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This is an instructable to show how to make version 1.1 of the Dextrus robotic hand from the Open Hand Project. It assumes you have access to a 3D printer and have printed the parts according to the instructions on thingiverse and have purchased all of the parts in the bill of materials included in the attached .zip file.

This project is still underway and it's by no means a completely polished product. It should be a great project for someone that is interested in robotics or prosthetics and want's their very own robotic hand!

Please download the attached .zip file which contains the bill of materials and .stl files (and source files) of all of the 3D printed parts.

This instructable will take you through the assembly. I would rate it as "difficult", but hey, if I can do it, anyone can! If you have all of the parts to hand, assembly should take around 2 hours.

The general process of the build will go as follows:

1. Assemble the finger.
2. Assemble the motor housing.
3. Attach the finger to the motor housing.
4. Assemble the thumb housing.
5. Repeat steps 1-3 for all of the fingers and the thumb.
6. Assemble the hand.

Tools required:
- Small philips head screwdriver.
- Small flat head screwdriver.
- 0.9mm Allen key.
- 2.5mm Allen key.
- A pair of pliers.
- A bicycle chain link remover tool. (amazon)
- A crimping tool (can use pliers instead).
- A drill with 1.5mm, 2mm and 3mm drill bits.
- Vernier calipers (I prefer digital like these). 
- 9V battery.
- M3 bolt.

Step 1: Preparing the bearings

First off, we'll need to prepare the bearings that go into the joints of the finger. They are friction fitted, and it's a very tight fit.

You will need:

- Bike chain tool (like this one).
- An M3 bolt (6-16mm in length).
- Pliers.
- Vernier calliper (Amazon).
- 3 Standard ball bearings.
- 2 12mm steel dowels.
- 1 14mm steel dowel.

1. Take one of the standard (non-grovved) ball bearings and put a short M3 bolt through it, this acts as a guide to get the bearing positioned in the bike chain tool, and will be removed later.

2. Place the bearing in the bike chain tool and tighten the handle all the way (don't make it tight, just enough to have the bolt inside the bearing.

3. Tighten the bike chain tool from the other end (the bolt), this time you want to make it fairly tight to hold the bearing in place.

4. Unscrew the handle of the bike chain tool all the way and remove the M3 bolt.

5. Using a pair of pliers, get a 12mm steel dowel pin and insert it tapered end first into the bearing. With a little bit of pressure, you should be able to get it to hold in place. Make sure it's aligned as well as possible.

6. Tighten the handle of the bike chain tool so that it pushes the dowel into the bearing, the objective is to get it half way. READ STEP 7 NOW.

7. Measure the dowel to make sure it is exactly half way through. Although it should be 4mm on either side, I've found that due to the tolerances of the bearings and the dowels, 3.85mm works best. You could measure your dowel and bearing first to calculate this for your particular components. If you accidentally overshoot you can unscrew everything, remove the bearing and flip it around.

8. Unscrew everything and jiggle the bike chain tool around until the bearing falls out with the dowel snuggly in place.

9. Repeat steps 1-9 once with another 12mm dowel, and then again with a 14mm dowel.

End of part 1.


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<p>I finished the mechanical part with DC motors and servo. I changed DC motors on some cheaper from the Aliexpress but with the same dimensions. I changed the part-Spool Spool, because the orginal version was bursting at work.</p>
<p>do you have diagrams for the connection and control to arduino and power source?</p>
! it is..good... It is the best robotic hand I saw...<br>
<p>Can the finger move one by one or they can only do flexion?</p>
<p>Somebody has downloaded all the steps of assembly?</p>
<p>Hello,</p><p>My name is Tavor Bental and I'm a 3rd year Electrical Engineering Student at Afeka Tel Aviv Academic College located in Israel.</p><p>I was recommended to use your design of robotic arm in my graduation project specialized in image processing and computers. I would love to have your advice and get your help in the matter.</p><p>My project is a humanoid robot designed to solve problems of image processing that can be used for Industrial control systems such as industrial robot for production vehicles, interface between human and a machine. For the purpose of the prototype -the robot will recognize Rubik's Cube and will solve it.</p><p>My intension is to use your design in a way that the hand will manipulate the face of the cube on its own with no additional structures. It means that the hand should be able to rotate the left side and right side and also rotate the whole cube in all directions. When I in person solve a cube I use only one hand, but my question to you is can these fingers of the design make the needed manipulations? Do you think that this robotic hand with her finger's - space of movement - could do it ? </p><p>Assuming the hand robot cannot perform all the movements, which movements do you think the robotic hand could handle ?</p><p>I would like to hear your advice so I can decide whether to purchase the open-hand-project , or not.</p><p>Thank you in advance</p><p>Tavor Bental.</p>
<p>what controllers have you used ? Did you use motor drivers to run the motor ?</p><p>Thanks</p>
<p>I bought New Adafruit Shield motor controller for arduino Rev. 2. But I did not test that yet. Potentially u could use the cheaper one Rev 1. cost on ebay around 3 us dollars. To one shield u can connect 4 motors, or 2 servomotors + 2 5V servos. </p><p><br>Im building my hand as a Uni project. </p>
<p>I'm partway through building mine, although haven't got as far as the electronics yet. How are you planning to know when to stop the motors so you don't break the fingers by rotating the motor too far?</p>
<p>I will check resistance when motor rotating and when its stop </p>
<p>what kind of controller you use to control motors? Is the 9g servo connected directly to arduino pins?? Thanks</p>
<p>You're awesome and splendid . The respect i have for all working and the founder of this group. <br>to be frankly i was searching this and find this is something fantastic.<br>i will be putting some changes for my final year project.<br>definitely will share with you and all later.<br>May god bless you.</p>
<p>Great Instruct-able! I am doing summer research at the University of Wisconsin Milwaukee researching emerging technologies to fabricate prosthetic hands and with the help of the Digital Craft Research Lab(and all their 3d printers) we are interested in building one of these hands for the students to refer to, and see what is possible with 3d printing. I was just wondering if you knew of any distributors that may supply the DC motors you have outlined in your bill of materials to the U.S? The only ones I am having luck finding will only ship to the UK. Thank you for your time!</p>
<p>I think we've spoken via e-mail now!? I'm not sure of a US distributor, I would have thought RS-Online would have delivered them to the US. Besides that, 16mm diameter is quite a common motor size so big motor manufacturers should have something.</p>
<p>The Respect i have for the creator of the project cannot be described within one comment :) .... </p>
<p>Thank you! :)</p>
<p>Can this hand tolerate <em>independent finger movement</em>?</p>
<p>yes</p>
<p>I wonder if i could make it without a 3D printer...........</p>
<p>I would suggest using nitinol springs as artificial muscles in the hand. It's nickel titanium memory wire that when a current is send through it contracts with a 1:400 weight to power ratio. You can buy the springs pre-made, or make them yourself with .02 nitinol wire (20 bucks for 50 feet on ebay).</p>
<p>where can buy this motor type?</p>
<p>There is a link in the bill of materials in the download, here it is again:</p><p><a href="http://uk.rs-online.com/web/p/dc-geared-motors/4179706/" rel="nofollow">http://uk.rs-online.com/web/p/dc-geared-motors/417...</a></p><p>Happy building!</p>
<p>Wow, this is a great demonstration of how 3D printing can help people. I love how you used a bicycle chain breaker in your assembly process. </p>

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