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 the final output string using the TPFE tubing around the side of the elbow this time and then across the forearm and over to where I have setup my Archimedes pulley system from before. This Archimedes pulley system is getting a total overhaul. Many improvements planned for it. So that is up next, overhauling that. And then I will be ready to connect the turn in place winch pulley and its 2.4:1 or so downgearing with the 16:1 Archimedes pulley downgearing to achieve around 38:1 downgearing in total.
I must say it is a bit demoralizing and annoying to rebuild the winch in place pulley system 3-4 times now but I guess it’s fine. That is part of the trial and error refinement process and learning process. That is how we improve on it and correct any false presuppositions we had. That is why experimentation and testing are important. So in some sense, even just having to build it just 3-4 times is a testament to the design process actually going pretty smoothly. Much better than having to do 20-30 rebuilds to get it right. So we were pretty accurate then on our overhauls and can limit rebuilds if we think it through well and do a great job. I hope this time we got it perfect and can move on to other things! Testing will tell.
Ok so I’ve been now working toward creating the latest iteration of the Archimedes 16:1 pulley based downgearing system and as part of that I decided to remake some of the pulleys with grooved outer races as I had discussed previously wanting to do - in order to prevent the fishing line from walking to a corner of the pulley and wedging itself in between the bearing and the plastic disc sandwiching in the bearing and becoming jammed that way. Previously, we had glued in a very tiny piece of clear thread to block this gap anywhere I found the tendency for jams to happen, however, to create a grooved outer race from the outset is going to prevent this issue all together!
So to do it, I took my little 1x3x1mm ball bearing and pinned it down with my left thumb against wax paper on top of a stack of post it notes, so holding it all with my left hand in the air. I used my highest zoom on my visor magnifier to see what I’m doing. I then loaded very tiny amounts of super glue onto my xacto knife with sewing needle tip instead of blade tip and using this sewing needle tip, very carefully placed super glue into the joint where the ball bearing outer race meets the wax paper. I did this for about 1/3 of the bearing then carefully lifted off the pressure of my left thumbnail pinning it down and rotated the whole thing then repinned the bearing down again with my left thumbnail and repeated the process of adding glue little by little. When one side was done, I was able to carefully peel it all up from the wax paper, flip, and do the other side.
This needs to be carefully trimmed down still but the idea was a massive success. The bearing still spins freely and the grooved outer race is done! That fishing line can’t go ANYWHERE now to jam anything! The photo is just the ball bearing and the glue. So the plastic discs will now be able to go over this and the fishing line won’t be able to walk across the outer bearing surface and jam itself between the bearing and the plastic discs anymore!
Note: my concern about this procedure was that the glue could potentially walk underneath the bearing and glue the outer race to the inner race and thereby ruin the bearing - but this did not happen! The gap between the underside of the bearing and the wax paper which were both firmly pressed together by my thumbnail was too tight for the glue to travel into there and ruin anything. So the glue only went where I wanted it - which is on the outer race of the bearing forming the intended groove on that outer race. A huge success. I used 401 glue btw.
Here’s a better image of the grooved outer race with more refinement. To refine it I cut away excess glue with exacto knife and then sanded it with a nail file a bit to smooth it out.
Blender is no longer free unfortunately. Unless, you get it cracked. But not on a mac
Ok so I was struggling to plan out how the flat spiral coil constant force spring would maintain constant tension on my first winch in place pulley the past couple days and I was studying how tape measures use these springs. Then it hit me when a colleague was mentioning belt pulley based downgearing that a belt pulley based downgearing for this first pulley would remove all the issues of derailment and need for constant tension during whole duration of travel a winch style would require in this design. Also, since its just .4lb-.8lb of force for the first pulley downgear, as long as the belt is reasonably tensioned and has some decent grip to it, I should not deal with a ton of slippage issues and the motor’s output should be passed along well. So here is my beginning attempt at converting my first pulley to a belt based pulley instead of fishing line winch based pulley.
This is made just using adhesive transfer tape applied to one side of a nitrile glove and cut out into a 1.1mm wide strip and applied to the two pulleys directly. Built in place.
Early testing shows it needs more layers to have less stretchiness or needs to be reinforced internally with fishing line wraps between layers to prevent so much stretch to it which causes slippage. Also, the motor output shaft acting as the winch pulley is a combination of a bit too small in diameter and a bit too smooth to create a proper grip. So I’m thinking of thickening it up some and adding a grippy surface to it so that it grips the belt better with less slippage.
I am considering using silicone rubber to coat the motor output shaft or several wraps of nylon upholstery thread and super glue to thicken it then coating that with carpet anti-slip paint. Or silicone.
I’m considering making the belt from a cloth coated in silicone or carpet anti-slip paint and then sewn tightly into place over the pulleys - creating a sewn seam for a tight grip.
I’m considering a tensioner pulley but I think that’s overkill and should be avoided unless it proves absolutely necessary.
I have not explored purchasing options at this time but of course I’m open to look into this in the future. The thing about a premade is it would have to be a perfect fit in both length and width and I’m not sure if that will be easy to find or not. This is all a very new approach so I can investigate that later. For now I’m happy to just move quickly on the prototyping with materials on hand.
