Moving mirrors with heat
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- Опубликовано: 20 июн 2024
- Deformable mirror using thermal actuators. Route to DIY adaptive optics for hobbyists? Maybe not, but it is an interesting demonstration project!
Also, new shop who dis? Apologies for audio and sketchy camera work. Crisp cinematography and audio will be back soon 😅
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==== Links ====
- Vdovin, G., and M. Loktev. "Deformable Mirrors with Thermal Actuators." Adaptive Optics for Industry and Medicine. Springer, Berlin, Heidelberg, 2005. 17-24.Vdovin, Gleb, and Mikhail Loktev. link.springer.com/chapter/10....
- "Deformable mirror with thermal actuators." Optics letters 27.9 (2002): 677-679. opg.optica.org/ol/abstract.cf...
==== Timeline ====
0:00 Intro
0:47 Thermally-actuated deformable mirror
1:57 Temperature probing
3:00 Adaptive Optics
5:30 Failed attempts to quantify the deformation
8:58 Test indicator probing
10:07 Is this practical? 
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Hey! Ben Krasnov (Applied Science) was using a laser diode with internal sensor as interferometer. It's quite impressive how sensitive and precise so inexpensive thing can be. And it works with relatively rough surfaces.
Good Thought !
Which video are you talking about?
@@RafaelAcurcio ruclips.net/video/MUdro-6u2Zg/видео.html
@@RafaelAcurcio it's called "laser diode self-mixing", posted 3 years ago.
@@RafaelAcurcio ruclips.net/video/MUdro-6u2Zg/видео.html
I really appreciate the summary of the year-long process including failures and sharing things that didn't work. It's rare to see and really shows how much work and experimentation goes towards getting that one really cool working demonstration.
Also - future content - MLCC (multi-layer ceramic capacitors) exhibit a reasonably strong piezoelectric effect and can be used as a very low cost actuator. It's actually a nuisance effect that causes PCBs to flex and vibrate, acting as a speaker. It would be interesting to see this experiment repeated with those.
Thanks! MLCC looks interesting, I didn't realize they did that. Will dig into it more, cheers for the tip!
A laser pointer from the dollar store usually includes different lens caps to project a pattern or image. You could use that projection in the laser lever to try to visualize the deformation. Very cool video.
Feel like aluminum tig rods with little induction coils to heat them would be more effective and consistent than those resistors.
You could also add active cooling so the response time is faster
@@Jonathan-ex3sl Active cooling could also provide a greater range of lengths by making it possible to shrink the element with cooling.
@@cavemandanwilder5597Then you could have small aluminum tubes to circulate coolant with induction heaters to expand
Why? the resistors are calibrated, and the heat expansion of materials is well understood. How would making it more complicated improve it?
I add to that and use silicon bronze tig wire, instead of alu
I know you don't like uploading incomplete or imperfect videos, but this was still both informative and entertaining. Keep up the excellent work.
Thanks! It's definitely true, I struggle to publish videos that aren't 100% fully explained, characterized and explained 😅 Slowly getting better about releasing stuff that is interesting but not perfect :)
@@BreakingTaps my power is out right now due to storms, but because of your videos, I made a power bank of lithium cells, properly balanced of course, and I'm good for maybe 12-14 hours.
I wonder if you could use LCD panels or other displays for cheap adaptive optics. I'm always amazed by how hobbyists can leverage the high density addressable matrices of ordinary consumer grade display panels to build the craziest stuff on the cheap.
Hey, you've got me interested, and i think i've only seen DLP chips iused like this so far
Could you provide a couple links/keywords to look into this further?
Small LCD shutters are also quite affordable.
@@bottlekruiser oculus has bought a company that stacks LCD panels and polarizers to have a select-able focus for VR purposes. an array of pixels which could dynamically refocus would be amazing, but for long exposures, even just a simple LCD or DLP in the path could turn pixels on and off depending on their current sharpness would probably be majorly useful.
This is so cool. I'm actually starting my electrical engineering masters with a focus on optics, so this is a really cool experiment. I love setups that don't require $1000 equipment.
Maybe instead of resistors, nitinol wires might be a better way to deform the mirror, as nitinol reacts to heat very quickly and deforms quite a bit depending on the heat and length of the wire.
You should try some type 2 ceramic capacitors(Like X7R), which have more of a piezo electric effect, and could have speeds in the Mhz, just make sure you bond to them with their stack in parallel with the plate.
Could you explain this in more detail? I'd love to build a cheap vector laser style display in a new fashion that doesn't rely on galvanometers. I've looked into acouso-optic deflection but piezoelectrics definitely seem like a step in the right direction
@@chewbaccabox Ok, so in piezoelectricity, there are materials which expand in the presence of an electric field. Class II ceramic capacitors can expand on applied voltage, much more than class 1. This normally happens in the axis of the electric field. But the expansion is not much. Its pretty low, like a few Nano-meters. But it also changes with voltage, and capacitance also changes with voltage...Leading to other issues... But unlike this videos example, it is not temperature rate based in terms of thermal dissipation, it is based on applied voltage. So in theory if you mounted a mirror on an array of type II or older capacitors then you could control the deformation of the mirrors very quickly. And mounting is important with most MLCCs having the anodes in parallel with the board they are mounted to, mounting them normally is good, but mounting them sideways will decrease the deflection. It depends if the cross section is square. If it is not then it will not be an issue. Just something to consider.
But for anything involving laser vector mapping I would use galvanometers. I have a 200W 3D metal printer based on a Q-switched Nd:Yag laser with galvos that works quite well. And it is very fast at moving the beam! On the order of tens of thousands of degrees per second.
as an astrophotographer I really liked this video, would be awesome to see you try tackle more conventional active optics techniques and see if they work in the real world.
I don't know if it was mentioned already, but if you would mount small glass mirrors (I know, tiny) in between your mounted actuators and then shine laser on those mirrors. Those would be as flat as can be, but your self-made mirror is more used as a platform to change shape accordingly. I dooe it makes sense. Then your 4x4 is a 3x3 grid of mirrors.
Cool video by the way, just ended up on my feed. Will check out other videos as well
Always a good day when you upload, as you can ensure you'll learn something interesting!
you should try SMD resistors to reduce the heat capacity and the time for response. Also try a smaller array (say 3X3) and current pulses more than 10ms.
Using resistors as thermal actuators is something that would never have occured to me. Incidentally could you get better thermal expansion coefficients if you used the resistor to heat something else? E.g. those wax thermal actuators they use in radiators.
Right?! Super clever but not something I would have thought of either, until I read the paper. I bet those wax actuators (or similar) would work great! Same issues regarding speed, but probably a lot more actuation range and probably a bit more linear too.
Bimetalic strips like those used in thermostats would be a better solution. Way more sensitive to heat.
@@BreakingTaps I remember a while back, AvE did a lot of testing on the wax actuators. Those things are strong enough that you could probably deform a much more rigid mirror.
What about that memory wire or muscle wire
My guess is that the PCB flexes more than the mirror when resistors heat up. Also, I wonder when soldering the resistors to the mirror, how much deformation with it end up as solder cools. Solder changes size with temperature, a lot. Maybe, solder to a piece of "flat thin" metal, and once at room temperature, glue the mirror, to avoid stress.
Here in my armchair ;), impressed by how easy it is to measure the thermal expansion of a carbon resistor, I need to try it.
The mirror (just a glass coverslip) is surprisingly flexible. It's only 300um or so thick so you can visible bend it with your fingers. But yeah, I expect the PCB was flexing some as well, stealing some of the actuation range. Note that I used silver epoxy instead of solder to attach the resistors, so there will be some shrinkage from that but not as much as actual solder :)
For the measurements part, I know nothing about optics, but have you considered finding/making something that has a mirror finish to use as the platform? I think you should be able to see some change in the reflection as the platform deforms. In a way it would be the same as you optical lever idea but a lot more visual
Mount an 8x11” fresnel lens and use these as point mounts to distort the fresnel lens into the strongest focal point. Tada, a self-adjusting solar point magnifier/laser!
Hehe, interesting..:::🤔
Aside from ceramic caps as piezo actuators, which were already mentioned, magnetostriction could be user to build an agile precision actuator. Solid chunks of magnetic material should simplify building a rigid setup, with minimal unpredictable static deformations, like from the epoxy. For bigger and slower changing displacements you can add heaters to take advantage of thermal expansion.
This makes me smile, it's so simple and elegant, yet also archaic at the same time xD
I think you might be able to get a picture of deformation across the whole mirror using a grazing interferometer. They don’t need such a fine surface and you can dial in the measurement range/resolution with the wavelength and grazing angle.
Great demo!
If you can get your hands on silicon wafers with a layer of silicon nitride (200-1000nm thick) you can make simple electrostatically actuated deformable mirrors.
Something like this that from Gleb Vdovin et al
A PCB works well for the electrode array.
I have made some prototypes for an adaptive optics system for my telescope, need to finish an interferometer to properly characterise the actuators.
wow, sounds interesting. What kind of voltage is required to actuate? If high, would the density of the electrostatic points be limited by the arcing distance between points?
@@dancollins1012 I am using 200V max, which is a limit of the AD5535B DAC I am using. At some point the spacing would be an issue due to arcing. It depends though, because the voltage difference between neighbouring actuators wont be too high for atmospheric turbulance
Congrats on the new shop. Thanks for the vid, thought provoking as always!
What a wild concept. I would have never thought to change the shape of the reflector. So many applications for this.
W O W - I imagine building a larger-than-normal ground-based telescope that packs up small, but shapes it's mirrors when it's set up. This is brilliant!
Thanks for the really interesting dip into a your experiments. Your shop looks really nice looking forward to more videos from there 😄👍
“The reason for that is … the whole thing is pretty sketchy.” Relatable!
I always start out with intentions of doing things cleanly and professionally... then ends up pure jank like this 😂
Like the new place and I look forward to seeing it evolve ! cheers.
The new space looks like it will be nice!
Now you've got me thinking about using resistors to actuate one of those flexture XY stages
Genius idea
Wow very coool!! Im wondering if you could use something like a DLP projector but backwards to achieve the same thing? They use this special DMD (digital micromirror device) chip which is an array of tiny mirrors to create an image for the light to bounce off and go through the lens. But what if you did that backwards? Took light from the lens, deformed it with the dmd chip and then used a sensor to pick up the mirror deformed reflected light.
Looks good!
Man you never disappoint with your diverse content of principle based videos! Good luck with your moving, I'm too, so I know how you feel:)
Beautiful video
This is a cool idea. If you ever revisit it; would it make sense to first solder the wires onto a platform, and then to glue a thin mirror on top with a low-shrinkage epoxy? That should give a fairly flat starting point I think. It might stiffen the top a bit the board below does not have infinite stiffness either. While you are mixing epoxy anyway it might make sense to cast the base into a sand-epoxy mixture because if it significantly deflects on both sides it will be much harder to achieve a target output shape.
Amazing work broo!
The correction of slow aberrations sounds interesting. I’ll go read the literature. You could make an optical system then make a custom deformable corrector plate. Wonder if it will handle higher order spherical aberrations, etc.
Love it!
Your video gave me hope that in 10 or 15 years or so we get consumer grade telescopes with deformable mirrors. Thank you! Also I hope that the next generation of earth bound telescopes use this technology.
The ESO space telescope is using a deformable mirror to compensate in real time for thermal distortions in the atmosphere. Atmospheric distortion is one of the big problems with high resolution earth based telescopes. Instead of a “wavy wobbly” view, the mirror is bent and buckled at high speed to compensate and produce a much clearer cleaner image. Engineering like this blows my mind - I should have been an engineer like my father and brother! Somehow I became a photographer (who loves building things). I blame my creative mother. Lol.
Did I just found a treasure at this channel?
Great video and very informative and interesting subject I've never heard of.
Keep this kind of videos up.
Hope the best for you ⚡
Seriously cool man!
Subbed!
This is a really cool approach to bring this technology into the hobbyist realm! I'd love to see amateur astronomy get access to deformable mirrors one day...
Agreed! I'm not sure if the thermal mechanism would ever be usable enough for astrophoto, but after working on this I could see an electromagnetic option being viable. Pretty low cost and easy enough to control. The wavefront sensor is probably the hardest thing, needing a high-quality microlens array. But all sounds doable!
@@BreakingTaps Has anyone done a video on how wavefront sensing really works on the hardware level? All I've heard is that they bounce a laser off the Carmen line. Converting that artificial star spot into mirror movements still seems like black magic.
This is so cool. Well, okay, warm, but you know what I mean. This is a great project.
😂 Thanks! ♥
You know, I think if, before the invention of the inkjet cartridge with heating elements, someone would suggest spitting paint by heating resistors, this idea would also seem far from being practical. However, by applying appropriate materials, miniaturization, and well-adjusted control algorithms, engineers have obtained a technology that is not only fundamentally suitable for printing, but also mass-produced.
Instead of using resistors as pushers, pretension can be applied, and then heating the element will lead to a weakening of that pretension. This should give greater accuracy and uniformity of movement, because using pushing the elements are likely to be bent, which leads to abrupt changes in the coordinate of the controlled point and uneven characteristics.
Was wondering why you haven't had any new stuff. Looking forward to more next level experiments.
This is cool in its simplicity! I reckon that you could use it for stabilizing optics assuming the changes required are slow. It would be interesting to see if SMD resistors could be bonded to the glass vertically in a large array and do some even more cool stuff with it!
I bet SMDs would work really well! Would probably have to place them by hand, not sure you could convince a PnP to do it... but it'd be a lot more neat and tidy than my abomination 😅
@@BreakingTaps why not a copper mirror? Polish one side of a double sided PCB to be a mirror *after* components were soldered/bonded to the other.
If that works, then silver coat .
@@BreakingTaps it's not an abomination when you can call it "Proof of concept" 😜
Intersting project, I think it's the same principle used inside DMD chips from video beam projectors
Genius genius ❤❤❤❤ this has los of applications
Uh oh, awesomeness in my feed. Didn't even watch it, but you never disappoint here. :)
🤗
impressive skills
What se heck :DD
Thats freaking amazing:D
Wow. When I came across your video I got excited. Being an amateur astronomer, I always thought how great it would be to have an adaptive deformable system available for the amateur market.
Nice effort though.
This is cool, reminds me about digital micromirror devices, but your example is literally using thermodynamics for modulation, would be interesting how it could be applied with the help of MEMs. This type of tech can be really useful, it has many advantages, first is it's low cost, I think thermal modulation could provide longer lifetime service and it can also be applied to focusing optics/lasers or any objects to a fixed position which doesn't require fast modulation.
Superb video, excellent topic. Here's an idea: fix the heating elenents to a small platform with a low thermal expansion coefficient, and then the mirror on the other side of that. Rather than distorting the mirror, it would just tilt it. With enough hexagon shaped mirrors controlled in this way, an image could be formed ala JWST. There may be some choice of material and geometry that could speed up the thermal movement - think bimetal coils used in passive temperature dials
Nice shop
This immediately let me think of cold solder joints. Whether this effect can be strong enough to create them and in that case if there are soldering techniques to prevent this from happening.
They tried using these on the aircraft born laser that was mounted in the nose of a plane. It kinda worked, but had a very limited operational range... like 5 miles. Even with adaptive optics the amount of both atmospheric distortion and horizontal lensing are so high even a highly focused dry chem laser can't keep it's beam together long enough to defeat targets more than 10 miles away.
You are a monster for not soldering all of those resistors in the same orientation..
😇
Very clever design! Maybe setting the zero-point at temperature higher than ambient (for faster cooling) and using some kind of feedback to drive the resistor at the required temperature faster can maximize the performance of this setup. I'm thinking about Constant Temperature Anemometers principle of operation for the temperature feedback.
Ah that's clever! Yeah I think hovering in the middle would help with responsivity a lot. Might even be able to get away with a surface mount temp sensor right near each resistor, and might be able to use SMD resistors standing upright too? Would make the whole setup cleaner and less variable
@@BreakingTaps All resistors also act as thermistors to some degree. So the sensor and actuator can be the same element.
The voltage drop across a diode varies with temperature, and probably gives a much stronger and thus easier to measure signal. Silicon diodes have a relatively low voltage drop. Light emitting diodes have higher voltage drops. LEDs also look much more interesting in operation.
In college we used to experiment with Defocal lens.
Yay! Video
This is a pretty good initial POC; you seem to have at least shown that deformation is possible, even if it's not easy to measure.
One next step might be to have a PCB made with a grid of surface-mount resistors; they'll be much smaller and much more even, and you could even lap or grind them to make them flatter before binding the mirror directly to them... You don't even need SMD skills if you have the board populated for you, and the pick & place machine will probably be way more even and consistent than you could do by hand.
Thermal expansion is proportional to the length. So, it's _important_ that this resistors are 10-15mm long.
SMD resistors will have what? 0.5-1mm or even less in the vertical dimension? So effect will be 10x-30x times weaker.
Hi, good job man. Have you ever thought about using shape memory alloys? possibly something to check. Keep up the videos that are very good, something hard to find these days with this generation of TikTok. Using a thermal camera to view the resistors firing would also be really cool. Good job.
You could do the same with big ceramic caps and the piezoelectric effect! Maybe solder them between two pcbs?
Ooh that's a clever idea, gonna look into that!
Very cool. What about wire wound resistors?
Have you heard about self-mixing interferometry ? There's a really nice video about it on the Applied Science channel and it seems fairly easy to setup.
Self-mixing interferometry allows you to measure sub-micron displacement using a bit of electronic and a simple laser diode, I think it would work really well for measuring the displacement of your mirror.
Will look into it closer! I recall seeing Ben's video on it but it's been a long time, and I had totally forgotten about it.
I've seen someone experimenting with stacks of SMD ceramic capacitors as cheap and fairly simple piezo actuators for micron-scale movements
re: suitablility for use in the last section, this seems like it could be a pretty good low cost way to make good quality flat mirrors with reduced precision in manufacturing, as long as you can measure the flatness. I don't entirely know what the application of this is but maybe it's useful as a low cost alternative in CO2 laser cutters, or for experimental optical systems where you could repurpose an adaptive mirror module between a series of iterations, configured to produce whatever topography is needed instead of buying new custom curvature mirrors each time
Dude, are you familiar with wax motors(basically thermal actuator)? I feel like they/an iteration of that concept would be easier I believe. If they were significantly smaller cooling down and heating up would be much faster if the cylinders were in a cooling tank
Yunno I was vaguely familiar with them before, but it never ocurred to me for an application like this. That'd probably work well! Or at least some kind of actuator based on that design, even if it ended up bespoke.
Bigclive did a teardown of one recently
@@BreakingTaps yeah I do know they pack quite a bit of force for their size. I think it'd be worth looking into for a fun concept. I'm not sure if there is an off the shelf version small enough but the concept is basic enough. And again if they were being cooled and had resistors like you had already for the heat to enable the motors movement I would bet that it would be more controlled and quick. Anyways just had that thought!
Ooo you could use piezo crystals to get hyper fine control too!!
damn i was looking for "DIY adaptive optics" since morning and didn't find any until now and realized that you have uploaded today. coming after your JWST actuator video which was awesome. cant you make a DIY solution for piezoelectric actuators / electromagnetic actuators? and what sort of thin/ thick mirrors they professionally use in observatories to couple with adaptive optics, certainly not thick blocks of glass mirrors right? and what should the resolution be of a practical DIY adaptive optics grid, like XX actuators/sq inch
ps - i was also interested in DIY telescope mirrors but hexagonal in shape, is it possible to craft those in a DIY setup?
thanks! you are the best!
I love the idea, thanks for sharing your explorations. One problem you didn't mention was the heat from the resistor travels up and down the copper wires and into the ground plane and then into the mirror. Perhaps a better plan would be to have the resistor attached to the mirror backplate with a glass or fused quartz short rod that will transmit the thrust but not the heat?
Definitely a lot of room for improvement! Better control, better fabrication, insulating as you suggested. Lots of room to play with this idea!
Hmm, for measuring, can't you use a kind of high resolution projector, and focus it onto the mirror and then to a wider collector?
Then have the projected image be some kind of alternating pattern, and then measure this using image processing?
I feel laser mice circuitry could work well for this (they do this exact method to determine movement).
Genius
Could a parabolic mirror be made like this to automatically adjust focal point say to a solar panel or pipe to boil water for a steam engine water heater etc.., as the sun moves. "Sungazer" 😎🌞 It would be extra neat if no electronics were needed and somehow the thermal expansion and contraction would happen with solar thermal energy.
You could experiment with metals with different expansion coefficients between the resistors and the mirror to increase deformability.
Some thoughts: Use 5 points, 4 corners and center. Use a shaft material with a high thermal expansion coefficient. Use an adhesive with more elasticity, the epoxy could be causing an issue with mobility, then again that may be of benefit once the actuation issue under control (possibly use epoxy on the center but plyible on the others?). Use tiny peltier devices on each shaft like the ones found inside the old Kinect devices for the xbox 360 behind the IR laser, this will allow you to heat AND cool the shaft material. Perhaps on the corners use ribbons of material as shafts to allow better coupling of the peltiers, mount the shafts at 45deg to the corners.
To just test the actuation and steering the mirror go with flat shafts in a bix 3/4 to 2/3 the size of the mirror square parallel to the sides. It will only explore pan tilt and piston for motion, but it should also help explore compliance of the bonding material for the perpendicular flat shafts. And will give you a better idea of what level of actuation to expect.
Thats just my unsolicited 2 cents on the topic. If I didn't already have a number of irons in a hand full of fires, this is interesting enough to fiddle with myself...alas, I am but a prisoner of my own procrastination 😅
All of that aside, another cool video, mate! Keep on keeping on! 😎👍
I had a similar idea, but my first thought was peltier modules
This is fascinating!
What voltage and current is across a resistor while heating?
Resistors mounted on a PCB with short lead lengths theoretically would be pulling and pushing against the copper traces that it's soldered to and eventually end up with what's commonly known as dry solder joints in electronic equipment which leads to equipment failure or induced noise.... And we thought that capacitors were the main trouble maker!
I might have to consider using the whole lead lengths of resistors to allow for resistor movement....
Interesting stuff indeed..
Hi, might be interessting for you. I have seen thermal actuators in industrial paper production. They are used to get an even paper surface and thickness in the beginning of the process, where they catch the paper out of the paper fiber bath. But these actuators have a length of a meter if I remember correctly 😉
Good luck getting the new space set up, moving is such a pain. (:
Thanks! Moving sucks soooo much 😢 But looking forward to the new location, it's a real upgrade to my last space.
... another pretty cool methode for hobbyists/DIY for deforming mirror-surfaces is a grid of small solenoids below a thin puddle of ferrofluid and a membrane-mirror floating on top of the ferrofluid -- here you'll deform the surface simply by controlling the current per solenoid ;)
Can you use this principle at macro scale? Perhaps directly on silicon like MEMS type? Perhaps the technology for DLP is more useful as it actually does something
Eddy currents. At 1 MHz with a 1/8" or 1/16" probe (or array thereof) you could probably get useful non-contact measurements.
Beautiful, can instead of deforming one mirror, you stick 3 onto a triangle/hexagon and get an amiable matrix without “moving” parts?
Cool
Ooh, a practical application of speckle! I knew there were some, but I was happy enough using it for how it trips people out when they look at it.
What is the software you used to monitor the deformation of the material? I would love to play with it!
DICe for calculating the speckle translation (github.com/dicengine/dice) and ParaView to visualize it (www.paraview.org/). Some more details about the software in this older video where I use it to measures stress/strain curves of 3d prints: ruclips.net/video/cp_EOxEyNHs/видео.html
im budgeting for a new shop and im wondering how much yours cost. i know its really gonna depend on locations but it would still be helpful.
perfect thing for my galvo 😆😆😆
Perhaps making a thin PCB with SMT resistors on the back of it, and glue the PCB to a thin first-surface glass mirror. A heat gradient across the surface should cause it to curl. You could even add temperature sensors on the PCB to provide some sort of closed loop feedback. Perhaps I should try this...
You could make a larger application with parafin. Ave had a wax solenoid on his channel. Theyre really strong.
The Resistor heated and expanded - check. Now how much heat was transferred to the mirror and then to the gauge prob to interact with their coefficient of expansion? When I'm making a part and chasing nuts-on, I always take a bit of a break before final pass/spring pass. wondered if you just didn't include that due to run time or what. You're really good at what you do, I'd like to know so I can apply to silly stuff I do. Thanks.
Hey, great experiment. Have you thought of Image Amplification, I think it can record the deformation of the mirror, showing surface position changes, allowing for readings to be taken to do further calculations.
Ooh, that's a good idea! I hadn't thought about it before but that might work well! I'll give it a shot when i get a chance
Oh, that effect of turbulant air causing abberations - that's mirage!
Or Marriage and a creative way to say stop talking.. I might use that one 😜👍
Have you tried searching for alloys with more thermal expansion? Sodium should be the metal with the highest expansion rate. You can keep it under an oil at the lowest possible temperature and have the mirror on top of sodium rods. Also, you should try keeping the rods in your design cool, selectively, with small thermo-couples (you can remove them from a TEC 12706 or 12710, which have 127 and 06 or 10 watts total, respectively), to increase the response time or you can use the thermocouples for everything, since you can reverse the current and have them hot or cold with the "flick of a switch". Possibly even ceramic heaters could be a candidate. They get hot REAL fast and you can easily reach hundreds of degrees Celsius in fractions of a second which could be ideal for metals/alloys which need higher temperatures. I bought a 2V to 18V mini ceramic heater of 10 mm x 10 mm by 1mm and it reaches 120 degrees C at 5 volts sucking 1.6 watts. They come with pure silver wires.
I also wanted to play with deformable optics in a newtonian for quite a while. I thought I'd use a silver coated or electroplated elastomer as a deformable lens, as a membrane on a box with variable vacuum, but I have not tried it yet. Another approach I though of was to use steppers with strings and/or linear actuators to pull various sections, to deform it in specific manners, but yet again, I'm not that much into astrophotography anymore.
You're definitely more knowledgeable than I am and I bet you got all this figured out, yet I still hope I can bring you some other insights with this comment.
Have a nice day, sincerely.
What about using the old Texas Instruments movable micro mirror array for DLP projectors? Not sure if they are binary or if they could be tricked into smaller deflections?
Oh that's pretty amazing! I can understand the issues involved with it. i.e. Heatsoak causing the deformation to change over time. I guess some form of micro-cooling could be used to maintain temperature stability, but thermodynamic hysteresis is really a b**ch. How to design for that to create a stable system is really where engineering shines.
It is slow, but probably one of the smoothest transitioning mechanisims for such a task. So if there's a need to produce a smooth (probably nonlinear) delta in elevation, this would be the way to go. Lightshows might be an idea, but then again it's probably easier to increase the resolution and use mechanical actuators
You are doing almost my dream job (almost because you are using imperial units time to time)
If some day you are looking for an assistant or maybe an intern for few months I maybe can help!
Hmm, could getting rid of the resistors and heating parts of the mirror itself allow for more complex deformations?