Animatronics & Robotics for Film & Television



Hexapod V4b (Developed 2005/6)


This hexapod is based on the V4 design used for "Harry Potter & The Prisoner of Azkaban", however, this version has some significant differences: Aluminium constriction, larger more powerful Tibia servos, and a new p.Brain-ds on-board locomotion engine.



p.Brain-ds - one controller to rule them all!


This is probably the most significant addition to the hexapod. The p.Brain has been in development for some time but the PIC18F version lacked the processor power to perform body rotation/translation and terrain adaptation and only ran at 30Hz refresh.


With this version, the same engine that previously ran off-board on a DOS machine, now runs on-board on the p.Brain and at refresh rates up to 100hz.


The pBrain-ds is being developed as a single solution to any hex or octoped with 3DOF leg arrangement. The p.Brain not only does all the leg locomotion, inverse kinematics, body rotation/translation and terrain adaptation, it also incorporates 24 channels of hi resolution PWM outputs, so no need for an additional SSC! and 8 analogue/digital inputs for ground contact sensors.


The p-Brain-ds can be user configured to different leg geometry and servo types via terminal software that gives endless configuration for any hexapod design. All that changes between designs is the motherboard that the p.Brain-ds plugs into. The motherboard supplies power, serial connections and distributes the PWM signals around the body. Control of the locomotion engine is via simple serial data, either RS232 or TTL level at 9600 or 19200bps.



Bluetooth control connection


The control connection to this Hexapod is through a simple bluetooth serial port via the p.Brain-ds TTL control port. The p.Brain has two serial ports that can be dipswitch configured as either control data or terminal data. In this case both control and terminal data are mapped to the same TTL port. There are future plans to add I2C control communications.



Unique Coxa Design


This hexapod has a unique coxa design which came about through having to make the body depth as small as possible for the V4 hexapod. Take a look at the third picture in the gallery to the left. You can see that the lower body segment is not below the coxa, but inside the coxa! This not only allows the body depth to be smaller, but also gives the added benefit of being able to remove a leg by unscrewing the coxa servo horn without the need to remove the lower body. Very useful while calibrating and for repairs!



Direct Servo Coupling


You may also notice that there are no servo horns being used! This design has had the servo spline punched directly into the Aluminium femur and body.



Future Plans


There are vague plans for this robot to go into the Kinetica museum, London. The idea is that there will be a head added with a CCD camera which will face track people watching the hexapod. However it will be within a glass case so it will not be walking around.



Tech Stuff


Servos: Futaba 3002/9206/9206

Battery: NiMh 4.8V 2700mah

Servo Driver: 1 X p.Brain-ds

CPU: dsPIC30F4011 (58.96Mhz)

Radio Link: bluetooth

Weight: Aprox 1.8Kg (with battery)



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