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 installed. So I still plan to reserve space for it on the CAD and ensure it can be done without any major problems or redesigns needed. It should be a smooth and straightforward upgrade option. But for a minimum viable product that can meet all of my goals, it is not necessary to implement in this stage of development. In fact, it is also possible to just have the robot install these on himself once he's building the rest of his own body. Which means me doing it would be a waste of time if the robot could do it later instead of me. So in any case, this acts as a MAJOR shortcut and time-saver for me and will be a big game changer IMO. I'm excited about it. These types of big shortcuts really move the project forward in development very rapidly in large leaps saving countless hours and I love them. As long as they aren't shortcuts that will come back to bite us later, I'm okay with them. I don't think this one will bite us later so I say let's go with it!
Note: it also just occurred to me that the robot could potentially have the extension actuation be in the form of geared n20 motors instead of reverse direction of the main 2430 bldc motors with pulley based downgearing. This would save alot of work but introduce noisy metal gearing to the robot. The reason I think this is okay to do is that these geared n20 motors would be slack lined and not interfere with fingers AT ALL nor be used on any way at all UNTIL the fingers need strong extension actuation - which as I said is incredibly rare. In this rare event, it tapping into these geared n20 motors for some extra oomph to get the extension to actuate harder would solve the problem and the little noise it created would be a rare occurrence type of noise. It would hardly be noticeable then and 99.999% of the time you'd never encounter this noise. The bigger issue would be noise in a common feature like blinking. Now THAT is annoying to hear gears EVERY TIME the robot blinks.
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