# A motor with no moving parts (sorta)

## Метаданные

- **Канал:** Breaking Taps
- **YouTube:** https://www.youtube.com/watch?v=wiRMdRi0LrI
- **Источник:** https://ekstraktznaniy.ru/video/42394

## Транскрипт

### Segment 1 (00:00 - 05:00) []

this little device is a motor and it has no moving Parts other than a cavity filled with liquid metal and it could potentially revolutionize how satellites control their orientation in space or maybe not I don't know I'm just a guy making videos on YouTube but it is a really cool idea and there are some attractive features to a liquid metal motor like this one so today we're going to talk about Magneto hydrodynamic liquid metal reaction Wheels this project was actually inspired by comment on my Liquid Metal Field emission project someone was curious if you could use a Magneto hydrodynamic pump to spin up a liquid metal and then use that as a reaction wheel and it completely nerd sniped me and I fell down a pretty deep research Rabbit Hole culminating in the video today so first what's a reaction wheel well it's basically just a flywheel that you spin up or down when placed on a satellite it allows you to change like the orientation of the spacecraft this is done through the conservation of angular momentum as the flywheel spins up in One Direction the spacecraft rotates in the opposite direction if you have three of these in three different axes X Y and Z you can control the fine position and orientation of a satellite and point it at a target of Interest like a feature on the ground that you're tracking or distant galaxies reaction wheels are super common on satellites and although there are a few different variants and Technologies they basically all boil down to the same thing a motor with a flywheel attached to it okay so what's up with this weird liquid metal thing that I built when a strong magnetic field is applied to the liquid metal in One Direction and an electric current is applied perpendicularly to that direction the metal begins to flow it follows the right hand rule that you might have learned about magnetic force is in this direction and the electric field which means the metal experiences a force in the third Direction perpendicular to both this kind of pump works with any liquid that's conductive so you can technically use it on things like molten salts or even seawater and there's a lot of interesting applications not in space using this kind of technology and if we pump the fluid in a circle we essentially make a rotating flywheel out of the liquid it's a Reaction Wheel okay so let's take a look at my prototype first so we get an understanding about um you know how it's constructed and how it works and then we'll talk about some of the pros and cons of this technology and why it's interesting for satellites my first device was very simple there's basically like a plastic body or housing made out of delin which has a channel in the middle to hold the liquid metal a ring magnet is placed on the outside of the body and smaller segment magnets are placed on the inside it's magnetized so that the North and South poles are on the inner and outer faces of the magnet rather than the top and bottom like you would normally see on magnets then we place an electrode on the bottom fill the Channel with liquid metal and place another electrode on top with the magnetic field horizontal and the electric field vertical the direction of force at the Liquid Metal Fields is perpendicular to both resulting in the liquid metal being pumped continuously in a loop you can't see anything with the full electrode but if we use a thin wire Loop you can kind of see the liquid metal rushing around and when the power is turned on unfortunately the surface tension and oxide skin means the motion is under the surface and it's not super clear on video to make it a little easier to see we can take a wire and just poke it into the liquid metal the electric field is contained to a relatively small region now so the pumping action is most vigorous next to the electrode and it grows weaker as it travels around the loop it's not nearly as efficient but it's a lot easier to see on video so does this work as a reaction wheel well normally these things are tested on an air bearing but as a quick and dirty approach we can just hang it from a long piece of string pretty cool I mean it's not the most amazing demo the power supply wires hanging down prevents it from spinning very freely but the fact that it Twitches at all means that the liquid metal is generating a torque and when the power is rever reversed it Twitches in the opposite direction so it's a reversible Reaction Wheel but you know without the mechanical bits like ball bearings and spinning rotors and that's precisely why they're being studied one of the main failure points of satellites are the reaction Wheels specifically the ball bearings that allow the rotor to spin bearings need to be lubricated but lubricants don't really like the Deep vacuum of space very much so you either need lubricants that are space rated which aren't as good or you need to enclose the entire Reaction Wheel in a pressurized chamber which adds weight

### Segment 2 (05:00 - 10:00) [5:00]

and complexity in addition to that any imperfection in the ball bearing will generate tiny micro vibrations which can affect the science payload and finally there are like stion forces when the reaction wheel is at rest and begins to rotate or when it changes Direction the stion can damage barings over time and also introduces vibrations and all of these issues are gone in a liquid metal Reaction Wheel there are simply no moving Parts other than the liquid metal no bearings to wear out no vibrations just liquid flowing in a loop it's also really flexible because you can change the geometry of the pump to suit your spacecraft you can make it out of simple plastic tubing or a custom printed design that fits the specific geometry of your satellite bus I wanted to make a larger model to test so I designed and printed a second device this one is a rounded square shape with a rectangular channel to hold the liquid metal and his big device means it needs a lot of liquid metal way more than I had purchased for the field emission project it's expensive to buy this pre-made but it is actually quite easy to make gallon stand I made myself a big batch by combining gallium indium and Tin together in a hot water bath a few minutes later and I had a few hundred G of gallon stand ready to go the metal is carefully loaded into the cavity and all the air bubbles are removed next we position the magnets at this size it's impractical to cover the entire higher surface with permanent magnets like the first design so instead we use two large magnets positioned near the two electrodes now I should say that these magnets are definitely not ideal I just had them sitting in my shop from some other project and they're crazy strong so I figured they would work fine but a real design would probably choose something a little more Compact and suited to the shape here you can also see like this steel horseshoe thing surrounding the magnets this is just plain carbon steel that I had laser cut they act as a back iron and help redirect some of the magnetic flux that would otherwise be lost it's not perfect in fact it's probably very bad and it's not the best kind of metal to use this but it is better than nothing and was really easy to make to test this one I hung it from an even longer string and used some very thin wires with a lot of slack to provide Power when energized there's a pretty dramatic rotation the power wires again prevent it from fully rotating but the motion is a lot more obvious than the first device The increased diameter and volume of the liquid metal means it can generate a much larger torque than the first one the circuit board that's sitting on top there that's a buck converter and it's used to step down the voltage and that's actually one of the big disadvantages of this kind of device the power situation liquid metal is highly conductive it's metal after all so it's almost like a dead short across those electrodes the power supply has to provide a very high current at a very low voltage the Buck converter is pumping out like 20 to 30 amps at about 1 volt which is relatively inconvenient to deal with on a spacecraft they're not really designed for those sort of power arrangements to really test these things out you're supposed to put them on an air bearing table and use a battery supply so there are no external wires influencing the motion I printed up two different kinds of air bearings a hemispherical one and a simple cylindrical bearing they are super satisfying to play with but unfortunately the hemispherical one was pretty hard to balance I did hang some copper weights below the table which helped lower the center of gravity but it was still too tricky to really use with the center of gravity being on top of the table it makes the whole thing just too Tippy so in retrospect it should really be redesigned so that either the payload is sitting inside of the hemisphere or you have long rods that can hold counterweights that reach below the table to lower the center of gravity and keep it at a more stable pose the cylindrical bearing worked a little better not perfect but it was serviceable unfortunately I could never really get the battery solution to work correctly I think my batteries have built in short circuit protection and this was tripping when they were connected to the buck converter so it was never really like juicing the liquid metal and providing any reasonable amount of torque whatever the problem was I never got it working and frankly I gave up because I just didn't care enough I did try a test with the power wires and managed to get a full rotation before the wires twisted up and not exactly what I wanted but it was neat to see it working on an air bearing even if it's kind of a janky setup so I should mention a few of the other disadvantages of these devices a big one is the liquid metal itself it's non-toxic so that's cool but it's highly corrosive to most metals so you really don't want this leaking on orbit otherwise it's going to eat your satellite from the inside out it's also a complicated design space to

### Segment 3 (10:00 - 12:00) [10:00]

optimize for there are frictional fluid losses which change depending on the geometry of the channel there's Jewel heating losses pressure vers flow magnetic strength like the list just goes on and on and a lot of these variables are tied to each other changing the electrodes and the magnets affects the pressure and the flow which might mean you need to redesign the channel geometry which then introduces more fluid losses and you get the idea so it's a complicated thing to design the permanent magnets also introduce a torque as they interact with the Earth's magnetic field which has to be counteracted or compensated for and then there are like complex fluid Dynamic issues like pulsing and turbulence in zero gravity but with all of that said this is not an entirely theoretical technology the group at Tu Berlin has flown one of these reaction Wheels what they call a fluid Dynamic actuator on a satellite called technosat back in 2017 and by all accounts it worked pretty well another OB ious question to ask is just how efficient these things are in terms of power consumption well the answer is that mine is not it's horribly inefficient uh I did some very rough calculations based on the footage and it works out to about 6. 2 millon meters of torque and 1. 2 Mill met seconds of angular momentum which are like decent numbers for a thing this size and again they're very rough calculations based on analyzing some very unci scientific footage but it was sucking down 22 Watts during that time which is terrible power efficiency luckily the Berlin group has published some numbers and theirs are much closer to traditional reaction wheels and in some cases surpassing them so mine is just horribly inefficient which is really no great surprise but the technology itself is potentially competitive with traditional spinning flywheels as with all new technology there are a lot of hurdles to overcome but there's a lot of potential upside here if the technology can be refined and I don't know I think it's kind of neat to see these things move without any moving Parts you might have noticed that I've really been enjoying these space related projects recently and well let's just say there's some cool stuff brewing in the background if you'd like a sneak peek go check out my patreon I've started posting update videos roughly every two to 3 weeks discussing plans for future projects or showing unreleased footage I'm starting down the road of some very long-term projects and expect a lot of details to be hashed out on the patreon in the coming months otherwise I think that's all I got for you thanks for watching and I'll see you all next time