robots – dave's blog of art and programming

Training teachers in coding, and thinking about e-waste/recycled robots

We recently had the second inset training day in programming related activities at Truro school. Following on from the previous session I didn’t want to introduce too much new stuff, so we concentrated on going back over Sonic Pi and Minecraft/Python programming in the morning, then discussed a lot more about our future workshops in the afternoon. These will include children from most of the primary schools in the Truro area and take place during the next term. I also wanted to use the day to work on some specific ideas the teachers wanted to get going. One of these involved running a Kinect camera with the Pi, which we managed to get more or less working – reading depth data in Python for potentially plugging into Minecraft at a later date.

The big idea I wanted to get feedback about was the use of robotics and electronics in conjunction with code (the photo above is my desk while preparing the day before). I didn’t have any lesson plans for this, but based on some comments from the first workshop and from playing a bit with this during CodeClub teaching I felt it might be good with this age group, who already know quite a bit about screen based activities. To keep costs down (as well as building in issues like e-waste) we’re planning to make use of recycled junk to extract motors from toys and hack them to do different things. It seems this doesn’t cause too many issues from safety POV (everything will be low-voltage and we can check everything beforehand), even the use of soldering irons seems to be acceptable as they have supervision.

The advantage of using code to move real things (as shown by a long history) is that it directly connects programming with the world outside of the screen (where it most certainly now has great importance in our lives), and at the same time results in teamwork – as it’s not easy for a single person to make a robot while programming it. When we tried this at Troon Primary they self organised into a group with one person programming while another was building stuff in lego and a third provided excited communication between them and more or less managed the task. Other programming activities tend to be more individualistic – with the possible exception of networked Minecraft, which is important but a very different form of collaboration.

Al Jazari 2 re-arranger robot program

Onboard a robot, who is following a sequence of instructions (in the spirit of the original Al Jazari), to pick up, carry and drops blocks in order to re-organise it’s environment. Halfway through we switch to a robot which is running code that makes it player controllable, so we can look around. This is all more than slightly influenced by teaching Scratch at Code Club and feeling the need for something 3D for them to play with. The scheme bricks coding interface is next…

Al Jazari 2 – minecraft meets fluxus

Some screenshots of the in-progress next generation Al Jazari livecoding world. This is a voxel rendered world, inspired in part by Minecraft but with an emphasis on coding robots in scheme bricks who construct artefacts from the materials around them. The robot language is still to be designed, but will probably resemble Scratch.

You can ‘jump on board’ the different robots (cycling through them with ‘space’) and program them with commands which include picking up or dropping individual blocks. The program above allows you to control the robot with the ‘w’, ‘a’, ‘s’, ‘d’ keys with ‘z’ to tunnel downwards, and ‘x’ to remove the block in front of the robot.

The world is built quite simply from an octree – which provides an optimised structure for rendering the 64x64x64 level cube in realtime. The view below shows the compression – large areas containing the same material (or empty space) can be represented by leaf nodes terminating the tree early without needing to store each of the 262,144 1x1x1 cubes. After each edit, the octree may fragment or collapse it’s tree (via setting new values in 3D space or a ‘compress’ operation). The scheme code can be found here.

Spork Factory: evolving a light follower robot

Continuing with the structured procrastination R&D project on evolvable hardware, I’m proud to report a pretty decent light following robot – this is a video of the first real-world test, with a program grown from primordial soup chasing me around:

After creating a software model simulation of the robot in the last post, I added some new bytecode instructions for the virtual machine: LEYE and REYE push 1 on the stack if we are detecting light from the left or right photoresistor, zero if it’s dark. LMOT and RMOT pop the top byte of the stack to turn the motors on and off. The strategy for the genetic algorithm’s fitness function is running each 16 byte generated program on the robot for 1000 cycles, moving the robot to a new random location and facing direction 10 times without stopping the program. At the end of each run the position of the robot was compared to the light position, and the distances were averaged as the fitness. Note that we’re not assigning fitness to how fast we get to the light.

This is pretty simple stuff, but it’s still interesting to look at what happens over time in the genetic algorithm. Both motors are running at startup by default, so the first successful programs learn how turn one motor off – otherwise the robot just shoots off and scores really low. So the first generations tend to just go round in circles. Then they start to learn how to plug the eyes in, one by one edging them closer to the goal – then it’s a case of improving the sample rate to improve accuracy, usually by using jmps and optimising the loops.

This is an example of a fairly simple and effective solution, the final generation shown in the animation above:

loop:
  leye 
  rmot 
  nop nop nop nop nop 
  reye 
  lmot 
  or 
  nop nop nop nop
  rmot 
  jmpz loop

Some explanation, the right and left eyes are plugged into the left and right motors, which is the essential bit making it work, the ‘nop’s are all values that are not executable. The ‘rmot’ before the ‘jmpz’ makes the robot scan around in circles if there is no light detected (strangely, a case which doesn’t happen in the simulation). The argumant to ‘jmpz’ is 0 (loop) which is actually the 17th byte – so it’s cheekily using memory which has been initialised to zero as part of it’s program.

This is a more complicated and stranger program which evolved after 70 generations with a high fitness, I haven’t worked out what it’s up to yet:

  pshl 171 
loop:
  lmot 
  leye 
  pip 111 
  pip 30 
  rmot 
  reye 
  pshl 214 
  nop 
  lmot 
  jmp loop

Evolvable hardware

I’m modding a robot toy for the next Spork Factory experiment, the chassis provides twin motor driven wheels and I’m replacing it’s brains with a circuit based on the ATtiny85 for running the results of the genetic algorithm, and a pair of light dependant resistors for ‘seeing’ with.

Here’s the circuit (made in about 20 minutes after installing Fritzing for the first time). It’s quite simple – two LDR’s provide input, and some transistors are needed to provide enough power to the robot’s motors (it’s using PNP transistors as they were the first matching pair I could find, which means logical 0 is ‘on’ and 1 is ‘off’ in the code).

The robot needs to be emulated in software so the genetic algorithm can measure the fitness of hundreds of thousands of candidate programs. We need to simulate the effect of motor speeds on it’s position and velocity – here is a test running the right motor at a constant rate, and gradually increasing the speed of the left motor.

This is the code snippet that calculates the velocity from the 2 motor speeds – more work is needed to plug in the correct values for the distance between the wheels and the actual rotational speeds of the motor drives.

// update dir and pos from current motor speed
float relative_speed_diff=m_left_motor-m_right_motor;
float angle=atan(relative_speed_diff);
    
// rotate the direction by the angle
float nx=(m_dir.x*cos(angle))-(m_dir.y*sin(angle));
float ny=(m_dir.x*sin(angle))+(m_dir.y*cos(angle));
m_dir.x=nx;
m_dir.y=ny;
    
// update the position
m_pos=m_pos.add(m_dir);