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.
Pair of servos from Hexy after his accident at the weekend
A small screwdriver allows access to the output gear-chain (left) a fresh set of gears is ready to be fitted (right)
Final small gear in the chain has snapped and removed some teeth
Half an hour later and Hexy's rebuilt with centred servos! Pretty painless really. Good to know he's back in action.
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
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.
Current project to teach Hexy to write his name is progressing nicely. Whilst the full robot inverse-kinematics is progressing, sometimes my brain can get too full of maths. Best fix I've found for this is tinkering in my garage. Hexy … Continue reading →
Today's insight is that QR Codes are hard. I'd hoped that when Hexy got his hands(?) on a pen that he'd not only be able to sign his name, but he might be able to draw a QR Code (that's … Continue reading →
After the non-ideal response observed in the inverse-kinematic exercise, I got to wondering where these inaccuracies came from. Assuming that the software controlling the legs was accurate, all that was left was the calibration or physical implementation (e.g. servos accuracy or the laser cut pieces). Continue reading →
Well, today was a big day for Hexy. It was his first trip outside to meet new people. Hexy came into work with me to meet some of my friends and colleagues, and by all accounts made a big impression! Continue reading →
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] Continue reading →