/robowaifu/ - Actuators For Waifu Movement Part 2 Waifu Boogaloo

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Actuators For Waifu Movement Part 2 Waifu Boogaloo Kiwi 09/02/2021 (Thu) 05:30:48 No.12810

(Original thread >>406) Kiwi back from the dead with a thread for the discussion of actuators that move your waifu! Part Two! Let's start with a quick refresher! 1. DC motors, these use a rotating magnetic field created through commutation to rotate a rotor! They're one of the cheapest options and are 30 to 70 percent efficient usually. The bigger they are, the more efficient they tend to be. 2. Brushless motors, these use a controller to induce a rotating magnetic field by turning electromagnets on and off in a sequence. They trend 60 to 95 percent efficiency 3. AC motors, Though there are many different type, they function similarly to brushless motors, they simply rely on the AC electricity to turn their electromagnets on and off to generate their field. Anywhere from 15 to 95 percent efficiency. 4. Stepper motors, brushless motors with ferrous teeth to focus magnetic flux. This allows for incredible control at the cost of greater mass and lower torque at higher speeds. Usually 50 to 80 percent efficient but, this depends on control algorithm/speed/and quality of the stepper. 5. Coiled Nylon Actuators! These things have an efficiency rating so low it's best to just say they aren't efficient. What they are though is dirt cheap and easy as heck to make! Don't even think about them, I did and it was awful. 6. Hydraulics! These rely on the distribution of pressure in a working liquid to move things like pistons. Though popular in large scale industry, their ability to be used in waifu's has yet to be proven. (Boston Dynamics Atlas runs on hydraulics but, it's a power guzzler and heavy) 7. Pneumatics, hydraulics lighter sister! This time the fluid is air! This has the advantage in weight. They aren't capable of the same power loads hydraulics are but, who wants their waifu to bench press a car? 8. Wax motors, hydraulic systems where the working fluid is expanding melted parafin wax! Cheap, low power, efficient, and produce incredible torque! Too bad they're slow and hard to control. 9. Explosion! Yes, you can move things through explosions! Gas engines work through explosions! Artificial muscles can be made by exploding a hydrogen and oxygen mixture in a piston, then using hydrolysis to turn the water back into hydrogen and oxygen. None of this is efficient or practical but, it's vital we keep our minds open. Though there are more actuators, most are derivatives or use these examples to work. Things like pulleys need an actuator to move them. Now, let's share, learn, and get our waifu moving! >--- < add'l, related links from Anon: >Soft muscles with origami-inspired skeletons: https://youtu.be/OJO4FP0DXgQ >Cavatappi artificial muscles: https://youtu.be/yXAJGH5s4cs https://youtu.be/MpCFumHFZvU https://www.designnews.com/automation/cavatappi-robot-muscles-have-5-times-strength-human-muscles >Nameless nanofiber muscle, probably Cavatappi: https://youtu.be/H19p43NFqp4 >Supercoiled polymer (SPC) muscles: https://youtu.be/QHiTJ_zgGME https://youtu.be/N4VMoYFrusg https://youtu.be/hFuzQ4ed-t0 https://youtu.be/2GXWIozM4oQ (bundled/braided) >TCP (the same?) https://youtu.be/S4-3_DnKE9E https://youtu.be/wltLEzQnznM >Twisted string actuators (TSA) <I had the idea that they should in some cases be build with a loop. Grippers would hold a part of it and twist that. For fast release they coul let it go and grab the next part of the loop. Designing the gripper will be a bit of a challenge, though. But I think this is doable. Can't image I'm the first having that idea. <Not sure if this here >>12589 is already something like it bc I didn't understand it. <Here's some passive returning mechanism, followed by other videos on TSAs: https://youtu.be/J26y1nn7JMM https://youtu.be/QBQMZsSQJQM (freaking loud) Effect of bending: https://youtu.be/zYrHGMiqC9A Life cycle test setup: https://youtu.be/PABVsuV7Y1M Frequency response ( I don't get it): https://youtu.be/YLWsh1P80Dc Mixed with fluid/gel tube: https://youtu.be/tP9B3aqc4CI Transmission ratio and speed switch: https://youtu.be/Y1uceDzhjKY https://youtu.be/5PtXTI1t3Po <I don't like it being used for fingers but it's a good technology. >Nylon fishing line muscles: https://youtu.be/Za0VeU9Ov7A https://youtu.be/2OuRX65xbKE <(Reminder: The do have a high life span >1M) <I plan to rather use water for heating and cooling. >Continuous ransmission (CVT) / torque converters https://youtu.be/kVPjhmTThPo https://youtu.be/cd2-vsTzd9E https://youtu.be/c9e2y-5DMNc https://youtu.be/PEq5_b4LWNY >Twisted string series elastic actuator (TsSEA) <This strikes me as particular interesting. https://youtu.be/VBXykAIBKtA >Printed pneumatics https://youtu.be/_X0rDW6NQ58 >Using sugar as soluble support material for printing silicone muscles: https://youtu.be/L0Z0-y3qpNk >=== -add add'l links

Edited last time by Chobitsu on 09/06/2021 (Mon) 10:07:57.

Kiwi 11/07/2021 (Sun) 03:27:39 No.14061

>>14039 That was never brought up in several HASEL research papers I've read. It's a good idea if you could figure out the appropriate additive to seal holes when reacting with oxygen or nitrogen.

Robowaifu Technician 11/07/2021 (Sun) 03:32:40 No.14062

>>14061 Thanks, then it was just my imagination. Would have been nice, though.

Robowaifu Technician 11/27/2021 (Sat) 02:19:48 No.14513

>>12810 >hasel actuators Would a continuous coil of the circlar disk actuators work? Also, I think the preferred direction of actuators are those that work in tension (contraction) or both ways (bi-directional) instead of expanion. This way, the actuator or string does not collapse on itself in buckling, easier to connect the pulling string, ect. A real muscle works in tension and tendons / joints / bones all work like wires in bowden tubes. I am going to start printing CF Nylon cycloidal gears with PC Max enclosures to make servos in the style of the anti-backlash cycloidal gearbox on hackaday. The carbon fibers, nylon, polycarbonate mix, and maybe some PTFE powder should give me plenty of dry lubrication that doesn't need frequent servicing. I would like to try planetary gearboxes, but I feel that any amount of warping from 3d printing very finely detailed gear teeth would lead to noise and backlash. Cycloidal gearboxes seem to be better optimized for 3d printing BLDC gearboxes at home. PolyMax PC/PC Max, PolyMax CoPA nylon, and NylonX are all higher temperature plastics with anti-warping compositions, and strong as fuck for being printable on entry-level 3d printer machines (all metal hot-end extruders, heated bed, and non-heated enclosures). Machining delrin gears would probably be better strength (~60MPa printed part tensile strength vs 83 MPa delrin tensile strength) and friction-wise. I will have to see how bad cycloidal gear vibration is for low-speed applications like a robutt muscle. If cycloidal gearboxes turn out to be heavy pieces of garbage, I will report back here with results and forge on ahead with planetary print-in-place gearboxes like I planned to originally, before I found an existing model for cycloidal gearbox actuators on hackaday.

Kiwi 11/27/2021 (Sat) 06:39:41 No.14517

>>14513 >Coil of disk hasel actuators Should indeed work, would be complicated to build though. >Contraction is better then extension You are correct. It must be said that unless gravity or a spring is used to provide a return force, you will need to pull both ways. >Cycloidal gearbox Mind sharing the link to the Hackaday project? Cycloidal gears are notorious for vibration, make sure you carefully balance the gears. Most modern designs use out of phase gears to balance out the forces, that can help a lot. Did you design a print-in-place planetary gearbox or, is this design online? Either way, please share links and information. Good luck, cycloidal gears have low backlash and high ratio to area potential, would be good to have as an option for Anons.

Robowaifu Technician 12/05/2021 (Sun) 07:04:20 No.14625

>>14517 >Hackaday cycloidal gearbox project https://hackaday.io/project/167855-simple-cycloidal-robot-leg-for-quadruped Also, >stepped gear planetary gearbox >file related Making a stepped gear in a single stage planetary actuator would give a working gear ratio with high backdrivability and low vibration compared to a cycloidal gearbox.

Robowaifu Technician 12/16/2021 (Thu) 04:31:28 No.14689

I got ahold of a BLDC dev kit (moteus) and tried it out. It is indeed the motor most suitable for human x robot interaction since it is light, backdriveable, powerful, available, long-lasting, and has a large platform of hobbyists doing development work right now. These beat shape memory actuators in precision and ease of use by miles. There's no working fluid, no compressors, no pumps or tubes, and they are ready to have many types of controllers bolted on right from the factory. This is the fastest way to build a good strong motor that isn't a non-backdriveable geared DC motor. The main downsides I'm noticing are that they aren't very cheap at 30-70$ for just a small low torque motor, 60-80$ in controllers per actuator, up to 500$+ for a geared high torque actuator. Also, there's effects at play that make the motor/actuator system surely undesirable for some people: >cost >bulky circular shape >cogging (motor has intermittent torque when the magnets align with the poles) which feels like it has "cogs" as you turn the motor with your hand (not perfectly smooth rotation like you might want) >noise (quiet static and grinding noise from electronics) >rigidity by virtue of being solid >backlash if using a gearbox with small motor >high inertia if using a big direct-drive motor If you don't care about the trade-offs, I'd recommend a BLDC + Controller system. I have a gearbox in the works to bolt onto the motor to see if 3d printed planetary gearboxes will work. I'd also like to see if there's a coreless/ironless/slotless motor that would be able to direct-drive a large surface (thighs) smoothly.

Robowaifu Technician 12/16/2021 (Thu) 04:48:26 No.14690

>>14689 One last thing I forgot to mention is the potential that low KV gimbal brushless motors have. They are used for camera panning, and have significantly higher coil turns/resistance, so they cannot have position accurately measured in the same way as some BLDC controllers are set up. The potential benefit is that they are cheaper and run on lower current that can be pumped out by cheaper controllers and power supplies.

Robowaifu Technician 12/16/2021 (Thu) 06:23:22 No.14691

>>14689 Thanks for the nice breakdown Anon, it's appreciated. I'd say cost is the most obvious (and limiting) factor for the significant majority of us. I hope we can at the least find alternatives for pricey single-use controllers, and spread the costs out among fewer, general-purpose drivers. >coreless/ironless/slotless motor What does 'slotless' motor mean?

Robowaifu Technician 12/16/2021 (Thu) 17:13:55 No.14694

>>14691 Please use "ctrl + f" to find information in the relevant thread. Slotless means coreless and that's been explained before in this thread. Picrel for more info

Robowaifu Technician 12/16/2021 (Thu) 17:51:49 No.14695

>>14694 Ahh, I see. My apologies for appearing lazy. I would guess the little micro motors in tiny drones are of this type. I know they get pretty hot, but the RPMs achievable are frankly, amazing. Again, thanks.

Robowaifu Technician 02/01/2022 (Tue) 00:36:46 No.15126

Anyone have any updates to building a robot actuator?

Chobitsu 02/09/2022 (Wed) 09:18:31 No.15174

>>15126 I'm not really aware of anything new on that front Anon. I expect we'll have something before long though.

Robowaifu Technician 02/24/2022 (Thu) 21:21:04 No.15313

>>15174 I'm making a nylon gearbox for the best feasable actuator mentioned in >>14689. I have about one or two more weekends until it is prototyped. This same actuator could even be applied in any other system for cheap power and precision.

Robowaifu Technician 03/29/2022 (Tue) 13:06:36 No.15735

In >>1002, there's some links to some decent looking electromagnetic actuators that are fairly simple to build. They're limited in that they only switch between two states, and do so quickly, without a smooth transition. I'm hoping to adapt them for arm and neck mechanisms in a mini robowaifu, and the current plan is to use a small spring and variable current to try and produce a finer position control/state transition. That said, this seems like an over-complicated method, so would anyone here have some recommendations for alternative avenues of consideration?

Chobitsu 03/31/2022 (Thu) 04:22:22 No.15741

>>15735 I think we'll probably find plenty of uses for fast-acting, linear actuators Anon. I hope to see work here along that line, thanks! >>15737 >DC motors are the easiest. Just get a gear motor that exceeds your torque requirements and add a potentiometer to control position or, just use a readily available servo. Good thinking, Kiwi. Can you sort of diagram that for us? I think I understand most of the general points there, but I probably lack understanding in some of the details.

Robowaifu Technician 04/14/2022 (Thu) 14:13:03 No.15878

>>15313 I've made a gearset prototype from 3d printed nylon, and it's garbage. However, I will be tweaking it and trying to make a wolfrom stage planetary gearbox the same way. Here is a paper which has some details (key points: human-safe, high backdrivabilty, high gear ratio, small size) https://ieeexplore.ieee.org/document/8867893

Robowaifu Technician 04/14/2022 (Thu) 17:21:24 No.15879

>>15878 Any chance you can post pics of your WIP Anon?

Robowaifu Technician 04/16/2022 (Sat) 17:44:31 No.15891

>>15879 >>15890

Robowaifu Technician 04/16/2022 (Sat) 21:49:17 No.15895

>>15891 Thanks!

Hik 06/09/2022 (Thu) 14:45:49 No.16629

My idea for an artificial muscle is to have a good stretchy material, which has a certain amount of liquid in it and no liquid will get added or removed, rather the stretchy container of the liquid will be squeezed in proper places to deform the container, thus changing the shape and causing it to contract so as to work like a muscle. Right now its just theoretical, I haven't tested anything. >>14018 I also kinda like this idea Maybe there could be special structures kinda like meshes that would contract when turned separate directions on each end and could do it really quick, I think I may have seen something like that before.. its kinda like how the lower arm bones go when the lower arm is turned

Kywy 06/09/2022 (Thu) 16:39:17 No.16631

>>16629 I'd recommend HASEL actuators. This post has good information: >>13966

Hik 06/09/2022 (Thu) 18:03:48 No.16632

>>16631 The only issue I see with the HASEL actuators is that they require direct current (DC) high voltages (3,000 - 10,000 V). I'm thinking maybe one could do this a different way using low power maybe with a small motor which controls clamps or something. but I guess it might get kinda unnecessarily complex.. 2 sacks with fluid could be connected and while one be squeezed the other be full or similar, might work well for an arm, just throwing out ideas.. eventually I'll do some tests to see what works well and what doesn't

Kywy 06/10/2022 (Fri) 05:03:48 No.16636

>>16632 At 15cm scale, you'd be best off implementing a rotary prioritizing selective mechanical multiplexer. With a power motor and an index motor that decides the output. This allows for a very small mechanism to provide high power to many outputs. (Relative to individual actuators for each joint.) Picrel is a decent example made with lego which should help make it easy to understand. Here's a link with valuable information: https://hackaday.com/2021/05/04/prioritising-mechanical-multiplexer/

Hik 06/10/2022 (Fri) 09:45:52 No.16637

>>16636 https://www.youtube.com/watch?v=tCQ2I_rga0k Apparently the squeezing actuators can work.. for certain applications. But you may be right that I should explore alternatives..

Robowaifu Technician 06/15/2022 (Wed) 01:13:10 No.16692

>>15126 I downloaded this code for making a cycloidal drive in OpenSCAD, and looking into it. https://www.youtube.com/watch?v=FdTGeYKB5NM - Code is in the video description (--write-description). I hope it works this time. I already had some small drone motors for a while, but also five Nema 17 coming in soon. The reason why I didn't do this before was that I had some tutorial for Fusion 360, but I wasn't capable of transferring that into Solvespace. I also had a builder for Blender, but this was before I got my new PC.

Robowaifu Technician 06/17/2022 (Fri) 01:22:36 No.16709

>>16692 There's a new video on eccentrically cycloidal drives, and generally a good video on cycloidal drives, by RoTechnic: https://youtu.be/qMDU5tlGUwU - I thought I posted about the eccentrically ones before, but can't find it right now. Whatever, I'm trying to finally figure out at least one way to make a more regular cycloidal drive that I can adjust to my needs and actually print and build. The online examples are all a bit different from each other and many require some very specific gearing, and the plastic parts are mostly only available as stl files, so I can't just adjust the files for another size or another gearing or another reduction. The eccentrically cycloidal version is highly interesting, but it's still under patent protection and making my own version in OpenSCAD would probably require math skills which I simply don't have (or didn't have, I think one video explains it very good). I'm gonna try it anyways. Maybe I can do it with his Python code: https://github.com/roTechnic/internalECGears Another video from the same guy: https://youtu.be/xv5cd7Bg7Uk and the one where he explains the design fundamentals of how to design a regular cycloidal gear: https://youtu.be/y9vLVXjz2c0 I'm also thinking about a bevel drive for the shoulder now, inspired by Dan Royer and his Sixi Robot: https://youtu.be/W6xzBVVuml8

Robowaifu Technician 06/17/2022 (Fri) 17:20:49 No.16720

>>16709 I think I found a finished model, which I can use to wrap my head around. Actually it's several versions in one file. Understanding the formula or not, I think I can print and use it, and probably also modify to my use case. https://3dmdb.com/en/3d-model/cycloidal-speed-reducer-in-openscad-by-mattmoses/9065832/ Same on Thingiverse: https://www.thingiverse.com/thing:8348/files > By request of Syvwlch ( http://www.thingiverse.com/syvwlch ) and WilliamAAdams ( http://www.thingiverse.com/WilliamAAdams ), here is a stand-alone public-domain OpenSCAD cycloidal speed reducer. As with the Wankel Engine and Roots Blower I recently posted, this is intended more as an example of an interesting mechanism than as a practical device. If you want a practical printable speed reducer, you might consider one of the other alternatives like > the worm drives on this Tank http://www.thingiverse.com/thing:8080 or > differential planetary gears http://www.thingiverse.com/thing:7390 or > cascaded spur gears http://www.thingiverse.com/thing:7379 > or this planetary gear reducer http://www.thingiverse.com/thing:8460 > There are several cycloidal-type mechanisms already on Thingiverse, such as http://www.thingiverse.com/thing:3617 and http://www.thingiverse.com/thing:3736 > There are also several interesting external sites like: http://www.zincland.com/hypocycloid/ > http://fabricationsofthemind.com/2010/07/09/extruder-design-1-printable-1001-hypocycloidal-gearbox/ > https://github.com/triffid/Differential_Hypocycloid > http://reprap.org/wiki/Differential_Hypocycloid > http://en.wikipedia.org/wiki/Gerotor > http://en.wikipedia.org/wiki/Gear_pump > and many many interesting youtube videos such as http://www.youtube.com/watch?v=bRn1K2XeWVE[Embed] > http://www.youtube.com/watch?v=3WvPF6uGCq4[Embed] > http://www.youtube.com/watch?v=CG2sPuqEXBg[Embed] > http://www.youtube.com/watch?v=AMtyFwMDL7w[Embed] > http://www.youtube.com/watch?v=h236SP86nnQ[Embed] > This present script is based on a design by M.F. Hill described in his 1928 patent "Internal Rotor", number 1,682,563: > http://www.google.com/patents/about?id=mdF5AAAAEBAJ&dq=1682563 > Note that this design is based on an offset hypocycloid, similar to Figure I in Hill's patent. Most of the contemporary designs appear to be based on an offset epicycloid, more closely resembling Figure V in the patent. > The motivated student can modify the code so it generates epicycloidal-based profiles. Hint: start by making a module ``epitrochoidBandFast(n, r, thickness, r_off)". The motivated student could also probably clean up my train-wreck of code and/or figure out how to do arrays in OpenSCAD. > Note also that these rotors can be used for pumps - see the gifs in the comments for an example.

sage 06/17/2022 (Fri) 18:05:55 No.16721

Great material Anons, thanks.

Robowaifu Technician 06/27/2022 (Mon) 04:59:40 No.16820

>>16629 I like the idea. Maybe we can use it somewhere. It's simpler than pushing in more liquid and then using a valve to keep it, till it can come out again. But it might also make more noise with the motors for the squezzers, and I'm not sure how strong it would be. Whatever, I think it's good to throw around some ideas. >>16637 Okay, cool. (Didn't watch it yet)

Smooth movement is important. Robowaifu Technician 07/12/2022 (Tue) 23:31:15 No.16890

I'm surprised you're not building a smaller 140cm version of the actuated ball joint dolls yet. We have standalone models for ai conversation now you can download from yandex. Anyway, here's how to have a smooth servo. https://youtu.be/jsXolwJskKM I should mention that vrchat supports osc out now. If you could convince someone over the web to be your waifu with some speech synthesis, you could use the movement of them in vrchat full body to remotely control your robo bjd in your living room. Have fun.

Robowaifu Technician 07/13/2022 (Wed) 03:05:03 No.16894

>>16890 Thanks for your contribution. But which "actuated ball joint dolls" do you mean?

Chobitsu Board owner 07/13/2022 (Wed) 13:22:10 No.16895

As with the other Anon, thanks for the contribution OP. But this support having it's own thread so I'll be merging it to one of the others. Not sure if its Actuators or TITS yet, since you touch on both. I'll think about it a bit. Cheers.

Robowaifu Technician 07/13/2022 (Wed) 19:21:03 No.16896

>>16890 >If you could convince someone over the web to be your waifu with some speech synthesis, you could use the movement of them in vrchat full body to remotely control your robo bjd in your living room. No, it's a way too risky and awkward. We would still need additional layers controlled by AI: >>9709

Robowaifu Technician 07/14/2022 (Thu) 20:46:17 No.16900

I'm currently looking into some bldc motor calculations, or guestimations. I found this calculator: https://www.societyofrobots.com/robot_arm_calculator.shtml and used it to get some idea about what might be possible. It's still hard and complex, since I don't know how to calculate the maximum fringe case of lifting a water container of 8kg near to the body with two hands. Then again, I don't really need it, I could go with a small water container. Size and batteries will be more of a limiting factor, I guess. Interesting in that regard (the tutorial): https://www.societyofrobots.com/robot_arm_tutorial.shtml I won't buy anything big soon, but wanted to start learning more about it. Gimbal motors seem to be the most interesting, though high torque bldc motors have more RPM and could be reduced to have more torque, but are heavy: GM8112 motor by iPower weighs 400 grams,, has 6 kilogram-force centimeter (kgf·cm) = 0.5886 Newton meter (N·m) A high torque one from Ato has 0.8 Nm, but weights 3kg: https://www.ato.com/250w-bldc-motor - but it has 10x more RPM, so would still be faster after reduction if I'm not misguided. Hmm.

Robowaifu Technician 07/17/2022 (Sun) 00:07:51 No.16922

>"Dielectric Elastomers" I finally watched this video here on inflatable muscles: https://youtu.be/iiStyGqAG9Y - Here some search terms for further research: Fergal Coulter, hexachiral structures, Minimum Energy Structure - these might be useful for creating other kind of inflatable or deflateable muscles or structures like soft shells: https://youtu.be/IJ1dgxSZuAY The process for creating such variant of dielectric elastomer based muscles is quite complex: https://youtu.be/Qmuf_6h7Kl8 >Multiple layers of hard silicone (Shore A 73) are printed with a seamless hexachiral structure on an inflated silicone balloon. >When the layers are cured, the balloon is deflated, leaving a Minimum Energy Structure (MES) tube. http://fergalcoulter.eu/?p=73 Searching for hexachiral structures lead me to this: >The objective of this study is to improve these two mechanical properties, without significantly compromising the effective yield stress, in the regime with significant material and geometrical nonlinearity effects. https://www.researchgate.net/publication/323503727_Auxetic_hexachiral_structures_with_wavy_ligaments_for_large_elasto-plastic_deformation (PDF related)

Robowaifu Technician 07/17/2022 (Sun) 02:33:36 No.16927

> (>>16908, >>16913 : artificial-muscle related)

Pareto Frontier 07/24/2022 (Sun) 03:17:37 No.16996

>>16900 This is a simple static calculator, which boils down to computing the torque needed to statically lift the described geometry (a center of mass placed at a distance from the root motor). On one hand, the dynamical motor load will be larger than a static estimate, on the other hand motors often have higher peak torque available. I think there is no realistic robot actuator technology on the market or in the engineering lab rn except for electric (BLDC), pneumatic and hydraulic actuators. Pneumatic actuators could be usable in theory for actuating fingers and face (and they are indeed used in some high-end japanese humanoid robots) if you can find a way to print/mold/produce the required valves and pneumatic lines and the pump cheap enough for that to make sense. Precision hydraulics is mostly impossible for a hobbyist. What remains is designing (because you likely won't be able to buy one) a BLDC+reducer servo for the most loaded joint of your robot arm, you know which one... And the hardest part here is a reducer (which could be solved by buying a batch of higher-quality load-bearing gears from a sympathetic machinist, or you could borrow ideas from SEA actuators and use a long ball-screw rod as a component: [1][2], or you could borrow ideas from [3] ). Peak motor power could be improved by an order of magnitude with water cooling and good enough power electronics, and it has been done: https://spectrum.ieee.org/schaft-robot-company-bought-by-google-darpa-robotics-challenge-winner Research-grade actuators of artificial muscle are for now useless, and look like a waste of time. I hope to see an excellent BLDC-actuated lightweight robot arm being designed and validated in our group, and I very much respect the prototyping of such devices being built by fellow anons. If/when you are serious about the alpha-version of the arm design, we can start modeling it in mujoco. 1. https://iopscience.iop.org/article/10.1088/1742-6596/1633/1/012052/pdf 2. http://www.romela.org/wp-content/uploads/2015/05/2014_design_of_a_compact_lightweight_electromechanical_linear_series_elastic_actuator.pdf 3. https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.435.2907&rep=rep1&type=pdf

Pareto Frontier 07/26/2022 (Tue) 00:23:14 No.17025

Excellent servo design: https://www.sciencedirect.com/science/article/pii/S2095809921005282 If we could manufacture a similar one, a question of hip actuator would be solved. There is a lot of metallic machined parts and a lot of gears (some could be bought though as these are relatively common planetary reducer gears), so a sympathetic machinist or a hackspace with a good machine shop is required. I also have some background thoughts about the backlash introduced by the planetary reducer (as opposed to cycloidal). But this is a straight solution of the powerful leg servo problem.

Robowaifu Technician 07/26/2022 (Tue) 02:02:16 No.17026

>>17025 Do I understand this correctly, the gear has a second motor attached to it, so the second one can help in certain situations?

Kywy 07/26/2022 (Tue) 02:54:51 No.17030

>>16996 Thanks for the PDFs >>17025 This is very similar to how planetary gear transmissions are used in automotive applications. https://youtu.be/9sPi7DEbyI0 https://youtu.be/xOiAfOH-fU8

Pareto Frontier 07/26/2022 (Tue) 04:09:01 No.17036

>>17026 Yes, there are two motors, the second is much smaller and its only purpose is rotating the ring gear with set speed, to regulate the transmission ratio of the main reducer. This way the system can balance torque vs speed as is required by the current situation. >>17030 You are welcome! I think PCM in this system is a bit of a meme, and it would be better served by the usual watercooling. Would be cool to get some standard planetary reducers (they are used everywhere, even in electric screwdrivers) and try to use their gear assemblies for a prototype of such servo. You would need an encoder, there are now good magnetic encoders (austria microsystems has a lineup of these https://ams.com/en/as5040 ) and a controller. There are some open-source/open-hardware servo controllers but I haven't seen a very good one, though maybe it still exists somewhere. We would have to either take some pre-engineered solution and adapt it or design our own. I could help here, but in the end someone will have to manufacture a prototype and iterate on it until it works.

Robowaifu Technician 07/26/2022 (Tue) 05:48:03 No.17040

>>17036 >controller For BLDCs we have simpleFOC. If you want to move abway from BLDCs then that's maybe not an option. I understood it so, that for BLDCs you won't need a additional sensor to measure the motor position.

Robowaifu Technician 07/27/2022 (Wed) 04:01:27 No.17063

>>16996 I agree with everything, and I've been stuck on fixing my printer to be perfect for a few months before I want to print all the components to a nylon gear BLDC actuator that I posted to this board before. Remember that ball-screw actuators have a very high backdrive force and aren't suitable for safe human interaction without a connection in series to an elastic element or equivalent. Pneumatic devices are loud, need plumbing, and need pressure sources that make them not ideal for human interaction.

Pareto Frontier 07/27/2022 (Wed) 04:41:39 No.17065

>>17063 >Pneumatic devices are loud, need plumbing, and need pressure sources that make them not ideal for human interaction. Yes, though that japanese humanoid https://en.wikipedia.org/wiki/Actroid managed to keep noise low somehow. Also I expect our planetary drive reducer to by very noisy, and I don't see non-arcane methods https://en.nanotec.com/products/9893-quiet-gearbox-first-stage-plastic-gears-helical-toothing of removing this noise. Hope the anons will solve this problem eventually. >I want to print all the components to a nylon gear BLDC actuator that I posted to this board before. Cool, hope you will keep us posted. Expect difficulties, but we'll likely route around them with out DIY engineering mindset.

Pareto Frontier 07/27/2022 (Wed) 04:45:11 No.17066

>>17040 Sure, the BLDC driver can measure the rotor position by native EMF sensing, but some method of absolute reckoning will be necessary anyway and a reducer is a nontrivial mechanism that may break and even if it works it will introduce backlash. Absolute encoder attached to the real joint solves this problem.

Robowaifu Technician 08/03/2022 (Wed) 17:18:45 No.17142

Related: >>17086 >Paradox Drive prototype >>17072 >Which BLDC for MaidCom?

Robowaifu Technician 08/03/2022 (Wed) 17:39:22 No.17143

I'm never sure if gears belong in this thread for actuators, but I think so. This video here https://www.youtube.com/watch?v=TzJkD87eQNI made me understand why planetary gears are interesting for robowaifus. I thought most of us would go with cycloidal drives, and ignored the planetary gears. Maybe because I one read something negative about backdriveablity, idk. However, different gear ratios in one gear are of course very interesting. Still need to catch up on the "Paradox Drive", though.

Robowaifu Technician 08/14/2022 (Sun) 03:57:40 No.17201

Drilled a hole in my 50$ 8318 and superglued in a magnet for the hall effect sensor. More progress to come on soldering to a moteus and printing the controller bracket before actuator is operational. If you guys put one of these in the hips, whoo boy, I can't remember the calculation result exactly but I think 80 amps or so and a 8318 bldc gives 4Nm torque without a gearbox. Going to assemble it and then test the torque with a cheap aluminum arduino force sensor.

Robowaifu Technician 08/14/2022 (Sun) 11:55:02 No.17206

>>17201 Thanks. Great to see some progress, I hope you succeed. I'm surprised you do this without a gearbox, and I'm curious about the results. (However, please try to size down your images, they don't loose detail while being 20% of that size, for Android 'Imagepipe' works quite well but it might be from F-Droid)

Robowaifu Technician 08/15/2022 (Mon) 04:32:33 No.17217

>>17206 >pic related Not my best work, but the power is soldered together with 100 amp banana jacks. Once I re-print the bracket for the controller I will do a test to see if it works.

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