Blog.OhBowz

I put together the Ice Tube Clock kit today.

It was a great Xmas gift!  You can buy them HERE

This test tells me I need greater resolution and strength on my joints.
There is a lot of wobbling, and creaking going on.
If the AX-12 servos can be made continuous rotation, I could gear up.

I will post more progress on this, eventually.

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I have not forgotten about you.

Though I have been spending less time on my robot lately (I blame my new Cintiq), I have been slowly working towards a more stable design.  I want it to stand freely when the power is off.

It’s getting heavier on top, a lot of pressure is focused on one servos connection to the aluminum beam, I’m going to add support to certain areas so my custom brackets don’t snap.

When everything “seems” stable to me, I will begin programming the movements.

Excuse the mess

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For those who are interested in where I found the parts to build my biped legs.

I’ve used a combination of Lynx Motion Servo Erector set parts, MicroRax aluminum beams, screws and washers from OSH, and the Dynamixel AX-12 servos.  There is a bit of improvising to get everything to fit together.  If you try to screw down the Servo Horn Bracket into the MicroRax Aluminum beam, there will be a small but significant gap, so a washer to fill that gap is necessary to keep everything tight and snug.  I also had to make a custom part to fit the servos to the aluminum beam.  Some may say that is overkill, and prefer to drill into the existing servo brackets. I found my approach more precise and neat, even though its more expensive.

Parts list:

Aluminum Interconnect / Servo Horn Bracket

Ball Bearing Hub Kit

Aluminum “C” Servo Bracket with Ball Bearings

Aluminum Robot Foot (Pair) (Brushed)

Shocks – 3.5″ (Pair)

Threaded Rod – 12″ x 4-40

Ball Link Set – 4-40

All MicroRax Parts

And I just found more here

Ax-12 Servos  (These make the project expensive)

And I’m using the Arbotix Micro Controller as the brain for now.  (More info on using this controller)

The shocks you see on the knees and ankles are there mostly for stability, the amount of resistance they offer will probably be an issue, and I might have to remove the spring itself.   I really just need some friction.

That’s the quick list of details, without getting into quantities.  My background is in Arts and Animation, that is my approach to this project.  I’m not thinking things through like an engineer would, which means I am probably making many errors, and this design is very inefficient.  I welcome all feedback on how I’m doing it wrong.  Take my advice with a grain of salt!

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More details in my next post!

Two Legs

This is the first step in making my own bipedal robot.  If I’m satisfied with this leg, I will build another and some hips.  I want this leg to operate using Inverse Kinematics .  I currently have no idea how to do this, so if anyone wants to give me some advice please email me! ohbowz@gmail.com

I am using a combination of the Lynxmotion servo erector set, and MicroRax to build the frame.  I chose to mix these two because I like the aesthetic achieved with MicroRax and the function that the Lynxmotion parts provided.

Dynamixel AX-12 servos are moving the thing, special parts were made to get these to fit the MicroRax.

The brain is an Arbotix Robot Controller, which is like an Arduino, with more beef.

AX-12 servo mounted to MicroRAX

I’ve been playing around with the Dynamixel AX-12 servo. It’s a nice little servo that has a variety of attachment brackets that allow you to build many cool things.  The problem is I want to mount the servo onto a frame built from MicroRAX. The brackets that come with the servo are too small for this, when it comes to screw hole size.

Original Bracket - No fit

Luckily we live in a day and age where a solution to this problem has an easy fix.  Since the cad file for these brackets are freely available online, I was able to remodel the screw holes to the size I want, then I sent it off to Shapeways.com where it will be fabricated in a 3D printer and shipped to me.

Shapeways Materials

I ordered it in three different materials to see which works the best.  The results are very satisfying, the bracket fits on the servo perfectly and mounts nice and tight on the MicroRAX beam.

Shapeways Bracket, and Original Bracket

Problem solved!  If anyone has a similar need, here are the resources.

Order the bracket at Shapeways.com

Dynamixel Servos

MircoRAX

OBJ File of Bracket  (Right Click and Save)

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My Brother got me an AdaFruit MotorShield for Xmas.  I’ve used it to revive an old project that I had temporarily given up on.  I was trying to build my own Helicopter drone, I ended up buying most of the parts from HERE. The brains of the vehicle cost over $400.00, which I am not willing to buy, so instead  I’m using the Motorshield on an Arduino to control the rotors, the input control is a pair of thumbsticks ripped out of an old Playstation game controller.  So far everything seems to be working.  We will see if it can fly when I put in the super battery (which freightens me)

MotorShield on Arduino

DC Brushed Motor

Playstation Thumbsticks

Thanks Ian!

The i-Phone Robot got mentioned on Net @ Night, a podcast with Amber MacArthur and Leo Laporte !

Check out the episode here http://twit.tv/natn162 or on i-tunes
They talk about this project at the end of the podcast, I’m thrilled!

Rock Band has been released on the iPhone, and even though its a lot of fun, I would rather have something play it for me. Preferably a robot!

The setup is pretty much the same as the other robots that play these kinds of games.

the setup

Light sensors are used to read the falling notes, I’m using ambient light sensors from Sparkfun.  They are small and easy to setup. (The iphone brightness has to be set to Max)

The light sensor sends data to an Arduino, which is waiting for a spike in the data. This means something bright has passed in front of the sensor.  I’m using an Arduino Mega, which is overkill for this project, but it does look really cool with those WingShields on it.

Under belly of the beast

The Arduino runs the sensor data through some averaging filters, and sets a threshold for on and off.  This could also be done through hardware, look up Hysteresis and Schmitt trigger.  If the sensor data becomes higher than the on threshold, the Arduino reads that as a note, and tells the servo to push the screen.  The servo will not release its touch of the screen until the sensor data drops below the off threshold.  The on and off threshold have some distance between each other to deal with bouncy noise.

Servos acting like little fingers

The iPhone touch screen isn’t like most PDAs.  It uses a capacitive touch screen.  More info about that HERE.  It would seem that the iPhone is looking for a finger sized touch, from living flesh.  According to the link, the screen actually looks for changes in electrical current.

I had some conductive foam laying around, its usually used for shipping sensitive electronics.  If I put my finger behind the foam and pressed on the iphone screen, it works.  If I used something non conductive, like a plastic pen, the foam would do nothing to the screen.  My solution to this was to put thin copper wires into the foam (I also used these wires to attach the foam to the servos) the other end of the wires were wrapped around the handle of an exacto knife.  When the Robot is playing the game I touch the handle of the exacto and the robot fingers are able to press the screen.  Another solution was to run all the wires into the Arduinos ground pin, but it had mixed results (not all wires were making contact)

Insert iPhone into robots pelican grips

Add all of the above together into a modified Pelican case, with a lot of hot glue (non glittery) and you have a robot that will gladly beat all your difficult songs, sit back and sip some fine tea.

The performance of this robot increases with the correct positioning of the servos, and the distance you set them to move in the code.  You may notice in my video that the right most servo had a hard time hitting its notes, it’s been glued too far south of the note position, something I may correct later.  I think it would be cool to package all of this together as a portable unit, with an Mini Arduino running the show.

Here is the code I made for the Arduino, it’s a modified version of my other project.  If you want to make your own, you will have to tweak the sensor threshold and servo settings to fit your setup.

Iphone_Rockband.pde