I thought I’d post pics of my latest bot - he/she/it’s a pentapod, ie: it has five legs. It started out as a quad, but when I realised it could only lift one leg at a time (without a dynamic gait) I added another. The idea is that I can lift two legs at a time and keep a tripod on the floor. I haven’t got the software working yet (BA28 and SSC32), and unfortunately I have to hand it in at the end of next week (its part of my coursework), so I won’t get it back until the summer 
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Pics:
putfile.com/pic.php?pic=4/9610280812.jpg&s=x10
putfile.com/pic.php?pic=4/9610305511.jpg&s=x10
putfile.com/pic.php?pic=4/9610341017.jpg&s=x10
Why a pentapod? Because I didn’t have enough servos for a EH3R replica at the time!
Next on the list is to build some super-servos. I’m looking into using the gearbox from the servo and adding a worm gear for some real torque - I want to replace the electronics as well, but don’t think I have enough experience with I2C to try the Ultraservo yet. The plan is to use these in a really big version of the EH3R, something that can carry a significant playload (like a laptop or my lunch) and navigate my house, although its all just thoughts at the moment.
Looking good!
Don’t let I2C scare you away. Once you get started you’ll find it’s easier to deal with than standard serial communication. Before long we’ll surely have some sample code for most micros. Others who are communicating directly from a PC are using I2C bridges. The most common of those is the Dimax usb to i2c. There is already a great deal of code for that device, and considerably more is on it’s way.
Just FYI, my “quad” is walking with a static gait, by using a servo to adjust the COG dynamically. I suppose you could say it’s a dynamic gait, but the legs are not the dynamic part.
Here’s the discussion:
lynxmotion.net/viewtopic.php … c&start=30
Pete
Wow, very neat!
It looks like it’s deadly.
Did you laser-cut those brackets?
Andylippitt: thanks - I2C will definately be the way to go. I can see how it can be simpler than serial, but I’ll need practice and practical experience to really understand it - I’m going to buy the SRF08 (newer version of the SRF04 lynxmotion carry) as it has I2C interface and lots of example code for Atom and Picaxe.
Saipain59: thats a really clever way of doing it! Can it/will it be able to walk omnidirectionally? I can see how it moves to tip the COG over the line between the two legs that are on the floor, but will it work if you’re moving sideways? My goal was to be able to input any vector and have the bot walk that way. I think using a weight on a rotating arm could accomplish almost the same thing in a radially symmetrical bot, so more legs could be off the ground at a time.
Nickreiser: thanks, I wish I had laser cut them. I made prototypes from PVC usig a milling machine which went really well. Then I used Lexan and because of its comparable strength it kept being lifted up by the cutting tool and making a mess. I had to follow the tool around with a metal stick to hold the lexan sheet down when cutting. If I do anything similar in future I’ll definately use either the SES or custom laser cutting like Pololu do.
Yes, shifting the COG works in general in any direction. It is not required to have the COG itself move in any direction - just moving it forwards or backwards within the triangle formed by the 3 down legs is enough.
And yes, sideways walking works.
The hard part is the transition between moving in one direction (forwards, for example), and then going another way. It’s all do-able, but making a smooth transition is complicated.
Pete
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