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21
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 23, 2025, 03:17:29 PM »
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.
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Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 22, 2025, 10:53:35 PM »
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.
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Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 21, 2025, 09:43:40 PM »
I did some research of some loose ends today on chatgpt and discovered that my .1mm x 4mm x 60mm sections of nickel strip on my bldc motor controllers that run from the battery to the motor controller mosfets and from the mosfets out to the motor are too high in resistance and at 30a they would within a few seconds get so hot that they would desolder my low temperature solder paste. So to solve this I will be placing two side by side solder wick braids hugging the underside of the nickel strips which will lower resistance so much that temperature will stop being an issue. They will be a combined .1mm x 4mm x 60mm. Then on future mosfets for this portion I will just use the solder wick braids for this section and not use nickel strips at all because they add too much resistance under this high of amp flow. The 2430 BLDC motors are rated to 25a continuous so my conduit has to also handle that easily without overheating.

Another really cool discovery I made today was on the topic of measuring current. I'd been putting this off till now but finally got around to deep diving it with chatgpt and discovered something shocking. So basically it was saying to use a shunt resistor inline with the ground side running from the motor controller to the battery. All the current of the motor controller (30a on the high end) will pass through this resistor as its only path. The special thing about a shunt resistor is that its resistance is so low that it doesn't affect voltage or amps a whole lot. I asked chatgpt if I can use nickel strips as my shunt resistor since a smd shunt resistor it said would overheat fast at 30a. It said yes! So I'll be using a .1mm x 4mm x 30mm section of nickel strip as part of my wire run going from the motor controller back to the battery on the ground side. This will act as my homemade shunt resistor. Now the way the arduino will read the amount of current is the analogue input pin will feed into the upstream side (closest to motor controller) of the shunt resistor section of nickel strip and the arduino ground will attach to the downstream side of this nickel strip shunt resistor. It will measure the tiny amount of voltage drop that occurs on account of the shunt resistor's resistance. What is really cool is that the voltage drop changes at this resistance and amp level are read granularly enough by the Arduino analogue input pins that I don't even need to amplify them to read them in meaningfully. Some things like strain gauges provide such tiny resistance changes that you have to use a OP AMP amplifier to be able to read the changes in with your analogue input pin of your arduino to detect them meaningfully but in this case, the resistance changes are large enough and the analogue input pins are granular enough to be able to read them in without any amplification. This means reading in the current for my motor controllers requires ZERO components! It's literally just nickel strip which I already had for the battery tab making and some jumper wire or w/e to take in the readings and that's it! No parts to buy. I had bought some hall effect based current sensor kits and they are not needed at all. I wasted my money on them in the past because I did not know about this shunt resistor option at all at the time. Had I known I would have never bought hall effect based sensor kits - a waste of money. Not to mention they were relatively huge whereas this takes up like practically zero space to measure a shunt resistor section of conduit between the battery and motor controller. So it's awesome news!

Note: the current sensing is meant to tell my control system anytime a new unexpected load has hit the motor so it can slow down the flow rate of electric to the motor to prevent burning out something for example or it can also detect any kind of snags or w/e anything getting stuck. It can also help monitor amp flow for the sake of holding the motor in place with stall current kept low enough to prevent overheating etc. It can also act as collision detection if trying to monitor its interactions with its environment and know if something has hit something - which is insanely useful for situational awareness. So it's extremely useful and basically not even optional frankly. To now know that adding this feature is free and super easy to implement and will take up practically ZERO extra space is very exciting to me.

Note: my diy shunt resistor (.1mm x 4mm x 30mm section of nickel strip) will have a .005 ohm resistance which is pretty much perfect for my use case it seems (unproven but chatgpt sounds sure of it). It will enable me to monitor the range of 5a to 30a and detect a change in amperage with like 1a granularity.
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Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 19, 2025, 02:33:40 PM »
I have two great breakthroughs to announce.

First, it suddenly occurred to me that I don't have to print onto PCB transfer paper and then transfer that over to the copper clad Pyralux flat flex PCB but instead I can simply tape the copper clad Pyralux flat flex PCB directly onto my envelope and feed that through my laser printer directly. See, I previously ruled this out when originally researching this stuff because I was planning to use FR-4 PCB which is not flexible nor flat enough to feed through a printer directly. However, now that I am using flat and flexible blank PCB there's no reason not to feed it straight into my laser printer that I'm aware of. Now I haven't tested this but if it works it's a game changer. Will make DIY PCBs that much faster and more streamlined to make!

Next, on the subject of attaching the 6 solder wick braids to the mosfets, I was struggling going through the various methods whereby I can tightly clamp it to the mosfet drain and add electrical isolation barrier to the connection point. It's very tight spacing and has to be a very tiny clamping mechanism and the clamp from most directions would have things getting in the way of any clamp design I visualized. It was a nightmare problem IMO. However, my solution I came up with today is game changing: I will simply solder the braids directly to the mosfet drain! This will maximize conductivity off the drain into the braids due to the metal on metal direct connection and eliminate all need for any kind of clamping at all there. Unfortunately, this will make these braids live electrically, but it occurred to me that this is not a big deal. I will simply wrap them in fiberglass window screen to allow them to have great airflow and breath-ability for emissivity of the heat they will be wicking off the mosfet drain and the fiberglass window screen will also act as a physical barrier to them contacting other live metal parts. Window screen is also non-conductive and has good abrasion resistance IMO. I don't anticipate these short wire braid runs to have much contact with anything as they are going to be making short runs from the motor to the water cooling pipe anyways and the exoskeleton mesh that holds up the rubber skin will create spacing and cushion contact bumping or w/e coming from the outside. All in all I think this is a safe solution for the most part and we'll have fuses anyways to prevent major problems in the low risk event of two neighboring live groups of solder wick braid breaking out of their window screen and contacting eachother thereby shorting the circuit. I just see this as highly unlikely but it's covered by the fuse in any case.

That all having been said, the electrical isolation barrier stage we now can place at the location where these solder wick braid ends attach to the copper liquid cooling pipe. There at that attachment point I'll put my electrically isolating thermal tape between the solder wick braid and the pipe and clamp things down by tightly wrapping it in electrical tape at the connection point. This is trivial to achieve compared to doing this at the location of the mosfet drain. So we kicked the electrical isolation and clamping problem further downstream than the mosfet drain connection point in order to make the problem a piece of cake.

Note: chatgpt said I should tin the braided copper solder wick to prevent oxidization of it which would potentially lower its emissivity. Not sure I agree on this though but I may do it just to be safe we'll see. I'd use MG Chemicals Liquid Tin to do this which I already have on hand for tinning circuit boards.
25
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 07, 2025, 02:30:41 PM »
Ok here's the populated board. I tested it with 5v positive and ground and the LED came on so it is for sure not shorting and has continuity so is most likely all working. The next test will be the full low-side switch with this board acting as the drive of the main mosfet for the switch. And once that is validated we can test the entire half bridge (both high and low-side switches). If that checks out, it's all rinse and repeat to make the full motor controller (which is just 3 total half bridges).







note: I just wanted to hold off on attaching the heatsink for the moment as I validate the first half bridge and once that checks out electronically then I'll get the heatsink attached and go from there.
26
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 06, 2025, 09:44:50 PM »
I successfully made a viable flex PCB on my second attempt.



I started by printing the circuit onto a mailing envelope using my laser printer. Then I taped a piece of toner transfer paper for PCBs shiny side up directly over where the print on the envelope was. This way I could use just a tiny bit of the expensive toner paper and know the printer would hit that exact spot again when I reload the envelope in the same spot.







The print landed right on the toner transfer paper according to plan.



I then sanded with 400 grit sandpaper the Pyralux flat flex PCB copper blank and wiped it off with a alcohol prep pad. These actions clear any oils and oxidation and give more bite for the toner to cling to the board better.



I then taped directly onto this toner transfer paper print the Pyralux flat flex pcb copper blank. No need to even take it off the envelope. Just taped it right over it and fed the whole sandwiched assembly through my laminator a few times envelope and all.







When I peeled back the Pyralux flat flex PCB my laser printer's toner was indeed transferred over to the Pyralux flat flex PCB's copper.







I prepared etchant solution mix of 1 part etchant powder to 4 parts water. I just eyed this roughly and think I did not put in enough echant which causes undercutting of the traces under the toner and slower etching. Lesson learned.







I mixed it in a silicone earplugs container. My aim was a small container to make a smaller batch of the etchant to cut down on etchant used since I'm only doing a very small PCB.











The first board I left etching for a couple hours unattended which was a mistake. It was unusable. A ton of the copper under the toner was missing which is called undercutting. I left it etching for too long which causes this.



The second board came out pretty good. But I used the exhausted etchant from the first board which was already too diluted and so the results were meh but good enough to use IMO.







Note: the prints going onto the toner transfer paper are not very high quality and sometimes has missing spots so AFTER transferring it to the copper I used a Straedler permanent lumocolor super fine tipped pen and magnification to carefully color in any missing spots where the laser printer failed to deposit enough toner or the toner failed to transfer perfectly enough. I used stippling method with the pen - just dotting over and over rather than drawing to get max precision for cleanup of the tiny pads and traces on the copper.



Note: I never had to use water to remove the toner paper from the pcb. Just laminating it a few times through my laminator was enough for the transfer to take place and I was able to cleanly peel it away. This meant the toner transfer paper could remain taped to the envelope and be reused indefinitely. I reused it a few times successfully as I dialed in the processes. This is very nice. Saves time for sure.



Note: I did attempt to not sand nor alcohol treat the Pyralux copper PCB blank and toner transfer onto virgin copper blank but it did not adhere well enough so I reverted to the recommended sanding and wiping after all. Was worth a shot to save steps but did not work out.



Note: I used heavy paper setting in Photoshop during the print dialogue settings because the normal print settings were kind of messing up for me. I also think this printer is not very well suited for this. My other laser printer has a "best" quality option and did very nice prints but this one is a cheapo I'm using and only has "fast" quality but worked well enough nonetheless for the most part.



Note: I assumed I could use this etchant over and over and over but chatgpt said it gets exhausted and loses efficacy and should only be used once. Some acids people made online you could use over and over but I guess not this type not sure.



Note: the acid etchant I'm using says it only releases oxygen so the fumes I guess are not bad like some other kinds of etchant - correct me if I'm wrong on that though.



Note: I used a q-tip and lacquer thinner to remove the toner after the etching was done.
27
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 05, 2025, 11:01:24 PM »
So armed with my successful electronic test of my prototype highside switch with driving circuit all passing, I determined now it is sufficiently validated to go through the process of converting it into a printable schematic and doing the whole DIY flat flex PCB making and acid etching process to streamline the development of the rest of the motor controller and most likely many more motor controllers as well.



I opted to use photoshop as my circuit making software of choice as I'm very familiar with it and use it often. I first dropped my top view photo of my prototype circuit into photoshop then I redid its layout a bit to make it more compact, moving around copied pieces on the photo to achieve this. Next, I used the pencil tool to color in blue pads and traces connecting all the pieces of it together. I then hid all but this pads and traces layer and printed it several times, tweaking the printing scale until it fit the size of the pieces IRL. 7.5% scale was the perfect fit.











Next, I will need to refresh my knowledge of the transfer paper print and transfer of the ink off of this paper onto the copper clad blank flat flex PCB and then acid etching away all unwanted copper and then removing the ink to reveal the fresh copper traces and pads. Then I can solder all the SMD components onto this. Heck I may even make a solder paste stencil and place components and bake them on. But perhaps just hand solder for now? Not sure. The former is faster in the long run but takes more setup and is quite committing. I'd rather validate my designs even further before going that far.



28
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on December 03, 2025, 02:23:24 AM »
I just tested the positive high-side switch portion of the motor controller and everything seems to be working as intended. The section including all parts involved is circled in a bold blue line to indicate the portion I just tested successfully.









One issue I'm having though is that the drain of the A09T attaches to the 100ohm resistor tightly and is a weak point that broke off twice now. Hardly any wiggling at all on the arduino input line and ground line leading into the A09T mosfet causes the drain solder attachment to break off. I am wanting to glue it all down onto the mosfet but I'm supposed to tape the heatsink on under all this stuff so I don't think I should glue it down. I need some kind of backing sheet to glue things off onto (where a PCB normally does this job). Which will provide much needed strain relief at all attachment points. I guess I'm learning the hard way why PCBs are used in general. Without a flat backing plate or substrate of some sort the attachment points between components are vulnerable to flex and breakage super easily. This surprises me.









To perform the test I used one lab power supply set to 20v and one set to 8.07v and used a 18650 lithium battery as the 4.12v to simulate the arduino output pins. I carefully electrically isolated all the metal lines with packing tape for now to ensure no short circuits and then I connected the lab power supply pins to the correct locations with alligator clips. Finally I connected the 18650 lithium battery 4.12v to simulate the arduino turning on the A09T mosfet - I did this using the two nickel strips for this portion joined to the battery with neodymium magnets. If I had a 3rd power supply I could get 5v off of I'd have done that but I didn't have one in arms reach so the battery it was. The LED came on and I tested the output line to the motor was indeed 8.07v. I then disconnected the + side of the battery and verified the line going to the motor was 0V. It was - although if I kept the multimeter on that line longer I noticed it would creep up to like 3.4v but something similar happened on my last test run and chatgpt said this was like parasitic capacitance involving the multimeter or something and nothing to worry about. The main thing is it would START at 0v when I first connected and then rise up to 3v or w/e over time on the multimeter screen and this behavior was ok last time so meh. We're good I think.



Where to go from here then? Well I'd say I make the other (lowside) portion of the half bridge and then test the full half bridge to ensure it's all working. I think then my design is validated enough to move into diy flex pcb for some of these portions that are on the layer that goes onto the main beefy mosfets.
29
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on November 11, 2025, 01:30:34 PM »
Okay so here I have attached the LED and resistor pair with their 30ga wire wrapping wire onto my highside mosfet's front face. I may add conductive silver paste to the wire wraps in the future if any issues come up there. However, I am wondering if just tightly wrapping it in electrical tape would more or less guarantee the connection doesn't open circuit. We'll see.









I also finished soldering together six braided copper solder wick strands which will act as my heatsink for my highside mosfet. I am still deliberating on how to attach it to back of mosfet in such a way that it will be electrically isolated but thermally conductive. I am leaning toward thermal tape for this.



30
Mechanics and Construction / Re: My Advanced Realistic Humanoid Robot Project
« Last post by artbyrobot1 on November 07, 2025, 06:58:19 PM »
Couple updates:



An audience member redid my brushless DC motor schematic in the traditional commonplace formatting which for most is easier/quicker to read and understand due to familiarity. So I'm reposting it. It looks mostly accurate although I have since added a 100nF ceramic capacitor between the gate and source of the highside mosfets to reduce ringing issues. Standard practice according to chatgpt. I also changed the LED color to orange because chatgpt said blue would show through the silicone skin more and add a cold inner glow and we want it to look like real skin so no blue.



As to why the highside mosfets get a 100nF ceramic gate capacitor but not the lowside, here was how chatgpt explained it to me:



-High-side MOSFETs:



Their source pin moves up and down with the motor phase (it?s not at a fixed potential).



During switching, the drain and source both move rapidly, and the gate voltage must track that movement precisely ? any ringing or inductive noise can momentarily over-stress Vgs.



That?s why we add the small capacitor across gate and source: it tames that high-frequency ringing and helps hold the gate steady relative to its moving source.



- Low-side MOSFETs:



Their source is solidly tied to ground, so the gate always swings relative to a fixed, quiet reference.



They don?t experience the same ?floating? gate drive or large dv/dt transitions on the source pin.



So, the gate is inherently more stable, and you don?t need that extra 100 nF G?S capacitor.





Anyways, here is the audience member schematic:







Here is my updated schematic with the changes I mentioned:









In further news, I tediously installed the new 100nF ceramic capacitor between gate and source of the mosfet. Due to the close proximity to the 10k ohm Vgs resistor and various other low temp solder joints in the immediate vicinity, any heat applied would surely have caused those to desolder and the whole thing to start falling apart so I ended up just soldering nickel strips to either side of the 100nF ceramic capacitor (by itself off to the side) and then used the tip of a sewing needle to apply a tiny amount of conductive silver glue onto the gate and source nickel strips coming off the IRLR7843PBF mosfet and then pressed the nickel strips of the ceramic capacitor into that. I put that in front of a mercury vapor bulb for an hour or so to cure and then applied another generous helping of conductive silver glue over the top of the joint. I then baked that another 7 hours under the mercury vapor bulb again. This photo shows the final result.







It appears to be a solid joint and I think this is a great way to make attachments when you can't use soldering! It might even be better than soldering in some cases from a ease of application perspective but not sure yet on that.
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