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Author Topic: Need some help for a science project.  (Read 9668 times)
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Example sketches of the hand?

There IS no example sketch for the hand: that surely is the whole purpose of the project, to learn how to do that.

As to where "the Arduino and the servos come in"....  well your p003 link very glibly says:

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Once you have your robot hand, you will need to add small servo motors......... To control the servos, you will need a hobbyist microprocessor board

By its own admission, p003 is an abbreviated project idea, and list as a pre-requisite:

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Once the hand is assembled, adding the servo motors, connecting the microprocessor, and writing the code for the microprocessor will require familiarity with a hobbyist microprocessor board (like ones using ArduinoTM, PIC®, or similar). The student should be comfortable with connecting, programming, and testing projects on these boards.

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Oh. Now I understand what you mean. I did sweep and it worked, but I haven't tried knob yet, because I don't have a potentiometer.
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I'll figure it out myself I guess.
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I'll figure it out myself I guess.

Well, yeah isn't that the whole idea? (But with a little help from your friends here too.....)

So, what you need to do now, now that you a) have a hand and b) can get a servo working ala sweep, is figure out how to get the servo to activate the fingers.

You see by now that the servo axle (with one or other of those plastic thingies attached- they're called "horns") goes back and forth. So you need to experiment with how that can (for example) pull one of the finger strings to clench the finger. That experiment will involved figuring out how to mount the hand and the motor on some kind of support, in the correct position relative to each other so that when the horn moves, the string clenches the finger without anything snagging.

I haven't read the hand instructions fully.... what opens the finger when you release the string?- is it just the "springiness" in the straw's plastic at each knuckle? Assuming that, then moving the horn one way will pull the sting and clench the joint; moving the horn the other way will release the tension and the straw will spring back.

Once you have that working on one knuckle you can then extend the idea to the whole project. I think you will be challenged by the space that the motors will take up: you'll have to engineer the positioning carefully to get the strings pulling and releasing freely.

Edit.... you should consider micro servos, like the one I show in my previous pic of the "elbow"... they take up about 1/8 of the room of standard servos
« Last Edit: January 19, 2013, 11:20:07 pm by JimboZA » Logged

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Thank you for the advice. I'm going to be working tirelessly on this project all weekend and on my day off from school too.
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That's the spirit! I had a time when I would bring a bunch of electronic components and sometimes my Arduino to school and secretly experiment during classes.
Good luck!
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bunch of electronic components and sometimes my Arduino to school and secretly experiment during classes.

And the result was the spaghetti tangle in your av, right?  smiley-cool

@Falchion.... take it slow and carefully. Get a plan together, don't try attach a zillion servos to a zillion strings: get one joint working then one finger. (Here's a thought.... it might be an idea to make a "test-finger", as distinct from the hand, just to simplify things while you get that sorted.) Then extend that thinking to the hand as a whole.

I think each knuckle has a string?- in theory that means one servo per knuckle... maybe you can "bunch" strings together and use one servo to move a finger?- I don't think you need to move each finger segment individually do you? So if you pull all the strings on a finger at once, you can probably clench the whole finger.

If it comes to that, maybe you can clench the whole hand with one servo?

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This is the only part I don't get. I just don't understand how the servo will move the fingers..  smiley-confuse
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The servo is connected to your Arduino, I presume you will be connecting strings from the fingers to the servo, like a pupet. Then you write a program for the Arduino to rotate the servo quite exactly. (Eg. 25 degrees left)
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Ok, I'll try explain but difficult without a model. Have a look at the photo I attached below. I can't remember where it came from, so thanks to whoever's pic it is.

The pic isn't what you have, obviously, but shows the principle; best I can do right now. As you can see it's a gripper, so like a pair of scissors: One side stays still, the other moves. The servo is at bottom left and a wire goes from the horn (the white plastic thing with holes) across to the right hand arm of the gripper.

When the servo rotates say 20 degrees clockwise, the wire pulls the arm to the left and closes the grip. Rotate servo anti clock, and the grip is released because the wire pushes the arm back to the right

So similarly, your servo horn will pull a string and clench the finger. Only difference is (if I understand correctly) is that your string (being string) can't push, so the finger un-clenches by the springiness in the straw.

That help?


* robot gripper.JPG (13.18 KB, 204x184 - viewed 24 times.)
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Where would I put the strings? Here is picture of the "hand" if it helps at all.


* photo (1).JPG (414.15 KB, 960x1280 - viewed 34 times.)
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consider the way in which your muscles and tendons bend the fingers of your own hand.
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Just what I was going to say. Look at this- it will help
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Well you need to attach each string to the horn of a servo- perhaps more than one string per servo if that works.

You can probably lose those rings and just tie the strings to the appropriate holes in the servo horns.

I guess you need some kind of frame to support the hand and on which you can mount the servos.

Instead of a gazillion servos, use as few as possible, enough of course to give a smooth clench of the fingers, and perhaps use a few small hooks and eyes - see photo- to route the strings so they don't tangle. If you make some kind of wooden base or frame you can screw them into the wood.

EDIT.... 15 strings means 15 servos if you don't attach more than one string to each servo. That's going to take up a huge amount of space, and be impossible to hook up to a Uno. You basically have to attach more than one string to a servo, and you'll need to figure that out by a bit of trial and error. If you pull all strings at once, does the hand clench? If so, maybe one or two servos will do the trick. Otherwise as a maximum I'd say one servo per finger. Even 5 servos will take a lot of space: if you haven't bought them yet, consider micro servos.


* hooks.jpg (5.95 KB, 225x225 - viewed 21 times.)
« Last Edit: January 20, 2013, 12:43:00 am by JimboZA » Logged

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I UNDERSTAND NOW!


* awesome_smiley_sticker-p217764211963271445en7l1_216.jpeg (10.52 KB, 216x216 - viewed 19 times.)
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