Monday, February 20, 2006

Static Equilibrium On One Leg

Here are some pics of the right robot leg (I havent made a left leg yet). It is pretty stable thanks to its oversized foot. The motors a powerfull enough to drive the joints to all positions without stalling (and that was only using 3volts!).

Its so stable that I'm pretty sure I could get something like this to take simple steps in an open loop feedback system without any proper controller. - I dont really intend to do this but I think it could work.

As you can see it is pretty close to my original drawing of the robot. I havent decided yet whats going to go above the waist but Im sure it will be a similar style to whats below it...

Thats just balancing statically and most of the joints are set to about 45' to the normal. The weight is noticably at the front of the foot (Where a big toe would be).

Robot Leg Subassemblies

I decided to make this robot as easy as possible to construct and duplicate so I built it from easy subassemblies which all use common parts.

Each leg consists of three parts each containing two servomotors. These are shown below...




As you can see it really is simple to construct. All I need to do is put thses assemblies together and drop in a servocontroller circuit board...

New 3 DOF fully articulated leg

This is my initial plan for the biped section of my new android. The construction of the real thing looks strikingly similar to my original idea.

I was thinking about using standard off the shelf parts like easily accessible gearmotors and boxes so the robot could be constructed easily cheaply and quickly.

The robot assembly has 3 degrees of freedom in each leg which means it can perform similar movements to a human leg.

Each joint uses a Como Drill 810:1 ratio motor for maximum torque for at low weight. The motors are coupled to potentiometers giving positional feedback. The whole thing is controlled by a Picaxe microcontroller run as a servocontroller.

Im planning to create a 3D computer model of the robot using the Direct X API so when I write the rest of the control software the robot will have a spatial model of itself. I plan to use Denavit Hartenburg 3Dimensional coordinates do the robot will know exactly (by measurement) where all of its joints are at any given time. See below

Thursday, February 09, 2006

I abandoned that project ages ago but recently I had the idea of building another android, but this time doing the legs differently. Previously I had used a double hinged mechanism with only 6 motors for both legs but this led to an underactuated design. It was also a bit to flexible too. Ive come up with a new simpler design using 6 motors per leg. And thats what I've come up with.... Im going to put in the other three motors on saturday.  Posted by Picasa

There he is sitting in my window sill waiting for some more rewiring..  Posted by Picasa

Once upon a time I thought you could get away without using microcontrollers in these sort of robots. I built this TTL multiplexer to control my robot. It interfaced to a PC using the parallel port. nice idea but you soon realise that serial/usb comms are far superior. Still it was pretty cool to see those LEDS flashing away inside the robots chest as it moved about. Posted by Picasa

I went to Rajani's (a bargain basement in Bristol England) and they had these weird gyroscopic gamepads that they obviously couldnt sell. i bought one and took out the gyroscope (thats what that thing in the middle is). I was going to write software to use it as a roll/pitch attitude stabiliser to stop my robot from falling over. Posted by Picasa

Then I realised that in order to walk usually you really need to add motors for shifting the balance left and right. Posted by Picasa

Now I dont know about you guys but I thought it would be easy to just add the legs I'd made to the torso of my robot. Posted by Picasa

I built clusters of servomotors together on one board. They are controlled by a standard Milford 8-channel serial servo controller. The servos used a PICAXE 18 (standard) microcontroller using a BASIC program I wrote. Posted by Picasa

I built some legs for the robot. (These are the earliest biped legs I built). I built my own remote positioning servomotors using Como 810:1 drill motors and potentiometers. They are completely compatible with RC model servos but use a higher voltage.  Posted by Picasa

Theres the robot tired after a hard days work.Sitting on top of its charger. Posted by Picasa

Monday, February 06, 2006

It all started with this guy.I thought it would be cool to build a robotic head that could see, hear, speak and perceive distance. So I built MR_HEAD. Posted by Picasa


A while ago I was watching TV and thinking about all the old fashioned portrayals of the future, they always had robots running around doing stuff. I got to thinking "Well its the 21st Century so where are all the robots?"

Then it struck me.. There were none! So I thought I'd better do something about the situation and took it upon myself to build some funky robots.

So here we are, a couple of robotics and AI projects Ive been tinkering with..