My Advanced Realistic Humanoid Robots Project

Project Logs

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Flexible PCB Making - Improvements and Issues
Larry • 7 hours ago • 0 comments

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...
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BLDC Motor Controller Schematic Optimizations and Prepping for Printing and Etching Custom PCB
Larry • 01/25/2026 at 23:29 • 0 comments

Ok so I realized I don't have to feed in 8v+ from an external wire when I can just pull it from a neighboring pin on the chip that has 8v+ already fed to it from one of the big 8v+ copper traces attached to one of the big 8v+ pads on the underside that connect directly to one of the side pins. That side pin can then be routed to any 8v+ requiring pins if I can find a path for this routing - which I did find. So that is one less external wire input needed - bringing total external input wires needed to 3 instead of 4 as far as the 30ga wires I need to attach. So now all I need for 30ga wire attachments are 5v+ from arduino, GND from arduino, and PWM from arduino. This saves work and simplifies the wiring so its a great improvement.

Oh and I also did the same thing for the 8v- feed, pulling it from a local pad rather than a external wire feed for that.

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.
Inline Half Bridge Per Phase of BLDC Motor Built into Wire Run Idea
Larry • 01/20/2026 at 19:47 • 0 comments

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 nested 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 bulge 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).
Fixes to Discrete Components BLDC Motor Controller Variation Schematic
Larry • 01/20/2026 at 07:54 • 0 comments

OK, so when I was thinking of using both my discrete components motor controller design parts I already made and then also separately implementing the integrated half bridge IC design going forward, it hit me that the 8v- and arduino gnd tie together on the half bridge IC by necessity but this ruined their intended isolation I needed for my discrete components motor controller design particularly for the lowside switching portion of that schematic. On the lowside switching portion, the little mosfet has 12v- and arduino gnd tied to its source pin. If on the integrated half bridge I also have to tie arduino gnd and 8v-, then that means 12v- and 8v- and arduino gnd are all tied together always.

That completely ruined the necessary isolation between arduino gnd/12v- and 8v- that I had intended to be in place for my lowside switch setup. So that was bug #1 freshly introduced that I would then need to solve for in my discrete components motor controller design. When studying this out on the discrete components motor controller design, another error hit me: when any lowside switch turned on in the design, the 12v- dedicated power supply gnd and the 8v- motor supply gnd become connected as long as that lowside switch is on. Since every lowside switch had always access to 8v gnd on its source pin, then even one moment of 12v gnd and 8v gnd attachment anywhere on the robot would cause every lowside switch in the entire robot to immediately turn on at the same time. So if any turned on, then all turned on. This was a huge oversight. For some reason since I only designed and focused on one half bridge conceptually at a time, I did not consider the effects one half bridge has on its neighboring half bridges. This just never occurred to me. I guess conceptually I envisioned that every half bridge had its own personal 12v ground from its own personal 12v supply that was electrically isolated from the entire rest of the robot. But of course that's not practical even if it is technically possible. So in testing, things did work, but would have failed as soon as I tried to test more than one half bridge at a time. So I caught this bug before testing revealed it.

I discussed this horrible situation with chatgpt and it taught me that in a complex system like a robot, grounds of all your different supply rail voltages cannot be relied on to be isolated from one another like I was treating it. Even if at times they were momentarily, one switch, one change and suddenly they are not and it all becomes a common system ground again. So if I can't safely assume a ground for any given voltage is safely disconnected from the grounds of other voltages, I should not rely on switching on and off access to any particular ground to any of my lowside switches. Instead, I should be shorting the gate driver of the lowside switches to ground to shut them off rather than messing with their source pin's ground connections like I was before. I am to leave the source pin's ground connection as 12v- and its gate connection as 12v+ at all times except when I want to shut it off - at which point I short the gate pin to gnd using my logic level mosfet to do so.

The fix was very straightforward and minor: I just had to add a 100ohm resistor in series with the gate pin of my big power mosfet lowside switch and then reroute my little mosfet a09t drain pin to the big lowside mosfet's gate pin instead of its source pin. The connection to its gate pin must be downstream of that 100 ohm series resistor so that the path from the big mosfet's gate pin has almost zero resistance when traveling through the little mosfet's drain line and over to its source line into ground. This way when you turn on the little mosfet, the big mosfet's internal capacitor quickly empties out, flushing into the path to ground created by the little mosfet and that discharges the big mosfet, shutting it off. When you want it back on, you shut the little mosfet off, which allows the big mosfet's internal...
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Schematic Changes to Use the Integrated Half Bridge IC Chip for my BLDC Motor Controller
Larry • 01/18/2026 at 08:34 • 0 comments

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. Then instead of the heat transferring down and then outward in all directions on very thin copper, mine travels down then in a single direction outward away from the IC on that trace. The trace will need to be as wide as possible as soon as possible. I expect to get it from 2mm width - the width of the pad - to 5mm width within a few mm. This rapid transition to a wider width combined with the use of much thicker copper compared to a multilayer PCB's copper thickness of its layers means I should be able to exceed the thermal performance of a multilayer board using my approach. Especially since I also plan to quickly fork off...
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Half Bridge Integrated IC Chip Discovery for Use In BLDC Motor Controller Design
Larry • 01/17/2026 at 05:27 • 0 comments

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. It is also top cooled which is interesting. I'm envisioning using silicone thermal adhesive to glue on a copper pad that has my braided solder wick wires already soldered to it. These will carry the heat away to my water cooled pipe system.

I'm kind of amazed that nobody really seems to use these for BLDC motor controllers. They seem perfect for it. Maybe I'll start a trend. Assuming I don't find out the hard way why they are never used for this application!

note: the full product title: "(5pcs)100% original New CSD95481RWJ 95481RWJ CSD59950RWJ 59950RWJ QFN Chipset"

note: for my previous BLDC motor controller design I was needing to use 6 digital IO pins to drive a single BLDC motor controller's 6 power mosfets by way of their control circuitry. But for a BLDC motor controller design using 3 CSD95481RWJ H-bridge chips, I will only need to use 3 digital IO pins on the microcontroller. These CSD95481RWJ H-bridge...
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Custom BLDC Motor Controller Progress Update
Larry • 01/03/2026 at 21:50 • 0 comments

So I did manage to add a pair of braided solder wick wire as a added layer over the nickel strips of the highside mosfet setup and I insulated that with red electrical tape folded over it. I also insulated everything else in sight for the most part. I lost the original control circuit so I made the replacement flat flex pcb style which should be more robust. I also added a yellow 30ga wire for the 20v input line of the gate pin of the main mosfet. I also got my fiberglass window screen mesh ready to be installed to insulate the solder wick wires acting as heatsinks. So this setup is getting close to install ready now but I want to test it again to make sure its still working after all the major changes and messing with it so much.

On another note, I noticed that stacking the 0.1mm x 4mm x 100mm nickel strip plus braided solder wick to reduce resistance and increase conductivity made the lines a bit thicker than I'd like, especially after adding tape. So to resolve this I decided to roll with 0.2mm x 6mm x 100 mm hand cut out strips of pure copper plate. I was not aware of this option before but I was able to find copper in .2mm thickness in a roll on amazon that I can use for this. With this thicker size and the much lower resistance of copper I should be able to run 30a through it with less than 1w of waste heat which is great. And this will still give me a way thinner result than what I used on this first one while lending lower resistance by getting rid of nickel strip entirely for the high amp stuff (aside from the shunt resistor nickel strip which I still plan to keep).
A Frustrating Session but Lessons Learned and Pivots Made
Larry • 12/25/2025 at 04:55 • 0 comments

Well I tested printing directly onto Pyralux copper and it was a massive failure. Not even one spec of ink stayed on it and the print came out a inch off the location of the copper. Chatgpt said this is because copper can't hold a electro static charge long enough to take ink onto itself or w/e. Ah well I can fall back to the method I already used successfully.

On that note, I realized printing my blue circuit is bad since a black and white printer won't print as densely and darkly a blue thing as it would a black thing so I have to make my circuit black before printing it. Also I should set my dpi to 600 dpi instead of 1200dpi which will create denser thicker prints for better transfer. Also I should select label paper instead of heavy paper which will work better. Also using Lumicolor Straedler pen is not good as it can be undercut easily supposedly. Better to use oil based marker instead. So I ordered that in 0.3mm tip. These are all improvements chatgpt suggested and I plan to use when printing onto the pcb transfer paper and hand touching those up if needed. I'm getting ready to make a bunch of flex pcbs for finishing this motor controller. I already started doing it.

Another disaster happened to me as well: my highside circuit I just soldered the solder wick wire onto, when I was analyzing it closely on the front I noticed that excess solder from the drain side of it oozed and dripped toward the front side of it and attached to the gate pin! I heated up that attachment point from the front side and my capacitor and resistor from gate to source both came off from the heat! Anyways I heated it up to remove that short circuit and used a xacto knife to wedge between the gate pin and back of mosfet's drain pad which had a solder bridge. I got through the bridge successfully but now have to redo the gate to source resistor and capacitor. Ugh! Two steps forward one step back. Then while inspecting and cleaning everything I moved the control circuitry a bit too much and it broke off for the 3rd time! So that has to be done again. This time I'm using flat flex for it. I've had it with the non flat flex variant breaking. The flat flex is way more solid mechanically. So that's a redo needed. Ugh.

Then to top it all off, the solder wick braids recent idea I had to electrically isolate their run near to the mosfet so that they aren't live for very long - which had to do with wanting to eliminate any short circuit risks in their longer run as well as remove any potential for antenna affects - yeah... well after cutting them all in half to do this transition idea, as I was doing it, I realized the surface area where the hand-off takes place between one section of solder wick braid and onto the next seems very small to me (2mm wide by 6mm long) and it seemed to me that the passage of heat across this tiny bridge of thermal tape might be severely compromised and would depend on how tight I made the squeeze of the two pieces of solder wick braid together as well. And I'm not sure I can clamp it tight enough with just tape wrapping it firmly. And if it gets quite hot I'm concerned electrical tape will get gooey and come loose over time and not hold it well. I'm not sure how tight kapton can wrap things I've never used it before so I'm inexperienced with using it and trusting it is hard without experience working with it. This all cumulatively gave me enough doubt that I said heck with it, I'm going to revert to the former plan to just run it live over to the water cooled pipe 3-4" away and use the thermal tape at that junction point where it wraps the pipe. This ensures alot of metal volume is directly tied to the mosfet which means more heat sinking directly with little risk of trapping heat near mosfet - which could happen if my thermal tape junction of copper braid to copper braid were to fail for example by being pulled apart by accident for any reason. Too much risk there IMO. And the risk of a short on account of live wiring it for 3-4"...
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Electrically Dividing My Heatsink Wire Runs Idea
Larry • 12/23/2025 at 21:15 • 0 comments

So it hit me that having these braided solder wick wires live all the way to the water cooled pipe distal attachment point is not necessary. And could cause some EMI or noise related issues that is avoidable if I do the following: I can simply cut them off 1/2" from the mosfet, stick thermal tape on one face of the cut off stubs, then stick the rest of the braided solder wick wire run against that thermal tape, then wrap this joint tightly with electrical tape. Finally we then electrically insulate the braided solder wick that is live but leave the braided solder wick section that is now no longer live completely exposed on the duration of its 3"-4" long run from near the mosfet to the water cooled pipe. This way we have electrical isolation near to the mosfet, no antenna effect, no need for window screens now, and no live wires hanging out that aren't properly insulated. Thermal conductivity is reduced negligibly with this solution. This should be trivial to implement as well. It's the perfect solution here and very fast to implement. It may even be slightly less work than dealing with window screens would have been.
Attaching Solder Wick Braids as Heatsink Success
Larry • 12/23/2025 at 04:47 • 0 comments

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.