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• [R] Electromagnetic simulators

  kelvinA • 09/20/2023 at 22:55 • 0 comments

  [20 Sep]

  I've more-or-less have the mental 3D model of the new Tetrinsic concept, but I'm not modelling any of it until I've first set up and simulated some coils. I've got at least 360 of these I need to either create or buy from a manufacturer in China (since the MOQ is likely high enough for one to take the order). I'd like to know the performance of both a foil and wire coil before I continue further. 

  Ideally, I'd also like to simulate so that I can find the optimal location for the hall-effect sensors.

  All this means that I need to find and learn how to use a new simulator, as Fusion 360 doesn't do this.

  EMWorks 

  The first thing I found was a webinar on linear motors:

  It seems that the force exerted on the mover is what I ultimately want to find out.

  The price of this software is "Contact Us" though.

  FEMM

  Looking into the free options, I found this forum post from 2010 that asked the community to pool together any finds on this kind of software. FEMM was mentioned, and it already looks like the kind of program I'm looking for.

  They also seem to have a lot of tutorials. Hopefully, one of those is how to get force data.

  Elmer FEM

  I then found this resource that is a list of electromagnetic simulators. In addition to coils, it seems there are simulators for PCBs and antennas that are also in this list.

  One program I found was Elmer, which seems more recent than FEMM, and I started watching this webinar:

  This part is interesting because it shows that it can support the "stranded" and "foil" types of coils. It also sounds like this programs is rather large, so it's most likely going to take a while to learn how to use it.

• [T][R] Concept Fantastic4

  kelvinA • 09/03/2023 at 21:05 • 0 comments

  The next Tetrinsic concept was going to be "Tetrinsic Concept4", but partially because this project needed a hero and partially because I was thinking about the intro music from the 33 second mark of the Fantastic Four: Worlds Greatest Heroes as I was thinking up all the improvements I could make from Concept 3.2X2, the internal code name is "Tetrinsic Concept Fantastic4".

  The idea that forms the basis of this concept was from @RunnerPack all the way back in January, and is something I didn't really want to work on until after I actually had a proof-of-concept to test since it would involve more 3D printed / custom components. I wanted to be able to compare the off-the-shelf hardware solution to the more custom made solution. 

  Now that the 580KV motor is no longer available and I know that cogging should really be 0, I'm going to have to go through with a custom motor solution. While I was at it, I wanted to see if I could increase the stroke : body length ratio.

  Initial thoughts

  I thought about a solution for about an hour, and this is what I envisioned:

  • Tetrinsic becomes a linear BLDC motor with integrated hall effect and pressure sensors.
    • Part of the reason is so that I have more space to make and place coils.
  • I move all the logic back to Tetent / Tetrescent like I originally planned at the start of Tetrinsic Concept1
  • The motor controller is already designed to let me bundle 4 motors to one CS pin, so I just need 2 CS pins for all 5 linear motors
  • I can use the 3 hall sensors that are sometimes installed into BLDC motors as the position encoder.
  • I only need 2 bent tubes, and the turning pulley can fit inside the loop instead of outside
    • This assumes I can create a surface that can turn on a 7mm diameter radius
  • Coils will be on the top and bottom of the linear motor section, which makes the magnetic field much more consistent and means that I don't have to worry too much about air gap
  • The belt can be printed as a "Spiralise Outer Contour" (vase mode) of TPU
    • The guy on the Mass Production Hack Chat said that TPU was the best in terms of layer adhesiion.
    • It can also be made from a magnet-band-magnet sandwich, where 2 seperate magnets are stuck on each side of a thin loop of material.
    • I later realised that this would mean that the Thumb Tetrinsic would have to be a different height than the Finger Tetrinsics so that the loop could go around them.
  • On the connector board, I can use a 5 input Sigma-Delta, 24bit ADC for the load cells and up to 5x multi-channel 16 bit adc's for the hall effect and current sensing 
    • (I've been hearing multiple times that the ADC on the esp32 isn't great)
  • Encasing the top-down coils in a ferrous material should further increase the field strength between the coils and the magnet embedded belt.
  • See this video for more information.

  My idea is to take a linear motor like the one shown below, and swap the coils and electromagnets:

  The design shown above also looks like a scaled up version of a voice coil actuator, which can be used for haptic vibrations.

  Anyway, cogging is eliminated because there's nothing magnetic in the stator. The first time I saw the video about cogging, I didn't fully grasp it, but the thumbnail actually does a good job of showing what's actually going on:
  

  From the perspective of the magnets, the copper coil may as well not exist. The ferrous stator teeth it's wrapped around is a different story. Because of the gaps between the stator caps, there's actually an inbalance of attrative forces. (remember, magnetic materials are attracted to both north and south poles of magnets). I'd imagine that, to solve it, you'd either need to remove the ferrous stator entirely or design the stator such that the attractive force is equal across the entire perimiter.

  Magnets

  The first reason why Me In The Past didn't think that the embedded magnet idea was persuable was because I was mentally simulating...

  Read more »

• [R] Looking for a new brushless motor

  kelvinA • 08/28/2023 at 08:44 • 0 comments

  [09:30, 28 Aug] 

  It first helps to define what Tetrinsic needs to be at this point in time. It needs to:

  1. Be no wider than 18mm.
  2. Use a 45mm load cell or some other precision force sensing technology.
  3. Precisely detect finger position.
  4. Provide a grippable, low resistance, linear sliding medium for the fingers and thumb, ensuring fingernail compatibility.
  5. Have a brushless motor that exerts at least 300gf at point of finger contact.
  6. Allow for the below sliding medium configuration, unless another suitable ergonomic solution is found.

  ---

  I've looked around AliExpress and there are a few motors that have a diameter of 16mm and lengths of 23mm and over.
  

  Of which, the one with the best KV is this 1632 motor:

  Specification:
  
  Voltage range: DC 8V-18V.
  Speed: 5600RPM-12000RPM.
  
  Motor length: 32mm.
  Motor diameter: 16mm.
  Shaft diameter: 2mm.
  Shaft length: 7mm.
  Weight: 23g
  
  Precision 16mm brushless motor with inner rotor, body length 32mm, the appearance of the bulk motor is somewhat scratched by transportation, the motor is relatively good quality, all aluminum alloy shell CNC processing, motor front and rear ball bearings, built-in Hall-type brushless motor.
  
  The rotor is composed of 4 rare earth neodymium magnets. The magnetic force is very strong. It is obvious that the reluctance of the motor shaft is rotated manually. This motor does not have a drive, so it needs an external brushless drive to run.
  
  The motor should be nominally used at 12V, and the measured voltage can also be used between DC 8V-18V.
  
  Test data:
  Voltage: 8V       No-load current: 0.08A       No-load speed: 5600RPM.
  Voltage: 12V       No-load current: 0.13A       No-load speed: 8200RPM.
  Voltage: 18V       No-load current: 0.16A       No-load speed:12000RPM.

  The RPM at 12V is 17% higher than the 580KV motor. The KV range of this inrunner motor is 700 - 667KV. It also sounds like the cogging torque of this motor is notable.

  ---

  I then watched the following:
  

  The summary:

  • Matching KV to the application is the most important
  • Generally, inrunners have a higher KV than outrunners
  • Inrunners can be more efficient as the windings can conduct heat through the case
  • Cogging happens in a slotted but not slotless motor [relevant video]
  • Cogging is stronger on a 6 pole motor.

  Looking in the SmartKnob discord, it seems that for a device which is supposed to dynamically create it's own dedents, cogging is understandably not toleratable. This is what the creator means when he says that a motor has no cogging:

  Even if that 1632 motor didn't sound like it had cogging so strong that the seller thought to mention it, I currently can't imagine a geometric configuration that I find acceptable.
  

• [A] Motor. Is. Missing!!!

  kelvinA • 08/27/2023 at 19:41 • 0 comments

  Have you ever had that time when you're idly thinking and the thought "I should do something about that one thing before a problem arisises?". Well this morning I remember thinking 

  You know, if those motors go OOS like what happened with SmartKnob, it's game over, right? Like... just saying... we should finalise this design fast or even just buy 20 motors now.

  before replying to my other self

  They've been on the market for like over a year at this point. I think we're fine.

  ---

  Well, I was scrolling though this lovely looking website of the Ratchet H1, which is the first commercial haptic knob I've seen, and was thinking "Ok, maybe I was a bit too hard on myself complaining that the £25-or-so Tetrinsics were too expensive, considering this is almost 6X the price."
  

  Then I remembered that I hadn't updated the BOM spreadsheet since Concept3.2 over a month ago.

  First item: LCD screens.

  Me: Oh, that's no longer in here. Delete that row.

  Second item: 580KV Motor.

  Me: Oh yeah I better go check to see that the price is still the same.

  First link: £1.95

  Me: !

  Second link: £2.54

  Me: ! !

  The message over the basket: Sorry, this item is no longer available!

  Me:

  [  !  ]

  AliTools search: Nothing remotely like the motors

  The music I'm now playing in the background: Thunderbirds Are Go - Chaos Crew Theme (a fast paced, orchestra boss music track)
  

  Me: Starts scrolling my wishlist where I certainly saved the motor

  The background music when I manually get to the bottom of the page, seeing nothing: Quiet and ominous [00:47s]
  

  Vivaldi: 0 search results for "BLDC" or "580KV"

  Bing: Shows 4 results, all of them wrong

  Google: Links me to the £2.54 listing 

  ---

  Sigh. And just when I was feeling a bit excited with some "we are so back" energy. I was already kind of worried that these small motors were just old stock from something random. I've also read my fair share of products that have manufacturing or sourcing issues (like almost every hardware Kickstarter, Prusa, even Apple with the Vision Pro).
  

  If the 580KV motors don't magically come back, or an alternative motor (I somehow missed every time I searched for it over the past 12 months) isn't discovered,

  it is so...

  over.

• [M] 2mm rods instead of 1.5mm tubes

  kelvinA • 08/27/2023 at 14:35 • 0 comments

  I first mentioned this in this Tetrescent log, but I've spent 3hrs modelling a new solution. The main reason being that most Aliexpress listings for stainless steel rods start at 2mm:

  Secondly, even though one is probably never going to push down 500gf onto any Tetrinsic when in normal use (my thumb usually hits 420 - 450gf max and 300gf when not putting in the extra effort), the safety rating of 2.0 isn't ideal. 

  It turns out that the solution to the question "Should I have the rods go over or under the collector?" is actually "Both.":

  This is to allow the collector to obtain minimum wall distances of 1.2mm whilst also allowing the ball chain to slide past. I've also added this smooth curve to ease the transition from air to the side of the pressure collector:

  The new assembly has a much nicer looking displacement profile:

  The minimum safety rating is over 3, but it's unexpectedly in the area just under the load cell: 

  Now that I've slept, this could be caused by the rod-ending offsets being too close together, meaning there isn't enough overlap where all 3 rods can bear the force. Increasing this offset to 27mm (from 20mm) reduces displacement to 0.300mm (from 0.324) and increases the safety factor to 3.78 (from 3.20). Reducing it to 10 increases displacement to 0.359mm and reduces the safety to 2.78:

  I'll go with a 29mm offset to leave about 20mm from the last bend:

  I'm now trying to see if I can actually obtain simulations for multiple force points by making the ones that have no force applied "frictionless":

  No, that failed:

  I'll just have the forces without the "frictionless" constraint. I'll assume that the extra bodies have a negligible weight.

  It seems that Fusion does each solve sequentially. At least that means I could be inspecting one study while another one solves on the cloud. Anyway, here are the results:

  I've set the displacement to "Actual" above, but to better see what's happening on a micron level, "Adjusted" is below:

  It seems that the "minimum of minimum safety factors" is 2.94, when the force is applied near the ends of Tetrinsic. The outer force position has a max displacement is only 0.35mm, so it should feel rather solid throughout, even when pushing down at 500gf.

• [M] 500gf Simulation

  kelvinA • 08/24/2023 at 17:00 • 0 comments

  So I'm considering a 125mm solar cell for Tetent, and since this is much longer than my initial assumtion of a 75mm Tetrinsic, I thought I'd actually get a simulation.

  I've modelled the tubes with a 60 degree inwards bend (instead of a 90 degree straight-down bend) so that the ball chain can take a shallower angle from the sprocket to the sides of the "pressure collector" as I call it. 

  ---

  I've got a 500gf load exerted from the middle of the area, and it's already not looking so good, acheiving a minimum safety factor under 2. The good news is that, as expected, the load cell has almost no displacement, meaning that the force sensing area is symmetrical when under load.

  The displacement is rather high, at 1.15mm. My goal is to cut that in half somehow.

  This is where the outer tubes have their cutout not in the centre, which aims to have at least 2 tubes providing stiffness across the entire collector. I planned to do this on the 90mm Tetrinsic, but there wasn't enough length on the ends (only 5mm) before it needed to bend. Even still, this solution would be geometrically invalid since the tubes would intersect the countersunk screws.

  Unfortunately, the displacement only improves by 0.1mm and the safety factor is unchanged.

  Returning to the aligned-end tubes and having them made from solid steel (so they're more like 1.5mm thick wires), I get a displacement of 0.86mm and a safety factor of 2.

  Interestingly, the displacement is still 0.86mm when the force is applied directly under another Tetrinsic, but the right side is greener than the left side. Green means over 0.4mm of displacement.

  The displacement is more balanced with the uncentered cutouts. I probably should go with the other solution, whereby the collector is on the "outside" of the loop.

  ---

  So this is it. It certainly looks more complex. The main benefit of this strategy is that the finger force pushes the tubes further into the collector, instead of pushing the tubes out of it. 

  The main drawback is that the ball chain will have to slide over plastic to be moved out of the way. At least, that was the drawback I thought of when comparing the two strategies before I started modelling. Due to the way I designed the first collector, the ball-chain would still rub against plastic.

  Another benefit is that, similar to a boat through water, I can print a seperator that splits the dual chain.

  With this, I get a max displacement of 0.77mm and the base has a displacement of 0.34mm.

  Considering print orientation, it's probably best if this face was horizontal instead of perpendicular to the tubes. 

  it seems that a height offset of 5.2 - 5.5mm would be required:

  As will M3x10 countersunk screws:

  So these bolts were actually causing the simulation to fail until I did a combine-cut to eliminate the geometric intersection between them and the load cell.

  Now, for some reason, trying to simulate forces from distances over the 9.3mm set in the above simulation caused the simulation to fail. I tried a few different things and red the error logs, and I've been able to get a 25mm force sim to succeed by reducing the mesh setting to around 7%:

  I simulated 50mm, and for some reason, only the "Displacement" view is glitched:

  45mm worked though:

  It does seem that I should also have a 0.75mm spacing below Tetrinsic to allow for this part to flex uninterrupted.

• [M] Concept 3.2X2 modelling... started.

  kelvinA • 08/15/2023 at 20:08 • 0 comments

  It's not much, but it should give you a slightly better idea on how everything fits together. It seems that I've sketched the mirrored version of what I intended.

  Also note that the bottom of the steel tubes are slightly closer together than the top, This is to give the ball-chains more space. The angle is only 2 degrees, which isn't significant enough to have 2 slightly different bending jigs. It's possible that I increase the angle should I need more space, but right now I've kept a 1.2mm gap for the walls of the printed part that holds these in place. The tubes also act as reinforcement for this printed holder.

• [A] Interwoven Tetrinsic possible?

  kelvinA • 08/14/2023 at 00:13 • 0 comments

  Since this new Tetrinsic now has 3D geometric considerations to uphold, I was having trouble thinking about the solution. Thus, I decided to create some rough sketches of the problem in Paint3D. Being able to digitally sketch to help solve problems is the main reason behind the Sketchθ mode in Tetent.

  Initial Drafting

  Basically, it was a bunch of drawings to figure out what could and couldn't go where, as well as making it easier to see how design decisions would propogate.

  Once it seemed that I had an idea that could work, I continued the sketch in Fusion360 where I could get accurate scaling. It seems that 4.8mm is a good starting point as a Tetrinsic offset. I'm also planning for space for a 4.1 inch HMI, since it's almost the same dimensions as the panel by itself with the main difference being thickness.

  As explained in this log, I believe the HMI is the best solution but it's also the one that uses the most space, thus if I can accomodate this display, I could later decide on going with any of the other solutions discussed instead.

  In the free space available, I've found this 356575, 2.5Ah battery:

  To allow for enough space, I've gone with 17 teeth sprockets. The total height is thus 27.5mm. That's the same height as the TestTetrinsics I printed.

• [T][P] Interwoven Tetrinsic? (and steel tubes arrived)

  kelvinA • 08/11/2023 at 12:40 • 0 comments

  Starting yesterday, I've been conceptualising a way to get a fifth Tetrinsic to fit. 

  One of the ergonomic issues with Thumb1 is that it and Finger5 are both what I'd call "aligning fingers". As one would expect, the solution ergonomically fails if only one of them is in alignment. That's part of the reason why the main Tetent concepts have only used 4 fingers:

  Unfortunately, any ergonomic solution failed geometrically due to the size of Tetrisic. #Tetent TestCut [gd0139] is no longer geometrically viable with how large Tetrinsic has grown now.

  However, with this new idea that I talked about in the previous log, I feel that there's a possibility of obtaining one of the best ergonomic solutions possible whilst still being ergonomically viable, though it could be harder to manufacture since a closed loop would form around the FingerN Tetrinsics. The good news is that I can make it ambidexterous without needing an additional Tetrinsic, now that it's so long.

  This strategy actually goes all the way back to this log here where there's even a handy diagram. Right now, I'm targetting a height offset of 6mm. Conveniently, the 1.5mm stainless steel tubes arrived. 1 tube alone already feels unmoving, so the 3 tubes that make up the sliding surface of Tetrinsic should be stiff enough for the task.

  I'm also removing the LCD/Solar stuff from Tetrinsic. I'll still be keeping compatibility by exposing pins on Tetrinsic PCB, but it now seems that the aesthetic should be determined by the device that Tetrinsic is implemented in. For example, why have a small artisan keycap when the entire free area could be one, such as a topology map:

  At the moment, I'm expecting the visible area to be about 75mm x 75mm for Tetent. This approach to lighting has come full circle, as the Tetwin Switches were designed to be transparent so that an external light source could shine though.

• [E1][T] Tightrope / Abacus Inspired Concept?

  kelvinA • 08/09/2023 at 11:52 • 0 comments

  So, unfortunately, with the expected size of Tetrinsic, it's looking like a possible Tetent solution would be very similiar in dimensions to an AirBerry (my Let's Split keyboard), just rotated 90 degrees such that it's 6 rows, 4 columns instead of the other way around. I was imagining something like this:

  It's... fine... simple yet modern... but it's not exactly the kind of device I hoped to get out of 19 months of R+D work.

  However, just after writing about the linear motor research in the previous log, I thought of what a new Tetent could look like with one and thought of sometihng similar to this:

  But then I remembered that a) the ball-chain of the current Tetrinsic runs on a stainless stainless steel tube, b) that tube is probably stiff and c) that a good part of the proposed Tetrinsic is empty space on the bottom half. Thus, why not turn the concept up-side down and bring back some level of future-modern, Apple-esque aesthetic that I'd expect to see on Yanko Design?

  The most notable benefit of this is that a larger, single display could be used. However, as a larger screen means more pixels to drive, I'll most likely be sticking with the 2x 1.14" LCDs. Additionally, the only OLED I could find, the 3.8" one I was planning to use for #Tetent TimerSpy [gd0136], actually has poor black levels in ambient light. I can clearly see the difference between "black" on the OLED and the black bezels from this video

  Another notable mention is that this extends to any material, such as a photovoltaic cell or a porcelain tile. Lastly, a benefit is that the pressure plates won't be right next to each other, meaning that I could actually have the Tetrinsics closer without worrying about manufacturing tolerances.

  The next Tetent concept is currently a work in progress, but this sketch (which is one half) should give an idea as to the strategy I want to try. For starters, I'm thinking that the squiggly bit is where I could have a fancy design on the outside. Behind that, on the inside, it's where the load cell, battery and top screen would be. The square (highlighted below) is where the memory LCD would go, and the motors behind it. 

  Hopefully, this strategy makes the resulting Tetent designs look more futuristic, even if I might not be able to make Tetrinsic as thin as I'd like.

  The 3D of the above looks like this, though I'll post updates on the overall design in the Tetent project:

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