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linear actuations for everyone!

cheap artificial pseudo-muscles here

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Some time ago I thought... Why linear actuators depend on usual mechanics so much? Gears, worm-gears... Come on! So here it is, something what semi-soft, has no gears and also implements a lot of interesting concepts, like using pulling force and pivoting torque at the same time! Linear electric motor, if you wish :)

Target of this project is to create cheap semi-soft linear actuators for everyone to use
Project has two parts:
1) Structural one, about mechanics
2) Effective control

Structure
Structure is on the top picture, main idea - to use pivoting torque and pulling force at the same time, it works like a linear electric motor. Two electromagnets on each side generate magnetic field, which orients magnetic momentum of each segment of the stripe.
Structure shown here has two stripes stitched together, each stripe has 4 segments containing permanent magnets. Arrangement  of magnets helps to prevent sticking together.

(^ picture of the old stripe with magnets)
You can read more about production of stripes in logs of project, here I would say only that it's quite simple to fabricate, you need only to 3d-print mold. Then, you pour few liquids (including epoxy) there and clamp nylon stripe inside (mold has this function also), as simple as that!

Control circuit and effectiveness
"Are electromagnets effective enough?"
- Yes, you just need to control them properly. We don't have to waste so much energy during their work, my theory is what electromagnet has a top energy capacity assigned to specific current and by cramming additional energy inside you do nothing, what is usually seen as a not energy-efficient behaviour of electromagnets.  You can withdraw and insert energy there cyclically without exceeding of any limitations.

Our control circuit correlates with this principles, it was successfully tested and retains at least 79% of energy. Also gives freedom to tune process on the go and reacts to sudden changes, doing that with quite pretty schematics! First version has only 2.5$ worth of components and it's easy to build, because it doesn't require any tuning. You can read more about that in logs.


Benefits

A) They are reliable
A.1) Comparing to traditional rigid mechanics they don't care about shocks of any kind very much, also there is nothing wrong with bending - no requirements for precise placement for them.
A.2) You can parallel them - many hands make light work. If one fails - it's not fatal. And paralleling rigid motors isn't simplest task.
B) They can be fast
C) Why do you need to simulate muscle with complicated math models, if you just can use something, what is very close (talking about behavior)?

  • 1 × Epoxy glue usual epoxy
  • 1 × Nylon strap typical nylon strap, 2000 x 20mm
  • 1 × Magnets 10x6x3mm rare-earth
  • 1 × LM2903 SO-8 comparator
  • 1 × SN74LVC1G series logic gates NORx2, NANDx1, ANDx1

  • Modular... Elecromagnets?

    CapitanVeshdoki4 days ago 2 comments

    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!

    I tried to show it on the left side, you can see one turn of a coil there. Seems logical!

    And what are our benefits?

    - we achieve amazingly big surface area here!
    - with help of this surface area we can use only first layer around each coil
    - it delivers amazingly strong field inside of a coil
    - so magnet becomes more powerful
    - we can construct cores of different shapes using similar elements!
    - coils are placed INSIDE of a core, so it makes electromagnet more compact

    Oh. And pretty sorry - I made a mistake in previous logs, thinking, that more current is more important then number of turns. They are equally important!
    But diameter of wire affects resistance significantly, so by reducing wire diameter two times, we increase number of turns only twice, while resistance increases 4 times.
    That's why I had an idea, that current is more important.

    So now, before arrival of induction heater I can check this theory also.
    It has some sort of Sci-Fi look with all those honeycomb shapes! huhuhu

  • Long-term log

    CapitanVeshdoki5 days ago 0 comments

    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.

    Also, I want to upgrade coilformer, because it wasn't optimal

    As stripe attracts to the core (mostly), fixating stripes directly to the core is the best decision. I want to do that by drilling 4 holes in the core and using steel wire (or something similar). I hope what my drawings are understandable enough - you can see there stripe is being held by a steel wire - compact and lightweight.

    Current prototype of an electromagnet showed, that winding wire onto rectangular shapes is quite questionable process - it leaves gaps between core and coil (this is very bad), so i think, what I would use something between ellipse and rectangle for that purpose, then I would figure out how to cast properly.

    Also, I would be happy to find someone, who is really into designing electromagnets!
    And maybe has an idea how to make them extremely powerful, as never before : )
    As they are effective as never before now, thanks for that decent control circuit,
    I've thought a lot about that, I still can't find another approach, except of  using better core material

    It would work, howeveeer... I think, that there should be a different way

  • Power of syrup! (log13)

    CapitanVeshdoki05/18/2019 at 14:24 0 comments

    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.

    And here I move upper bound, different runs coloured as previously.
    I think it shows it pretty decent now, thanks for greater inductance of a new electromagnet : )

  • log(12.5)

    CapitanVeshdoki05/15/2019 at 19:44 0 comments

    Log about fabricated stripes and accidental capillary effect!

    My first reaction after producing new stripes was: "H-o-w?"

    If you remember from previous log, I predicted ease of fabrication for new structure with two big magnets. And it was almost evident for me, that if gap between sections is 30 times bigger, then it at least 15 times harder to ruin bending ability by epoxy rushing there.

    And result was totally different! So I poured more oil onto nylon stripes and tried again.
    Result was better, but not like previous time, with 4-magnet structure.

    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:

    Looks similar to the preview version, now it is sectional to be easily printable. Eager to complete electromagnets part! This is the last step before first test of an actuator. Except mold-fixing, haha

  • Structural... what??

    CapitanVeshdoki05/12/2019 at 20:07 0 comments

    This update is going to be quite clumsy, but... It's a pretty important one!

    Why clumsy and also important? Because during yesterday's midnight design troubleshooting (also chill out) I made everything simpler and better. I guess so, because discovered things are pretty neat. 

    //
    And a-also-o, showing them is a hard task, so I would try to describe it without pictures.
    Let's start from some questionable stuff :D
    Bird here shows me yesterday, thinking about bending. Bending is quite important part of construction, as it is semi-soft and it's being squeezed along with bending of stripes...
    And yes - bending is a tough guy.

    Why so? Fabrication process is amazing, but still had hardcore part - fighting with capillary effect. Epoxy loves to ruin stripes bending-abilities in all sort of places. We used oil to prevent that stuff and it works. However, it requires some skill.

    Either way, even if you managed to fight back epoxy, you still have small gaps between stiff (containing magnets) sections, it also affects bending. On the other hand, to make small angles between elements possible, we also used a lot of epoxy on sides of magnet, and this is no good... So!

    So there it is. After some too complicated solutions I've got an idea, what we can just leave central sections untouched. It showed as a question marks on that strange picture above.

    And there fun things started!
    - we use bigger magnets, one big instead of two medium-sized
    - by that we reduce epoxy/magnets ratio, good
    - magnetic field near magnets is pretty dense
    - so we get greater pivoting torque and pulling force, as magnets are bigger and closer
    - distribution of magnets mass is more reasonable now, that is very good
    -
    yep, it's softer now and can withstand small twists, great
    - also, doesn't require precise pouring of oil, because it wouldn't change much
    - so, easier to fabricate overall, use of epoxy also lower

    I see there only positive sides. As control circuit worked pretty well, structure with drawbacks annoyed me pretty much, and it makes me happy to know that they were solved at the end!

    So there is new version of mold! I want to 3d-print it tomorrow:

    Fun fact - it is also noticeably smaller, so even that requires less material to produce : )

    P.S. I found some electric steel today, also I bought wire. Now I can make electromagnets with desired shape, I think? Without induction heater this time, but hey! Enough novel things at once!, ahaha)

  • electromagnet /something/

    CapitanVeshdoki05/10/2019 at 16:47 0 comments

    As almost everything was done with electronics,
    (v1.2 control circuit PCB's are on their way)
    it's time to think about structural questions.

    And first one - electromagnets.

    If we even can control them efficiently, it doesn't mean, that we solved problem of energy density, which defines how much force we can get from the electromagnet within some weight and size.

    There are some things which I discovered recently:

    - according to precious Coil64 (big thanx to developers, very useful software), with limited voltage best way to improve pulling force - is to use wire diameter as big as possible, however, too much current would generate big energy loss on semiconductors, so it's a questionable decision. Control circuit has a way to regulate amount of energy being pushed into coil during a cycle, so it might be a solution. Also, smaller capacity on C3 means significant rise of voltage (comparing to a supply voltage)

    - cores with great permeability are wild! They can increase inductance (read as "top energy of magnetic field for a specific current") very much. I don't know where to find Metglas cores with needed dimensions, seems to be impossible now, but I've bought induction heater to produce "very-pure" iron, annealed in hydrogen. Permeability of such iron is very close to Metglas and it's possible to fabricate for yourself (of course - you need to be careful)

    Combination of a great core material and control method should do the job, maybe I'll come up with additional ideas about increasing energy density later

    A concept how it might look, with coilformers, cores e.t.c ->

    Fe cores are grey there, main reason why you can see them - nothing is between coil and core on sides (only electrical insulation), minimizing gap between wires and core is a crucial thing, as it defines inductance pretty much!

    Stripes there are glued to the deep-purple parts, their main task is to transfer tension from the stripe to bearing at the back of electromagnet. If you need to swap stripe - then you should unscrew deep-purple parts, electromagnets untouched.

    So,

    Now I have:
    - 2x stripes
    - control circuit (previous version)

    And one thing I miss to get the thing done - cores. Hopefully, I would find some material for them on Sunday.

    P.S. I'm pretty curious about energy dissipation, because I can hardly feel heat from electromagnet with which I tested control circuit previously. It would be quite surprising to find out, what it's not heating at all. Quite strange.

  • Control circuit V1.2

    CapitanVeshdoki05/06/2019 at 21:07 0 comments

    Hooray! I've managed to simplify circuit even more!
    Choose of electric components is more reasonable now - main MOSFET in D2PAK package and stabilizer for 5V logic voltage in small DPAK package, as logic gates never consume too much.

    Here is how new schematics looks:

    New:
    - one transistor instead of two
    - low-pass filters on inputs, it can use PWM output from a MCU
    - as well, filters are helpful to suppress high-frequency noise

    Still, it has all experimenting stuff - V_TRG isn't connected to BAT+, so it's possible to play with it (or place wire between them) and still there is a possibility to try another approaches to measuring current with help of jumper JP1.

    PCB
    Around 5x5cm now, with mounting holes
    Now it's time to fabricate it and check everything, but I'm pretty sure what it should work, because previous version worked as needed:

    And there is only one major change in schematics (of course, previously there were two transistors, but anyway, C3 is connected to ground on last PCB and D2 was connected to ground in experiments manually by wiring, while I was working onto question how to read current on electromagnet properly),

    I've thought about flow of electrons here for some time and I can't find any flaws in new design, happily :)

  • /Thoughts/

    CapitanVeshdoki05/03/2019 at 14:51 0 comments

    Last two days I've spent in nature's lap, now I'm ready to think about ongoing things to do.

    First of all I measured energy retaining rate more precisely:
    - blue channel is voltage on gates of FETs
    - yellow channel represents current on electromagnet, as always

    - typical current here must be around 108mA (10V, 40% duty cycle avg.)
    - we have 20.7mA
    - 5.3mA is a consumption of a stabilization circuit and logic gates
    - so, we can assume what electromagnets consumes 15.4mA
    Result: approximately 86% energy retained!

    All is great with that, but one problem is still there - noise. An it isn't a noise from switching circuit, experiment shows, that it depends on power supply voltage. Possibly it seen only on the oscilloscope and control circuit just ignore that, but it isn't something very pleasant : )
    If you remember, we have ridiculous amount of wiring over PCB and this can be a source of oscillations.
    Next task is to minimize them by designing a better board, now with two layers.

    Also, we've made different top-cover for mold and it proved, what all problems of getting a great stripes was on account of not pressing everything tight enough. (see "log(6)" in project logs)

    Next tasks:
    - to develop a better version of PCB, minimizing HF noise
    - to fabricate electromagnets with needed shape and resistance
    - to connect everything together!

    Not-so-close tasks:
    - to built a hydrogen camera with inductance heater to manufacture pure-Fe cores for electromagnets, it supposed to improve characteristics of an electromagnet and also can help to get cores with needed shape

  • log(8), Hooray!

    CapitanVeshdoki04/28/2019 at 20:44 0 comments

    This time I fixed problems from log(7.5) about PWMed output of an Arduino, I added two voltage dividers as an temporary alternative, now they work as a reference voltage source:
    And yes, it seems that everything works now!

    First of all, about changing energy oscillation boundaries. There is three pictures, each is made with the same settings of energy oscillation, but with different voltages:

    13V, as you can see, it's difficult for circuit to charge magnetic field as needed, so process of charge is really slow and uneven

    15V, there you can see absolutely fine shape due charging process and adequate timings
    18V, everything goes even faster, it's logical, because with greater voltage you can achieve target energy (current on coil) quicker

    You can change oscillations of energy by changing reference voltages also

    Well, what about conservation of energy now?
    Here you can see current on a coil. I think it's legitimate to say, that there we see about 67% duty cycle

    And also 15V VCC with 65mA power consumption.
    Connected directly to a traditional driver with same voltage and duty cycle electromagnet would consume about 295mA, so we can talk about 78% energy retained.

    Pretty good for 2.5$ worth of components! :D

    Later, deeper investigation of circuit's behavior would be taken, as well - improvements, if needed.
    As this schematics and theory was a source of 90% doubts and that's proven to be true and fully working - only a question of time to make remaining things. Even if not very fast - well, now it's 99.9% possible!

  • log(7.5) + energy saving!

    CapitanVeshdoki04/26/2019 at 19:47 0 comments

    Here it is. Resistor connected to ground directly this time!

    First of all I noticed stronger magnetic field, as well - low-frequency oscillations. I was happy about that and that is what I've seen on gates of MOSFETS:

    196Hz square wave, Nice!
    As predicted, everything was great on I_COIL input too:

    (Yes, time/div on this pictures isn't same, but length of impulses is same for sure)
    And on capacitor:

    Then I felt very frustrated, I realized what reference voltages (which should affect energy boundaries) unable to change behaviour of board much. And then I discovered that:

    What it means? It means what output from Arduino is just PWMed thing, no DACs magic at all!
    And I don't think what it's any good for our circuit, then it seems what some low-pass filter is needed... Or I would connect that to the voltage dividers, temporary, because it's easier and works pretty well.

    Overall, everything is going as needed.

    I can't say much about retaining of energy now, but if you very curious:
    - Board consumes 30mA
    - As you can see from control signal on gates, there is 30% duty cycle
    - Usually it consumes around 270mA (connected directly to PSU)
    - So it retains about 60%+ of energy somehow!
    (even with wrong behaviour of PWMed reference voltages)

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Ian wrote 05/04/2019 at 05:37 point

Excellent work! I'll definitely be following this project closely. It seems you are progressing rapidly now, and the muscles are even more efficient.

Any chance the 3D mold files or PCB schematics will be made available anytime soon? I'm eager to join in on developing these actuators for a robotics application. I think they would make a suitable alternative for brushless motors if the torque could be maximized. Much more power efficient too!

  Are you sure? yes | no

CapitanVeshdoki wrote 05/04/2019 at 19:19 point

Molds are prototypes, there are still minor things to improve (talking about convenience of fabrication e.t.c.) and this is a main reason why I'm not into uploading alpha-versions now.

Talking about schematics - you can find it in project logs, it works pretty well already, on this week I gonna trace new version of a control circuit and PCB would be uploaded here. So yes, control circuit will be made available soon :)

I have intention to finish first version of an actuator in this month - 99% sure that full build instruction would be available in three weeks (3d-models, PCBs and related - as they are done, right with project logs)

  Are you sure? yes | no

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CapitanVeshdoki wrote 04/25/2019 at 11:10 point

Thanks!
Looking forward too - can't wait to implement them in some projects
(especially crazy ones)

  Are you sure? yes | no

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