My Advanced Realistic Humanoid Robots Project

[artbyrobot]

Okay, so I finally got the Dinah robot hand sewn in and it is looking pretty good. The fingers could use some tweaking but overall I'm quite happy with how it came out. It's solid and fully articulated.

Here's a photo of it in place:

Now that out of the way, I want to announce I'm officially canceling the Dinah project as far as its current goals and here's why: so basically I was thinking it would be nice to just crank out a working robot using some shortcuts and just do something quick and dirty as a learning experience side quest to get something going. It seemed reasonable at the time. Plus I could pace myself to match the build pace of a fellow roboticist and loosely follow his project's designs. But some things I missed in this decision: #1) I'd be lowering my commitment to excellent quality with no shortcuts - ignoring the adage "do it right the first time" #2) by cutting down on workmanship maxing, I'd be inviting harsh criticism on the new lowered bar of build quality which is the last thing I need when already inviting heavy criticism for a extremely ambitious set of goals to begin with #3) I'd be going against my outspoken commitment to campaign against loud metal gear noise based robots that are completely impractical for home use due to sounding like a construction site #4) it would take away from the focus on my "real" robot projects by creating a "ghetto" side quest robot that could have just been skipped altogether. #5) this would in turn delay me truly solving downgearing by pulleys and actuating the robot arm silently once and for all, proving it can be done and proving that achieving a fully human level DOF human hand and arm while maintaining a human form factor and making all of this silent can and should be done for humanoids.

So is Dinah robot just trash now? No. I still plan to have this project be done, but like Adam, it will be shelved until such a day that the other robots, when ready, complete building these shelved robots for me. And when they are built, it will be using the best methods I have including silent BLDC motors with silent pulley based downgearing. So I'm returning to work on the Abel robot whose arm will build the rest of his own body and then he will build the Adam, Eve, and Dinah robots for me.

 

[artbyrobot]

Here is a progress update on the silent pulley downgearing system I came up with using thumb tacks and a #2 fishing crimp sleeve and little plastic discs. It is some tiny fine precision necessary work but I'm getting it done and things seem to be looking pretty good so far.

For now, I ended up just using 401 glue to glue the thumb tacks down onto post it note paper. I then put another coat of the glue over the tops of the thumb tack heads to secure it further. I am planning to use nylon upholstery thread lashings to lash all the tacks down onto the top of the 2430 bldc motor tightly and glue the lashings down as well in order to make the thumbtacks even more solidly set into place. Now I'll grant welding them down would be ideal, however, not having a micro tig welder made yet (future project), I just wanted to get going fast and I thought with enough care, it is possible these can be constructed solidly enough with composite material techniques to function reliably. I'm crossing my fingers. We'll see.

 

[artbyrobot]

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.

 

[artbyrobot]

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.

 

[artbyrobot]

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.

 

[artbyrobot]

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 but not too close. You want the string to be able to easily angle up and down from your finger pinch point to ride up and down the height of the pulley creating layers of wraps evenly as opposed to all wrapping in one area and not having a well distributed wrapping. If you study how to wind a bobbin on the top of a sewing machine, you see the string take 3 turns and go through a metal wheel that places tension onto it and only then does it enter the bobbin which it then winches onto the bobbin rapidly to wrap up the bobbin with string. These are all designed to create tension from the otherwise loose and floppy string leaving the main spool of thread you are feeding into your empty bobbin. I need to create a similar type of tension system to feed onto my pulleys which are acting just like that bobbin and need the same type of setup to succeed.

To create the eye that centers the string and forces it to neatly stay on the bobbin and not derail so easily, I plan to use 28 ga tinned copper bus wire. I will cut out a small section of that wire and glue it to the base platform the thumb tacks are glued to and then run it vertically and then form the eye shape that acts as a guide and derailment preventer. The eye will just be a oval with a couple legs glued down with 401 glue to hold that oval into position.

For the tension maker, I'm planning to use just a couple windings of tension spring with two small square pieces of plastic which will sandwich together and be pinched together snugly by the tension spring and the fishing line will be fed through this. I will use the same produce container plastic I'm using for the pulley discs. The fishing line will not be abraded/damaged by this in theory but only some pinching force applied to it to give it some tension and cause its feeding action of winching onto the pulley to be tight and snug to help prevent derailments and tangles and loose wraps. This system is meant to emulate and replace holding the string snugly between thumb and index finger as it's fed into the pulley tightly.

Note: I'm not surprised I'm having these issues. The system was not under tension with the spring tension system I posted in my last post yet so that's largely why this is all happening. These measures are mainly resolving issues caused by that lack. However, by adding these problem preventers into the system, I make the system more redundantly protected from any issues coming up in the future. It's like backup systems for problem prevention here.

Note: thinking back to the tremendous struggles and trial and error I watched the engineer on the YouTube channel "StuffMadeHere" has been an encouragement to me in this struggle. His videos never really have just perfect flawless success the first test run. There is always problems and tons of trial and error tweaking to resolve each issue and creatively work around it until he ends up with these beautiful and elegant solutions in the end that work great. This seems par for the course so I just have to remember that this type of headache phase is typical.

Note: it is VERY tedious to have to untangle messes I've made due to lack of tension and proper guidance etc for the string windings. We have 5 total windings each around 3 feet long and all within a envelope close to the area of my thumbnail. It's all compact and tedious and little precision needle nose tweezers or the tip of a sewing needle is the only stuff small enough to even get in there to grab anything. Just a overwhelming mess to fix issues. Not for the faint of heart. If I did not believe this has strong potential I'd give up but everything so far isn't proving lack of merit but moreso is user error and not having a good setup going yet. But even that is a good thing as studying the error and causes of error is giving me great insight into what needs to be done to prevent future error and make the system reliable. I need this first hand education to preempt future errors.

 

[artbyrobot]

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 pulley design. I think that method might be a little more robust and I kind of just want to use both methods at this time. Both have their pros and cons. I feel using both methods can help me learn which one is superior and learn to perfect both as I see which one is more durable long term, which one has more incidents, which one tangles from time to time and why and resolving those issues if they come up.

The great thing is this: the compact pulley method (thumb tack method) is giving us 8:1 downgearing roughly. Of the 27" of total draw, that brings output draw at that point down to 27/8=3.37". So the final two downgearing stages will be reducing 3.37" draw down to 0.84" draw. So 3.37"/2=1.68" then 1.68/2=0.84". So the Archimedes pulley system only needs TWO pulleys (down from whatever huge number we had before in our previous monstrosity of wraps and turns we had to do). To make just two pulleys is a piece of cake. Also, given 3.37" is all we are working with for the first pulley, and the pulley is equidistance in the center of that stretch, the total draw length of the two string halves wrapping around that first pulley is only 1.68". And the next pulley's total length is .84". So 1.68+.84=2.5" give or take is the total length of the pulley system for this. This edition of the Archimedes pulley system adds 4:1 downgearing to the compact thumb tack pulley system's 8:1 downgearing. Giving us a total of 8x4= 32:1 downgearing. That 2.5" total length Archimedes pulley system setup is so small compared to my original 16:1 Archimedes pulley system I published earlier that it is a lot more practical to use and we still save a ton of space.

 

[artbyrobot]

Note: I could do the rotate in place style pulleys but just put them on the forearm instead of the motor as the motor is already getting quite cramped and tedious to work with. Or I can do Archimedes pulley system style with pulleys that move lengthwise along the forearm. Both styles are good. I lean toward the latter though at this time. Both would work though. I kind of just like the variety for learning purposes but I'm not 100% sure on this decision.

Note: an advantage to completing the final 4:1 downgearing on the forearm closest to the finger joint is the total distance of string travel from the motor to the finger joint and the total bends it takes all adds friction and when that friction is placed with a large force on it, it is harder on the teflon guide tubing. But by only doing partial downgearing at the location of the motor and saving the next phase of downgearing for being closer to the finger joint in question, we avoid a lot of forces and frictions in the teflon guide tubing running longer distances to get to the finger. In some cases, I have motors intended to actuate finger joints placed in my CAD as far away from the finger joint as the upper spine area and some in the lower latimus dorsi area! That is a LONG travel to go across the torso, past the shoulder, down the humerus, past he elbow, down the forearm, and then FINALLY to the finger joint it is actuating. That is a LOT of friction and turns introduced. So to navigate such long distances, it is ideal to have it be just high speed low torque during that time-frame and only beef up the torque with downgearing NEAR the finger joint it is actuating.

Note: the fishing line selected for downgearing while in the early phases of downgearing gets to be very fine low test strength fishing line like the 6lb test braided pe fishing line I'm using here. However, as the downgearing progresses, trading speed for torque, so also the fishing line selected for these sections needs to progressively get larger in diameter to accommodate the higher tensile forces involved. So we'll be graduating from 6lb test to 20lb test then 70lb test then 130lb test. So we'll be changing fishing line diameter 4 times in the routing from the motor output shaft to the joint itself! That said, keeping the downgearing near the motor minimal is best since it enables us to use the finer diameter fishing line for the long travel distance from the motor to the finger area. Then only once near the finger do we do the final downgearing stages and beef up to the larger diameter fishing lines. Then another advantage to all of this is the teflon tpfe guidance tubing we are using as guide tubing gets to be smaller diameter guidance tubing for those long fishing line runs. This saves space and enables us to make tighter turns without as much consequences in terms of wear and tear on those turns and tension/friction concentration at those turns. Also, when making turns AFTER full downgearing, the higher forces involved tend to want to crush and deform the TPFE tubing - which is why sometimes metal spring is used on the outside of the TPFE guidance tubing to make it into a Bowden cable and reinforce it to make it non-collapsible under the high tension forces that get involved by that point. We avoid all of this by keeping the downgearing at the location of the motor more minimal.

Note: that all said, our downgearing at the location of the motor thus far is planned to be 8:1. The motor outputs .45lb at our distance from the center of the motor shaft roughly. So 8x.45= 3.6lb of tension force as the output at the motor then. This means we get to use our 20lb test fishing line for the long travel from the motor to the distal forearm where we will do the final 4:1 downgearing bringing us up to 32:1 downgearing. That 20lb test line is only 0.2mm diameter so it and the TPFE guidance tubing we pair with it is very fine and can easily weave its way past everything and get to the distal forearm without taking up too much space or having to be reinforced by metal spring to prevent crushing or distortion of the TPFE. At least not in theory. If this proves not true, I can always add metal springs to any sections that are getting crushed or distorted to reinforce the outer diameter of the TPFE guide tubing in those areas - probably areas near tight turns? We want to take as few turns as possible though and make the turn radius as large as possible to cut down on friction as much as we can during the fishing line routing runs.

 

[artbyrobot]

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.