The Lazarus Hand

Introduction: The Lazarus Hand

Hello, we are glad you have chosen to take interest in our project. We hope you find the instructable helpful in whatever project you are currently pursuing. I am Chase Leach and my partner is Micheal Grebeck. We are currently sophomores of the WBASD S.T.E.M. Academy and we are submitting this project for the Butwin Elias Science and Technology Award. The Lazarus Hand is a prosthetic hand which was made entirely in a 3D printer with exception to the motors, rubber bands, and fishing line; used in the project's construction. The intended goal for the project was to create a functioning prosthesis that would be capable of using a special sensor in order to tell what parts of the hand were intended to be in use at any given point in time. This would theoretically help with doing tasks typical of a hand such as; grabbing and scratching. In the end, Mike and I were quite proud of the final design. Thank-you for considering us and allowing us to be involved in a competition which has allowed us to have as much fun as we've had in designing The Lazarus Hand and overcoming the challenges it's presented and without further adieu we hope you enjoy.

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Step 1: The Cost of Construction

In the end the total amount of money that was spent on this project was surprisingly minimal. The only things we really had to purchase during this project were the motors used in the prosthetic, the rubber bands and the fishing line. These items are relatively inexpensive; see the list below of supplies that were need to tackle the project. Past the items we had to purchase we had somethings which were already accessible to us including; the 3D Printer, 3D Printing Trays, and the 3D Printing Material. The programs we used didn't cost us anything either and were relatively easy to use.

Supplies & Costs

  • Alliance, Advantage Rubber Bands, #64 (3 1/2" x 1/4") 4oz. Bag, Natural Color from Walmart (Cost: $1.48)
  • Clear, 10 lb test, Ultracast Ultimate Mono fishing line from Walmart (Cost: $3.09)
  • 9g 360 degree DF Robot Micro Servo Motor from (Cost: $12.36, Quantity: 3)

Supplies Already Available

  • 3D Printer
  • 3D Printer Trays
  • 3D Printing Material
  • Electrical Tape
  • Wire
  • Hot-glue
  • Crazy Glue
  • Wooden Dowel

Programs Required

  • RobotC for VEX Robotics 4.x
  • Inventor

Step 2: Time Consumed

The time really flew by while we were working on the design and construction of the palm. One week we'd be working on the project during and after school to try and design the finger and the next the palm. Then, we had to pull a complete overhaul on the hand and we had to redesigned the entire thing so most of the time was spent on the designing of the hand which, looking back, came out to about 72 hours spent on just that. Then, we spent 20 hours printing the parts. After that, we spent about 36 hours on the assembly of the hand. After the Assembly was done, we spent about 28 hours programming the hand. Finally, we spent about 24 hours testing the hand.


Designing took 72 hours, printing took 20 hours, assembly took 36 hours, programming took 28 hours, and testing took 24 hours which means we spent 180 hours creating The Lazarus Hand.

Step 3: S.T.E.M. Applications

Science- The science of our project came into play when we were determining how much power to send to the servomotors. It also came into play when were determining how to make the hand anatomically correct. Another aspect of the hand that science came into play was when we were thinking about the resistance of the rubber bands and when we were determining how much stress would actually be placed on the fingers and hand to come up with the best design possible to keep the hand from breaking from use or drops.

Technology- The technological aspect of our project came into play when we were learning how to code the fingers using C++, when we were installing the motors, and when we had to turn the female connections that the motor originally had to male connections so they could properly hook them up to the VEX hub which we had connected to our computers. It also came into play when we were using the 3D printer, using inventor, and translating the parts over to STL files so we could use them to visualize how the parts would fit together and creating a 3D presentation of the assembly which we hope to present to Adam Iseman when he comes in.

Engineering-The engineering this, of course came into play while we were designing the two halves of the palm, the fingers, the thumb, and connection piece for the thumb. It came into play in the redesigns, the identification of problems when they had arisen, and the solutions we came up with for the problems.

Mathematics- The math involved in the creation of the hand came into play when we were looking for a finger size which would look proportional to the size of the palm we'd designed. It also came into play when we were looking for acceptable differences in size required for the holes and the pegs to match up and fit into one, another. We also had to figure out how far the fingers needed to be a part when they were attached to the palm in order to have them smoothly slide past each other.

Step 4: The Parts in the Form of Ipt Files

The documents in this step are for download or viewing purposes but remember that the fingers of the hand are supposed to be different sizes which are given bellow:

Finger Part 1 (Beginning Part of The Finger-Closest to The Palm)

0.4 Finger 1 (Pointer Finger)
0.6 Finger 2 (Middle Finger)

0.4 Finger 3 (Ring Finger)

0.3 Finger 4 (Pinky Finger)

Finger Part 2 (Middle Part of The Finger)

0.461 Finger 1 (Pointer Finger)

0.672 Finger 2 (Middle Finger)

0.766 Finger 3 (Ring Finger)

0.4 Finger 4 (Pinky Finger)

Finger Part 3 (Finger Tip)

0.575 Finger 1 (Pointer Finger)

0.55 Finger 2 (Middle Finger)

0.5 Finger 3 (Ring Finger)

0.471 Finger 4 (Pinky Finger)

If you want to know how the hand was finally put together, then refer to step 15. There is an instructions video with an explanation of how the hand works.

Step 5: The Plan

The hand will be comprised almost entirely of 3D printed parts. When the hand comes together, the three motors will fit inside of the two palm halves and they will be connected to the axles we designed in order to maximize the efficiency of each motor. The fishing line ties onto the axle by pulling the line through the hole in the wheel of the axle which will be shown later in the instructable. You'll want to tie the fishing line onto the wheels which will serve to windup the line to pull in the fingers. We'll need three motors because of the constraints of the size of the motors. Two of the motors will reel in the fingers with the first attached to the pointer and middle fingers and the second being attached to the ring and pinky fingers. The third motor will reel in the thumb by the same means as the fingers except the axle will be cut off at the first wheel. The finger parts and fingers, along with the thumb will be attached to one, another via wooden dowels with a thickness of 0.2 inches. If you are still confused, please refer to the video provided on step 15.

Step 6: Bottom Palm

The first part that we're going to be looking at is the piece which we aptly named the bottom palm piece. This piece had gone through several redesigns going from a bulky and thick piece with only four holes for line coming out of the palm as we were not originally planing to tackle the thumb but at a later date figured out a way to get it to move properly. Then, we came up with a slim and sleek version of the part. One that was thinner and more efficient but it still didn't have a thumb hole and the pegs had stability issues. Finally, we came up with the design you see before you; a design with a thumb hole and pegs that won't break as easily. If you take a look at the Inventor ipt file for this part, you will be able to see how this part came together in the end and you'll be able to print your own 3D bottom palm piece. This part took a couple of attempts to get finalized but we were satisfied with the result. This part was capable of coming together with the other half and house the motors perfectly. The fingers also attached well once the wooden dowel was placed through the hole created by the two halves of the palm.

Step 7: The Top Half of the Palm

This part is the other half of the palm piece which connects with the part which you've seen in the previous step. the peg holes were able to fit the pegs on the previous part very well with enough space to hold the palm together on it's own, even without glue. The rubber-band anchors on the top of the palm functioned as expecting considering they were design specifically for the rubber-band that was listed in our Cost of Construction step where we listed what we bought to make this. The original design for this piece was essentially identical to the Bottom Palm part with four holes in the front for the fishing line to be run through. Our original idea was to have motors on both sides to pull the fingers back and forth but the idea was scrapped when we had finally gotten around to buying motors for it and we couldn't find any that'd be small enough for the design. When we got to that point we almost entirely needed to start from the ground up again and we came up with several ideas to fix the problem like finding a different type of motor and running a spring through the center of the fingers to get rid of a set of motors but we eventually settled on the rubber-band design you see before you. This led to us needing to find a way to attach the rubber-bands which is when we came up with this idea. Instead of just making plain square boxes we decided to do some research and found that the double I beam design, you see being used for the anchors, would be the best shape to fix our issue. The thumb anchor does look different from the rest which is due to the awkward angle the thumb needed to come down on. It needed to be able to get some more movement for stretching more to the right or left. If you click on the ipt file of the Top Palm Part you can see all the work that went behind it.

Step 8: The Thumb Base

The thumb base was a part that wasn't really thought of until later as we weren't originally planing to tackle such a complicated part of the hand but we had decided to go all out for the hand when it really started picking up steam. It was an awkward part to come up with a design for because of the way the human thumb comes to a close when you make a fist but we solved that issue by simply rotating the original hinge design 45 degrees creating this part. Another consideration we had to take into account was which hand the person would be missing if it were the right, it'd be easier to just attach this thumb piece to the top or bottom palm piece but we wanted the person to have the ability to switch the side the thumb would be on and thereby which hand the prosthesis was for. That's why it's separate, however you will have to change the side the Top Palm piece's cut out for the thumb. It would turn out pretty well in the end.

Step 9: The Thumb Part 1

This next piece is the first part of the thumb for the prosthesis. If you look at the ipt file we've provided you can see how we put this together. The fishing line tube at the bottom of the first part of the of the thumb turned out well but if we could change anything about it, we'd add a tube for the rubber-band as well to keep it in place better. This piece didn't have any real redesigns simply because it didn't come until later in the project.

Step 10: The Thumb Part 2 (The Tip)

This part is the end of the thumb or the thumb's tip. If we could change anything it'd be adding an anchor to the top of the thumb tip to tie the other end of the rubber-band. The part, again didn't really have any major redesigns because it came about later in the project. The part has a fingernail just like the rest of the fingers of the project which was a consideration on our part. We figured the person who used the prosthesis would probably want to customize the fingernail of the prosthesis so we made it long enough to do so, you may clip them in the same way that you'd clip a normal fingernail with a fingernail clipper and it'll hold up to the strain. We tested it. It also isn't so long that it'll get in your way if your using it. View the ipt file for the how the thumb tip was created.

Step 11: Finger Part 1 (The Beginning Part of the Finger)

This part is the first part of the finger. It also has a fishing line tube and we also would've liked for it to be on both sides. Check the ipt file for how to make it. The first extrusion which you'll find in step 4 does change depending on which finger you're making but there are no other differences between the fingers. We did come up with a prototype for this part which didn't turn out well as it was designed for the original palm design.

Step 12: The Finger Part 2 (The Middle Part of the Finger)

This part is the finger part 2 which is the middle of the fingers. It has a squared off hinge for you to tell the difference between it and the finger part 1. It also has a fishing line tube and you can see how it was made in step 4. The only change we'd make is with the tube for the rubber-band. The first extrusion changes depending on the finger which you are making which you can find in step 4.

Step 13: Finger Part 3 (The Finger Tip)

You can find the ipt file for this part in step 4. This part has a fingernail just like the thumb tip. It also has a grip at the bottom of the finger tip which is supposed to help when it comes to grabbing stuff with the prosthesis. It does work rather well. The only change you should make is to create an anchor at the top of the finger tip.

Step 14: The Axle for the Motors

The axle for the motors is one of the most important parts because it is required for the hand to function correctly. There is an ipt file for this one too which is provided in step 4. The axle is designed for our specific motor, however if you want to use a different motor then all you'll really have to do is change the size of the hole at the bottom of the fit whatever the gear is on top of the servo.

Step 15: Pictures of the Assembly of the Hand

The hand assembly was rather simple as it was a matter of hot gluing the servo motors to the inside of the palm in such a way that it leaves enough room for the motors to operate and pull the sting that you should have tied to the axles through. The rubber-bands were as simple as hot-gluing the ends to the fingertips and tying the other side to the anchor. Watch the video provided for further understanding.

Step 16: Coding

What Follows is the code we used for the fingers and thumb of the prosthetic hand so far but we do plan to continue to write it in order to get the hand to function even better. if you are following along then you can copy and paste the code into the RobotC program ad use the hand that you should have built in the previous steps

#pragma config(Motor, port2, Thumb, tmotorServoStandard, openLoop)

#pragma config(Motor, port3, PinkyRing, tmotorServoStandard, openLoop) #pragma config(Motor, port4, MiddlePointer, tmotorServoStandard, openLoop) //*!!Code automatically generated by 'ROBOTC' configuration wizard !!*/

* Project Title: Team Members: Date: Section:

Task Description:



task main() { startMotor(port2,-127); wait(2); startMotor(port2,-127); wait(2); startMotor(port2,-127); wait(2); startMotor(port2,-127); wait(2); startMotor(port3,-127); wait(2); startMotor(port3,-127); wait(2); startMotor(port3,-127); wait(2); startMotor(port3,-127); wait(2); startMotor(port4,-127); wait(2); startMotor(port4,-127); wait(2); startMotor(port4,-127); wait(2); startMotor(port4,-127); wait(2);

//Program begins, insert code within curly braces


Step 17: The Testing of the Prosthetic Hand

When we were testing the hand we did have a few issues arise but we are currently working on the kinks and should have a better working model by the time the awards ceremony rolls around.

Step 18: Possible Improvements

When we sat done to come with ideas for the hand some of our considerations were adding an anchor, like the one that we have on the top of the palm, to the ends of the fingers instead of hot-gluing the rubber-band ends on. another consideration was adding the stability tubes we had on the bottoms of the fingers to the tops as well to better hold the rubber bands in place. That was pretty much it as far as improvement ideas went because the hand actually functioned rather well. We can't wait to present our project and hope you're as excited about it as we were and still are. Thank-you again for the consideration of our project.

Step 19: More Videos of Our Work

Step 20: Our Work on the ZSpace

In S.T.E.M. we have a computer called the ZSpace which creates three dimensional models which can be viewed as if they were real life objects that could be held. We have taken the liberty of copying all of the ipt files and changing them into stl files in-order to present a three dimensional model of the hand which you will be able to take apart and view the hand in pieces as well as see it coming together in a three dimensional presentation. I would like to take time to thank our geometry teacher Mr. Elias for teaching us how to use this.

We hope you enjoy

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