So I have bought a hexbug spider with the idea that I can reverse engineer it and have a simple, but creepy, hexapod walking robot driving by just two motors. Then we can use the animatronic eye, or a new version of, that I worked on with Richard Sewell, to make a really creepy facetracking eye on big spider legs!

The hexbug spider is a very simple and yet complicated mechanism that I have been staring at intently to work out how it works. Here is a quick video of it running around my table;

To work out whats going on i started to take it apart,

What I have found is that there are two motors, one determines direction and the other drives. The driving motor pushes a drive rod up and down in an elliptical motion. There are two independent tripods of legs that are 180 degrees out of phase with each other. The two tripods share connection with at the end of the drive shaft. This point has on the drive shaft is also connected to a two direction guide that moves up and down and left and right 45 degrees out of phase with the direction of the spiders forward movement. The produces the loci that moves the legs effectively. Anyway, once you see it working its easier to know whats going on. So far I have cadded up a quick attempt of what I understand in solid edge, although its still missing the drive rod guide at the base.

Hopefully I will have a full working simulation soon, and then on to making it bigger and real!

I went to IROS 2011 in San Francisco! it was pretty awesome. Have some pictures from the exhibition…

Willow garage PR2

NAO

FESTO trunk & gripper

KUKA star wars

Shadow hand

ASIMO

ROBOTIS & DARWIN

iCub

More pictures on my Flickr

Getting opencv to run on ubuntu 11.04 is not so easy due to problems with ffmpeg. However, If you compile and install ffmpeg from source it should allow for opencv 2.2 to install hassle free. Sabastian Monabone explains the process better than I could here.

I am currently developing on 3 platforms at work so I am trying to manage the source code in a tidy manner and version each module etc… Shared object files in linux and dll’s in windows have always been pretty easy but I have not tried to created a dylib (.so equivalent) in mac xcode before. I have made it work, im not sure if its the correct way but its linking and runs.

First i had a standard command line program that I wanted as a library so I went to the project settings and changed Mach-O Type to Dynamic library. This means the compiler does not look for a main function.

Next I need to rename the output file. For this I find the target in the project explorer, right click and get info, build tab. In the packaging sections change Product name to name.dylib. Build the project and it should now produce you a shared library file.

To use this library in another project you need to make a few further steps.

First add the associated header file directory to the header search path in the project settings.

Secondly add the directory of the library file to the library search path.

Finally create a new group in the project explorer named “libs” or something similar and drag the library file to this group. When you build it should all link up and execute. I have had some issues where the executable cannot find the library. With a brief googling it seems that xcode at least at one time had a conflict of build versions unless the library file is not in the execution directory. I hope to resolve this, but for now I just copy the library file over.

Ive been setting up TCP communication between windows 7 and my mac and I get kept getting a ringing sound when sending a certain packet. With some more investigation it turns out at a printf with a “\a” or ASCII 7 produces a beep to occur from the system. Im really not sure why I would want this to ever happen, and its really off putting to hear your code beep all the time!

The proxy at work has been blocking any svn activity for me on my mac, heres the solution

1. Open terminal application
2. Use vi application to open configuration file

   vim ~/.subversion/servers

3. http-proxy-host = www.url.com/127.0.0.1 (whatever the proxy is)
4. http-proxy-port = 8080

And now it works

More info and pics soon!

To continue the cephalopod obsession, I had noticed that my friend Richard had made a brass squid for a recent steampunk festival and so I asked him to show me how to make one. This is a quick photo diary showing how we made a squid from copper using some simple fabrication techniques.

First of all I made a paper template the rough shape of a squid.

Then we raided Richard’s garden for some spare copper.

Trace the template and cut it out.

Anneal ready for some bending and hammering.

Hammer with a rounded head to stretch the copper into a rounded shape.

Some more hammering around a round shape.

Add texture dimples with a flat hammer over a dome shape.

To make an eye use a tube to create a circle indentation and a blunt centre punch for the pupil.

Bend the edges round to create a more lifelike shape.

Twist the tentacles with pliers.

Gives it a slight polish and finished!

The cnc machine is now complete so I can explain what Ive done to turn a minimill into a working cnc mill. It will be fairly brief but youre welcome to email me and ask for more details.

First I bought one of these …

This is a SIEG X1 super micro mill mk2 from Axminster tools. Its built in china, its cast iron and its relatively cheap. It has its downsides like poor lead screws and nuts, and a slow spindle speed (2K rpm) but its good enough for me for now. So this will work as a nice stand alone desk mill cutting most materials, although I haven’t tried any steel yet.

Next you need some stepper motors. I bought 3 of these hybrid nema 23 stepper motors from motion control products.

The stepper motors need drivers to power them with 24v 2.5A so from the same place I bought these.

The drivers need step signals to amplify to the motors, so you need some kind of controller. I wanted to run everything off a small net book so it needed to be USB. There arent many USB controllers on the market. I went with the ncPod as it was recommended by a friend. Its still in beta and doesnt look like its full anticipated functionality will ever be realised, but the company were responsive and the board is a good price and everything it can currently do is more than enough for me.

None of this will work without power. I originally hacked a pc power supply, but it didnt supply enough volts (24 is best for these drivers) or enough current. This means the motors will only go slow when cutting or they’ll slip. The quicker you can run your machine the happier you will be. I eventually went with this supply from farnel. XP Power PSU 160W . To power the ncPod you will need a 5v switching regulator.

To attach the motors to the machine you need some kind of motor mount. You can buy kits from cnc fusion for the X1 but theyre expensive and you can make them easily yourself.

To make a mount you just need to rigidly attach the motor in line with each lead screw, and connect the shafts and lead screws with motor couplings. Couplings can be expensive so I went to ebay to save money. They were not the best quality but they work fine.

With all the mechanical stuff attached you need to wire the steppers, drivers and controller. Spec sheets should show you how to do this so I wont give the details. I used 4 pin xlr connectors on the box that houses all the electronics. It makes the cabling robust and looks more professional.

To talk to the ncpod, and make anything move you need some kind of cnc software. There are free examples available, typically on linux, but they wont work with a usb controller, so Im stuck with windows. Mach3 is a well developed free hobby come professional cnc tool that reads gcode and deals with all communication to the electronics. Its well worth the £100ish pounds… Mach3

Once you have Mach3 up and running you have to configure it for things such as the number of clicks per rotation which is determined by your motor resolution, screw pitch and microswitch resolution. You will also need to determine the maximum speed and acceleration for the motors. This is trial and error. I have my acceleration quite low to reduce the risk of the motors slipping. If you press tab when in Mach3 it provide you with a jogging window to move the motors or you can input gcode commands into the command line.

The final piece of software you need is to produce the gcode. For this I use CamBam. Its still in development but its already very good. You can define all your cutting paths and even do 3d profiles. I tend to not use the CAD functionality as I prefer AutoCad/SolidEdge but it will do most things.

So all thats left to do is CAD -> CamBam for gcode -> Mach3 to execute -> Watch your machine cut stuff!