Advanced, Realistic Humanoid Robot Project

Ok so I had multiple failed attempts to solder the chip on. Despite pretinning the PCB, on both attempts when the solder went molten the chip did not center itself and lock into place as would be expected but instead slid out of position significantly both attempts. After the first attempt I assumed it was the outlet bus/landing pad on the left side of the board that was to blame - it being a larger solder mass than the other solder masses on the other edges of the board - causing the chip to slide its way harder and pulling it off center. However, even after cutting off that part of the board entirely and trying again I still had the chip slide out of place during reflow attempt. It's unclear to me the cause of the issue at this point. I put on AMTECH tacky flux that expired in 2022 onto the pcb and then placed the chip as close as I could to centered and then put it onto a hot plate for cooking food or boiling a coffee pot those AC electric hot cooking plates. I had the heat set to max on there. The first time I had the board on the whole heatup time period and watched it gradually smoke off flux vapors and eventually the solder go molten and then I switched off the hotplate but it didn't matter since the chip slid 5mm off center. The second time I added it after plate was much hotter to avoid so much flux burnoff during the heating up process. I also added some flux while it was molten after which time it slid off center. Perhaps that was my mistake? Not sure. In any case, after the failed second attempt I cleaned everything up really well and chose to hand solder it. This seemed to go better. For this process, since both chip and PCB were fully tinned and no shorts to my knowledge, I proceeded to line up the pins the best I could under max magnification and then while pinching it in place I held my solder iron tip onto a trace near a pin for 5-6 seconds to get the solder very hot and hopefully locally heat the whole trace up to and under the IC's pad. I did this for trace after trace. Then to clean up since it was I guess cold joints at this point I applied flux and drag soldered all around every edge. This cleaned up the appearance and got all flux properly seated on traces since it was drifting a bit in the previous step and looking quite sloppy and bad. I did not want to have flux involved during the initial alignment phase and tacking down phases because once that is on I cannot see well the alignment from the sides since the flux blocks my view. Even without the flux its hard to see the traces and their alignment with the pins of the chip. The chip does not have pins is the problem. It has pads on its underside and little pads on its sidewalls. I have to use the sidewall pads as to verify the pads on my pcb line up with those and any flux in the way prevents me from seeing this clearly even with max magnification on my visor. So anyways yeah, this whole thing was a bit of a disaster but MIGHT have ended ok in the end. For now hand soldering instead of reflow looks like my best bet at least until I can figure out what i'm doing wrong... Note: I'm not sure if the flux expiration matters I haven't looked into what that means for performance. Note: I still have no way to verify all joints are good until I test the whole finished PCB I guess. And my confidence they are all good is a bit low. Sucks that I have to invest even more time to finish the PCB while doubtful it will even have reliable connections at present ugh! Note: I had to remove the trace from the previous post that ran under the chip because during my reflow and cleanup from failed attempts while cleaning some of the solder mask came off and I just wanted to remove that potential short or source of issues as a variable entirely for now. I can always run a bodge wire to reconnect those two points of the board later on.

Ok I managed to apply the UV solder mask today and it seems like it worked quite smoothly. I used the tip of a small sewing needle to spread it over the trace and then held the UV light on it for 10 seconds to play it safe. I used transparent UV solder mask so you can still see the trace but its a bit more murky/cloudy when you see it. I used the tip of an exacto knife to put little scratches on the UV solder mask to test its thickness by feel and test its durability a bit to scratching. And ensure it was fully cured. It was very hard and durable and seems to have gone on fairly thin. The question is, is it too thick/proud of the surface for the soldering on of the chip over it? This is the million dollar question. Because if the mask lifts the chip up off the PCB even a tiny bit then the soldering may not reach between pads on the IC and pads on the PCB, failing to bridge the distance. That is my main concern. If I have any issues with that, I will have to reroute this trace to go around everything rather than on the shortest path like it is now. The shortest path leads it under the IC and led me to have to mask it. Extra steps like this are a bit annoying. I kind of wish I just routed it around everything out of the way more. Then I would not need to UV solder mask at all. Perhaps in a future board iteration I will do this improvement but we'll see. For now I made several boards and want to stick to them since it would be more work to remake them all.

Ok so the Relife RL-UVH902 UV fast cure solder mask order has arrived and so has my order for a Relife UV curing light to cure the solder mask quickly and effectively. So now I just need to solder mask off that little trace that goes under the half bridge IC chip. #robotics #android #gynoid #electronics #diy #handmade

So the plan I have for the heat sinking main conductors that attach to the bottom pads of the IC chip I decided to draw up to explain it. It will be in layers. First you have the chip on the bottom facing bottom side up so the pads are exposed upwards. Then on the first attachment layer I cut out matching shaped copper plates from copper sheeting and solder that down with low temp solder paste and a soldering iron. In theory, this first layer attachment will basically just be extending the pads up past the viewing window of the DIY PCB with cutout viewing window we've made so far so that the DIY PCB we made so far and this first layer of copper plates together act as layer 1. Ideally the copper plates would be slightly proud of the printed PCB in height I think. This first layer copper plates that we are soldering onto the pads of the IC carries the current and the heat sinking to layer 2 without the need for vias. In a multi-layer PCB made industrially, vias would take the heat sinking and current to layer 2 of the board and we are just using solid copper plates instead which should be even better than vias because its solid copper instead of just via holes so more surface area than vias would offer. Now on layer 2 we can create a much larger sheet that extends out past the PCB way off the chip and that portion that extends way off the chip acts as a tab we can solder the V- wire to. It also acts as a tab we can solder our 6 strands of solder wick wire that act as heatsink fins to. Layer 2 also has a plate that brings the V+ to layer 3. For layer 3 we just attach a large sheet of copper which also extends way out past the chip and acts as a tab we can solder our V+ wire to and our heatsink solder wick wires to.

Ok I used the tip of my exacto knife to carefully scoop on low temp solder paste and then carefully drag soldered it over the key areas I wanted pre-tinned. There do not appear to be any short circuits and the amount of solder on each pad and trace seems a decent amount to me. I forgot to wipe it with alcohol wipe but have done so since taking this snapshot. The next step is I have to carefully uv cure solder mask that little trace runs under the IC chip. It definitely will short a pad to something I think if I don't. I have to apply it very thinly so it doesn't prevent IC chip from seating flat and soldering into place well.

So as I fast approach motor controller wiring phase, I figured I would revisit placement again. Upon further reflection I decided hovering midair motor controllers attached to nothing might not work as they'd perhaps be a bit in the way of getting at the motors and just be a bit overwhelming. I'm not positive on this and could revisit the concept but for now I'm thinking of just mounting it side saddle onto the motor again. I decided to place them side by side with inlets on the output shaft end and outlets on the BLDC motor wiring's end. I drew this sketch of the layout and wire flow as a visualization aid.

Here's the center cutout now which was the last thing I needed to do before soldering down the chip. This access window will enable me to solder the main power lines to the main pads on the bottom of the chip. The circuitboard is aimed at tying into the various perimeter pins of the chip but this window is for the high power lines on a separate layer below. I was able to cut this window out with the highest zoom setting of my magnifier visor (I think like 20x zoom?) and an exacto knife. Quite a challenge but made it happen!

I got together my temperature sensor and my hot plate and my glass container and some water and figured out where on the hotplate temp dial I need to be to get the desired water temperature. I then used label paper sticker and marked it off and wrote 118f on it which is the average temperature of that spot on the dial. It has about 15 degrees variance I think up or down. Good enough. Next, I mixed up a batch of water and PCB etchant (Ammonium Persulfate crystals and water mixture) using a postal scale to get the ratios right. I mixed it into the bottom third of a wet ones baby wipes container. It was 0.8oz total. Then I submerged the etchant mix into the warm glass basin of heated water to bring it up to temp. I noticed the etchant wet ones container wanted to tip over so I used scotch tape to tape it off in all 4 directions to the glass container and pull it under water a bit too in order to maximize temperature transfer from the hotter outside water into the etchant container contents to warm it efficiently. I skipped the automated agitator entirely opting to just stir the mix with a hot glue stick manually. All in all, it did etch within the 5 to 8 minutes range and I think etched even faster when the temperature was closer to 130f - closer to 5 minutes then maybe even 4 minutes I didn't time it. It was lightning fast compared to room temperature etchant which took 2-3 hours to etch a single board. So indeed, the instructions that said room temperature is fine were wrong. All that leads to is undercutting. Anyways, with the stirring and the warm temps my results were significantly improved and almost every board was usable. I produced 8 or 9 in total. Enough to do at least 2 motors and part of a 3rd at least. So plenty for now. I had still a tiny bit of undercutting on the fine traces, but rarely enough to break their continuity. I will make the traces slightly wider in Photoshop for future prints with the expectation that around 15% of the outer edges will be removed so we print wider to compensate and then the result will be the width we wanted in the first place after the undercutting has done its thing. This way the undercutting is worked with and non-detrimental. That's my planned workaround for it. In the rare instance of pinholes randomly in the center of pads or traces or a tiny open circuit on a thin trace, I am confident that a coating of solder over all of those areas will correct that. These little holes and whatnot are microscopically small so very easy to solder bridge as needed. I think for the most part my boards are almost all fully usable as is. I'm sure my methods will improve as I continue to tweak and iterate techniques over time - but the fact that we can already produce working circuits at this extremely fine detail and miniaturization level is already very encouraging. Any improvements from here is just icing on the cake IMO. My next step will be to solder on the half bridge IC chips using the method shown in this video - a method I think looks very impressive and sound and hopefully not too hard to replicate on my end: https://www.youtube.com/shorts/r-HaRjBvWgU

Full Post: https://forum.allaboutcircuits.com/ubs/llm-assisted-coding-custom-ecosystem-i-am-creating.1927/

The n20 gear motor is like $1. Super easy to make. Can handle my 15g of etchant sloshing easily. Simple to make. Does not have anything going INSIDE the acid which would then be spinning and crashing into the PCB and possibly causing issues there. We want just a bear minimum amount of etchant batch per PCB job and so even a spinning stir rod with magnet setup would be hitting the PCB and tossing it around violently etc I didn't want that and didn't want acid on that and having to fish it out and clean it of acid. Prefer nothing going into the acid but the PCB itself. So rocking the whole container makes sense for this and resolves that problem. The rocker apparatus consists of a n20 gearmotor ($1 on aliexpress), a little wheel (paper and superglue composite wheel), string, a little block to get the motor up higher in placement than the etchant container. As the n20 gearmotor rotates it lifts the string, raising up one end of the etchant container. As it reaches 180 degrees of rotation (6 o'clock) it has lowered the etchant container back down. It repeats this raising and lowering of the container over and over in a cyclic pattern which will cause the etchant solution to slosh back and forth over the PCB improving the rate of the chemical etching reaction and moving copper ions away from the PCB surface being etched more efficiently. No pwm motor controller is needed I don't think since you can change the rock speed by changing voltage setting on the lab power supply and/or changing radius of the wheel that is turning and doing the lifting and lowering action.

So I ran into some issues trying to make the DIY flex PCB for my integrated half bridge IC chip. This chip has extremely fine 0.4mm pin spacing so the PCB has to be insanely accurate. My previous discrete components BLDC motor controller variant enabled me to create much more crude and less dialed in flex PCBs and things still worked. But with this flex PCB it has to be very dialed in and with very high execution precision. This is no joke. The first issue is that my laser printer does not adhere well to the pcb transfer paper I bought on amazon. It prints on it with some of the toner showing up mirrored a inch or so away from where the print originally lands onto the PCB transfer paper. This means the ink isn't setting onto the transfer paper enough and is coming off onto the fuser roller or something and that is corrupting the fuser roller. This can destroy my printer's performance over time and cause improper fusing onto all prints going forward even for normal office use which means addresses I print on envelopes are smearing off while in transit and envelopes are being lost in the mail system for me. This is VERY VERY bad. So I had to ditch using this transfer paper. Thankfully chatgpt recommended using glossy magazine paper and so I gave that a try. I used Psychology Today magazine paper and the print went onto there PERFECTLY. I used 600 dpi setting, heavy as paper type. I prepped my copper flex PCB blank (Pyralux) with 400 grit sandpaper followed by alcohol prep pad wipes. Next, I laminated the glossy magazine paper print onto my copper flex PCB blank (Pyralux) with my laminator a few passes. Next I soaked the magazine and flex PCB sandwich in 110F water for around 30 minutes which turned the glossy magazine paper mushy/pulpy. I then rubbed the paper repeatedly with my fingers working from the outside edges and was able to roll it off gradually and gently. It came off in two layers. It leaves a bit of pulp residue behind on the pads but that is ok it doesn't affect the etching process later you can leave that. And with this method I got the cleanest traces on there EVER. But when I went to etch this clean PCB with toner in place, things fell apart again. I used room temperature water with my Ammonium Persulfate crystal and water mixture. So it was 68F water. I did not agitate the etchant much. The etching took about 2.5-3 hours! That is horrible etching speed. The larger copper planes took their dear time to evaporate and meanwhile the finer traces had undercutting so bad that the entire copper under the toner etched away and evaporated and the toner came off having nothing to stick to anymore and whose sections were lost. The total etching time is supposed to be no more than 5-15 minutes. 3 hours is totally unacceptable. I found out from chatgpt that the reason it took forever was I failed to heat the etchant to 110-120F and I failed to agitate the mix (stir or vibrate or w/e helps). I also learned from chatgpt that for every 10F increase in temperature of the etchant, the etching time cuts in half. So a increase to 110F will mean the etching time should come down to the 5 minute range pretty likely if I also agitate well. The instructions on the container of etchant crystals said room temperature and no agitation is fine. THEY WERE WRONG for SURE on that. So to address perfecting the etching process I plan to get a AC hot plate with temperature adjust which I already own - one for like pans or kettles cooking/heating. I also determined that the easiest way to agitate would be to put the etchant and PCB in a small container and create a apparatus that lifts and lowers one side of the container in a rhythmic way so that it rocks the etchant back and forth across the PCB. Below is my simple apparatus design for that. The advantage of this approach is its free if you have the very few parts needed. I can power it with my lab power supply.

Also, I have separated out the PCB traces themselves and made them black instead of blue for printing them onto the PCB transfer paper and laminating this onto the blank Pyralux flex PCBs for etching them. I also mirrored it since it prints and laminates backwards onto the PCB.

Ok so I was thinking now that each half bridge is just a tiny IC rather than a pair of hefty power mosfets, the space taken up overall by my entire bldc motor controller is going to be about 3cm x 1cm x 2mm which is insanely small for 30a continuous at 8v motor controller! This realization caused me to reconsider whether I even need to treat this as a single motor controller cluster that has to be sat like a horse saddle onto the side of my bldc motor - my original intention for my discrete components original design for my original bldc motor controller. What I realized instead is that things are now so small that I can simply build a half bridge for each phase as a inline element nexted inside the cable run leading to each phase wire of the bldc motor. So instead of having a dedicated spot for each motor controller, I'm going to have just a slight bulge in the phase wire leading out from the bldc motor and that buldge will contain the half bridge that handles that phase wire. All nested inline. This is the easiest way to implement and most streamlined I think. It also means the whole motor controller will just be "floating" in midair, not actually mounted to any motor or anything at all. Just part of the wire harness nested right in there. This is a radical approach IMO. Only made reasonable by the fact we miniaturized the design by such an insane degree. So the previous version of the schematic was intended to be mounted to the side of the motor like a horse saddle and had an l shape so inputs would come up from bottom and outputs out to left side toward motor phase wires. These L shaped half bridge setups would be stacked next to eachother side by side. In the new variation everything is inline, inputs coming from right and outputs exit out left side to motor. Here's the updated inline variation of the schematic (no longer L shaped flow like before).

Well I deep dove into the CSD95481RWJ IC route. I estimate it will cut the work in half roughly for every motor controller made and cut the size taken up by about 60% compared to my previous discrete components approach. Now I will note that I did come across the BTN8982TA which is rated to 40v and can handle 30a continuous 50a peak short burst. But it's TO-263 form factor so about 4 times as big as the CSD95481RWJ. It also costs about $2 each so double the price. It's not a bad option though all things considered but just not quite as good as the CSD95481RWJ for the reasons mentioned. I note it here so I don't forget about it. It can be a great option if the CSD95481RWJ doesn't work out in the end or something. Anyways, for the thermal concern - which is my biggest concern, I plan to top cool the CSD95481RWJ using a .2mm plate thermal siliconed into place on top of the CSD95481RWJ and then solder a bundle of 4 braided solder wick wires to that and run that off to the water cooled copper pipe about 4" away. The top cooling only handles about 30% of the cooling according to chatgpt. The most important 70% is from the bottom cooling through its pads on its bottom. For this I plan to use double stacked .2mm thick copper plate soldered to its IC pads. So that's .4mm thick. Also it will be around 2mm wide where it attaches to the pads. It will then route out from under the chip and swing upward into free space and head over to the 8v+ and 8v- buses coming from the 8v motor battery banks in the robot's lower torso. These thick copper traces I will fork off of with braided solder wick wire right near the CSD95481RWJ IC chip for thermal conductivity reasons. This braided solder wick wire will be live so I will wrap it in fiberglass window screen so nothing can touch it - preventing short circuits. It will then be electrically isolated from where it connects to the water cooled copper pipe with thermal conductive tape. The braided solder wick wire attaching to these thick copper traces will be a bundle of 4 per trace. The various decoupling capacitors this chip calls for I will connect to its output pins using flat flex PCB DIY hand made. I'll be attaching this PCB first and attaching the thick copper traces to the underside pads second as a separate layer that goes underneath the flat flex PCB layer. The flat flex PCB layer will mostly stay around the outsides of the chip and have its center cut out and removed - the part of it that would get in the way of the underside main pads under the chip. So the flat flex PCB will just hug the outsides of the IC mainly in a U shape around the chip leaving the center of the bottom of the chip free to solder to with my thick copper traces. Note: the thick copper traces will be cut out with scissors from a roll of .2mm copper sheeting I bought on amazon which I mentioned a few posts back. Double stacking it wil double its thickness and increase its conductivity both electrically and thermally. Note: in a usual setup with this CSD95481RWJ IC, a multilayer board with a array of vias is used to bring the heat downward off the chip and into another lower layer within the multilayer board where it can then radiate on said layer outward in every direction. In my approach, I use thicker traces than the layers of a multilayer PCB has so I have alot more local copper in play.

I was randomly talking to chatgpt about how I have been feeling burdened by having to make my own BLDC motor controllers for my robot lately and it randomly mentioned integrated half-bridge power modules as something I could use to cut down on my labor load in making these motor controllers. This immediately stood out to me as something I'd never heard of and something intriguing. I have so far been working on my lowside switch and highside switch which together form a half bridge. Many solder connections have been involved and alot of discrete components are involved. The concept of an integrated half bridge on a single chip - meaning two big power mosfets and all the drive circuitry for those power mosfets all condensed into a single chip would be a huge reduction in size and component count as well. So I researched if any are able to do 8v 30a for my 2430 BLDC motor's needs. Turns out there are some out there. At first I was looking at Texas Instruments CSD95377Q4M Half‑Bridge Driver (30 A) which can do 30a continuous so perfect for me. However, I didn't want to lock myself into a single vendor chip that may one day be discontinued. I prefer something ubiquitous with many competitors making it that can be purchased from aliexpress. Something commodity level. This way I future proof it and don't have to worry about any one manufacturer discontinuing parts I'm using and prices soaring because of that or simply the part becoming unavailable. So after a bit further digging I found CSD95481RWJ QFN chipset on aliexpress sold by several vendors and one was under $1 each. So it is equivalent to two power mosfets plus all drive circuitry for each power mosfet all for under $1. This one also has 60a continuous rating. It is only 5mm x 6mm in size which to me is insane. This is so much smaller than the setup I've been working on yet just as powerful. They are usually used for tiny buck converters and used directly on videocard PCBs and in servers and in automotive PCBs and much more. In any case, using 3 of these half bridge chips you can drive a BLDC motor. The consolidation of so many parts into such a tiny package is truly blowing my mind. So I ordered 60 of these chips - enough to drive 20 BLDC motors. I am leaning toward using these for all my motor controllers if working with them is easier than working with discrete components like I have been. They are cheaper to work with I think - I'd have to run the numbers on that though. They even have built in temp sensing we can read in which is a bonus. Their built in current sensing will not work for BLDC motors so I'll still need my shunt resistor current sensing circuit setup external to it but that's ok. All in all these appear to be a game changer in terms of reducing part count so less potential points of failure and also reducing board footprint so miniaturizing my electronics even more which is very good for us. I'm still needing to work out now how I want to hook these up in terms of PCB making for it and any discrete external components needed to support it.

I used my jumbo Weller W100P soldering iron to attach my 6 solder wick braids to the back of the highside mosfet today and it attached instantly without a hitch. I used low temp solder paste liberally between the two on both surfaces then with my left hand smashed then together with the tip of a xacto knife pressed down onto the solder wick braids from the back. Then I brought in the giant soldering iron and it liquefied the solder in about 1 second despite all that metal involved because it holds such a massive amount of thermal energy that it can deliver on demand very quickly. Such a easier time than trying to do bigger soldering jobs with a micro tip regular soldering iron which often ends with cold joints and stuff. Also since the liquefication went so fast nothing nearby desoldered which is a huge plus. Next up: add the solder wick braids to the underside of nickel strips to lessen resistance there and then insulate this highside switch assembly and install against motor and start finalizing wire run plans. Then I can rinse repeat this for the lowside switch assembly. Then I'll have one of the 3 half bridges done for the motor controller.