Hey folks! I am Nirzaree, an electronics engineering student from India.
Me and my roommates have made a very simple robotic arm which can help patients with their physiotherapy exercises.. !
It uses a controller board, atmega 32 in our case..(it could b any..) and a dc motor..!

V have a very elementary mechanical design and very simple interfacing currently.. Better to come soon..
Lets have a look at a very simple, exercise aiding robotic arm ..

Step 1: The Idea..

we friends keep discussing a lot of stuff in the hostel..
just one day, 1 of my roommates Varsha thought of making something that could help patients..n then the thought process began..

Many patients who have to exercise their limbs have to take the help of Physiotherapists.. The more they exercise properly, the earlier is the recovery. So when the therapist is away, a patient could simply wear this arm and exercise on his own.

Step 2: The Design..

As u c in the pic, To build the arm, you will need:
1. few aluminium strips (as they are light weight), as the frame of the arm
(preferably those with bent edges, so that they dont hurt the patient's hand)

2. a dc motor of as many low rpm as possible (we used 30rpm)

3. leather belts available at a watch repairer (to fix the hand with the robotic arm)

4. screws and bolts,etc.

Well, we started off by cutting the strips pf aluminium into appropriate size. Mainly, one piece for the part of the hand above the elbow and one for the below part.

You could use any other material, or any other design too.. :)

Step 3: Fixing the DC Motor

After the elementary design build of the arm, we fixed the motor to the lower part of the arm as shown in the figure .
We used a dc motor, you could use a stepper as well.
The only issue is that the motor should be able to take the load of the hand. So preferable a high torque motor should be chosen.
We initially took a 100 rpm motor but it couldn't take the load of the hand well, then we used a 30 rpm motor which worked quite well.

Then all you need to complete the arm is to take 2 belts, available at a clock repairer's, drill holes
at appropriate distances, and attach them at the 2 ends of the ARM.

The arm is now ready for the programming!!!

Step 4: Motor Driver Circuit

As we know, we will need a motor driver circuit for the DC motor to run.

The controller board, commercially available ones, generally has a motor driver (an L293d ) in it,so all you need to do is give the logic(clockwise and ) to the controller pins connected to the l293d which is in turn connected to the motor.

A DC motor is the simplest to interface. Giving power in one way makes it rotate in forward direction, and in the other way makes it run the otherway.

If the controller board doesnt have an inbuilt motor driver IC, then you need to make a small circuit. (see d pic)

We made it using 2 relays and a 7805.
Working: in our program, either the motor had to run forward or reverse. So whenever the pulse from the controller was 0 1, one of the relays would turn on, and the other would turn off and the motor would turn in (say) forward direction.
After certain delay, when the controller would send 1 0, the relays would switch their operations, and the motor would run in the other direction.

But the simplest motor driver would be to use L293D IC, which can s drive 2 DC motors and 1 Stepper at a time. But since we had this circuit ready, we used it.

Its really easy..! Give it a try! :)

Step 5: Code

The coding for the arm is very very simple.
Even if you arent at all familiar with a controller and its programming, you could do this one.. :)

In India, the 8051 and AVR boards are quite popular. We used an atmega32 controller board available easily.

The code is written in C.
Right now, we have programmed it, for 45 degrees of to-and-fro motion.

We can make it customised by using an lcd and a keyboard, along with the board, and then entering the value of the required motion.

I have attached the C code,which we have run.

(The first code (dc_motor_1) attached was written for an 8051 board. I have attached it since its very simple to understand. The 2nd one is the one written 4 the atmega32 controller )

(The code works, so even if u dnt understand (though i hope u do), u ll definitely succeed in making the arm run your hand. :P )

Step 6: The Final Step.. the Run..

So when u r done with the design of the arm, and the code in the controller, we are all set to test the arm.
Wear the arm. Turn on the controller board and see how d robotic arm moves your hand..
:)
I have attached the videos of the arm.. a lil issue with our design is that v have to hold the motor's rear end, so that the hand moves and not just the rear end. We will clamp it some way, n i ll update it soon...

Hope ya folks try n make better designs n post em..

Take care!