Ok so a quick couple updates.
First, since the ideas for downgearing with pulleys have been coming in fast and furious, ways to do it easier or ways to fit it here or there or what have you, it's getting a bit scattered and I'm now starting to tear down my work too much for my comfort. It's like I'm chasing the next shiny new approach a bit overly now. So I decided to stick to the current approach as long as it is viable enough to be "good enough" so as to not waste my hard work anymore as I was starting to do. For example, the pulley system I was testing with a 10lb dumbbell did not need to be torn down and rebuilt I don't think. Stuff like that is starting to cripple progress in some sense. So my new approach is when I come up with a idea for a possibly better downgear implementation, I will just write it down and put it in a queue. Then on the next joint actuation I will use these. This way I can have like 10 different downgearing approaches over 10 joints and I can compare and contrast them, note the pros and cons of each, and over long term testing I can find the clear winners. This will also give me a greater understanding and experience and take more out of so much guesswork and into more concrete and tested territory on this stuff.
A side benefit is that people tend to think I've progressed zero with pulleys since I keep building them then taking them apart and starting over. At least under this new approach, I get joints done and over with and working before building the next downgear iteration so the progress feels more tangible and the robot gets done rather than just being in iteration and tear-down cycle hell where it appears from the outside like I am not actually accomplishing anything. So that part will be nice.
Another cool development is that I realized I can put a pulley downgear inside a tube. Normally up to now I was exiting the guide tubing to do a downgear and then afterward the string goes back into tubing to go to wherever. But I realized particularly if doing a fishing hook eye downgear that the entire downgear phase of that can fit into a tiny tube and that has some nice perks. For example, if the 2:1 downgear is the first downgear right off the motor, and the motor is reeling in 32" of string, that 2:1 will be 16" long. Well now that I can do my first 2:1 downgear all within tubes, I can run the downgear from the shoulder to the wrist, giving me PLENTY of room to deal with that amount of runout. This is quite exciting and just gives me more freedom and flexibility. I might do something with this for the first couple downgears so a 2:1 downgear pulley #1 and a 4:1 downgear pulley #2 but then do the rest in the forearm as initially planned and most likely using ball bearing based pulleys for the more heavily downgeared higher force phases of the downgearing process.
That all said, I have the downgear system of 44:1 downgear now done and attached to the finger fully and the extension spring attached to the extension side of that joint fully. So I am ready to begin testing and see how much that spring fails to extend the joint due to friction and motor magnetic cogging issues. I will then add more and more springs until it works. That is my solution. Yes, those springs collectively are fighting the motor when the motor goes to actuate grasping, however, that is just a concession we have to make with this design. Other downgearing designs that don't involve springs for that aspect but involve bidirectional motor actuation with pulley systems for either motor direction are coming next. But I'm finishing the spring based design I was talking about for some time now rather than scrapping it as I was planning of late. It is not THAT bad and it deserves to be at least tested and shown the light of day. It would be a shame to waste that work. It was good work. Also, I realize it MIGHT be the best solution. My theory says no but I can be wrong. Testing is the only way to know 100%. So it's worth keeping it as one of the downgearing methods I'll be testing out.
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.