Need some help for a science project.

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!

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? 8)

@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?

This is the only part I don't get. I just don't understand how the servo will move the fingers.. :~

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)

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

Where would I put the strings? Here is picture of the "hand" if it helps at all.

consider the way in which your muscles and tendons bend the fingers of your own hand.

Just what I was going to say. Look at this- it will help

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

I UNDERSTAND NOW!

awesome_smiley_sticker-p217764211963271445en7l1_216.jpeg

[highfive/]

Excellent....

Word of caution with servos: even tiny ones are quite strong and they move quite quickly.

Here's what I'd do: build a dummy "test" finger that you can afford to destroy if the servo goes wild... That way you won't rip your whole hand to pieces. Then set up a test rig with that finger and a servo mounted on a wooden frame or something, and or rope some folk in to hold stuff for you. Position the servo and its horn so that it looks like it will pull smoothly, then turn the servo motor by hand to test it, ie not under power! Note that where you push the horn onto the servo- called a spline- you can position the horn on the teeth to get the best angle.

You've used the sweep program you said?- so modify that just to sweep from say 0 to 10 and back. Increase the delay to much longer one just to be safe, and then make it smaller again once you check nothing is snagging. If you get a snag I think the servo might tear stuff, so be careful.

Well done so far... you're doing great and you get 10/10 for persistence!

Do you need help programming the Arduino?

I need all the help I can get.

Falchion:
I need all the help I can get.

Yeah but not to the extent where you don't learn anything.....

Get one servo working, clenching a finger using sweep as I suggested, with suitable changes for the range of movement and the delay.

Then tie another string to another servo.... change the program to have more than on servo attached and double up the part that does the movement of say myservo1 and myservo2 (or finger1 and thumb or whatever) and get two fingers or knuckles or whatever clenching.

Get each piece working as you go, and save old versions of sketches so you can backtrack to the last version that worked if you make a screwup

I don't understand how to add multiple servos to the breadboard... I read this tutorial (http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html),and I don't get how he added the last 4(?) servos towards the end. I did Sweep on the Arduino UNO, but I don't think there are enough ports on it to support many servos at once. Can I get some help? :frowning:

I did Sweep on the Arduino UNO, but I don't think there are enough ports on it to support many servos at once.

A port consists of 8 pins. It only takes one pin to drive a servo. The UNO has more than enough pins to drive 4 servos.

I don't get how he added the last 4(?) servos

Well you only need one pin per servo for control remember, the power being taken care of off the Arduino. Let's say you have the following lines in your code (extract from sweep):

Servo myservo;

myservo.attach(9);

myservo.write(pos);

You could have this (incomplete code!) for three servos:

Servo myservo;
Servo myotherservo;  // <<<< note new names; you would call these "thumb", "middlefinger" maybe
Servo yetanotherservo;

myservo.attach(9)
myotherservo.attach(10)  // <<<<<<< note the new pin numbers for the yellow / orange control wire
yetanotherservo.attach(11)

myservo.write(pos);

myotherservo.write(pos);

yetanotherservo.write(pos);

So how did you get on yesterday?- Did you get one finger clenching and unclenching?

What is that cord on the battery holder called? I really need one.

No idea

I'm on step 3 of this tutorial (http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html) and the servo doesn't move when I upload the sketch. Can I get some help?

Falchion:
I'm on step 3 of this tutorial (http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html) and the servo doesn't move when I upload the sketch. Can I get some help?

Post your sketch and a picture of your wiring.