Project: Melissa Hands - Perhaps a little easier..
Project: Melissa Hands - Perhaps a little easier..
by PaulL
Mon Feb 15, 2010 3:42 am
I know this is the Home Built forum, but I am taking a different approach to the hands I'm making for my RN-1 that is a good bit less work.
I bought some Igus E-Chain, E03-05-010-0, along with some end brackets, 03-05-1Z. I had to insist that this is the correct part number and that I didn't want "pairs" for both ends.
This chain is the smallest chain Igus sells, and the smallest I have ever seen. It is "large" by comparison to other Melissa hands I've seen, but I think the size will suit the look of my RN-1 quite nicely.
In the pictures:
I have a .015 inch thick by about .198 inch wide white Teflon strip connected (tucked for now) into the tip of the index finger and running through the finger in some of the pics.
The tips of the fingers have 4-40 sized aluminum screws in tapped holes, I just didn't screw them down or lace up all the teflon for the pics.
I have inserted UHMW blocks into the E-chain to keep the Teflon riding on the inside of the finger, the blocks at the tips of the fingers are tapped 4-40. I machined these blocks in manual mode on my CNC mill, but it wouldn't take much to do this by hand- just more time. If you look closely, you'll see two protrusions in one pic that "lock" the block in place so it doesn't slide. The thickness of the teflon and the height of the block is such that the blocks go in first, then the teflon is fed in underneath, locking the blocks in place. These blocks are from white UHMW died with black Rit Dye- it doesn't take perfectly, but I think the gray looks nicer than off-white.
I have not modified the travel of the e-chain to 90 degree angles, but I could. I think this will work fine as it is, but I can snip off some plastic and get them to bend at 90 degrees, I've done that on a couple of pieces to test.
The "base" of the hand is just a piece of polycarbonate to prototype finger position and shape.
The "spikes" from the E-Chain at the palm of the hand is how the e-chain mounting brackets are made. For now, I just have them pressed into the polycarbonate. Ultimately, they will get screws, and the spike will get snipped flush to the aluminum palm plate to prevent rotation, as there is only one screw hole in the end brackets.
As you can see from the pictures, there really isn't all that much work here, and finishing these up with a single servo won't be much work either.
However, I am seeking a solution to individually move the fingers. I started by trying out some M2 threaded rod on micro-motors, but not enough torque and way too fast when I could get them to turn. Besides, motor control circuitry would all have been custom.
I'm looking into a suitable nano / micro servo that will work. With Teflon, I can pull the finger fully closed at 8 oz of weight easily. I can go lighter, but that works out to a 4 oz/in servo with a half-inch arm (and it will need to be shorter than that, with about a 10cm throw for the teflon strip).
You can see from the pics, it shouldn't look too out of place to have the servos protrude into the space of the palm and the back of the hand.
One last note, the teflon strip must be supported more than about .3 inches, not a real problem, but a design consideration.
Thoughts, Comments, Questions?
Paul
Pics:
I bought some Igus E-Chain, E03-05-010-0, along with some end brackets, 03-05-1Z. I had to insist that this is the correct part number and that I didn't want "pairs" for both ends.
This chain is the smallest chain Igus sells, and the smallest I have ever seen. It is "large" by comparison to other Melissa hands I've seen, but I think the size will suit the look of my RN-1 quite nicely.
In the pictures:
I have a .015 inch thick by about .198 inch wide white Teflon strip connected (tucked for now) into the tip of the index finger and running through the finger in some of the pics.
The tips of the fingers have 4-40 sized aluminum screws in tapped holes, I just didn't screw them down or lace up all the teflon for the pics.
I have inserted UHMW blocks into the E-chain to keep the Teflon riding on the inside of the finger, the blocks at the tips of the fingers are tapped 4-40. I machined these blocks in manual mode on my CNC mill, but it wouldn't take much to do this by hand- just more time. If you look closely, you'll see two protrusions in one pic that "lock" the block in place so it doesn't slide. The thickness of the teflon and the height of the block is such that the blocks go in first, then the teflon is fed in underneath, locking the blocks in place. These blocks are from white UHMW died with black Rit Dye- it doesn't take perfectly, but I think the gray looks nicer than off-white.
I have not modified the travel of the e-chain to 90 degree angles, but I could. I think this will work fine as it is, but I can snip off some plastic and get them to bend at 90 degrees, I've done that on a couple of pieces to test.
The "base" of the hand is just a piece of polycarbonate to prototype finger position and shape.
The "spikes" from the E-Chain at the palm of the hand is how the e-chain mounting brackets are made. For now, I just have them pressed into the polycarbonate. Ultimately, they will get screws, and the spike will get snipped flush to the aluminum palm plate to prevent rotation, as there is only one screw hole in the end brackets.
As you can see from the pictures, there really isn't all that much work here, and finishing these up with a single servo won't be much work either.
However, I am seeking a solution to individually move the fingers. I started by trying out some M2 threaded rod on micro-motors, but not enough torque and way too fast when I could get them to turn. Besides, motor control circuitry would all have been custom.
I'm looking into a suitable nano / micro servo that will work. With Teflon, I can pull the finger fully closed at 8 oz of weight easily. I can go lighter, but that works out to a 4 oz/in servo with a half-inch arm (and it will need to be shorter than that, with about a 10cm throw for the teflon strip).
You can see from the pics, it shouldn't look too out of place to have the servos protrude into the space of the palm and the back of the hand.
One last note, the teflon strip must be supported more than about .3 inches, not a real problem, but a design consideration.
Thoughts, Comments, Questions?
Paul
Pics:
by billyzelsnack
Mon Feb 15, 2010 4:43 am
What about putting the finger servos elsewhere like on this guy..
http://www.plasticpals.com/?p=2942
http://www.plasticpals.com/?p=2942
by PaulL
Wed Feb 24, 2010 9:06 am
Tyberius: Thanks! Yours is looking pretty sweet, too!!! I have to say, this is much easier (and lighter) than fabricating them from metal... What sort of product is it you've got there for the fingers?
Billy: I've pondered servo locations for finger servos, and there isn't any easy way to do it without limiting range of motion and having difficulties getting the servo movement down the arm to the hand (cables, rods, pulleys, etc). I think I will be able to get a decent look with them in the palm, but I need to settle on some cheap micro / nano servos- lots out there, but I don't want junk, either!
Robotbling: That's what I'm hoping to do. I'm not so much into having him pick up things, though he should be able to clench something against his palm- I'm more interested in the communication aspect of hand gestures... LOL!
Regarding 5 servo control in one hand: I don't want to have to run a huge lot of wires down the arm, so I'm looking to use something like this: http://www.pololu.com/catalog/product/208 to put in each hand so that I only need to run the serial interface and power to each hand.
Take Care,
Paul
What sort of product is it you've got there for the fingers?
Billy: I've pondered servo locations for finger servos, and there isn't any easy way to do it without limiting range of motion and having difficulties getting the servo movement down the arm to the hand (cables, rods, pulleys, etc). I think I will be able to get a decent look with them in the palm, but I need to settle on some cheap micro / nano servos- lots out there, but I don't want junk, either!
Robotbling: That's what I'm hoping to do. I'm not so much into having him pick up things, though he should be able to clench something against his palm- I'm more interested in the communication aspect of hand gestures... LOL!
Regarding 5 servo control in one hand: I don't want to have to run a huge lot of wires down the arm, so I'm looking to use something like this: http://www.pololu.com/catalog/product/208 to put in each hand so that I only need to run the serial interface and power to each hand.
Take Care,
Paul
by Tyberius
Wed Feb 24, 2010 7:12 pm
RN1AsOf091407 wrote:Tyberius: Thanks! Yours is looking pretty sweet, too!!! I have to say, this is much easier (and lighter) than fabricating them from metal...
Take Care,
Paul
I believe I used the E2 Micro Series 03 instead of the EZ series. The E2 is fully enclosed rather than split like the EZ is.
by PaulL
Fri Mar 05, 2010 11:23 pm
Two options I have ordered to test are:
http://www.hobbycity.com/hobbycity/stor ... oduct=9658
and...
http://www.hobbycity.com/hobbycity/stor ... oduct=7026
The tallest of these two servos is .944 inches from base to top of servo horn, which is amost as thick as the e-chain I'm using when doubled back on itself, as it appears in the pictures when the hand is clenched, viewed from the side. I think I can stack these servos side-by-side and make them look appropriate in the hand. The routing of the teflon strip to the thumb is the only question I have mechanically, and I may do some sort of twisted guide to get what I need for that.
Just looking at the specs, I'd prefer the U.S. $24.92 servos for more torque and all metal gears, but if the U.S. $9.60 servos work well enough, I will use those.
There are cheaper "nano" or "micro" servos, smaller than these that might work, but these seem to be the best candidates I've seen so far. Perfect would be a 3kg/cm linear actuator with 10mm travel at .2 seconds in about a 7x7x20 mm space running about 6v / 100 mA at stall, but I haven't found one of those yet... (yes, a joke)
http://www.hobbycity.com/hobbycity/stor ... oduct=9658
and...
http://www.hobbycity.com/hobbycity/stor ... oduct=7026
The tallest of these two servos is .944 inches from base to top of servo horn, which is amost as thick as the e-chain I'm using when doubled back on itself, as it appears in the pictures when the hand is clenched, viewed from the side. I think I can stack these servos side-by-side and make them look appropriate in the hand. The routing of the teflon strip to the thumb is the only question I have mechanically, and I may do some sort of twisted guide to get what I need for that.
Just looking at the specs, I'd prefer the U.S. $24.92 servos for more torque and all metal gears, but if the U.S. $9.60 servos work well enough, I will use those.
There are cheaper "nano" or "micro" servos, smaller than these that might work, but these seem to be the best candidates I've seen so far. Perfect would be a 3kg/cm linear actuator with 10mm travel at .2 seconds in about a 7x7x20 mm space running about 6v / 100 mA at stall, but I haven't found one of those yet...
(yes, a joke)Hi RN1AsOf091407. I made a 3D model for you.
by bonmot
Sat Mar 06, 2010 5:38 am
Now you can have more ideas
by PaulL
Sat Mar 06, 2010 5:55 am
Very Nice, and Yes, that's very close to what I had in mind, only with the servos level to the back of the hand with splines up.
Using teflon as I have, or nylon as others have, the general "trick" is to have force applied and removed on one side of the hinge point of the fingers. I hold the teflon strip to the inside of the finger with the blocks I fabricated (grey blocks). If you use wire or other without resistance, knuckles don't open and close evenly. Teflon, nylon, these make the knuckles move in unison when extended or retracted.
Nice Work!!!
Using teflon as I have, or nylon as others have, the general "trick" is to have force applied and removed on one side of the hinge point of the fingers. I hold the teflon strip to the inside of the finger with the blocks I fabricated (grey blocks). If you use wire or other without resistance, knuckles don't open and close evenly. Teflon, nylon, these make the knuckles move in unison when extended or retracted.
Nice Work!!!