Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Limbitless Arm for Alex (V1)

by UCFArmory, published

Limbitless Arm for Alex (V1) by UCFArmory Jul 29, 2014


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We are uploading our design for the Limbitless Arm. This will include a parts list, instructions for developing the electronics, as well as the CAD and STL parts for printing and editing.

Additionally contact http://enablingthefuture.org/ for resources and the community of developers.


See the Instructions File attached for Building the Circuit.
Parts List:
To Print:
Forearm Lid
Flexy-Hand (at 80% for current version of arm)
Muscle Sensor: (http://www.advancertechnologies.com/p/muscle-sensor-v3.html)
Arduino Micro: (http://arduino.cc/en/Main/arduinoBoardMicro)
Aircraft Servo (150 oz-in) (http://www.amazon.com/gp/product/B0006O3XLS/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1)
LiPo Batteries (Currently configured for two 3.6 V and one 7.4 V, though we are reducing it to a single battery)
Battery Chargers
Shoulder Harness:
Shock Doctor Shoulder Brace (Optional) : (https://www.shockdoctor.com/ultra-shoulder-support-with-stability-control)
Velcro Straps: Lowes
Small Rubber-bands or elastic wrap (we are moving to a hinge and track design for the next version however)
Foam Inserts
Velcro with adhesive back
Flexible Shaft Bitholding Screwdriver: this makes life much easier
Helicoil or anchors for mounting the hand/elbow.
Kevlar Survival Cord (.036")
Fishing line to thread the cords
Micro-grip finger tips

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Hello, where can I find detailed instructions?

What sized printer would I need to print this for an adult?

I am trying to build the limitless arm as a college product. I noticed that the sensor you posted has been discontinued but they are offering this one instead http://www.advancertechnologies.com/p/myoware.html. The dimensions have changed a bit. Will this still work for this arm design?

Help, help, I made printing and hand size is an adult.
I need this hand print in size to a child, like the photo:


How do I print the hand of the hand size of a child?

Not sure if you got your answer yet, but here is the google folder from e-NABLE DEVICE and it has suggestions for the percent scaling you can use based on the child's measurements. For scaling it, you can do it in your CAD program or just about all of the printing programs will also have the ability to scale .stl files. If yours doesn't, I would suggest grabcad print if that works with your printer. It is free and has some great functionality in it.


Hi I was wondering what the minimum platform size was to create this arm. I was hoping to purchase a smaller makerbot printer.

Hello, good day from Queretaro Mexico, could get in touch with anyone of you advise me on the feasibility and to print this arm for an 8-year amputation above the elbow. I have pictures and measurements.

I am David Lopez , Industrial Engineer and I have a 3D Print my mail is
[email protected] and [email protected]


This project has entirely changed who I want to be as a designer, never before has one story captivated me so. The work being done here is truly beautiful and inspirational, it is the road I intend to explore for my Major Project this year. Exciting times ahead!

I am trying to open those files but it's failing to do so, I need help because there are people who are counting on me to manufacture this arm

I'm making this hand and I have a problem with the batteries and the power that the arduino needs. Does anyone has a schematic of the circuit?
Thank you.

What size wire is used for the bionics, and how long should the screws be for the attachment of the hand to the arm? I cannot find any mention of either in the instructions.

Inspirational stuff. Well done UCFArmory.

Would it be possible to get these files in and .iges or .x_t (parasolid)?

A friend shared your story with me through this video:

I wanted to let you guys know, in case you hadn't heard about his project/story, but this French sculptor/modelmaker, based in Paris, Gael Langevin, built a really well designed motorized hand, one thing that I liked about it a bit more than most, is that the motors are in the hand:

He's building a full sized and open source humanoid robot called InMoov, in case you like his work and are considering doing other kinds of prosthetics. Of course it's all home 3D printing based designs, and using low cost servos.

Hope this helps. You guys are incredible.

InMoov finger prosthetic project

Would you suggest printing the fingers with or without the raft? Also would you suggest printing on standard or high quality? Where did you order the shoulder harness from? Thank you!!

It would make more sence printing the fingers with a raft and the higher the quality the better but I would just print the whole arm at the same quality.
Hope this helps :)

So is anyone free to download this and reproduce it? What if we have access to software and tech that could be used to alter it. Say I have ideas of how to possibly improve the overall design? Is there any system in place for adding on to the existing designs?

We LOVE it when people improve our designs. Currently, we are quite a few iterations beyond this arm, (twitter.com/robertdowneyjr) and will be sharing our newest improvements in the upcoming weeks (we do not, however, have permission from Marvel to share the Iron Man arm... yet). If you have suggestions that you would like to implement, go for it! If you have suggestions you would like to see us implement, you can contact us at [email protected], or visit our website at [email protected]

We encourage people to reproduce our arm, with the understanding that nothing is to be sold.

No one should profit at the expense of a child needing an arm.

I am making your arm. I made the elbow yet having trouble with the forearm and lid. The computer is reporting to me that "too large" yet in looking at the file size the elbow is larger???Anyone else have this difficulty?? Contact me [email protected]

The elbow may be wider, but the lid and forearm pieces are longer. Some printers have build volumes where one dimension is larger than the others (wider than deep, taller than wide for example). Try aligning the length of these parts with the longest axis your printer has, and try again. If not, you can always scale the model, and experiment with that.

Good Luck! We look forward to your Make photo.

hello, this is Josh Trulove and I had a stroke 13 years age. I not use my right hard. I play guitar but hard time. my cell phone is 817-706-6137 and e-mail is [email protected] thank you.

Hey my name is Logan and I am 14 and I live in Pennsylvania. I don't have a left hand, but I have a little bit (about 2" from my elbow to the end of my nub.) of my left arm. I can bend my left elbow. I as wondering if there was anyway that I could make this into a left hand?

Can you contact me us through our website? We can send you the new version of the arm and connect you with our partnership in Pennsylvania to help get you set up with people who can support you arm build. http://www.limbitless-armory.org/

Yes it can you just have to mirror all of the printed parts. You should be able to do that easily in repetier host.


This is Alkesh from Mumbai, India.

have gone thru the article, feels like mother nature as given option, Alex and my daughter who is now 3 yrs old are on same page. My daughter doesn't have the arms since birth.

I will be great full if you could please help or advice on this robotic arms. I will definitely go for it if my daughter finds it comfortable.

If you could please share me your email id, I can send pics of my daughter for better understanding.

Thanks & Regards

Thanks for the reply. I'm hoping to see how this attaches to his limb and see how it fits on his limb. How did you fit his residual limb into the device and is it custom molded to his limb? Did you take an impression of his residual limb, or did you scan it? Thanks again for your efforts on this.

The elbow joint is not molded to his residual limb. It is simply a standard shape that we scale up and down to fit different sized arms. To attach the arm, we simply slide his arm into the elbow joint and strap it down. We then use a shoulder brace to redistribute the weight of the arm across his torso.

Comments deleted.

Great work on this. Can you please post more images of the socket? I'd like to see how it connects to the body.

If, by socket, you are referring to the Alex_Elbow, there are 4 holes which line up with 4 holes in the Alex_Forearm(body). In our design, we bolted the elbow to helicoils installed in the forearm, but this can be accomplished easily with 4 nuts as well.

We are also working on a video walk-through, to be published soon.

Comments deleted.

Fantastic stuff, very inspiring.

Nice work. It's great see a child smiling from your hard work. Could you make a vid of the hand/arm in action (not on the child) just see how it moves?

Thank you for all you've done to make this project a reality. This is exactly what the original Flexy-Hand was designed for.