Let's Make Robots!


Avoid obstacles... look cute... lots of programming to be done.

update: added code (older version 1.1) as attachment

update: Frontplate is mounted. Turned the IR sensors. Lost the abiity to detect cliffs :( 


This is my second robot. The first one was for practicing soldering using a picaxe 08M prototype board. It had two modified servos, a led, an infra-red eye and a switch. I couldn't get the speed control right using the servos so I figured I should use PWM. The other problem I ran into was the program size. The 256 bytes on the picaxe08M is just not enough. 

the board 

I bought a Picaxe 28 starter kit which is great for playing around, but it lacks a few features I wanted. First of all, the picaxe chip supports I2C, but since the I2C pins are fixed as digital inputs on the board. That means no eeprom chips and no I2C display. Also, the PWM pins of the picaxe 28 are also configured like that and I really want speed control.

So I decided to put my newly acquired soldering skills to the test and build a board from scratch. I intended to put the power-stuff on the board together with the motor driver and build it as a I2C slave. When I was done I figured I had enough space left to add two 32K eeprom chips and a few headers (for the sonic rangefinder, infrared and servos)

The 32K eeproms are to store texts, movement sequences and sensor-conditions. I don't know how yet, but I allready tested some primitive menu using the serial cable to fill the eeproms from my laptop. This program uses about 500 bytes so I might be able to leave it there alongside the rest of the programming. we'll see.

Here's the result 


 It takes 7.2V from 6 rechargable NiMH batteries. One jumper can be removed to provide a powerswitch and the second jumper can be removed to disconnect the logic circuit from the motor power, so you can use a separate 5V powersource. I added a diode just in case I put the power connector on the wrong way.

Hidden beneath the wires on the top, there is a third jumper which can be removed in case I want to use this board as a I2C slave. The jumper connects the pull-up resistors for the I2C bus.


The body

I am building the body out of expanded-PVC. It is great stuff! Very easy to handle and you cut through it like butter. The ground plate is 5mm thick with a hole sawn out. That takes 5mm of the first battery case, which is mounted under the plate. The other battery case is carried on the back, sort of like a back-pack.



The front will have a 2 x 8 character display from matrix-orbital (blue-ish letters on white background - looks very cool!) Still need to decide where to place a small button and the reset button, along with a few LEDs.

The main board will be skrewed on and hang from the top plate. Hopefully the serial jack connection will be reachable from the outside that way. On the front (bottom) two IR-rangefinders will be mounted to be used as bumper switches. I hope I can figure out some clever way to mount them at an angle. The wires on those IR thingies are really sticking out. Very hard to mount those things without the wires showing.


I use tracks to enable the robot to drive over stuff. (My first robot could get stuck on a magazine on the floor) Because the motors are pretty thick, I decided to mount two idlers below the ground plate so that the motor is inside the body. That should give me more ground clearance.  The idea is to get a Wall-e look.

The tracks are mounted using 5mm bolts from the local hoby shop. I bought some extra rings and stuff to get the distance right. It was a lot harder than I expected to get those tracks right. Too loose and the motor just spins without moving the tracks and 2mm too tight and the left and right tracks dont run at the same speed.



First Moves

OK. The top board is on. I didn't cut the hole for the wires of the head yet, but I really wanted to see this thing moving.

I renamed the robot to Edward (after Edward Scissorhands) because I'm afraid I don't have enough space to add any kind of arms or hands. He'll probably end up with dummies or no arms at all.

The treads are very smooth which is great for turning, but very bad when trying to drive over an obstacle on a wooden floor. 

head attached

Edward has sort of half a head now. I still need to fix a frontplate to cover the sides of the display, finish the head (not a very nice job I did now) and fix the sharp IR rangefinders. That SRF05 is not very good at detecting the floor. I guess the ultrasonic pulse just bounces off the floor and doesn't get detected. 

I was hoping I could get it to look down and "see" the floor or "see" cliffs or table edges. I'm going to have to use the IR rangefinders for that.



I'm calling this one finished. I'll spend a few cold winter evenings trying different programs, but this design just isn't very good. Lets look at what I think I've learned.

I tried a separate power supply, but that didn't solve the resetting of the display problem. Which means I'll need to shield the internal wires or something. Maybe the problem is that I use 7.2V through a diode, making it 6.6V and then through a voltregulator. Maybe the 6.6V is too little for the regulator, but I'm afraid those cute little servos will melt down when I give them the full 7.2V. Anyway: my next bot will have 2 powersupplies. 

Another problem is the motor driver. I really don't like the 1.4V voltage drop of the L293D. I'm experimenting with hooking up servo-electronics to different motors to be able to run them without the voltage drop and using 1 output pin for control. Maybe i'll drive the next bot with 9V or 12V and use a switching voltregulator to bring it down to 5V for the servos. I'll start playing around with relays. I want better speed!

Thirdly: the weight is distibuted wrong. I didn't think it would become a problem, but edward falls on his back quite easilly.

And then the sensors. I knew the optimal way to combine IR and US sensors would be to have the SRF05 on the belly and two IR sensors on the head, but I went for looks. The IR's are now mounted at an angle sideways so that they look in front of the treads. They don't look down though. So Edward cannot detect cliffs anymore The head is only usefull for detecting large vertical objects and for cute looks. I'm considering building a Frits!LDR with lenses. Something that is more stable then the IR sensors and less sensitive to surfaces that don't face the sensor directly.



This was a nice project and the result is a cute little bot with a display two 32K eeproms that I can program endlessly. On to the next.... 

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OK here's how Edwards body was built.

The bottom plate is cut out of 5mm thick PVC. The last 5mm at the front of the plate is 10mm narrower and the last 5mm at the back is 5 or 6 mm narrower. (see picture)


This way the front and back plates can slide over the bottom and fixed with glue. I use standard PVC glue. It is not the stuff that's used for pvc pipes because that stuff is quite thin. I bought a tube of general plastics-glue marked suitable for any kind of PVC.

So the front plate, the back plates (incl coverplate) and the "ears" are glued. The strips that hold the bottom wheels are glued and screwed on.The rest is screws only. Mainly because I need to be able to tweak, adjust and fix things inside.

But beware of the panning and tilting ultrasonic rangefinder! It cannot see the floor! The ultrasound simply bounces off. 

really cool robot, well done man :)
Wow cool robot I like how its put together so neet.
The Wall-E look is a lot of fun, and it looking around in the videos shows that. I like the LCD too, takes some doing getting those operational at times.
Yes yes very very cool!!! I hate to say this in fear of making you mad but the robot has the sort of feeling that the Wall-E robot has to it. Hey What if you made it so the kneck was collapsable you know like a folding chair? Might cost you an extra servo though :( And hey is that the PVC sheets that you can buy on solarbotics????

It does have a wall-E look. It is not what I originally had in mind. I started off with johnny-5 in mind, but a number of things made it sort of inevitable to steal some ideas from wall-E.


  1. Treads with the motor somewhat higher above the ground level results in triangular treads.
  2. A cube / box for the body is the easiest shape to make without difficult angles ot bending plates
  3. I really like the pan and tilt setup for the head. It makes it cute.
The head is not really very functional though. As I mentioned earlier; it cannot see the ground with the SF05. 
I like the idea of the folding neck; that would give it a lot more expressions / gestures. There's not much room inside the box for more headers and wires though.
I'm considering removing the display and just place some leds there. The display is much more sensitive to irregularities in the powersupply than the rest of the electronic parts. it keeps resetting when the servos and motors run.


The expanded PVC is the same stuff as on solarborics. They call it sintra.

Cool progress!! Very robot! :D

Awesome job on the whole struture.

I digging your frame sturcture.. !!




Very nice, I like it. This is a robot that has good aesthetics like rik was talking about in this blog post.

I dunno why I had never thought about it, but I really like the idea of mounting the sonar sensor on a dual-axis mount like that, almost like a mini-arm. I've seen pan-and-tilt brackets for them, but this one looks more like a neck, and I like that. I just like to imagine him edging up to the edge of a table and looking down at the cliff below, then backing away in fear :)


Thats sort of what I had in mind, but it doesn't work very well. Because it looks down at the table at an angle the sound bounces away and it doesn't read an echo. It can detect obstacles looking down, but no cliff detection yet.