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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 that 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
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.

(^ new design of stripes with magnets)
You can read more about production of stripes in logs of project, here I only would say that it's quite simple to fabricate them: you need 3d-printed mold. Then, you pour few liquids (including epoxy) there and clamp nylon stripe inside, as simple as that!

Also I try to research more efficient shapes for electromagnets.
And it seems, that I'm going in right direction!

This is how lovely this electromagnets look now. Why? Well... You can find that in logs also : )

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

  • Studying energy dissipation

    CapitanVeshdoki09/24/2019 at 17:54 0 comments

    I advise reading previous update ("Bye, DC!"), it's a crucial part - it contains important ideas about power & energy in electric circuits, revealing phenomenon of inductance and resistance on a new level - now it's my instrument of choice for working with electromagnetic processes.


    Hello everyone! Again : )
    Previously, I described a proportion, in which power allocates between charging electromagnetic field and heating a conductor and it was a bit of a shock for me, originally I wondered, how we can eliminate heat dissipation completely. Now it seems impossible? Not quite!

    I see two ways, how to come round that heating misconception:
    1) We can develop a new sort of electromagnets! If we assume, that proper distribution of charge in space (and not specifically in a conductor) creates a magnetic field, that means, that we can recreate it similarly to a capacitor. It would be a charge-dependant electromagnet, which can store electromagnetic energy as long, as charges present in it. In a traditional coil waste of power dictated by a unstable state of charges, covering a conductor - you need to apply external "force" to prevent "positive and negative charges" from collapsing, that's why applying voltage is an essential thing there. However, I failed to notice any sort of a magnetic field around flat capacitor. It doesn't mean, that it's 100% not there - it's probable, that Earth's magnetic field outruns weak field of a capacitor - it requires more studying. If I would get an idea how to make such a thing - I would share it here. It would be epic, if it's possible ; )
    2) We can exploit an interesting behaviour of a traditional coils. More on that in next part:

    Exploiting physics:
    Even an energy dissipation law has it's own backdoor! And this backdoor is a fact, that if you apply no power to a conductor and retrieve most of energy, that it gives to you, it's not likely to dissipate something into the air. Current might stay the same, who cares!

    I made some measurements:

    I submerged my electromagnet into a vessel with water and powered it up, recording changes in temperature. It takes about an hour to temperature to drop down for a 2 degrees in this setup, as it features some thermal insulation after all, water volume stayed untouched

    Here are results:

    Control circuit changed situation a lot - reducing energy dissipation for about 30%
    On the right side you can see oscilloscope date, isn't it looks familiar? :)

    That then, 30% is our upper limit? Not at all! Retention of energy goes on a constant rate independently of a charging rate, as it is a typical LC oscillatory circuit. We can use it in our favour, increasing charging speed. Here are few samples with another electromagnet:

    Using higher voltage, we get great charging:retention proportion, also - increase in a field-charging efficiency, according to a model presented in a previous update.

    Conclusion:
    Increasing retention time looks like a solution, can it be done by increasing capacity?
    Who knows! Time will show!

    Is it possible now to pump 300W into a electromagnet without burning it down?
    Theoretically - yes. But new version of a control circuit is needed.
    That one isn't suited to withstand such voltages & currents yet.

    Can we use these methods with BLDCs and stepper motors?
    Sure! With everything that has coils.

    It seems, that this project requires more time to finish. But it's so much fun!
    Then I started it, I never imagined, how many things gonna be uncovered.
    Stay tuned! I surely would finish it... Somewhere... )

  • Bye, DC!

    CapitanVeshdoki09/03/2019 at 14:30 0 comments

    This log would be very strange, I wanna introduce new physic theory
    Well, I tried to stop myself from doing that kind of work, kept saying "Just use that, don't trash your head with such an outrageous things, you have a lot of another stuff to do" - and here I am!

    Now, I want to list, what I don't like in conventional conception of electrical engineering:

    - If dissipated power is really U*I (according to Joule's Law), why then it's possible to perform any kind of work? To generate a field, which has energy, you should take that energy from somewhere, as we say that U*I equation is right 100% of time - it should be impossible, however, transformers, oscillatory circuits and electric motors have no problem with it.
    - If we say, that coil has an energy of field proportional to flowing current (L*I^2/2), then how on Earth it starts to charge? Traditional chicken & egg question. If we say, that there is no power without a current and no current without an energy...

    Needless to say, that traditional laws of physics had no chance to uncover the mystery how my circuit really works even partly. And I was OK with that, until I found efficiency problems in my design and tried to find a reason.

    I'm not pretending on universal truth and I have no intention to convince someone, but this theory explains electromagnetic processes much better, in my view, makes a lot of things clearer than ever.


    I want to start with a little bit of description, what is the origin of a stable current in the conductor. It's an experimentally proven (but probably not widely-known) fact: distribution of charge on the surface of the conductor.

    And it's fair to say, that as we have potential difference, we have potential energy between charged particles at least. Then I thought about reasons why my circuit is not as effective as needed, it was the first thing which came onto my mind: as I have diodes, it must be a tough work for magnetic field, to power up electric field and break through potential barrier!

    Idea of two energies on the surface of a conductor was very catchy and since that time I started thinking about it, as it seemed, that that charge is responsible not only for current, but for magnetic field, inductance and... resistance! Typically, we say, that we have two types of resistance: resistance and electrical reactance, probably it's an artificial division, caused by urge of numerical description and lack of understanding. That was OK for a typical AC applications, but not enough now, then we are talking about behaviour of an electromagnetic field.  Let's have a look:

    I wouldn't comment that a lot, as imagination is more important here. With same applied voltage, conductor with bigger section area have greater electric flux, and current raises proportional to R^2. On the other hand, electrical resistivity defines surface density of charge for a specific applied voltage, not a conventional "friction"  

    So every conductor has that properties. Difference is only how much "inductance" and "resistance" it has. Important to say, that potential energy between charged particle and energy of magnetic field are tied together. There is no magnetic-field energy without proper electric-field energy and vice versa!  For example: then you wrap wire around a steel rode, you add an object, which your wire needs to magnetize - it's harder now to cover a conductor with electrons and generate current, each potential difference there "costs" a part of magnetization process.

    Funny enough - there is even an interesting relation between temperature and energy, which you need to pump in. For some reason, potential energy between charges decreases with lower temperatures and conductor can gain more electrons proportional to that. I found that, then efficiency of my circuit increased as I put electromagnet in fridge. I think, same process takes place in superconductors (more pronounced) and in batteries at cold - amount of charge stays the same, energy decreases, there is no...

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  • log(22)

    CapitanVeshdoki08/22/2019 at 14:46 0 comments

    Hello everyone! I try not to miss my train, so this log gonna be short. : )
    Just want to write a little about experience I had with magnetic locks, which I bought yesterday:

    First of all, their efficiency isn't that great as I expected, for example, 60kg of pulling force doesn't mean, that they make field equivalent to a 60kg permanent magnet, because distribution of magnetic lines is different, so in stock (with 4W of power) they cannot mimic rare-earth ones, however, with this setup I pumped in around 300W of power, and it was enough. Now I know, that it's a working concept.

    However, if we talk about traditional way of powering electromagnets up, 300W of heat dissipation underlies there and it's a crazy amount of heat! In other words, even if we forget about power consumption, we have no way of making so energy-dense electromagnets without that interesting control board, which (hooray!) I already developed and have on my hands.

    And it looks like I found a reason, why efficiency changes so much through changing of PSU voltage, there was one stupid mistake I made, I would write a long log on this subject, it should break previous 75% efficiency barrier , )

  • 100% ready, 70%+ efficient

    CapitanVeshdoki08/12/2019 at 20:05 0 comments

    I wasn't there for a while, however I have some amazing news now!

    After 1 month of struggling, after a month of trying different complicated electromagnetic structures, I finally found electromagnet (which was lying on my table for 4 years for now and was a part of various experiments with control board) nice enough to try out something with them.

    As I told in previous post, I wanna utilize magnetic field better, then... here we go!

    Looks evident? Well, it wasn't evident for me, even if I knew, what magnet (which I have) produces same attraction force, as a reference permanent magnet. I thought, that field shape isn't proper for this use. Today, experiment shown, that there is nothing bad with it at all, silly me!

    And there is even a magnet with desired shape on a market!

    Yeah, that is a magnetic lock )
    Widely-available thing. Also can be hand-crafted, but it's not the point right now. Is it bad? Not at all! With it, our muscle supposedly can achieve 1.2kg contraction force with only 3W power consumption + work performed by muscle (in other words, by a magnetic field)

    What we have now?

    - fully-working control board, which saves 70%+ of energy for now, nice
    - fully-developed stripe production process, pretty convenient
    - electromagnets to power up everything!

    What remains to do to build first working prototype?
    Well, nothing! Except of urge to buy some magnetic locks
    Stay tuned ; )

  • log(20) Fire works

    CapitanVeshdoki08/01/2019 at 11:30 0 comments

    This time I faced with another sort of problem. I've decided to install smaller capacitor to check if it has anything to do with efficiency, I was interested to get significant voltage increase on capacitor during charging cycle, and I've got it ;D

    Energy goes from coil to a capacitor and in some cases, then energy oscillation is quite noticeable, it charges capacitor too much, voltage raises and does some bad stuff to LM7805 stabilizer, which powers comparator and logic gates. Couple milliseconds and they are on fire! Beautiful sight )

    My board has an option to connect logic-power (typically 14V, to power up MOSFET driver) and power-power (typically 21V and more) independently, so, you may ask... Why I'm burning components instead of doing that? Simple - I have only one PSU now. There is another 0-200V/5A on the horizon, based on compensator, I would use it in future, probably.

    Since last post I rescued control board couple times. Also I found, that overall inductance (as a capability of storing magnetic energy) is meaningful to efficiency, it just becomes a radio transmitter with small inductance (working onto 14 MHz frequencies)

    Also, I wasn't able to get efficiency higher than 75-80% on steel cores even with amazing coil of an industrial-grade solenoids. I tried ferrite core and got nothing from that too, but as I told - there wasn't enough inductance, so it's probable, that on more complicated winding it would work well, since ferrite isn't as conductive as steel.

    What I'm gonna do next? Well, it's an end of summer, I have no intention to skip this wonderful season, also I work onto another project, commercial one, so I have less time to work onto this one, sadly
    However, I have an intention to make my work easier: in this month I want to find more efficient way to utilize magnetic field produced by an electromagnet, instead of making that hardcore pure-Fe production line, this would make technology more convenient to replicate, it is already convenient in all aspects, excluding electromagnet production, it's a nice target , )

  • Quite interesting update

    CapitanVeshdoki07/14/2019 at 21:59 0 comments

    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!

    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:

    Gone wild! For some reason, supply voltage (and temperature!) affects it very much.
    Yes, I tried to put electromagnet in a refrigerator : )

    Temperature can influence resistance, however U^2/R equation (which probably not works in this case anyway, for many reasons) shows increase in dissipated energy as R decreases. So it's not the case.
    For curious - I found 30% increase in efficiency within 20 degrees Celsius, impressing!

    Most logical explanation which I found - that at lower temperatures core demagnetizes slower, as wobbling of atoms drops and it's easier to maintain them orientated, as well as their fields. 
    Sound earnestly and simple, however physics behind might be more complicated (as usual)

    And it seems that it requires quite steep signal slopes while pumping energy in. Why?
    Ahaha, I don't know why for now! All heat dissipation physics in electronics is quite strange and describes "simple" cases only, like stable current flows. Everything is different there: we work with unstable current - it's benefit and a punishment also - pioneering never been easy.

    70%+ efficiency isn't a bad result anyway, with better understanding of heat dissipation process we can make everything better, high-energy fields without overheating possible, "dense" electromagnets with awful core material as well. But it's quite hardcore and I don't know how long it would take for me to complete such an thought experiment : )

    So, I cannot escape need to make some pure-Fe cores, if you remember - actuators worked nicely on tests with rare-earth magnets, but making electric clone of them emerged into lots of problems to solve

  • Long time no see : )

    CapitanVeshdoki06/28/2019 at 14:05 0 comments

    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

    So it's must-have thing to wind half of them in opposite direction! Otherwise, you would need to connect opposite sides of coils, leaving loooong wiring between, that isn't pretty at all! Now I am into designing cheap winding machine for that purpose, motorized this time

    I've made only one half of magnet, because second half operates similarly:

    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.

    Using H2 intake as a heating element with O2 originally in chamber - it's the most simple solution, which I found, only requires some high-temperature clay, insulator (rubber?) and electrolytic cell.
    Plus remote control for the reason of safety, of course.

    It's possible to pump high amounts of energy into coil with control circuit, thanks to great efficiency. And probably... It's possible to use that instead of hardcore core materials, needs to be seen! To test that, I need to establish adequate bootstrap driver, because IR2117 has zero passion to work! >:{
    (probably it self-destroyed at some point, I need to built similar thing on NPN-PNP transistors now)

    With nice core materials it would work best anyway, so it's good to have ability to produce such things!

  • log(18)

    CapitanVeshdoki06/08/2019 at 18:04 0 comments

    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! 

    This is how schematics looks now. Nothing changed in current monitoring circuit, but now we have IR2117 (or IR2118) MOSFET driver here. What it does - it provides extra voltage over voltage on capacitor C3, so voltage difference between Gate and Source stays positive then needed even then transistor is in high side switching mode. That means, that transistor is fully opened, outputs that needed and dissipates less heat as well, so it wouldn't require hardcore cooling : )

    Also, there is additional transistor Q2 - while opened, R8 and R7 work like voltage divider and voltage on IR2117 "IN" pin is close to +0.4V (R7/R8 * +15V), then Q2 closed, we have +15V there.
    IR2117 has different logic levels:
    - low 0-6V
    - high 9.5V-20V
    So it's necessary to convert 0-5V output from TTL's to an appropriate level, that's why Q2 is needed.
    I think, tracing PCB's with MOSFET controllers only is OK for test purposes, so new revision of control circuit's PCB would be later, I don't want to waste time waiting for a delivery. And I want to go camping next week, so modular electromagnets experiment results release is going to be delayed )

  • Troubleshooting

    CapitanVeshdoki06/01/2019 at 11:48 0 comments

    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:

    Yellow - control voltage, from logic gates (5V amplitude)
    Violet - drain voltage

    Well, what's next? There is three options, actually:
    - One option is to find a way how to use common-source-amplifier schematics there, but I'm kind of skeptical about it, because such a control method leaves many limitations
    - Second option is to amplify control voltage to V_TRG level, by additional transistor, which works in common-source mode. This should work nicely
    - Third option is to use solid-state relays, they are cool, but kind of expensive, so I don't think that this is an option for small and not-so-powerful actuators

    P.S. You might wonder, why I made such a mistake. Well, everything worked well on a previous design! I have no idea why and how, because now I see that it shouldn't. However, it worked
    Maybe it was some kind of magical interaction between Q1 and Q2, uhuhu : )

  • PCB's there!

    CapitanVeshdoki05/29/2019 at 20:03 0 comments

    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

    Everything works?

    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:

    Magical thing! Not unsolvable, anyway : )
    [probably, I just messed up soldering, who knows]

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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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[this comment has been deleted]

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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