A prosthetic leg

G G S B 3

DRAKKAR - PRINTABLE ROBOTIC PROSTHETIC LEG

Problems: - KNEE: The knee has got “stops” that prevent to the leg to bend forward. This “stops” support the weight of the person and block the leg during the walk, but since this “stops” are thin and fragile, in the long term, there is the risk they might break down.

- BACKBONE: The structure is made up of 4 steel threaded rods.

These rods are put in order in parallel in pairs: the first couple serves as a tibia (shinbone), while the second one as an ankle. These rods are joined together and connected to the rest of the leg by a small component 3D-printed, on which weigh on the weight of the person, therefore it’s likely that this component could break.

Moreover, the ankle is the fulcrum, while the force is applied starting from the knee, so when the person put his/her weigh on the leg, the ankle serves as a “hinge” and, on the basis of the force (weight), the leg could flex forward or back.

- FOOT: All the components of the foot are 3D-printed, so they don’t have smooth edges. This affects the movement of the finger that have difficulty to rotate and sometimes they get caught.

GGSB1

Improvements: -APPEARANCE: The appearance has been modified so that the leg would have a human shape.

- BACKBONE: The ankle is made of 3 threaded rods (instead of the 2 rods of Drakkar leg) and this can solve the bending problem of the Drakkar leg, since that this 3 rods are placed in a triangle. In this way the rods support each others.

The shinebone is made up of 2 rods: this rods can’t swing because they are enveloped by the plastic structure of the calf.

- FOOT: The foot is made in fibre to give it more strenght and solidity. Moreover the appearance is more human.

Problems: - KNEE: The knee wasn’t modified compared to Drakkar leg, so the problems are the same.

In addittion part of the weight of the person weigh on the plastic envelope, which could break over time.

GGSB2 Improvements: -APPEARANCE: The appearance has been further increased.

- KNEE: It’s totally different compared to the Drakkar knee. This knee consists of 2 pieces. The upper one has two holes: one for the linchpin that turning the knee, the other one is necessary for setting up the vertical mechanic actuator.

- BACKBONE: There are 3 threaded rods that go from the knee to the foot and support the weight, which doesn’t weigh on the plastic envelope.

Notes: -The KNEE could be 3D-printed or be laser-cut using plywood thick 5 mm.

- In the previous leg, the linear actuator have the motor placed laterally, while GGSB2 has the motor and the piston aligned, to occupy less space.

Problems: - The piston force application site is far from the knee fulcrum, this beacuse the central space is occupied by the backbone.

- It’s possible that the 3 threaded rods twist during the walk.

GGSB3

Improvements: -APPEARANCE: The aesthetic of the plastic envelope has been improved.

- KNEE: The piston speed problem, caused by the distance from the knee fulcrum and, in turn, caused by the central backbone, has been solved removing the piston and using rubber bands.

- BACKBONE: The twisting problem of the 3 rods has been solved adding horizontal section made of plywood, that we have called “vertebra”.

Notes: In this leg is possible to add a Gas-operated spring.

GGSB3 Gas-operated spring

A Gas-opereted spring could be applied to GGSB3, connected to the knee, to facilitate the walk and amortize the step.

GGSB3 Alternative foot

This foot is composed of various laser-cut elements. The rubber bands allow the mobility of the ball of the foot, by facilitating the walk.

Notes: Being totally made of plywood the foot isn’t amortised.

The shoe will act as shock absorber.

G G S B 3

G G S B 3

Instep

GGSB3 Fiber foot

The foot designed to GGSB3 consists in a fiber foot made using juta and polyester resin.

Every components have been designed studying the structure of human foot.

Heel Ball of the foot

Sole of the foot

GGSB3 Fiber foot To create the Fiber foot, we have prepered molds using Styrofoam.

The Styrofoam has been cutted with the help of a cardboard templates, obtained from the foot technical drawings.

Notes: It’s better to use molds covered with plastic, or with silicone.

GGSB3 Fiber foot

The foot molds have been cut off from a woven fabric. These outlines have been covered with resin, put into the molds and pressend to expell the resin (polyester resin), in order to reach resistant outline, that will be used to create the foot.

GGSB3 Assembly

Components: - Bolts (6 mm) 32; - Screws 2; - Calf (3D-printed) 2 pieces; - Knee 2 pieces (26 sections); - Rubber bands 2; - Ball bearings 2 pieces; - Threaded rods ( 6mm) 9 pieces; - Pipes (6 mm inner diameter, 8 mm outer diameter) 14 pieces; - “Vertebre” q.s. (In our project there are 13 “vertebre”, but, in general, more “vertebre” confer more rigidity).

- Seeger ring 78 pieces;

GGSB3 Alternative: components 3D-printed

Components: - Bolts (6 mm) 32; - Screws 2; - Calf (3D-printed) 2 pieces; - Knee 2 pieces (3D-printed); - Rubber bands 2; - Ball bearings 2 pieces; - Threaded rods ( 6mm) 9 pieces; - Pipes (6 mm inner diameter, 8 mm outer diameter) 14 pieces; - “Vertebre” q.s. 3D-printed (In our project there are 13 “vertebre”, but, in general, more “vertebre” confer more rigidity).

- Seeger ring 78 pieces;

GGSB3 Assembly

KNEE: The knee is made of 2 components.

These two components could be, entirely, 3D-printed. In this case, we have cut the pieces using the laser cut on plywood (thickness 5 mm). The various parts have been sticked together to shape the two main components.

Note: To make sure the various parts fit perfectly together, during the bonding, it’s reccomended to get in position the pipes into the holes, using them as a runner.

GGSB3 Assembly

BAKEBONE: The threaded rods be entered in the holes present on the calf plastic envelope, entirely 3D-printed.

To ensure stability to the rods, within the holes, we have added some rubber pads, which serve as seal, making stronger the rods.

GGSB3 Assembly

BAKEBONE: At the bottom of the calf, the rods shall be mounted all at the same height. This is important because the foot will be assemblet at the end of the rods and it will be perfectly horizontal.

GGSB3 Assembly

“VERTEBRE”: The “vertebre” have the function of stabilise the rods, so a large number of these components ensures rigidity to the leg.

The “vertebre” shall be fitted, before, on the pipes and only then on the threaded rods.

Every “vertebra” has 3 holes: to ensure their stability it’s possible to use Seeger rings (2 per holes).

GGSB3 Assembly

FOOT: The foot consists of 3 elements (sole of the foot, instep and heel) joined with bolts, that’s why they need to be drilled.

The instep, joined to the heel, will be connected directly with the rest of the leg by the 3 threaded rods, which set up the ankle. While the sole of the foot is joined with the instep, where in a human foot there is the ball of the foot, and with the heel by way of bolts.

G G S B 3

DRAKKAR

GGSB3

Greta Aldeghi Riccardo Andreoni Andrea Braggion Licia Cerrito Elisa Manzato Course: Technologies and digital applications Module: Fab Lab academic year 2017/2018