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*This instructable is not complete, I will post code soon

The Arm:


This instructable shows the process of building a robotic arm using servos, Arduino microprocessor, a gyroscope and multiple bend sensors.

The user wears a glove containing the gyroscope and bend sensors which translate the movement of the users hand into motion of the  servos , in turn rotating the wrist and hand of the robotic arm. 

The forearm has full motion of a human wrist namely: rotation, radial deviation (movement towards the thumb) ,ulnar deviation (movement towards the little finger) ,flexion (tilting towards the palm) and extension (tilting towards the back of the hand).

The Hand also has movement of the fingers, this is limited as a result of the brittle material used.

All movement is provided by the Servos attached to an extension wire or piano wire. Each having different torque depending on its position.

The fingers contain touch sensitive resistors which provide haptic feedback and allow the user to know when the fingers have grasped an object.

 
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Step 1: Design

Attached are pictures of the design using 'google sketchup'.

I found this design of the finger on the net which allows a single servo to provide full motion of curl of a human finger.The design works best when Aluminium is used for the cut outs of the fingers, but as I had perspex available I went with the weaker option which resulted in brittle fingers. 

All the fingers are the same design but a variation of measurements, except for the thumb.  they can be found below:

The designs below are the ones I sent through to a laser cutter here in Johannesburg for about R350 for all cuts and material.
they required the files to be sent in 2d DXF format, so if you alter the design in sketchup, make sure you export it in the correct format.

The rest of the cut outs are made up of wrist and palm sections.
index finger, middle finger, ring finger is roughly the same size.

pinky is slightly smaller than other fingers.

Thumb has different dimentions

Step 2: Materials

- Arduino Mega (or an Arduino with enough Analogue input pins to support all the sensors)

- 20kg-cm torque Servos for wrist movement x3

- 2kg-cm torque Servos for fingers x5

- Atleast 40kg-cm torque servo for elbow and shoulder x1 or x3 

- 3 axis gyro breakout board (I used a L3G4200D, any will do).

- Force/Touch sensors x5

- Gloves x2

- Bend sensors/Resistors x5 (or 6 if you wish to build an elbow).

- Some small aluminium Plates.

- Length of flat pc wire.

- Connector pins.

- BreadBoard.

- Piano Wire 30cm pieces x4

Tools:

- Glue Gun

- saw to cut aluminium/Perspex

- Wire cutters

- nuts and bolts

Step 3: Hand

Picture of Hand
Photo 29-05-2012 17 49 35.jpg
Photo 29-05-2012 18 18 24.jpg
Photo 29-05-2012 18 50 31.jpg
Photo 30-05-2012 11 54 11.jpg
The best way to attach the finger joint together is with grommets, this allows for movement of the joints.
I used small bolts and a glue gun which provided too much friction and the joints wouldn't work as intended. Any pressure applied resulted in the perspex fracturing. I decided to remove the joints and have the finger move as one unit.

- Attach the fingers into the slots of the palm cut out. Img[2]
- Attach the servo arm to the smallest disk and bolt  the arm to the servo.
- Glue the palm onto the smallest disk to provide the wrist section, add supports for strength.
- Glue the servo to the larger disk with the rectangle cut out , this separates the hand from the lower wrist and allows for 180 degree rotation. Img[3]

Step 4: Wrist Joint

The wrist joint needs to act as a ball joint, with radial and ulnar deviation ,flexion and extension. This requires 2 Servo brackets which I made from aluminium. One within the other, rotating about a bolt , providing 2 degrees of freedom. Attaching the rotation servo to the upper bracket with a plastic bracket mimics the movement of a human wrist.

I used Rod bolts as the forearm structure to act as the radius and ulnar. Attach these rods to the wrist joint by drilling two holes in the lower aluminium bracket and tightening them with nuts on either side.

cable tie the leads of the servo to one of the rods.

Step 5: Lower Forearm

Attach the larger perspex disk to a side panel as in Img[2] and bolt the two rods of the forearm to this disk. Make sure you use washers so that you do not crack the perspex when tightening the nuts.

See pictures below to get an idea of the final product:

Step 6: Attaching the servos

The arm of the wrist servo needed to extend beyond the sides of the wrist. I attached 2 smaller arms to a central larger one which turned out to be quite rigid. The holes also provide a nice attachment area for the piano wire. Img[2]

The other side of the piano wire attaches to the sides of the wrist disk so that when the servo twists, it tilts the wrist in that direction.

- Solder Pin connectors to the ends of the flat cable wires, each servo has 3 leads, and there are 3 servos in the wrist and 5 in the hand, that's a total of  24 individual wires. if you are using the touch sensors, its an additional 10 wires that need to reach the hand, so strap the wire up neatly so that its easy to troubleshoot.



Step 7: The Hand

-Slot the micro servos into the rectangle cutouts of the palm, they will provide the push pull for the fingers (either by piano wire or a flexible wire , the finger is then pulled closed by elastic.) make sure the arm of the servos is facing outwards, except for the thumb servo, this one faces inwards.

- I glued the reverse side of the pressure sensors to the tips of the fingers, then soldered extended wires to their leads.(this is for the feedback. Img[7-11]

-Connect the finger servos the the extension leads that you soldered pins onto earlier.

Step 8: The Glove

Picture of The Glove
Photo 16-07-2012 21 42 37.jpg
Photo 16-07-2012 22 32 36.jpg
Photo 17-07-2012 11 28 12.jpg
Photo 17-07-2012 11 48 20.jpg
Photo 17-07-2012 13 13 15.jpg
I bought a pair of cloth gloves for this part:

- On the outer side of the fingers of the glove , glue a bend sensor with the glue gun.
- connect extended leads to the 3 axis gyro pins and label each wire.
- Glue the gyro to the centre of the back of the hand.
- Extend all the bend resistor wires.
- put the glove on, and slip the other glove over , this helps keep everything in place and also looks a lot neater.
- Glue the rim of the gloves together.

This completes the control glove.

On the other side of the extension wire, about 1.5 of a metre down, strip the wires and attach connector pins.

Step 9: The Stand

Picture of The Stand
Photo 21-08-2012 21 45 27.jpg
Photo 21-08-2012 21 45 37.jpg
Robotic arm circuit diagram.png

I wasn't sure how to mount the arm as I initially wanted to build an elbow joint and shoulder joint, but as the servos for this weren't in stock at the time,I decided to stick with the forearm on its own.

- I found an old stand from a Samsung screen and glued the arm to the slot in the base. this worked better than expected.

- Glue a breadboard power strip to the base or lower arm. this will be plugged into the power supply, and provide power to all servos and Arduino.

Step 10: Resources

Code below:

- Wrist code  Rotation, side to side, up and down using the gyro.

- Finger Control

- Complete Code with filtering

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PhanA214 hours ago

hi.quite complex mechanical parts, I can buy one?

jensara21 days ago
Hi, this is great project and i want to do it also...Do you think that it is possible to modified it that the arm could stretch?what would be the possible materials?thanks...
garciadelfin3 months ago

Hi, I really loved your project and i wanna do it. I have a question,
I supose that your foce/torque sensors are to measure the force applied in the finger tips, am I right? So what is the benefit of this in your project?????

Riyn110 months ago

great project...

Hi.. bluebean, which bend sensor you are using 1k-20k or 20k-50k? thanks

bluebean (author)  Riyn110 months ago

Thanks,

I seem to recall 1-10k (I could be wrong its been a while since I looked at this project), but it shouldn't make a difference, all that changes is your values for the pull down resistors like in the diagram in the last image of this instructable. Or you can alter you comparator/shmidt trigger in the Arduino code.

tommychev1 year ago

Awesome instructable bluebean, a kid on one of my classes built something similar but with only finger control. Had he more time he would have added feed back to the fingers.

agomes61 year ago
Great Instructable!

By any chance can you post your wiring diagram of the gyro? I am a bit confused to see you using all pins with I2C and no interrupts.. I have been using similar gyros and I usually stick to:

GND - GND
VCC + SDO - 3V3
SCL - A4 (20 on mega)
SDA - A5 (21)

Thanks in advance
bluebean (author)  agomes61 year ago

Correct, It is connected as you stated above. I just soldered all the wires on for future use. heres a link to how its done.

http://bildr.org/2011/06/l3g4200d-arduino/

theres also code there to test it out

what kind of connector pins did you use, i am finding types from d-sub connector pins to 5pin female gold pins and I am not sure on what to get.
aanurag1 year ago
hey why have you used pressur sensor..tere is no connection in in the arduino.. and is this program code is totally right ? can we use this code directly or we need some change?
bluebean (author)  aanurag1 year ago
Hi, at the time of posting the pressure sensors were not connected but they are used for feedback. They can be connected to the analogue pins in order to measure the change in voltage.

The code worked perfectly fine for my project, but each system is different and i would recommend tailoring your code to suit your project and if needed use mine as a reference.
Im a highschool student attemping this project with my teacher. will you send me the part numbers and the code? this is my back-up email account: catfansey@yahoo.com. Thank you!
hello this is my email: joebabayan@hotmail.com
please send me the microcontroller's code plus the circuit diagram if you drew it out
massive thanks
can you please post the circuit diagram of the project's circuit and the microcontroller's code?
bluebean (author)  bubble trouble2 years ago
Hi, I have posted the code at the end of the instructable as a '.ino' file, if you cant download it i can email it to you. Il have to get back to you on the circuit diagram as i didnt actualy draw one out.
bluebean (author)  bluebean2 years ago
Sorry its a '.txt',
ctwal122 years ago
Is the gyroscope necessary?
bluebean (author)  ctwal122 years ago
The gyroscope is what detects the users movement, without it the wrist would not move at all. Alternatives can be used, such as a variable resistor (pot) , on all 3 axis but the glove would be more of a solid structure. In the project the gyro is pretty much the whole point.
ctwal122 years ago
Did you make the hand on your own or did you buy it from somewhere? And if possible, can you send us a link to a cheap arm which will be good for this project?
bluebean (author)  ctwal122 years ago
The project took about 1 and a half months. Arduino has its own software , you can download from the website. From my instructable you can see i designed and built the hand completely from scratch, i didnt buy any ready made parts. This is not a simple project so if it is your first i suggest you start with a simpler one.

Ive seen people remove the controls and interface with this one quite easily, and its relatively cheap:

http://www.thinkgeek.com/product/b696/
ctwal122 years ago
How long did this take you to make and is there a specific program for the codes for the arduino?
ctwal122 years ago
sorry for the messaging we really have to get our materials together, so if you could send us a link to the 20 and 2 kg torque servos. Please answer back soon we are in a hurry.
bluebean (author)  ctwal122 years ago
This is where the 45kg servo is:

http://www.robotshop.com/gws-servo-en.html

go back a page and look at the other servos, as I said, theres no need for 20kg-torque , anything above 10kg is more than enough, for the fingers micro servos of 1.6kg is even ok.

This is where I got 20kg ones from for another project:

http://robotics.org.za/index.php?route=product/product&path=64_214&product_id=138

they are not the best quality or accuracy.
ctwal122 years ago
Is there any way to use the arm wirelessly via bluetooth modules?
bluebean (author)  ctwal122 years ago
there is, look at the bluetooth shield for arduino, also look at RF communication. I havnt used the bluetooth modules so I dont know much about it.
ctwal122 years ago
How long did this take you to make and is there a specific program for the codes for the arduino?
ctwal122 years ago
thanks again if we need anymore help will contact you
ctwal122 years ago
Hi again bluebean, we could not find some of the materials on your materials list, it would be a huge help if you could send us links or tell us where you bought some of your materials. Ill leave a list below if you can please tell us as many of the places where you bought these items :


1.) BreadBoard

2.) 20kg-cm torque Servos for wrist movement

3.) 2kg-cm torque Servos for fingers

4.) 40kg-cm torque servo for elbow and shoulder x1 or x3

5.) Force/Touch sensors

6.) Bend sensors/Resistors

7.) connector pins

Thanks in Advanced
bluebean (author)  ctwal122 years ago
Hi, i got most the materials from www.robotshop.com, touch sensors, force sensors, servos and gyroscopes. But most of it you can get off ebay for cheaper, as all of this was quite expensive, theres even an instructable on how to build your own bend sensors. A breadboard you can get from any hobby/circuit shop. The wrist servos dont need to be 20kg, they can be 10kg torque. I also didnt land up building the elbow (the servos were continuosly out of stock) so the 40kg-cm servo wasnt neccesary.
ctwal122 years ago
ok thank you ill keep in touch if you ant we can send it to your email if you give it to us. anyway thanks
ctwal122 years ago
Dear bluebean, what are the codes for and how do you use them for the glove. WE are trying to use this idea for a project and it would really help if you reply as soon as possible. Thanks for everything!
bluebean (author)  ctwal122 years ago
At the end of the instructable there is a .txt file containing some code for the Arduino, you can use it and edit it as you please. It contains the servo controls and the gyroscope and bend resistor feedback. Is your question directed at how do you set it up in the Arduino invironment? please send me your project updates as im interested in how it turns out.
Mateo_2 years ago
This is amazing, I'd like to make one but I'm having trouble downloading the .dxf. Could you send it to me please at mateo.galceran@gmail.com.
bluebean (author)  Mateo_2 years ago
hey, sorry for the late response, will email it to you as soon as I get a chance. If you can I recommend downloading the sketchup file instead , and generating a 2d dxf from that, that way you can edit the shapes a bit since they were slightly off in measurement because the (3d) pieces wernt lying completely flat in sketchup.
bkiierstead2 years ago
Have you uploaded the finger control yet? By the way this is awesome, great job.
bluebean (author)  bkiierstead2 years ago
Thanks, I uploaded the finger code now just for you :p . The full code with filtering is there aswell (on the final step) . I had to uploaded it as a txt, just copy and paste in into an arduino sketch. Try improve the code if you can. Gud luck
Thanks a bunch, can the hand throw or crush things by any chance?
bluebean (author)  bkiierstead2 years ago
I guess in order to throw an object the arm would require an elbow as well. The wrist motion (depending on your servo torque and 0->180' speed) would probably send an object in the air, but not very far.

Crushing force would depend on torque/ strength of the servos in the fingers as well as the material of the structure in which the hand is built . The small servos I purchased are cheap and the gears are made of plastic. The fingers themselves are cut from perspex which is quite brittle. Therefore the hand itself could not crush much more then a piece of cardboard, but if the hand were to be made out of aluminium; the servos to be high torque with metal gears, I rate the crushing power can easily crush a can.

Im not sure exactly what force crushes a can, but remember, in the hand you have 5 servos, so if a high torque servo is used for each finger such as 20kg-nm, that would be 5x the torque.(neglecting the length of the fingers)

hope this helps.
091530262 years ago
hey how are i made something similar but my flex sensor got broken because to connect them you would had to solder them the cables so my question is where did you bought your? i see that they have the cables already. if you could reply to my email it would good of you. : deltony025@gmail.com
thank you .
also if you could share some detail for the legs.
thank you once again.
bluebean (author)  091530262 years ago
Hi,

I got the bend sensors from robotshop.com. They wernt cheap, like $10 each , so if you worried about messing them you can try and make your own. Theres an instructable on it, basicaly its just a voltage divider.

If you are interested in the legs, go to my profile and look at the instructable on them, its called "Arduino Biped".

Enjoy
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