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.

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.