My Advanced Realistic Humanoid Robots Project

[Artbyrobot]

Originally Posted by Halcyon

My guess,
you always have to keep some thread-windings around these axles, esp. close to the motor, otherwise it will slip (and hard to restore when everything is already assembled).

This whole project is going to take a lot of work and perseverance. Goodluck with it.

yes that's correct. Keeping them wound tightly around is very important to prevent the string from derailing off track. For this purpose I have had to develop tensioner designs that keep the string taught at all times to prevent any issues. Avoiding failures like the one you foresaw has been one of the great challenges of this pulley based downgearing stuff.

[Artbyrobot]

Here's my completed V2 archimedes pulley system finally done! It is 16:1 downgearing and this pairs with my 2.77:1 downgearing on the turn in place pulley on the motor for a total of 44:1 downgearing.

[Artbyrobot]

Here's progress on a return spring for extension of the finger after pulley system has caused it to grasp.

[Artbyrobot]

Ok so I did a big refactor of my pulleys and ran a test again and it still is not working. The first set of archimedes pulleys tops out and can't move anymore while the finger still hasn't moved. This is because of slack in the lines. I did not calculate slack in the lines into my calculations at all and am shocked by how much there is... Rather than do a major new overhaul with new math and new draw distances on every pulley AGAIN, I'm going to just drop the final pulley of the system so instead of 44:1 it will be 22:1 now. While we cut half the grip strength with this move, this might be okay after all. It still gives us 20lb of of burst grip strength I believe and 11lb of casual easy sustainable grip strength. Most common tasks should only require 8lb of grip strength anyways for a single joint tops. Because remember, I'm not doing a single motor for all 3 finger joints but one motor per joint which helps alot in the strength department and control department. So anyways, this hack I think is okay also because it hit me lately that I highly doubt I'd use the full beast mode burst strength of a 44:1 downgear anyways. I'd be too worried about the wear and tear on the fishing lines and pulleys and maintenance times getting too short between maintenance overhauls if the robot is using that level of grip strength for tasks. In reality, I am now imagining I will only let the robot do VERY minimal strength stuff to reduce the maintenance to a minimum. Like sewing, cutting, and delicately picking up small loads. I will treat it like it has the strength of my 4 year old just to baby it and make it last longer between repairs. Kind of like having a old beater car you don't trust and never throttling the engine hard but just gradually easing on the gas pedal to avoid blowing a gasket so to speak and avoid a trip to the mechanic. So that said I think 22:1 might actually be okay. And with that final pulley out of the way, I'll have WAY more than enough draw distance to bend the finger 90 degrees and account for string slack AND account for string stretch over time without any issues at all. Much better. Not to mention we do pick up speed this way and that might be a VERY nice feature when all is said and done. A faster moving finger can speed up its work I think. Like notice how 3d printers go way faster and that speeds up prints. So speed might be king over grip strength in the end perhaps. It's a tradeoff.

Another update is I realized I can wind a second very fine 0.08mm fishing line on the output portion of the winch in place pulley mounted next to the motor and this second line coming off that pulley will be attached to a tension spring consisting of a bracelet jewelery making cord for jewelry for kids. This line will maintain tension on that winch in place pulley and the motor output shaft at all times to prevent derailments. The metal tension spring that extends the finger will then have the help it needs to keep the whole system taught. That's the plan anyways. The runout of this line will need to be 12.48" of tensioned draw. To achieve that I need a length of this cord of about 15" I think which stretches to 27.48" at full extension. This would occur each time the motor causes the grasping actuation and it would be playing tug of war with the motor so that when motor relaxes or reverses direction, the winch in place is remaining tautly in opposition.

[Artbyrobot]

A note on fishing line durability. I think this was mentioned in passing quite a few times but at some point, a mention of durability concerns becomes that final mention that makes you really start to question it more and so I finally did some research on chatgpt and found out a human finger joint probably will actuate like 1-2k times per day which blew my mind since that would add up to like 10-30k times per month and so basically, once a month the main finger fishing lines will likely need replacement. I looked into alternative materials but didn't have much luck. So what to do?

Well after thinking about this a fair bit, my conclusion is to just shrug and move forward as it stands with the fishing line approach. I'll treat them as a consumable. My plan now is to just expect 1 hour of maintenance for every 20 hours of runtime. Or maybe to be more conservative, lets bump that to 1 hour of maintenance to every 10 hours of runtime? Maintenance will involve redoing pulley systems with fresh fishing line, or swapping in full new pulley systems to replace older ones every so often. It can have a pre-emptive maintenance schedule. My intention is that one robot will maintain his neighbor and the two will have a buddy system of maintaining eachother. Once I have expected time to failure of fishing lines established, they can swap in new ones automatically to prevent failures from happening during work times.

I don't think this is too bad of a deal or a deal breaker. Yes, hopefully materials advances will give me a better string one day, but for now, I'm okay with this maintenance scheduling thing. As long as its all automated, I think this is fine.

After all, our bodies muscles constantly need repairs and they grow from the repair process. So what do you expect for artificial muscles that can't self heal? Maintenance has to be a regular thing IMO.

[Artbyrobot]

Update: I bought several sizes of kevlar string to use to replace the PE fishing line particularly in the high tension areas that may face the highest durability challenges. I found it on amazon in many sizes. I just bought one of each size: 0.5mm diameter 50lb test, 0.8mm diameter 100lb test, 1.1mm diameter 200lb test and 1.3mm diameter 300lb test. This is probably a game changer for my project IMO.

[Halcyon]

You are one mad scientist.

Fishing line is durable (many years when applying radius and no kinks) but also stretching a bit and smooth (slippery).

Dyneema or kevlar rope is good choice, it does not stretch and is very strong. But beware can also cut in your pulleys due to pull force.

[Artbyrobot]

Thanks Halcyon. I did not know fishing line is durable I'm hearing different opinions on that so I hope you are right since for the very small diameter stuff like 0.08mm fishing line I use for the first pulley, I can't find kevlar that fine so I still plan to use fishing line there. The kevlar will be for the higher force and higher friction areas of the later pulleys in the downgear process.

[Silas Loki]

Hello Artbyrobot

I've just found your thread. I'm working on a "similar" project - but with a completely different outcome in mind

That said, I see some interesting cross overs - and I'm not going to lie - some of your points have inspired some considerations for my own project.

That said, and focusing on your specific desired results - I think there are some fundamental aspects of the orginal concept that you might want to consider.

1. What is the specific driver for the "robot" to look / pass for a human? On a purely physical level - a human is a human based on evolutionary needs - every aspect of human physiology has evolved to help the organism thrive in it's natural habitat - however, it would be stretch to say that human physiology is "perfect" - so the question is, why constrain your design to mimikry of a "flawed" design - when you would have the ability to tailor your physical result to your specific use case.

2. While you seem to be putting a lot of effort into the mechanics of movement and physical replication - ultimately, the biggest (understatement) hurdle you will have is the "Brain" - you use the term "Robot" - and this has a specific definition in engineering terms - but to be specific - are you looking to create an Android or an Automaton? There is light years of difference between the two products. Assuming you are looking to create an animatronic "human" - then, I'm sorry to say, there are lots of resources that you could follow to get the job done without - well - "reinventing the wheel" - a lot of the challenges you are or will face - have already been solved for animatronics and there are even D.I.Y projects that you could follow (and improve upon) to get to your goal quicker and without the waste of resources and time that is native to this type of project.