Degrees of Freedom in an RN-1 and Melissa Hand Possibility
Degrees of Freedom in an RN-1 and Melissa Hand Possibility
by PaulL
Sun Jan 24, 2010 3:42 pm
I have replaced my RN-1 bracket set with a "blue" kit, and I have to say, it looks really nice. This has given me an entire set of spare brackets to test with, and I can use the original brackets to test some alternative options to increasing degrees of freedom in my RN-1 without modifying the installed bracket set.
I have read a few of the hip modifications, and it seems from reading that inserting the height of another servo in the legs causes stability problems. I'd guess this is due to height and play in the servo shaft. My goals- I don't want the height altered significantly, and I don't want to add significant instability. I want him to be able to perform all of his stock moves with little or no modification.
What I am planning on trying is to place the servo behind or beside the two brackets at his hip (using a plate on one of the brackets extending out to mount the servo, to the top bracket if behind him, to the bottom if on the side of him), inserting bearings (one or two ball bearings and one thrust bearing) between the brackets, and rotating the joint via a linkage to the hip rotation servo. I am not looking for 180 degree rotation, I think for him to rotate his leg in a bit, and out 90 degrees should be sufficient. The added height should be about 0.2 inches. To minimize play in the linkage without binding, I'm thinking of using ball bearings at the linkage pivot points. I contemplated using a toothed belt, but the size of the pulleys is prohibitive. The thrust bearing I'm considering is around 1 inch in diameter.
Thoughts?
Melissa Hands - I like the look, as do many, but I want bigger hands, more squared around the fingers such that my RN-1 can still do cartwheels with them. And, I don't want to spend hours upon hours building them. In metal, they're very labor intensive, and I respect those that have put forth the effort to build their own. For the size I want, they'd be heavy if machined out of aluminum, and not squared around the fingers if built from sheet metal.
I had an idea, and a piece of "Igus" e-chain. I snipped off some plastic to tighten the chain radius, and inserted a nylon wire tie. It's large, about a half inch in width, but it works just as the metal ones do, and the radius can be altered such that the knuckles bend to 90 degree angles. I checked out Igus's site, and found that they have much smaller chain, .34 inches in width, .31 inches in height. I'm going to see about ordering some Monday (E03-05-010-0) and see if it can be made into respectable fingers. If they turn out OK, it will be quite a time saver (and not too expensive, either). The main drawback is that the lengths of the joints are fixed, but I can't make a judgement on how they'll look until I have some chain in hand, trimmed, and mounted as fingers. The fingers will be relatively big, but that's the look I'm after. They should be fairly light weight as well, and I won't need to paint them, nor worry about paint or anodizing wearing off at the joints.
Paul
I have read a few of the hip modifications, and it seems from reading that inserting the height of another servo in the legs causes stability problems. I'd guess this is due to height and play in the servo shaft. My goals- I don't want the height altered significantly, and I don't want to add significant instability. I want him to be able to perform all of his stock moves with little or no modification.
What I am planning on trying is to place the servo behind or beside the two brackets at his hip (using a plate on one of the brackets extending out to mount the servo, to the top bracket if behind him, to the bottom if on the side of him), inserting bearings (one or two ball bearings and one thrust bearing) between the brackets, and rotating the joint via a linkage to the hip rotation servo. I am not looking for 180 degree rotation, I think for him to rotate his leg in a bit, and out 90 degrees should be sufficient. The added height should be about 0.2 inches. To minimize play in the linkage without binding, I'm thinking of using ball bearings at the linkage pivot points. I contemplated using a toothed belt, but the size of the pulleys is prohibitive. The thrust bearing I'm considering is around 1 inch in diameter.
Thoughts?
Melissa Hands - I like the look, as do many, but I want bigger hands, more squared around the fingers such that my RN-1 can still do cartwheels with them. And, I don't want to spend hours upon hours building them. In metal, they're very labor intensive, and I respect those that have put forth the effort to build their own. For the size I want, they'd be heavy if machined out of aluminum, and not squared around the fingers if built from sheet metal.
I had an idea, and a piece of "Igus" e-chain. I snipped off some plastic to tighten the chain radius, and inserted a nylon wire tie. It's large, about a half inch in width, but it works just as the metal ones do, and the radius can be altered such that the knuckles bend to 90 degree angles. I checked out Igus's site, and found that they have much smaller chain, .34 inches in width, .31 inches in height. I'm going to see about ordering some Monday (E03-05-010-0) and see if it can be made into respectable fingers. If they turn out OK, it will be quite a time saver (and not too expensive, either). The main drawback is that the lengths of the joints are fixed, but I can't make a judgement on how they'll look until I have some chain in hand, trimmed, and mounted as fingers. The fingers will be relatively big, but that's the look I'm after. They should be fairly light weight as well, and I won't need to paint them, nor worry about paint or anodizing wearing off at the joints.
Paul
