3D printing: Shells and Infill (Part 1: Introduction)

Before we begin: The aim of this short study was to decrease the weight/material of our 3D models (the hand). We have successfully printed a hand (link) however it was too heavy. If the hand was lighter, it will be more portable and easier to make future add-ons (such as wrist or arm).

In this post we will introduce the terms 'shells' and 'infills'. We believe that we can significantly reduce the weight by removing the unnecessary material inside 3D models.

The SHELLS, also known as perimeters, are extruded outlines defining the shape of the layer. Extra shells strengthen objects.

INFILL is what happens in the space left over.

It's usually extruded in some kind of pattern. The main setting we're dealing with here, though, is infill percentage. (refer to the image below)

More infill will make an object stronger. Less will make it lighter and quicker to build.

Objects for display often won't need more than 10% infill, while even objects that are going to see hard use rarely need more than 80% infill. Not using more infill than necessary will help us save time and plastic.

Source: http://www.makerbot.com/support/guides/printing/

Taken from http://blog.teambudmen.com/2013/09/understanding-shells-layer-height-and.html
Author: Isaac Budmen

Stepper vs. Servo

Article from AMCI Advanced MicroControls INC. Stepper & Servo: Basic Differences         Stepper motor Servo motor The basic difference between a traditional stepper and a servo-based system is the type of motor and how it is controlled. Steppers typically use 50 to 100 pole brushless motors while typical servo motors have only 4 to 12 poles. A pole is an area of a motor where a North or South magnetic pole is generated either by a permanet magnet or by passing current through the coils of a winding. Steppers don't require encoders since they can accurately move between their many poles whereas servos, with few poles, require an encoder to keep track of their position. Steppers simply move incrementally using pulses [open loop] while servo's read the difference between the motors encoder and the commanded position [closed loop], and adjust the current required to move. drawing courtesy of National Instruments Stepper & Servo: Pros & ConsSome performance differences between Stepper and Servos are the result of their respective motor design. Stepper motors have many more poles than servo motors. One rotation of a stepper motor requires many more current exchanges through the windings than a servo motor. The stepper motor's design results in torque degradation at higher speeds when compared to a servo. Using a higher driving bus voltage reduces this effect by mitigating the electrical time constant of the windings. Conversely, a high pole count has a beneficial effect at lower speeds giving the stepper motor a torque advantage over the same size servo motor. Another difference is the way each motor type is controlled. Traditional steppers operate in the open loop constant current mode. This is a cost savings, since no encoder is necessary for most positioning applications. However, stepper systems operating in a constant current mode creates a significant amount of heat in both the motor and drive, which is a consideration for some applications. Servo control solves this by only supplying the motor current required to move or hold the load. It can also provide a peak torque that is several times higher than the maximum continous motor torque for acceleration. However, a stepper motor can also be controlled in this full servo closed loop mode with the addition of an encoder. Steppers are simpler to commission and maintain than servos. They are less expensive, especially in small motor applications. They don't lose steps or require encoders if operated within their design limits. Steppers are stable at rest and hold their position without any fluctuation, especially with dynamic loads. Servos are excellent in applications requiring speeds greater than 2,000 RPM and for high torque at high speeds or requiring high dynamic response. Steppers are excellent at speeds less than 2,000 RPM and for low to medium acceleration rates and for high holding torque. Stepper vs. Servo: The Verdict Servo control systems are best suited to high speed, high torque applications that involve dynamic load changes. Stepper control systems are less expensive and are optimal for applications that require low-to-medium acceleration, high holding torque, and the flexibility of open or closed loop operation. From http://www.amci.com/tutorials/tutorials-stepper-vs-servo.asp

Hectic Feedback!

Part of the AirGrip project is to create a pair of gloves, namely the HUMAN GLOVE and the ROBOT GLOVE. The 'human glove' sends signals to the user via haptic feedback while the 'robot glove' contains sensors that can detect obstacles. We have actually made this one of our sub-projects (one of the three). Read more about the division of the project in a earlier post: link. 

Last Friday we took apart old mobile phones to locate its vibrational motors (link) to be tested as haptic feedback.  Unfortunately we were not so lucky with it. But that didn't stop us there!

After browsing through some websites, we've found some online shops who sells vibration motors ranging from 1.5V to 10V! We have also found that piezoelectric speakers, at an optimum frequency are a plausible alternative. 

First we have the Eccentric Rotating Mass (ERM) Vibration Motors. Below is an example of one such product call 'pico vibe' by Precision Microdrives. Images taken from: link

The same online store also stocks Linear Resonant Actuators (LRA) Vibration Motors. We are actually in the process of ordering one of these to test out how suitable it is for our glove. More specifically, the Precision Haptic 10mm Linear Resonant Actuator - 3.6mm type: link. 

Lets take a look whats INSIDE a LRA vibration motor. Image taken from: link

Before our sample arrives, we have been playing around with the Piezoelectric speakers. At around 150hz and supply voltage higher than 3V, we can generate a low frequency buzzing noise but also felt on the finger! We broke the cover to isolate the piezo from the plastic casing. 

We used an Arduino to generate a square wave at a specific frequency with the 'tone()' function which also allows us to control multiple Piezos. One advantage was the low current and low power usage. However, the vibrations was weak but strong enough to 'feel' and know that it is there. 

So we have to decide... LRAs or Piezos! 

Stay tuned ... for the verdict!

The Division of Love

The Division of Love

So we have decided to divide the project into three sub-projects. Namely the Leap API, Gloves and robot hand.

Leap API: building the necessary java script knowledge to write programs which allows the robot hand, gloves and leap motion to work in real time.
Boss in charge: Ashan
Minion: Vincent

Gloves: To build the hardware as well as the actual glove for the user and the robot hand. The 'human glove' will have haptic feedback actuators while the 'robot glove' will have sensors to detect obstacles.
Boss in charge: Vincent
Minion: Shen

Robot Hand: To build the hardware and the robot hand with 14 degrees of movement from the robot fingers PLUS rotation about the wrist.
Boss in charge: Shen
Minion: Ashan

We will attempt to prototype as soon as we can so we can pour more time into software.

Stay tuned!

Acetone Vapour Bath gives a shiny smooth finish

We can get rid off the annoying layers(rough surface) on the 3D printed objects by this method called acetone bath. But Acetone bath is only used for ABS plastic. So we cannot do it for our 3D printed hand.

Further doing some research, Yay! Instead of acetone, we can use tetrahydrofuran, or THF, as a solvent for PLA. The process for smoothing PLA with THF is the same as smoothing ABS printouts with acetone.

Here is the method,

The Future of Design

The nExt biG Thing

Finally we were able to print an awesome 3d Hand. The heat issue that we have on our 3d printer caused some dodgy results. Some of them are,

However after fine tuning the 3d printer we managed to print a complete 3d hand (Thank you Andrew  \m/). Used rubber pieces for the hinges as the 3d printer doesn't support the flexible materials. It was bit of a challenge to shape those rubber pieces and also to drill the fingers so that we can put the thread in. Also I had to sand the sides of the fingers so that it has less friction for the movement. Here are some photos.

It already has a lot of fans. :)

GREAT JOB GUYS!

Plenty of hands!

Throughout this week we've been looking through lots of different types of robot hands. Before we settled on the 3D printed hand from Thingiverse, here a few of the things we looked at:

The first thing we heard about was a 'grabber' that apparently Professor Jarvis had. Prof. Russell told us that it might still be in his office, or that Tom Drummond might have procured it. However, when we went to check, neither Tom nor the room had this thing. Instead, we talked to Andrew in the workshop and he showed us that there was a 4M toy robot hand which was probably exactly the same thing we were looking for:

As you can see here, there are only three controlling fingers for the five fingers - this is due to the fact that two of the wires are connected to four of the fingers. Andrew told use he would be able to re-wire it if we were able to buy it. We found, however, that we would be able to do it cheaper!

The next idea we had came from this picture:

This is piping that has some 'hinges' or 'joints' cut out of it, and wires threaded through to control the hand. This seemed to be a very simple option, and Ashan was able to acquire some piping from the Chemical Engineering department (thanks guys!). He made a finger from it, but ultimately we also thought that this was a little too crude. Someone out there has made it look better though! :

However, as I seem to stress over and over again, we decided to go with the Thingiverse hand. It's currently still a little crude, as we didn't follow the recipe exactly, but it's good enough to play with!

Talking with the professionals

This week we had a chat with Prof. Andy Russell about the robot hand we wished to build. We wanted to know where we should start and how we could go about making our robot hand.

His advice was very helpful! We learnt that there are 32 degress of motion in a hand, and that we had absolutely no idea what those were. We decided that we only needed a grasping motion, but he gave us a good idea with moving the fingers horizontally away from each other. The Leap Motion can give us the angle between the fingers, and thus we may be able to control each of those fingers in a new way.

He showed us different ways we could orient the joints and a couple of ways that joints could be constructed. This was helpful - but since we went ahead with the 3D printing, it ultimately didn't matter. It did help us with conceptualizing how the joints moved, though, and we thank him for that.

Prof. Russell also gave us a couple of suggestions on books we could read (including his own!) that could help us with the construction of the robot hand. Ultimately, these were mainly irrelevant for our purposes as we only needed a hand that could grasp, and thus the subtle researches that were done in those books were lost on our primitive robot hand.

Luckily, the Thingiverse hand worked! This will be updated in a future post.

A mission for vibrational motors

Being the highly resourceful group that we are, we were able to procure some mobile phones in the hopes that we could extract the vibrational motors from the circuit boards and use them in our haptic feedback for the glove.

As you can see below, toothpicks are the tools of champions to open up mobile phones :D

The idea was that if we were able to get them cheaply, we could use them to great effect in our prototype glove. However, as you can see below...

It's very hard to identify what component is what. The speaker and microphone are easy to identify, but EVERYTHING ELSE is soldered down or inaccessible with normal tools.

Thus, this mission failed. Plan B will be incoming - piezo-electric speakers!

Interfacing Leap Motion with Arduino

Using the WebSocket server in leapmotion SDK we can analyse the tracking data.

Its super easy! Just connect the port to ws://127.0.0.1:6437

I have used 'ws' library from node.js. To install the 'ws' library the following command is used.

npm install ws --save

We communicate with Arduino using the 'johnny-five' library. It's installed using this 

npm install johnny-five --save

Yeah! Thanks to node.js :)

You can find the code on github: arduinoleapcar

Have FUN! :)

Printing a Robot Hand

We have found a very attractive 3D model of a robot hand call Flexy-Hand on Thingverse (link) designed by Gyrobot, published on the 4th of March 2014.

Here is a description from the website:

A proof of concept printable hand with "live hinge" flexible joints. Individually activated fingers using Filaflex filament as tendons.
Printed in Makerbot Translucent Red and Filaflex hinges.
Re-mix this idea into your own robotic or prosthetic project. 

• Fingers open automatically, no return tendons or springs needed.

• "Frictionless" articulation - no rubbing parts.

• Stretchable tendons offering adaptive grip on irregular objects (only one motor required to activate all fingers).

• Fully printable solution, no vitamins required.

• Tough and rugged.

• Realistic form under a surgical glove (see image above). 

We have spoken to a few people from different Engineering departments about using a 3D printer.  

Will keep you updated about its progress!

Named the project!

AirGrip - A haptic feedback glove coupled with a robotic Leap Motion interface

Feel the illusion!

(to be continued...)

Haptic Feedback with the Kinect!

Seems very similar to what we're doing, except with a Kinect, which means it can track a couple more elements of a person. He incorporates flex sensors as well, which might be useful since the Leap Motion cannot sense the joints easily.

He also uses linear actuators, and from forum-trawling, it seems that some people use this site: Precision Micro Drives to find vibrational motors. We will probably be using some slimmer, smaller types of vibrational motors for the haptic glove.