As you can see taking a picture with the cell while trying to hold the control cables was not the best way to have a clean photo. I plan to take much clearer pictures with a camera when I make a more substantial model. This one is constructed from balsa, plummers putty, and chewing gum…
Tell me what you think. I know the servos aren’t shown but that will come later.
Each finger and the thumb has it’s own control cable. The Idea is that if your 'bot has the room you could set up each digit with its own servo. If space/weight/power is at a premium you could move them all with one or even move some with one and the others with another.
My final will be a bit more compact than this and will look more like a ‘mecha’ hand. The thumb seems a bit long on this one…
I am working out the final design in Solidworks. I plan on making the part injection molded. If enough people think it would be something that they could use I’d like to produce a kit. Otherwise I’ll probably just end up hand makeing them on a consignment type basis.
The arms should be usefull also.
I have some ideas about feet and ankles too.
Please do stop in and offer any help you can since you are a builder yourself…
I think it is only a matter of making it work. I am sure there will be a lot of interest in this if it works out that you can actually build it. I have an idea for a 4 legged walker that actually uses biped type legs.
However, right now I am knee deep in my Octapod Project. I will be starting construction in a couple weeks - as soon as I can get the parts into my hands.
Well, I’m certaintly interested!
I made a hand almost exaclty like this (though it was about twice as large as a human hand) in a high-school class.
We did it out of oak wood, eyelet screws, string, and syringes as actuators.
It hadn’t occured to me that the design could be applied to this, as well.
You said that each finger has it’s own cable.
I assume that this cable closes the finger when tensioned.
Are the joints spring-returned to open, then?
I think servos are a bit overkill in terms of weight and current draw, for most bots.
Have you thought of using a solenoid or some other small linear actuator?
I’ve seen some really small ones.
One could do away with the normal linear-feedback worries by placing pressure sensors on the fingers themselves and using that for PID feedback.
It would mean that you couldn’t tell your robot fingers to go to a specific position (other than full open or closed).
But it would mean that you could tell your robot to close it’s hand until it reaches a certain firmness.
In other words, you couldn’t tell it what positions it needs to put it’s fingers to pick up an egg without breaking it.
But, you could simply tell it to close it’s hand gently, and it would automatically adjust each digit to hold the egg without breaking.
IMO, the latter is well worth the inability to do the former.
I like the Idea of using the force sensor (I like the look of the foam style stuff) it removes the necessity of putting some resiliance in the control lines. There will be room on the finger tips and the palm for such. Since the servo(s) that actuate the digit(s) are going to be able to be located anywhere on the 'bot I don’t think the weight issue will really be a factor. In fact the arms I am planning to fabricate should be very light thus enabling quick movements.
I always thought that solenoids were heavy and wasted huge amounts of power, especially if you were going to maintain a grip with them (keep them activated).
SN96,
Did you post any piccies of your creation? I’d like to see them. Working with digits this small has been a hobby of mine for some time and I’ve collected quite a bit of information from other creative people that has been a very helpful muse to me.
I will be spending more time here. I am excited about absorbing everything you all have created…
I’m not sure what kind of biped you have, but I’m afraid mine wouldn’t be happy carrying around four more servos.
Well, I found a bunch of solenoids that were extremely light and small, but you’re comment about their power waste still applies even there.
The ones I was looking at drew 1/3 of an amp at 12V, which is indeed quite power hungry.
In that case, I’m gonna go check out my SDP SI books and see what options there are for tiny rotary-to-linear needs.
I’m thinking allong the scale of pager vibrator motors (the kind that are used in small solar robots).
Motors that small probably won’t draw noticeable current and the whole 5DOF apparatus might even be small enough to fit inside a single servo case.
If it’s possible, then you could have the actuators in the wrist without a sweat.
I’m sort of envisioning Luke Skywalker’s replacement hand.
By the way… about how much pull distance is necessary to close a fully opened digit?
Your project seems to be a perfect application for Muscle Wire (a.k.a Bio Metal, a.k.a. a ton of other names).
Jameco’s robot store www.robotstore.com has a ton of it.
I’m not sure if the project in the video was pushing the limits of those buggers (I sort of doubt it, based on the size) but it’s probably worth a look-see.
Something like this would be great, though, since the spring itself would provide the necessary give for the digits.
From a brief look, the wire’s aren’t too expensive, especially compared to the equivalent price of a servo.
And, they’re insanely light, to boot.
I wonder what their power consumption is like…
Anyhow, if you like the idea of extra servo, then go for it!
Just wanted to throw out some ideas.
The grippers can be moved by a lone servo if a person wants to limit himself in such a mannor. Most of grippers I’ve seen to date are powered directly by a huge servo at the end of the wrist/arm. My unit will be remotely actuated allowing the arm to be lighter at its end thus freeing up movement. I have seen and tested the NiTi wires. They respond to power quickly enough but you must wait for them to cool a bit before fireing them again and the force required to return them to they’re stretch out state is almost as prohibitive as all of the crimps and wireing requirements. Also, they too require a sustained amout of power in order to accomplish a continuous grip on something where a servo driven gripper can be moved into position and left alone. I have an idea for an alternative actuator involving a ‘hydraulic muscle’ closed loop system but that is MUCH further up the road as R&D for that particular project has run into a wall of monitary decrepitude. That same wall has kept me Bi-Ped free. I have however ordered a servo control board and the software to drive the servos that are offered by the fine folks at Lynxmotion. My gripper should be able to be run by microservos if fortune and inginuity pay off.
Please keep throwing the ideas at me. It is fun and you have made me think about things that will effect the shape of my grippers (the sensor foam).
Your design is beautifull. My design is basically the same. In order to create a smaller gripper though I have simplified the joints and have made the routing of the control cables the most complicated part of the design. I did this in order to realize an opposable thumb. My digits are returned into position using ‘springs’ as Nick surmised earlier thus eliminating the need for a second control wire.
The spring on the ‘tendon’ idea is a good one but it requires you to route another wire in the digits. This adds to the amount of friction/wear points that you have to deal with. Having a passive ‘spring’ at each joint also allows the grip to conform to whatever your 'bot is trying to manipulate.
I have made a second prototype that is about half the size of the one above. It is much stronger and moves with more freedom than the first. I also am working on an ‘Insectoid’ leg. I am planning on my first bot being a hexapod with a humanoid torso that protrudes where a head would be on an insect. Her body will be a cross between a cockroach and a crab shape. She will have two arms and two hands that articulate. I will post photos as I progress. I am supposed to recieve my SSC-32 and the sequencer program monday… Woo HOO!!!
What are you using to make the hands? Also, I’m not understanding what you are saying about the springs on your setup. Perhaps a photo of this would be what I need. I’m a picture kind of guy.
In this image, the line represents where the spring and wire will go.
Use a linier spring like a rubber band on the back side of each knuckle.
The design you show here is very elaborate and would probably be necessary in a larger gripper. I just use a piece of cloth soaked in cryanoacrylate adhesive to join the two joints together and to act as the hinge points. I use standard rubber bands to return the joints to thier original positions. The segments of the joints are construted from balsa wood ATM and thier stiffness is what enables the hand to keep its shape. This kind of construction is also much more forgiving and easy to repair than a more complicated design.
Balsa wood always gets a bad rap, but, pound for pound, it’s one of the strongest materials on earth.
I used to have a brick-sized piece of it.
I won a lot of money betting my friends that they couldn’t break it.
I have to wonder why more people don’t use materials like balsa and foam on their prototypes and even their projects. It makes sense to use lighter materials on smaller creations.
