This summer I have had access to the waterjet at NREC where I had my internship.  The current pedal design calls for a series of 2-dimensional parts that I knew I could cut on the waterjet very easily (it can cut through stuff faster than 10 inches/minute, so it’s preferable to a CNC for this application).  Unfortunately I put off cutting these parts until the last week of my internship.  At 10PM on the last Tuesday night of the summer, I realized that I needed to prepare the .dxf files (files that define the shapes of a 2-dimensional part) I would need to cut some parts out after work.

When I went to make the .dxf files, I realized that I could make the entire pedal assembly out of welded steel plates cut from the waterjet.  That night I started making a new version of the pedals (version 9) and had the rough outlines of all of the key parts by the time I went to bed at 3AM.  I also never made the .dxf files I wanted for the next day.

Wednesday night I made the .dxf files I needed for the old pedal design, then spent the rest of the night optimizing the brake pedal assembly for weight.  Here are some renders of the design, as well as some FEA results:

Stress Plot

Factor of Safety Plot

An Exploded View Animation of the Assembly Process

Fabrication

On Thursday night I stayed after work to cut my parts on the waterjet off-hours.  It took about 5 hours to cut three sets of parts for the old design and two sets of the experimental pedal.  Though the brake pedal hasn’t been welded yet, the tabs were easy to press together to get a good sense of what it will look like in real life.  I was really impressed that I could go from concept to completion in only 48 hours, thanks to SolidWorks, NREC, and the waterjet.  Mike was kind enough to take some glamour shots of the final product:

I still need to find a cost effective way of turning a bipolar stepper motor on and off using just one pin.  I want to have the ability to use a powered brake, and I want to be able to use half-stepping control of the motor for smoother rotation.

Half-stepping gives the motor higher resolution, which is good for my application because one full step cycle is enough to move a single ball through.  The 4-stage process from before turns into an 8-stage process when you change to half-stepping.

t=0  A=1  B=0  C=0  D=0

t=1  A=1  B=1  C=0  D=0

t=2  A=0  B=1  C=0  D=0

t=3  A=0  B=1  C=1  D=0

t=4  A=0  B=0  C=1  D=0

t=5  A=0  B=0  C=1  D=1

t=6  A=0  B=0  C=0  D=1

t=7  A=1  B=0  C=0  D=1

t=8=0

The Solution

I noticed that in half stepping (and full stepping) if you view the logic for each of the four wires as a wave, they are always 90 degrees out of phase and have a specific shape.  I wanted to create four unique signal lines, one for each of the four wave patterns, and transmit this signal to each of the 30 stepper controllers.  At each controller, I should be able to choose either some default value (like a powered or unpowered brake) or let the motor run off the signal.

Because my focus was centered on the powered brake, my initial idea was to take my on-off line at each motor and perform a logical AND with three of the four waves and a logical OR with the other wave.  The OR would drive its input high while the AND would drive its inputs low.  This solved my problem, but unfortunately I couldn’t find a chip with an AND and an OR circuit on it.

You can build any logic gate with a combination of NAND or NOR gates.  It takes two NAND gates to build an AND gate, and three NAND gates to build an OR gate (and vice-versa when building from NOR gates).  They sell IC’s with 4 NAND gates in them, so I really wanted to find a way to do my OR operation with only 2 NAND gates.

Eventually I realized that if I negated the signal wave coming from the Arduino (by using 1 NAND as an inverter) and then performed a NAND operation with the wave signal and the on-off signal I got the exact output I wanted!  of course, if I had just used an AND on each of the four inputs, I would have an unpowered brake and less of a headache.

I made this circuit on a protoboard, and tested it with both full and half stepping.  It worked like a charm.  The next step is to see if half-stepping combined with a smaller diameter wheel will be able to push balls along without jamming.  Here is the protoboard layout:

Pros

This setup allows for full and half stepping.  It costs less than the shift register design, about $2 per unit (only $0.75 from the two NAND ICs).  Each of the four inputs is completely isolated from the others, so the wiring is simpler (which makes the PCB layout easier).

Cons

There are now 4 common signal wires instead of just one.  These 4 wires will need to be jumped from board to board, potentially requiring some sort of transistor to keep the voltage from dropping as it moves across the boards.

More Photos

I need to be able to turn 30 identical stepper motors on and off individually.  I can only afford to have one unique wire going to each stepper unit because I only have ~40 digital outputs to work with.  I can afford to have a few common outputs that are jumped from board to board.  basically I need to turn four inputs that go in a pattern into one input.

The four lines on the motor driver (H-Bridge) basically take turns going high when I want the motor to turn.  When I want it to stand still, only one of the lines should be high.  This is called “wave driving” a stepper motor.  Here is what happens when a bipolar stepper motor is wave driven.

t=0:  A=1  B=0  C=0  D=0

t=1:  A=0  B=1  C=0  D=0

t=2:  A=0  B=0  C=1  D=0

t=3:  A=0  B=0  C=0  D=1

t=4=0

The Solution

A Serial in Parallel out (SIPO) Shift Register does basically exactly what I’m looking for.  If I have one common clock (a line that goes high every 1/4 step) and connect the 4th output to the data input, then the four parallel outputs will shift through my 4 states like a champ.  The only catch is that I need to seed the circuit with the initial “1″ so that the “1″ can move along the shift register.

Luckily, because a shift register is just 4 flip-flops lined up in a row, I could build my own shift register out of flip flops, and access the set/reset abilities of the individual flip-flops.  So in the final setup, I had a single clock coming from the Arduino (pulsing at 100ms intervals) which controlled the speed of the motor, and a “stop” pin coming from the Arduino to control whether or not the motor was turning.

The “stop” pin was tied to the reset pin on the first flip-flop and the set pins on the other 3.  This means that when the “stop” pin was driven low, it would force the shift register into the “1-0-0-0″ state, and when it was released the “1″ would shift sequentially at the speed of the clock to drive the motor.  Here is a view of the protoboard layout (the center IC is the motor driver, and the other two each contain two flip-flops):

Pros

This is a huge improvement over controlling all 120 lines individually.  An Arduino mega can easily output a single clock and 30 control lines.  The cost of each circuit is about $4 in parts (three Integrated Circuits, or ICs), more if you PCB it.  It works, and it lets you do a powered brake as well.

Cons

The two IC’s with flip-flops are about $2.50 0f the total parts cost.  For this price ($2.50×30=$75) it would technically be cheaper to buy some other board that can take serial from the Arduino and control the 120 outputs.  Also, the wiring is a bit complex and uninsulated because each flip-flop’s output feeds into the next one’s input.

More Photos

With the current direction for the Vibraphone design, the notes are played by dropping a steel ball onto the keys.  There are several ways to actuate the balls, but considering the cycle times we want to achieve and the cost of each device (since we need 30 total) using a small motor and a wheel to push balls off of a queue and into free-fall seemed like the best idea.

The club has a few sets of tiny motors that have been donated, and each set has as least 30 motors of that kind.  The two sets we investigated are the tiny DC motors from the handheld fans, and some tiny bipolar stepper motors.

There are two trains of though for what to put at the end of the motor.  One possibility is to put a circle with a squishy perimeter on the motor, and use friction to pull balls through the mechanism one at a time.  Another concept is to cut ball-sized notches into the perimeter of a plastic circle, acting like a sprocket on a row of queued balls.

We have tested both concepts on the fan motor, and they each have their advantages and disadvantages.  After testing them both on the stepper motor in a more controlled way, we should have a better sense for which type of wheel will work best for us.

Here is a photo of the notched wheel Mike Ornstein and I milled in the roboclub CNC mill the other night.  The notches fit the balls great, but a consistent problem we had with the fan motor was that balls would jam if they tried to fill an empty queue.

Fan Motor

The fan motor is easy to control.  If you put a voltage difference between the two wires, it will spin.  If you give it a low voltage (1V) it will spin fast.  If you give it a higher voltage (3V) it will spin VERY fast.

From my observations, there just didn’t seem to be enough torque on the motor to handle the balls we were giving it.  Also, when testing with the notched wheel, the fan seemed to lack all braking ability.  Obviously with a friction wheel instead of a notched wheel the motor will be able to resist back pressure, so I look forward to seeing how that performs once we get a nicer friction wheel made (Plastic circle with a notch for an O-ring).

Stepper Motor

The club has a box of 150 tiny stepper motors with 4 wires coming out of each of them.  Starting the process knowing absolutely nothing about steppers, I eventually determined that our stepers were Bipolar Stepper Motors.  Basically, there are two pairs of wires and I need to follow a cycle of powering and releasing the pairs in different directions in a certain order so I can get the motor to ’step’ 1/48th of a rotation.

By using an H-Bridge configuration on each pair of wires, I could independently control the direction of the current in the wires with digital logic.  20 lines of C++ and an Arduino later, I had a great test rid that let me step the motor at whatever speed I wanted!

I was very pleased with the initial performance of the stepper motor.  There seemed to be a lot of torque behind the motor, despite its size.  The biggest advantage in my eyes though was the powered braking.  By setting only one set of wires in only one direction and leaving it there, the motor was in a powered lock.  This should help with the back pressure issue we were facing on the fan with the notched wheel.

Here are some photos of my final Arduino/H-bridge setup.  I was very happy because both the circuit and the program worked on the first try!  That never happens!

Structure

The large round plate is actually a 30-gon not a circle.  It is inscribed in a 32″ circle, and is 1/4″ thick.  There are 60 unique (thank you design tables!) plastic supports that slide onto notches in the aluminum.  Each plastic support has to be unique because of the awkward hole spacing in the individual keys.

There are already notches in the plastic for clips that should hold it into the aluminum plate (aka “Megaplate”).  However, depending on the design of the ball deployment mechanism, the retaining clips for the plastic plates should be incorporated into the support for the mechanism.  Here is a close up of the plastic supports:

Distribution

Finally, here is a close up of Mike Ornstein’s ball collection and sorting mechanism.  It uses brushes from the bottom of doors to pull balls up an archimedes screw into a paintball-style hopper.

Animusic is a group that makes great computer animations involving “impossible” instruments playing great music.  While considering actuation mechanisms for the RobOrchestra Vibraphone project, somehow we decided it would be a good idea to do something similar to the instrument that takes center stage at 1:07 in Animusic’s “Pipe Dream”:

Details

Right now, 3/8″ diameter stainless steel balls are looking very promising.  Mike Ornstein, Dan Shope and I have subconsciously split up the work into 3 sections.  Dan is working on the mechanism to take the balls and dispense them onto the keys quickly and with a short reload time.  Right now, it appears that this will be accomplished with a group of DC motors.  Mike is working on the mechanism to lift the used balls back up and dispense them to queues leading into Dan’s mechanism.  This is most likely going to be done with an Archimedes screw and a paintball gun style dispenser.  I have been focusing on the structure of the whole mechanism and collecting the dispensed balls and funneling them to Mike’s mechanism.

The biggest problem I am facing with this design is the awkward hole arrangement in the keys.  I basically have two very awkward hole lines I need to support for both the naturals and the sharps.  A string pulled taut needs to go through the holes in the keys and the supports to hold up the key and let it vibrate naturally.  My initial concept involved about $60 of waterjet-cut 1/8″ ABS.  Here is a render of this initial design:

This concept was that with angled plates in front of the keys sloping back toward the keys, as well as slopes over top of those angled toward the center, I could funnel all of the ball bearings into a channel between the two sets of keys.  Unfortunately it takes up a whole sheet of plastic.

Future Concepts

Moving forward, I want to find a way to eliminate all of the unnecessary material in all 32 of those vertical supports.  A bar or two mounted along the path of the key mounts could allow me to build much smaller plastic mounts for each key.  Look forward to another post with more designs, and watch my friend’s blogs for updates on their portions of the project!

• Intel i7 920 Quad-core @2.66GHz (currently not overclocked)
• ASRock X58 Motherboard
• Nvidia FX Quadro 580 workstation graphics card
• 6GB RAM
• 1TB Samsung HDD
• 650 Watt Corsair Power Supply
• CoolerMaster Hyper 212 CPU cooler
• CoolerMaster 335 Case

Build Observations

Putting together a computer was quick and easy.  Everything went super smoothly and was very straightforward.  I never really had to read the directions (although Mike Ornstein was guiding me heavily).  The hardest part was making sure all of my components were designed to work together.  I spent more time researching individual parts than I did assembling the whole system.

Overclocking seems unnecessary right now.  I have Solidworks running in RealView, and I can spin large models with no lag.  The biggest improvement is my rendering ability.  1920×1080 renders of complex geometries in Photoview used to take more than an hour, or just crash my laptop.  On the new computer, it takes only four and a half minutes.  This makes sense, considering that my Windows 7 Experience index raised from a 3.1 (Limited by graphics score) to a 6.9 (Limited by HDD score; Graphics and processor are highest – tie at 7.9).  I successfully played an HD movie over the weekend, and am very pleased with the results.

Software

With one computer that i use in my room (or remote into) and another I take around with me, it is important to make sure they play nice.

I found a file synchronization tool, FreeFileSync, that I really like.  I have a “SYNC” folder on each computer, with everything I want to have available to me on any computer (School/Project/Personal files, Music, etc).  FreeFileSync matches this folder from each computer against a backup I set on my external hard drive.  So I have three sets of identical data in three separate places.

I was having trouble syncing my iTunes playlists.  The way iTunes handles its playlists and libraries is very weird.  I decided to convert to Windows Media Player, and I’ve never been happier.  All of my music (4-5GB) and playlists are synchronized now.  However, because WMP playlists are just xml data with absolute mp3 file locations, syncing the playlists would make it not work on one computer.  I solved this problem by drawing on my 15-123 PERL skillz and writing a quick script to convert the absolute file names into relative file names in the playlists (which are identical between computers) and now my playlists can synchronize too!

I have set up remote desktop and have given my friends an account so they can render on my machine.  I’m curious to see if i start remoting into my workstation when I’m on campus, or if I’ll just keep using my laptop most of the time.

I look forward to installing Synergy which should allow me to control the workstation with the keyboard and mouse on my lenovo (which I love) as well as using my laptop and workstation screens side by side, as if they were one computer.

I don’t do that much with my computer.  I take notes in class with OneNote, and do schoolwork with Microsoft Office.  I browse the internet with Chrome, listen to music on iTunes, watch movies with KMPlayer, and chat with Pidgin.  My biggest computing needs come from 3D modeling in SolidWorks and its components, like the COSMOS FEA pack and the PhotoView 360 Rendering App.  These programs, which I frequently use for my projects, require a large amount of RAM and graphics processing capabilities.  Because there is no computer that is both portable enough to bring to class to take notes on and powerful enough to rotate a >1,000 part 3D model of a racecar, I am convinced that the best solution is to use two well synchronized computers for my two distinct use cases.

Current Computer: ThinkPad X61 Tablet

• Windows 7 – 64 bit
• Intel Core 2 Duo L7700 @1.80GHz
• 4 GB RAM
• Mobile Intel 965 Express Chipset Graphics
• 12″ screen @ 768×1024
• 320?GB ????rpm Hard Drive
• Docking Station – DVD drive with CD-RW
• Docking Station – Connects to External Hard Drives
• Docking Station – Connects to 24″ Samsung monitor @ 1080×1920

Workstation Design

Graphics Card

My primary focus was a graphics card that would let SolidWorks run at its full potential.  I needed a workstation card with openGL support to get the most out of SolidWorks.  I decided on the NVIDIA Quadro FX 580 because of its balance between price and performance.  It connects with the PCI Express 2.0 x16 port, so it began to limit my motherboard options.

Processor

Running Finite Elements Analysis always hangs up my laptop (or crashes it) so I wanted a processor that could handle the load.  The Intel i7 family seemed to be my best bet.  I needed to choose between the i7 920 and i7 930, a difference of about 140MHz and $15.  I went with the 920 because it seemed like the more popular model, which would make community support when I try to overclock it much easier.

Motherboard

I wanted to find the cheapest Motherboard I could that would get me by.  I needed the 1366 socket for my processor, a PCI Express 2.0 x16 plug for my graphics card, and room for some RAM.  I found an ASRock board that had just what I wanted and had room for another x16 card with SLI support if I felt the need to expand.

RAM

When viewing a model in SolidWorks it loads the assembly and all parts and sub-assemblies and sub-sub-assemblies and sub-parts etc. into RAM.  in order to view the full model of the racecar, I wanted to make sure I had enough RAM.  Because the i7 is tri-channel, I thought 3 x 2GB sticks would be sufficient.  The motherboard wanted DDR3 RAM, so that’s what I got.

Heat Sink / CPU Cooler

Even though the i7 runs at 2.66GHz, because most of the cores arent being used all the time, it is very easy and standard to overclock them to about 4.0GHz.  However, I needed a good cooler to get there.  I chose the CoolerMaster Hyper 212 because of its good reviews and good value.

Power Supply

I wanted to make sure to leave room for expansion, so I didn’t skimp on the power supply wattage.  I found a great series of deals, sales, and rebates that ended up cutting the price of a CORSAIR 650 Watt power supply in half.  I might regret not paying a premium for modular wires, but I think it will definitely get the job done.

Hard Drive

Because I already have external hard drive with all of my data, I didn’t see the need for anything fancy.  I found a good deal on a 1TB 7200rpm hard drive that is more than enough for me.  I may regret not buying a small solid state drive to speed up the time it takes for me to boot and the time it takes to start programs.

Case

I wanted an inexpensive case that was portable enough to be moved once or twice a year whenever I change where I live.  I also wanted to avoid any cheesy gamer cases with blue lights and annoying bells and whistles.  The CoolerMaster 335 seemed like a good, plain, simple, robust, economic option.

Optical Drive

I never use CDs or DVDs.  At Carnegie Mellon, the internet and intranet are so fast that it doesn’t make sense to transmit data any way besides the campus network.  I will not install an optical drive in the workstation, but if I need a CD drive desperately, I can always link to the docking station on my laptop.  I’m planning on installing the OS with my roomate’s 8GB USB thumbstick.

Monitor

I’m going to be using the same Samsung 24″ 1080×1920 I already have with my laptop and docking station, except I can switch inputs between laptop and Workstation.

Keyboard and Mouse

While I plan on using the old wireless Logitech USB mouse I already have when I need to, I prefer the Trackpoint mouse on my Lenovo laptop.  It’s so much easier to transition from keyboard to mouse when the mouse is already next to your right pointer finger.  Temporarily I will borrow a roboclub keyboard, but eventually I might indulge in this keyboard from Lenovo.  Also, I know there is some software out there that can link my laptop to my Workstation and let me use the keyboard and Trackpoint on my X61 to control my Workstation

Summary

Specs

• Windows 7 – 64 bit
• Intel Core i7 920 OC @ 4.0GHz
• 6 GB RAM
• NVIDIA Quadro FX 580
• 24″ screen @ 1080×1920
• No Optical Drive
• 1TB 7200rpm Samsung Hard Drive
• Trackpoint keyboard?

Expectations

I expect that when I’m in my dorm I will be using this computer, controlled from my laptop input with some synch program running between them.  While on campus I can take notes/go online with my laptop, but remote into my workstation for any serious business.  While off campus, depending on the internet connection, I might still be able to remote into the workstation to do serious work if I needed to.  The last component (i7 920) should arrive Monday, and I look forward to putting this together in the robotics room with the help of my friends.

This summer, besides working at NREC on the Strawberries Project, there are a few goals/projects I am working on.  Hopefully this blog will help me keep on pace to get everything done by the end of the summer and keep my friends and family up to date on what exactly I do with my time.  If I’m committed and get positive feedback, I might even continue once the school year starts.

Robotics Club – RobOrchestra Project

After taking over the RobOrchestra project one Richie P. left, I’ve been trying to add as many new instruments as possible.  The group got nearly $1000 from the URO for a Vibraphone project.  The proposed timeline has the mechanical design completed before the Fall semester, so this project will probably take priority.  Luckily, my roommate Mike Ornstein is also on the project, so he should be able to keep me in line.  I’m also still thinking about alternative string plucking and fretting options for an upgrade to or replacement of the Whamola instrument developed last year.

Formula SAE – Custom Software

After being appointed “Full Model Guy” for the next year on the Formula team, I decided I wanted to use some of my Solidworks API knowledge/interest/enthusiasm to help organize the team.  I’ve spent several hours staring at a blank computer screen though, because I’m having trouble defining what exactly I want to make.  I definitely want to make a piece of software that can extract features from a part and use it to generate a cost report document in Excel.  Beyond that, I can’t decide how much of a version control system/custom property manager I want to make, and what kind of interface (web, add-in, both?) I want in it.

New Custom Workstation Computer

This is a personal project, although I am getting tons of advice from tons of experienced friends.  Once the parts finish arriving on Monday, I’ll take some photos and post some specs.

Conclusions

I’m in the middle of a lot of other projects which I should continue working on casually over the summer.  There are other RobOrchestra instruments, electronics, and coding to be done.  I also have SAE design and fabrication commitments to take care of.  If I get around to it, I might try to make some backdated posts which give a little more background about those projects.  You can also expect me to share random Solidworks or Machining tips I come across as well.  Hopefully this blog will become a very thorough and accurate representation of my technical hobbies and interests.