Quite low, but it is required from my perspective to have small powerful coil. As you know - inductance rules and induction heater still being delivered, so that's why I can't make cores with high permeability now, sadly
However I made pretty pictures from oscilloscope and first version of control circuit with that magnet!
You can see current on coil (reminder: it represents energy of magnetic field), and how boundaries of energy oscillations can be changed with magic of this circuit - here I move lower bound, different runs are coloured differently.
Log about fabricated stripes and accidental capillary effect!
What's wrong? As soon as I realized, that not much oil is not the case, I've imagined this picture:
- On top you can see previous structure. Oil stays in place, because it is pushed by epoxy from two sides
- Bottom is a new version, there is big air gap. And come on! Epoxy pushes oil somewhere!
How queer! But looks reasonable after all
Now main target is to find a way how to prevent it, because new structure looks promising and bends not so bad even with this major flaw in design. I made a wonderful GIMPed picture of that:
Of course I had only one stripe which bends well, so I mirrored it on this picture, just to show how it would be then contracted. I don't know why, but I like how "geometrically" it looks : )
Also I found a core for electromagnet, and designed a coilformer for test purposes: