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• Latest Iteration of Winch in Place Pulleys

  Larry • 2 hours ago • 0 comments

  Okay so here is my latest iteration of my motor mounted winch in place pulley downgearing setup completed.

  I ended up doing a total overhaul of everything since my last iteration failed. In this iteration I made many small improvements. One thing I noticed is that the thumbtack shafts have a little bulbous section near their tip and I reasoned that perhaps this can catch on the #2 fishing crimp sleeve and impede it at times. So I sanded it off with a nail file so the whole shaft is now a cylinder with no protrusions. When I tested the rotation with the fishing crimp sleeve after this modification, it spun more freely than ever before by a long shot. So I think I'll do this every time going forward.

  Another improvement is I added more height to the sections of the pulley, taking up all the available vertical space that used to be planned to be used for reverse direction actuation which is now being done by a tension spring instead. The added vertical space on each pulley means that contiguous loops of string wrapping have more space and so the diameter taken up by the string as it winches doesn't change nearly as much as before which means it will have more consistent downgearing through the whole duration of the winching cycle. I prefer this. It is also easier to work with for gluing on the discs and whatnot with them more spread out.

  Another improvement is I added an extra pulley set on the top of the main winch in place pulley which I will use to attach a string which will be tensioned on one end by a spring and the purpose of this will be to put tension on the system to prevent derailments and ensure tight wrapping every time the winch releases its string (finger extensions). Now I may not actually need this extra tensioner pulley if the spring on the finger doing the extension actuation provides enough tension to the Archimedes pulley system and this winch in place pulley to cause them all to remain snug and tensioned, however, I think I probably should tension this winch with an additional tension spring dedicated to it exclusively even if it is just a redundancy just to play it safe and doubly ensure we get no derailments even when some issue may come up with the Archimedes pulley system. Last thing we need is a cascading of failures like Archimedes system fails so also winch in place pulley then derails and tangles so then we are really set back in the event of some unexpected issue. So better to have this redundancy.

  To provide constant tension on the winch in place pulley, I have considered using elastic thread used for making DIY necklaces, using a tension spring, and using a clock spring. The latter seems like it could be the best and most reliable option due to its constant tension. I bought a few sizes to experiment with from Aliexpress. Search terms to purchase such an item were "flat spiral coil constant force spring". They are around $2 each. Considering the motor is $24, $2 to have a extra spring isn't too bad. It could really make or break the reliability I think. Now the issue is the spring is supposed to provide tension for all 32" of travel of the winch. That is a long way. My mini tape measure surely has this type of spring in it and it has that tension spring the whole time and presumably uses the same type of spring I just bought. So it is possible for a tension spring to do this for this length of travel. So hopefully one of the ones I bought works for this. If not I may have to upgear it trading tension for more travel distance. I will have to fit these extra springs into the body which may be tough. Space is VERY constrained but hopefully we can pull it off without any issues. In any case, these are going to take a few weeks to arrive so I'll be testing without it at first.

  Another improvement is I made the diameter of the larger pulley of this turn in place winch bigger which means it will provide more downgearing. Not sure how much maybe an extra 5% or w/e but it's something.

  I have routed...

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• Compact Pulley System Test Went Badly...

  Larry • 7 days ago • 4 comments

  I just ran a test of the second turn in place winching pulley and ran into several problems. First I noticed my main lines turning the motor were not the full 27"+ which I thought they were but just remeasured and found they weren't. My bad. So I have to rewind those to fix that. Next, I noticed that just as we depart from the motor output shaft we experience mechanical advantage with each downgearing, so also when traveling from the downgeared area back to the motor output shaft we experience mechanical disadvantage. Up-gearing. Which means the bolt hanging as a load to place tension on the pulleys during a release cycle was not enough weight anymore (was barely enough before now clearly not enough). Now note that the bolt represents what a tension spring will normally be doing, tensing up the winch system to keep it all solid and tight. I don't want this to have to be much heavier than the bolt. I want the system to not need much pulling to remain good in tension. The friction of the teflon tubing plus mechanical disadvantage etc was causing the pulleys to not remain tense (and their not being lubed yet on the junction between fishing crimp sleeve and thumb tack. So my solution I'm now contemplating is either moving one of the turn in place winches down to the location of the Archimedes pulleys on the forearm area and putting the tensioner apparatus between it and the previous pulley mounted on the motor so that the tensioner apparatus does not suffer as much mechanical disadvantage due to up-gearing OR I get rid of the second pulley entirely and just have the winch in place be a single pulley 2:1 and the Archimedes system be 16:1. Which still works as we have then 32:1 which is great still. Under such a system, the original 27" winching would be reduced to 13.5" by the winch in place pulley attached to the motor. The Archimedes pulley system then needs to go down, around one pulley, back up, around another pulley, then down and around another pulley, then back up and tie off. The total travel for those one down, one up, one down, one up (4 trips) is 13.5/4 so 3.4". And we'd sit at 8:1 at that point. so adding two more pulleys beneath that first group would add another 4:1 for 32:1 total. And those two pulleys would add another half inch tops so that gives us around 4" total length of the Archimedes system and not too crazy many turns in that first system like we had in our first prototype. Still quite simplified comparatively speaking. So this is a very viable solution. And that 4" is around 10cm and we had 11cm already planned for this purpose in the CAD in the forearm from before. So we are still within that target and viable still without any change to the CAD at all which is great.

  Anyways, back to the test's issues discovered. Oh yeah, also, the load (in this case a bolt hanging) struggled to keep the turn in place winches under tension while the motor was releasing the bolt (loosening or unwinching itself) not only because of the mechanical disadvantage from the pulley upgearing itself and from the friction in the TPFE guidance tubing but also from the friction of yet another pulley and its friction between its fishing crimp sleeve and its thumbtack. So I was having to manually pull down assisting the bolt, pulling down fairly hard just to get the system to stay taught and release without becoming a derailed tangled mess.

  One other work around if I were insistent on going with more than one winch in place pulley would be to wind up extra line onto each turn in place winch pulley and have that directly attached to a tensioner spring placed wherever on the robot. This would always keep tension on just that winch in place pulley and be responsible for just that pulley and suffer no mechanical disadvantage beyond the TPFE guidance tubing it has to pass through to get there which shouldn't be too bad if the spring can be nearby. This is a valid solution but adds another layer of complexity to the winch in place pulleys...

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• Current State of Motor Mounted Pulleys Update

  Larry • 11/07/2024 at 06:47 • 0 comments

  I have added the final pulley and rigged the guidance TPFE tube up to that pulley and routed that to the general vicinity of the Archimedes pulley downgearing system. As seen in the photo, I used super glue and post it note paper to form a TPFE guidance tube support structure to hold it in place as well as wrapped it in fabric tape and soaked that tape in super glue. I applied the super glue with the tip of a sewing needle as a precision application method.

  The next step will be to test the pulley system as is and make sure everything is working really well.

  If all testing passes, we will then modify the Archimedes pulley system on the forearm that we were using before to simplify it some since it now deals with only 7" or so of string compared to 27" of string it dealt with when we did not have the turn in place pulley system in place. So it will now be much more compact and fewer pulleys needed in it. So a bit of redesign and part recycling and we'll be good to go on that. Also, before, it was a 16:1 Archimedes pulley system whereas now it will just be a 8:1 system.

• Downgearing Tweaks to My Plans

  Larry • 11/07/2024 at 04:59 • 0 comments

  After further deliberation, I have concluded that I should put 4:1 downgearing on the motor's top with the turn in place pulleys and put 8:1 further downgearing located nearer to the joint being actuated - in this case the distal forearm.  My reasoning for this is as follows:  the routing from motor to near the joint is facing turns and friction etc and these become smaller factors when under lesser loads.  So leaving things more high speed low torque initially during this phase of the routing is advantageous to lower friction and issues relating to deformation and compaction on the guidance tubing.  This means less wear and tear and lower maintenance as well.  Next, the turn in place pulleys are quite difficult to work with being very small and compact and lots of winding and whatnot is hard to deal with and tedious.  Further, the turn in place style, when fully winched in has a much lesser downgear ratio compared to when fully extended due to the relative diameter size ratios of the pulley pairs involved changing in size during the winching.  Whereas in the Archimedes pulley downgearing system the mechanical advantage is fixed and doesn't change during the entire flexion nor extension process.  This makes it more reliable and limits our losses during the near end of the winching phase that are incurred in the turn in place technique.  This ensures we retain adequate mechanical advantage during all times.  

  Another important update is I have added axial rotation to the proximal finger joint in CAD.  My index finger has a little bit of this type of control to it so I think it will be a nice boost to control and dexterity for the robot.  Really maxing out the ability of the robot to finely manipulate its finger positions and improve performance of the fingers at all tasks.  I added the necessary 4 additional motors to achieve this into the CAD as well.  You can see the highlighted pair of axial rotation red indicator arrows which show the angle and location of the tendons from where they terminate to where they will exit the guidance tubing - the range of motion if you will.

  Yet another important update is I now plan to just use a spring for the extension actuation force rather than the reverse direction turning of the motor.  This is admittedly going to give the extension less strength and the flexion less strength.  The flexion will have less strength because it is now fighting against the extension spring to get the finger to flex.  The extension will have less strength because a spring alone is making it happen rather than a strong motor making it happen.  I don't mind either of these trade-offs though because it will greatly simplify the routing - cutting it in half, simplify the motor mounted pulleys, cutting it in half, and simplify the Archimedes pulley systems, cutting the amount of them we have to make in half.  That is just a massive amount of time and effort saved.  I just am not convinced that spending that level of time and effort just to have a stronger extension of the finger joints is worth it.  Relatively passive spring powered extension of fingers is very common in hobby humanoid robot hands from what I've seen and although I've always viewed it as a lazy solution, I do see some merit in embracing more simplicity at times.  Especially if you cannot JUSTIFY the added work of the alternative.  The more I think about when I have needed finger extension to be very strong, the more I find that it seems to be a relatively rare occurrence.  It just doesn't seem to happen often.  Now as the robot grows more able with its AI and more sophisticated, and gets into more and more types of work, the occasional scenario where fully powered extension of fingers will start to crop up more and more as a need.  So at that time, I am thinking we can revisit this and get the extension actuation...

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• Animated Pulley Downgearing Test

  Larry • 11/05/2024 at 03:58 • 0 comments

  This is a slow, careful hand test of the pulley. Everything looks good. Also, I did fast tests but didn't capture a nice shot of those with good hd closeup like this. In any case, this can show you some idea of how it all looks in action so far. The motor shaft is not turning electronically but is being turned by me pulling string wrapped around it to screen left is my hand pulling. To screen bottom is a hanging bolt that is being winched (not shown its cropped out of the image).

  I wanted to avoid working on the electronic actuation which is a rabbit hole in itself until I have the pulley system fully done and tested. THEN I will make it all work electronically as the next phase.

• Compact Pulley System Test Setup and Test Results

  Larry • 11/04/2024 at 06:53 • 0 comments

  I managed to implement a friction device for both main manual input pulleys for manually turning the motor shaft and one for creating tension on the system at all times. The former I made by just running the fishing line through a tension spring between the coils which pinched the fishing line enough to provide friction and feed it snugly into the motor shaft as it winches it. This successfully replaced the need to feed it in by hand between thumb and index finger with snug pinching action to get it to winch in tightly. For the tension on whole system need, I ended up just hanging a bolt from the final output string which put the whole pulley system under light tension.

  You can see the tension springs sewn into the bone fabric on the left hand of the pulley system in the attached photo. You can also see the thread going through those if you look carefully. You can also see the output pulley on the right hand side of the system and see the little metal 28ga wire eyelet I made and the string being fed through that eyelet as it heads toward the camera lense shooting the photo. It then drops down out of sight. So you have to visualize it tied to a bolt. The bolt is currently taped off to a piece of bone since I removed the tension after testing to do some repairs.

  So to the results: with these little modifications, the testing went much better. It was fairly reliable. The only times anything tangled up was when the bolt caught on something when I wasn't paying attention which relieved the pulley system momentarily of the tension created by the weight of the bolt pulling down by gravity and tensing up the system. As soon as the system lost that tension, it began to unravel and created a tangled mess. This happened a few times in testing and was user error. Although one time a pulley just stopped turning randomly despite the tension created by the bolt. That concerned me alot. I don't know if something got wedged in it or it was cockeyed just right or what but sometimes it gets stuck a bit. That cannot happen ever or the whole thing fails. Perhaps greasing the inside of the fishing crimp sleeve would prevent this from happening anymore. Also, the bolt is not THAT heavy. Using something with a bit more tension force placed onto the system could also help some more perhaps. I think using a tension spring as the tensioner - as shown in a drawing I posted previously - will be just the right amount of tension. I think it might pull a bit harder than the weight of the bolt was pulling. So between those two improvements I think this rare fluke will be avoided. And so far, as far as I've seen, as long as the pulleys spin freely and no tension is lost, everything appears to work perfectly. I was able to go back and forth with no issues many times besides the few screw-ups I already mentioned.

  So the system appears to be a success so far from testing. I can now move onto building pulley #2 and 3 and testing them thoroughly in conjunction with pulley #1.

  Also of note: I thought pulley #1 was a 3:1 ratio and perhaps it is at times, but the mechanical advantage ratio changes over the course of the winching process because the larger pulley gets smaller as it unwinds and the smaller pulley gets bigger as it winds up. So their relative diameters changes. Therefore, I guess we have to treat it as what is the average mechanical advantage it produces. Well in the final measurement, it cut down the original 27" of string being winched in to 13" of string on the final output. Trading down that distance of travel is the key to the creation of mechanical advantage.

  We want the final output to be around 0.84". We want 32:1 mechanical advantage in the end. So pulley #1 got us to 2:1 mechanical advantage only so far. The next pulley likely will get us to around 4:1 and the next one 8:1. I am considering just stopping there. I have room for two more pulleys, but at the moment I'm considering doing the last two down-gears with my Archimedes downgearing...

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• Compact Pulley System Testing and Tweaks

  Larry • 11/02/2024 at 18:15 • 0 comments

  I started some testing on just the first pulley and lots of things went wrong:

  Twice I had to increase the pulley size because I wasn't able to use enough line winding onto said pulley for my total line draw need after accounting for the 32:1 downgear ratio. I calculated 27" as the very least it has to winch in at the motor shaft to get 0.84" total draw at the joint of the index finger which is perfect (27/32=.84). The pulleys were too small to accommodate 27" winched onto them so I had to increase the size - which meant removing everything, increasing size, then rewinding everything by hand for an hour plus! Just so tedious and annoying!

  Another failure was one time, the string was too loose on a pulley and a tighter wrap got under the looser wraps and then the looser ones snugged against it binding it down like someone said would happen - which made it all stuck. Also I had many derailments where the string came off the pulleys and started wrapping up on the axle off all the pulleys and getting things quite stuck that way. I've been dealing with carefully untangling and rewinding tangled messes over and over. It's been a disaster. I thought of scrapping the whole thing a couple times.

  However, after taking a step back, it occurred to me that the tangling issues were largely due to forgetting to put the final outlet of the system under load to tension the whole system which would keep every pulley winding nice and tight and aligned well. So this was user error and oversight, not the fault of the basic concept of the system then. I just forgot to do those parts in my rush to start testing things. I planned to only add that stuff at the very end once the whole system was done and did not think I needed to do that just to start initial testing on a single pulley. That was a faulty assumption and an oversight. The whole system always has to be under tension to work right. My bad. Lesson learned and a valuable one at that. I did not fully grasp until I saw with my own eyes the disasters the importance of keeping it all under tension at all times. Yes I knew theoretically it was needed eventually, but I did not realize the whole thing was absolutely doomed instantly every time if it is not immediately under tension even for a first set of simple tests. That was revelatory for me.

  I'm glad I got to see the failures first hand though because it enabled me to study what failures can be expected when tension is not placed and know intimately first hand the importance of tension and how lack of tension causes the failures specifically. Valuable to see it with my own eyes instead of only imagining it. This has helped me come up with some cool derailment prevention and loss of tension prevention mechanisms to fool proof my system more - even beyond the tension spring drawing shown in my last post.

  Note: At the top of the motor output shaft, you can see two large pulleys where I have wound 2 pulleys for moving the motor axle clockwise and counter clockwise to simulate the motor moving. These are temporary windings just for testing manually without messing with electronics for now. These need to be fed in under tension at their inlet and their inlet needs to have a eye positioned in front of it that forces the string to stay in line and not feed in astray out of alignment. So also the pulleys for the main motor output shaft pulley for flexion I'm testing and the first pulley downgear I'm testing. Every place a string enters a pulley needs to have a small eye that guides the string onto the pulley perfectly in alignment with the plastic discs of the pulley and prevents it from derailing.

  I noticed that when feeding string into a pulley I intuitively hold the string between thumb and index finger and pull the string away from the pulley as its being fed into the pulley to apply tension on the line and tight wraps on the pulley. I also align the string with the center of the pulley and hold my fingers at a minimal distance away...

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• Pulley Downgearing Tweaks to Design and Rebuild Progress

  Larry • 10/31/2024 at 05:03 • 0 comments

  So it turns out that when the forward and reverse directions portions of the thumb tack pulley downgearing system are doing their thing, they won't always have the same mechanical advantage and so will be moving at different speeds. Therefore, I have to treat the forward and reverse pulley systems as entirely separate systems that have to be completely decoupled and handled independently, each pretending like the other one doesn't even exist. They can share the same thumb tack, but have to be decoupled. So I cut the #2 fishing crimp sleeve in half using my miter saw and have to redo the plastic discs phase.

  Each half #2 fishing crimp sleeve will have 3 plastic discs, one for outside of the larger diameter pulley and one for the outside of the smaller diameter pulley and one to split the two. Three total. And so with 3 plastic discs on each half crimp sleeve we have 6 total discs per thumb tack. We only had to deal with 5 before so things will be even tighter but it's fine. We have enough room.

  Next, since both sets of pulleys have different speeds that vary over time, the one that is not being actively winched in at any given time will be randomly releasing slack in a chaotic way. This can lead to tangling and all sorts of problems. To resolve this, we need a automatic slack tensioner system to aid the pulley system by keeping this releasing group of pulleys in a state of good tension at all times. This I will resolve by the pictured method.

  So basically a tension spring connected to a metal eyelet will at all times be trying to pull the fishing line out of alignment and draw slack out of it. So as looseness is detected, it will immediately draw that in removing it from the system maintaining taughtness everywhere at all times. This will prevent the pulleys from getting tangled or anything like that. This setup can be placed anywhere in the path between the pulley system and the joint the pulley system is to actuate.

• Pulley Downgearing Update and Tweaks

  Larry • 10/30/2024 at 09:23 • 0 comments

  I wound up my 6lb test Hercules PE braided fishing line onto the previous pulley system setup only to find out that the pulley could only handle about 21 inches of fishing line wound onto it before it started to come dangerously close to overfilling the pulley. The aim is to have plenty of the plastic disc overlapping the fishing line even when it is wound up fully to one side because that plastic disc acts as the guide to keep the line in its proper channel. I want at least 32:1 mechanical advantage out of this downgearing so if I want my final output to be 1" then the first pulley has to be able to wind 32" of fishing line onto it comfortably. So I realized at least the first pulley has to be a few more millimeters increased in diameter. So I had to rebuild the thumb tacks arrangement to accommodate these changes and make that first pulley bigger.

  With this increased size first pulley, I realized I'm getting what looks to be 7:1 mechanical advantage from just the first pulley alone! At least initially when it starts. As the fully wound up pulley gets winched in by the motor, the relative size differential gets smaller which means it will speed up and the torque will be less than the starting torque and increasingly so as the size differential decreases. This will create a natural sort of acceleration effect and high initial power and gradually less power. I think these side effects of this system seem to be quite good but I'll know for sure in testing. The next steps will be to wind up the reverse direction of the first pulley and start connecting the first pulley to the second pulley and so on. I may not even need all 5 pulleys but we'll see. With the first pulley being already 7:1, if the remaining 4 are 2:1 say, then we'd have 7:1, 14:1, 28:1, 56:1, 112:1 so 112:1 would be the final output. That seems quite overkill and perhaps will be too slow. Although very strong. The motor outputs about 0.42 lb on average so .42*112= 47lb! Now the lever of the joint itself makes you lose mechanical advantage due to the fulcrum location etc so it would drop down to say 15lb but my finger individual joint flexion power is only like 5-7lb so that's double mine. So a bit overkill. So I might skip using one of the 5 pulleys. Having it there is nice though just in case we wanted to trade speed for power for some of them we'd then use that one as an optional strength boost we can tap into in the future if we want to trade speed for strength so I might just leave it in the design even if I don't use it just yet. In testing I may find I prefer to use it afterall. Nice to have that option if needed.
  

• Thumb Tack Based Motor Pulleys Progress

  Larry • 10/28/2024 at 08:16 • 0 comments

  I got done cutting out the pulley discs and drilling them and mounting them to the thumb tacks and gluing them in place with 401 glue using a sewing needle tip as the applicator. They all are reasonably square and solidly in place I think. Everything is moving freely. Everything seems lined up okay. I then mounted them all to the 2430 bldc motor.

  These thumb tack based pulleys still need to be lashed down well and the lashings (upholstery thread) need to be coated in 401 glue to make them stiff and solid. I also need to add pulley discs to the 2430 bldc motor that are to line up well with the pulley disc slots the string is to go to. I then need to wind up the string sections themselves, loading up the system in preparation for actual testing.

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