/random/ - random

The winch in place pulley in question:

>>128964

Here is the tension spring in question from the previous post. I want this spring inside the tubing though which is not shown in the drawing of it.

Good news: I had mentioned before I was planning to use 2mm OD tension spring for the winch in place pulley tension solution but once I got the 3mm ID 4mm OD PTFE tubing to go over the spring, I saw that the 4mm was just WAY too big once you multiply that out to 300 motors. 300 of 4mm OD tubing starts to take up a massive area at that point and I struggled with that. I MUST be miserly on space taken up by parts to get all the crap I need to fit in there to fit in there! Anyways, I fortunately discovered that you can buy tension spring down to 1mm in OD! I was unaware of this before now! You can find it if you search "0.2x1.5x1000mm tension spring" where 0.2mm is wire thickness, 1.5mm is OD, 1000mm is length. So I ordered 1mm OD tension spring and 1.5mm OD tension spring to test and see what seems best. If the 1mm OD spring seems reliable to me, I'll go with it. Anyways, since the spring is now smaller, I can use also a smaller PTFE tubing to house the spring so I ordered uxcell PTFE Tubing 1.8mm ID x 2.2mm OD off amazon. 2.2mm OD tubing compared to 4mm tubing is SHOCKINGLY smaller when you look at them. So it will be WAY more space efficient now.

Here's my updated tension spring concept drawing:

Ok so I currently have an order for 0.2x1x1000mm tension springs stuck in customs for weeks and placed another order just today for the same in hopes it goes through faster. But at $9 for a single spring that is 3ft long, I am feeling RIPPED OFF on price. It is bullcrap. All relating to the tariff nonsense. So I decided today to pivot and just roll with the elastic band in place of tension spring. It's a jewelry making elastic band I bought some time ago in a roll. WAY cheaper at $0.03 for 3ft instead of $9 for 3ft. That's 99.7% off! Talk about a discount! The issue I had before when I looked into this option was the tie-off point. I would need a way to tie PE fishing line to the end of the elastic band without the tie point being bulky. Well I figured out a way to do it without any bulk at all! See I want this to fit into my 1.8mm ID PTFE tubing to keep size down. My solution was to just glue the fishing line lengthwise directly to the elastic band. No knot at all. No turns at all. Just literally lay it on top and glue it down flush. I figured about 6mm length of joint would be solid. And I did this on both sides with my PE fishing line. I used 0.08mm 6lb test braided PE fishing line for this. So now I have two fishing line segments coming off the end of it for double the strength of this connection. But I only wanted one piece of fishing line to go the distance to attach to the motor end so I twisted the pair of fishing line segments together and glued the twisted pair with 401 glue then cut one of the two away leaving just one of the pair to go the distance to the winch in place pulley that this is all supposed to tension for me.

I will use this string and elastic band method for now as I wait on springs and stick with this method for at least this first motor actuator setup for now. If the elastic bands don't last, we'll upgrade to the metal springs later on during maintenance or w/e.

Note: the total length of the elastic band I am using for this is 2ft and it stretches to 3ft snugly without too much force. I'm just going by feel and instinct for this measurement. If I were to go 1ft with 1ft of stretch, the stretch is more intense and the pull is harder. But I don't think I need much pull for just tensioning the winch in place pulley and I also think the more tension you place the more wear and tear on the elastic band which will shorten its lifespan. So playing it conservatively with the 2ft length selection for now.

Note: to apply the 401 glue I used an exacto knife handle with a sewing needle in place of the xacto knife blade and the tip of the sewing needle acts as my precision glue applicator.

>>133486

The actual implementation.

Sometimes to get the braided PE fishing line threaded through the fine PTFE tubing can be tricky, so I came up with a neat device to assist in this. I will be making a threading tool based on a needle threader tool I've been using. It's basically a wire folded in half that you shove through a needle eye and then stick your string into its end and then pull it back through the needle eye. In my use case, I'm creating a custom one of these threading tools that will feed through my entire length of tubing till its folded end comes out the other side and I can thread my string through that end and then draw it back, bringing the string through the tubing with it.

The original tool looks like this

Minor update: I have now carefully mounted the PTFE tubing that leads to the elastic string tensioner for the winch in place pulley. I mounted it snugly to the side of the PTFE tubing coming off the same winch in place pulley that leads to the Archimedes pulley system. I routed both of these using my CAD for reference in such a way that their routing will not interfere with the next motors that will be installed later. I mounted this PTFE tubing that leads to the elastic string tensioner using ONLY 401 glue which is something I've never tried before now. Usually I first wrap the tubing in adhesive transfer tape and spandex cloth wrap and coat the cloth in 401 glue but skipping that made it able to be more snugly mounted to the other tube by way of only glue. We'll see how that holds up without the other reinforcement the cloth provides etc. Seems to look so far so good though. They are in turn glued to paper soaked with 401 glue and to a little piece of stainless steel wire bent at a 90 and that wire in turn glued to the winch in place pulley mount baseplate which is itself made of paper and 401 glue. So basically everything is becoming 401 glue construction! I have some concerns about how this will hold up in the event of a fall or w/e but perhaps we can create some sort of protective cage around any delicate outcroppings like this in the future. For now I am just going for ease of construction and speed of construction to get things back on track and rolling again.

Note: The PTFE tubing that leads to the elastic string tensioner for the winch in place pulley is 0.66mm ID 1.16mm OD PTFE teflon tubing. The string coming off the winch in place pulley feeding into this tubing that will act as tensioner string tension carrier string is 6lb test 0.08mm PE braided fishing line. I was able to thread this fishing line into this TPFE tubing by hand with no issues at all very easily.

The next task will be to mount the end of this string to the 2 feet of elastic string for jewelry making and thread that into 1.8mm ID 2.2mm OD PTFE tubing and tie it off at the end of that tubing and then mount that tubing to the gray string hanging from my ceiling for now. That will conclude the tensioner mechanism for the winch in place pulley and this will usher in the next round of manual hand testing to see how much tension that is giving us. I also will be moving the tension spring mounted on the motor to align it better and shorten it more since it only moves like 4mm and so can be way shorter than it is now.

I finally finished making the tensioner mechanism for the winch in place pulley and I taped it off up the string descending from the ceiling and taped the far end of it onto the ceiling. I noticed I have to keep it as straight as possible since when curling with too much turning the elastic bracelet cord grips the sides of the PTFE tubing which could interfere with the amount of tension it brings to my winch in place pulley. So this will mean on the robot itself it will have to go from the shoulder all the way down the torso in a straight line and then down the leg to about the knee as well. It's 44" long in total. I ended up bumping up the elastic bracelet cord to 30" long to reduce the amount of tension it puts on the winch in place pulley more. The longer it is the less tension it brings and the shorter it is the more tension it brings. If it really can't fit into the leg I can cut the elastic bracelet cord in half and place braided PE fishing line in between the two halves and have that make a 180 degree turn around a pulley and thereby have the same length of elastic bracelet cord but separated into two halves mounted parallel to eachother that create a in series matching tension but taking up half the overall length. This way I could keep it out of the leg area if needed. However I think it might fit into the leg area fine perhaps. Not sure (once we get all the other motors and their tension strings that amount of 2.2mm OD PTFE tubing will start to add up.

Note: I'm also considering taking the elastic bracelet cord out of the tubing and lubing it then putting it back in since lube on the grippy elastic bracelet cord would take away it gripping the sides of the PTFE tubing some I think. Silicone lube is best for this according to chat gpt.

Note: to secure the far end of the elastic bracelet cord I used 401 glue to glue on PE fishing line onto its end the same way as we discussed before and then took the far end of this PE fishing line and came out the end of the PTFE tube with it and taped it off onto the outside of the tube. We'll see how that holds up it might need to be glued down if it gradually is pulled through the tape over time which would be no good.

The tension spring mounted to the motor setup upon further testing seems like a somewhat bad method. The issue I'm having is too much play in the tubing running between that spring and the finger joint. When tension is applied to that spring by way of the tubing, the tubing recoils and moves quite alot and allows alot of slack out to the joint so that the spring has very little involvement in the joint and doesn't really get used much period. So the full range of motion of the joint is just absorbed by tubing slack. When I tried to pretension the tubing so that the joint movement translates to the spring, the total tension placed on the joint by this became too high.

Fortunately, I came up with a much more elegant and simple solution for all of this. Basically, my plan now is to just use the bracelet cord tied point to point across the joint directly on the joint and that will be my spring for extension that counters the motor. This eliminates the need for metal springs at all which cuts costs, it also eliminates the PTFE tubing run, saving some space, and should be easier to install and easier to give precise amount of elasticity/resistance to taste. If I want more springback on the joint I can just add more bracelet cord in parallel to the first. This way I can add more resistance pretty easily.

So in recent testing a fresh issue I ran into was the TPFE tubing would start gradually pulling through its tightly wrapped tape sleeve to my surprise. Its low friction surface gradually pulls free of the tape over time. To resolve this, I decided to thread through the tip of the tubing to create a mechanical bond for the tip and once threaded through I just 401 glued down the ends of each thread onto the sleeve that was originally supposed to hold it in place to begin with. This seems to work great so far in the little bit of testing I've done since.

I figured out a robust way to make the extension cord for finger extension using the bracelet cord and a fishing crimp sleeve. The idea is to crimp the two ends of a folded in half strip of bracelet cord and this way both ends can be sewn down into the fabric without any gluing which could potentially fail or be a weak point. I am planning to use this in place of the tension spring style finger extension setup.

Ok I figured out a bit easier way: tie a knot at each end of the strip of bracelet cord and then tie my nylon thread off onto the bracelet cord inside that bracelet cord knot. The bracelet cord knot on each end acts as an endstop. Seems to work great so far and cuts down on materials this way over the previous way I proposed.

Okay so the bracelet cord self untied quickly so I'm going back to my previous approach of tying off both ends of the bracelet cord with a fishing crimp sleeve.

While trying to cut in half fishing crimp sleeves with my mini miter saw I noticed it was a difficult process and not ideal. So I came up with a easier method which was way faster, cleaner, less setup and takedown, no deburring needed, etc!

The method is to lay the fishing crimp sleeve on a flat surface and line up a exacto knife blade perpendicular to it across its top and then apply moderate downward pressure to score the metal and then slide the knife carefully back and forth creating a perfect scoring line that grows deeper with each pass. After several passes the fishing crimp sleeve halves separate cleanly! This method uses a similar principle to a copper pipe cutter used in plumbing.

I installed two tensioners for the robot and they were seriously successful overall in testing. So much so that I am now confident enough in the entire pulley system to move onto the custom mini BLDC motor controller to get the motor to run motorized tests of finger movements next. Well after a couple very minor tweaks that is.

So the first tensioner I installed on the extension part of the index finger joint we are working on. I used the bracelet cord folded in half and fishing crimp sleeved then sewn into the bone fabric. It seems just about perfect except for one thing: I want to keep it under mild constant tension but the bone fabric creeps/moves slowly when put under constant tension like this because it is taped into place on the bone after all. The tape is allowing the movement. This means it does not stay put and my anchor points move over time so I can't set a tension and rely on it staying at that tension long term. To resolve this I need a mechanical connection at the tension point anchoring location.

To mechanically connect my anchor point, I have decided to use tiny self tapping screws. I have avoided screwing into the bones till now but I'm making an exception here. The screws won't be going that deep and the finger bones are unlikely to break anyways IMO. So I feel comfortable with this. Here's the screws I ordered for this from Amazon:

Next, I created a tensioner for the middlemost archimedes pulley. That pulley was creating significant drag and slowing down the finger extension during testing due to rope friction. So adding a tensioner line to pull it back down toward the fingers during extension was my solution for this. It worked amazingly well. To make this, first I tied off a fishing hook eye to the bottom of the radius bone just above where my TPFE guide tubing entrance is. Then I glued a 7cm piece of bracelet cord to a piece of 6lb test .08mm braided pe fishing line with 401 glue. I secured the top of the bracelet cord to the top of the archimedes pulley system and then threaded the other end through the fishing hook eye and back up and to the bottom of the archimedes pulley where I tied it off. So it ties off at top, comes down to bottom, goes through the fishing eye then comes back up and connects to my pulley. It creates just enough downward pull to delete the rope drag slowing down that pulley from coming down and this enables the system to unwind and extend back to its starting point after each time I contracts/pulls upward to cause finger contraction. This means the finger extension now happens swiftly with no hangups and the whole archimedes pulley system is now under constant tension at all times which keeps things neat and prevents tangling issues pre-emptively. This rig was a massive success and took up hardly ANY space at all.

I put the post it notes behind the archimedes pulley tensioner so you can see it. It's hard to see otherwise without a contrasting backdrop. It works amazingly well.

Back on the electronics again. Have been going over my BLDC motor schematic and making some little tweaks to it. Here's the updated schematic. It's a combination of lots of other schematics I've found online as well as some chatgpt help. With 1 being no clue and 10 being absolute expert tier in BLDC motor schematics I'm probably a 5 IMO. So take my design with a grain of salt. It will be very fun to see if it works. Note that I put a couple schematics of Electronoobs - a great youtuber on the left hand side as reference and study material. My schematic is the big one on the right. Electronoobs series of videos on BLDC motor controllers has been extremely helpful in me forming a rudimentary understanding of this stuff.

So I plan to just gradually add components little by little and test after each thing is added to ensure it is working right still after each little change and this way gradually build out the circuit, proving each thing works as we go. This is because things have all these gotchas and "oh you didn't know this little detail?" that keeps coming up and proves it was more complicated than I thought. So I just have to prove every little thing as I go. To try to find out what is wrong after the whole thing is built would be WAY harder than to figure out what went wrong when a single component is added and it was working before said component was added. So that's how I will be able to overcome this challenge best I feel.

Note: Reminder: I am building a custom BLDC motor controller because an off the shelf one would not have enough miniaturization to fit into the tight space constraints I have to work with. Also, building my own gives my software more precise control of every little advancement of the rotating magnetic field and along with that I'll have the ability to PWM the advancements to make them more smooth, less noisy, and have torque control as well this way which means the fingers can be rough and fast in movement as needed or slow and gentle and dainty or slow but powerful etc. I can also create acceleration profiles that match human finger joint acceleration in order to have the movements look very natural just like a human's movements which is very important to me. Just alot of fine precision is possible when its all my own circuit I feel. While off the shelf ones may have some of this functionality, the price often reflects that and is then prohibitive. But in any case nothing is off the shelf with this level of control AND the ability to so finely tune its form factor and volume envelope to fit my exact needs in space on a per motor basis.

Well I finally got back to the electronics after about a month long detour real life interruption. All kinds of stuff slowed my progress on this session. But I got stuff done nonetheless. 0603 LED to 0805 resistor and some nickel strip leads coming off. Tested and working. This will be the indicator light for when the lowside mosfet comes on for one section of the custom BLDC motor controller. 0603 LEDs are extremely tiny for hand soldering and they don't take solder well either. I was originally going to go with blue LEDs but chatgpt said that would give off a unrealistic color through the silicone skin so orange would be better to give a more natural and less silicone skin piercing indicator light. Somehow I ran out of 470ohm resistors so I had to order more and I used my 200ohm ones instead for now. Which are a bit too bright. But chatgpt said I can diffuse the LED with a glob of silicone tinted black to darken and diffuse the light it gives off which sounds like a good idea to me. I am planning to use wire wrapping wire to come off of this assembly and tie into things. Somehow just attaching these two parts and testing it took me almost 3 hours. Between studying the schematic to refresh my memory on what is going on, visualizing placement options, overheating and destroying one LED, trying to locate the right color LEDs, shopping for replacement 470ohm resistors, researching and substituting in 200ohm resistors, discussing LED color options with chatgpt, figuring out how to solder a 0603 LED directly to a 0805 resistor part to part by hand, accidentally breaking a part off of its nickel strip lead and having to redo the connection, etc etc. All of it just crawls. Hard to stay patient with electronics sometimes and I do things in inefficient ways often. Learning what can and aught not to be done is tough from a patience perspective. But I insist on trial and error and experimentation which takes time. I just need to get into a daily habit to stick with it till completion. It's all complicated. Trying to figure out how to electronically isolate it all next. Thinking of using lamination plastic taped around it all so I can still see it all and visually troubleshoot. Also I'm considering how I can use solder wick braid as a heat pipe for each mosfet and run that over to the liquid cooling system. But it can't conduct. So thermally it can conduct but electrically it can't. Trying to figure out whether to create a barrier of micah or just thermal silicone for this and the routing needed. Also considering if I need mini coaxial shielded cable for the wiring of each or just regular wire wrapping wire when going from microcontroller to mosfets etc. Also trying to figure out if I need hall effect sensors or back emf reading or no feedback but my potentiometer and the implications of each option. Just so much to consider in all of this. And all of those considerations also slow things down even more as I have to make decisions on it all. It's quite overwhelming.

Ok so I decided to use 30 gauge wire wrapping wire and wire wrap that onto my nickel strips that I connected onto my LED setup then trim off any excess nickel strip. What I like about this is this wire is very fine so it takes up hardly any space and by being able to wrap it on I did not have to apply heat which could have desoldered my smd components by accident. I also like that it is already insulated and color coded so I don't have to worry about insulating my nickel strips the whole run to wherever this connects. To insulate the whole LED contraption here I used packing tape so I can see all my components well but still have them electrically isolated. I just folded the packing tape over the whole assembly like closing a book over a bookmark.

note: after wire wrapping the wire wrapping wire I noticed it was not that tight on there. I did not use a wire wrapping tool because I lost mine so I just used needle nose tweezers to manually wrap it around and around. Anyways to tighten it well I just crimped it with the tip of my wire strippers that has some kind of toothed pliers that crimps things well. After doing that the connection appears very solid.

I just ran a successful test of the highside mosfet section of the diy bldc motor controller circuit. Onto the lowside next.

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.

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 exhuasted 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 lumoocolor 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.

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 lowside 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 lowside 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.

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.