Hexy Got Hurt!

Whoops. Hexy got hurt. Maybe he's showing his age, maybe I'd had a beer and was demonstrating Hexy's latest tricks to my friends. Either way Hexy's hurt his hip and a knee :(

His hip was entirely my fault. Usually I'll move Hexy's legs about when he's not powered his servos so that I can access parts of him, this time (of course) the servos weren't off. Grabbing a leg and rotating a hip: bad idea.

A few moments later, Hexy was doing a very good job at reversing. Reversing so well that he nearly fell off the coffee table. This quite abrupt movement knackered a knee joint.

Fortunately, these servos can be easily fixed. The gear chain that translates the high-speed low-torque motor to a low-speed high-torque output is a user-serviceable part. A spare set of gears will cost you about 75p. Bargain.


Half an hour later and Hexy's rebuilt with centred servos! Pretty painless really. Good to know he's back in action.

Big Bang Fair - TODO list

Hmm, got me a little over a month to get Hexy ready for the Big Bang Fair, and I keep thinking of things that I need to get done. Figured I should make a list and check things off as I go.

  • Repair Hexy
  • Take some photo> and produce a postcard to give out
  • Record letter shapes for a Hexy writing library
  • Re-jig PoMoCo to minimise the interface
  • Order spares/ repairs
  • Add button to interface to allow custom signatures
  • Implement code behind fancy new buttons
  • Automate "Kill-All" servo control to limit damage opportunities (FAILED, ran out of time)
  • (optional) Move IK code from Moves folder into Hexapod class (FAILED, ran out of time)

Inverse Kinematics: Part 4 - Full Robot Solution

Success! Final few sets of measurements later and I've got enough information to turn the full leg IK solution from my last kinematics post into a set of functions that allow placement of any leg to a co-ordinate defined in a Hexy body-centric co-ordinate system.

This should allow Hexy to use that pen he's learned to hold to write, also new walking gaits (with minimum programming effort), body rotations etc. I've included all the maths that I used to get to this position (referencing my previous posts where necessary), put in some new code snippets, plus there's a Moves attachment at the end that wraps it all up for an IK Hexy demo :-)

[WARNING: maths in post]
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PS3 Controller Controlled Hexy

With a Dual Shock 3 controller (Bluetooth based) one should be able to either directly control Hexy, or possibly more likely use a smart phone as a bridge to link the two and do the complex move generation. Job for summer, perhaps. This will make taking control of the robot very accessible.

Inverse Kinematics: Part 3 - Full Leg Solution

Quick progress this time! Given that the hip joint is orthogonal to the lower two joints (who's positional solution was wrapped up in the first post) it's an almost trivial step to extend the maths to cover three leg joints and a foot position in three dimensions. Complication is that this new set of leg solutions is just going to introduce another coordinate system. By the time I get to finishing up the whole of Hexy, I'm going to be knee-deep in them!
[WARNING: maths in post]
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