I was so impressed by the video of the Pololu hexapod walker I thought I'd have a go at one of my own. This is a rebuild of my initial attempt using a PicAxe 08m. It's still held together with small dabs of hot-glue and will-power. I've refined the 'just make it do something' code and the new movement routine will be at the core of the program once I move this to an 18x. Currently it can dance and vibrate and can go forwards, backwards and rotate left and right at anything from an absolute crawl to full speed. Still a bit of code tweaking needed to get gradual turns left and right and optimise the leg sweep.
The component layout is different to the Pololu model, having the batteries underneath and the servos at the front. The beads on the feet give it a carpet capability but still some experimentation to do here. For the gait to work, there has to be some slip but not too much. (*Just discovered - the mid legs need grip - I've taken the beads off the middle and now it's brilliant on carpet*) The pics and video are pretty rough - short of time at the moment, but I will post something better as it develops.
I'll be using an 18x later as code space on the 'm' range is too tight for the things I've got planned. I want to include elements of my Instructables 'Piecax' project in here as well as obstacle avoidance with a Sharp IR sensor.
Test bed for a 6 legged, 3 servo walker.
Actuators / output devices: 3 x 10.5g servo.
Control method: Autonomous.
CPU: PicAxe 08m.
Power source: 3 x AAA batteries.
Programming language: Picaxe basic
Sensors / input devices: None as yet - Sharp IR ranging planned.
Target environment: Indoor environment - Hard floor or short carpet.
Woot! Forget all this - I’ve done a rebuild so it looks a lot neater and written code to make it go forwards, back, turn left and right at any speed you like, and to vibrate and dance. Busy tomorrow, but I’ll try and get a new video up.
I’ve got the walking gait working really well now and it’s happy strutting across carpet or a hard surface. Tonight I’ve been playing with the Sharp IR distance sensor and the next step is to build the actual controller with a PicAxe 18x (rather than the 08m I’ve been testing with) and get the rangefinder attached. Then comes the really good stuff . . .
I may try that on the middle pair but at the moment I’ve taken the beads off the middle legs. Look at the slow bit of the video - The geometry of the triangle formed by the 3 feet touching the ground changes as the legs move. There needs to be some slip to let this happen. I’ve found by experimentation that having the middle pair grippy and the other 4 sliding give the best result.
I’ve gone off Sharp IR distance sensors. It works perfectly over the range it’s specced for but appears that it is a characteristic of the device that it gives an in-range output when there is no object in range. Very annoying. There’s at least one thread on this.
So I’m going ultrasonic with an SRF05 which I’ve used before and work over a larger range (but is a bit bigger). Still undecided whether to servo mount the sensor or just have it front-facing and use the legs to swing the body. Also, I’ve decided to go up to a 20x2 rather than an 18x 'cos it’s only 2 more pins and a lot more powerful.
