T08A2 / R3000 spider lightweight tank (from GITS)

Hexapod Robots

T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Tue Jan 13, 2015 11:13 pm

I started working on T08A2 / R3000 spider tank from Ghost In The Shell movie a year ago. For those who haven't seen the movie - I would highly recommend, it's one of the best sci-fi anime movies.

Image

First of all I wanted to make a replica / scale model of the robot. I also wanted to make it move like it moves in the movie. One of the biggest problems that I had from the start was non existence of blue prints, or actually anything that would be close to that. That's why scale is approximate :) So for "blueprints" I ended up with a few things:
  • Screenshots from the movie
  • Smaller resin model from ebay, which isn't proper quality :)
  • Someone made a 3D model, which I managed to acquire. It isn't very accurate, I would say it follows movie...almost...
So yeah, none of these were precise. Actually, even frames from the movie sometimes contradict itself. To make matters worse I wanted to make a model which could move, so following sizes and strength of mechanical components had to be taken into consideration as well... Robot in the movie has ball-joints, i.e. multi dimension freedom on a single joint. Of course there was no way I could make these joints for legs in real life :) although I managed to attach head with 3 degrees of freedom and all 3 axes intersect in one point - kinda ball-joint. The plan is to make it look like ball joint visually too :)

Size ~50cm. Scale 1:20 (roughly :))

Initial idea was to make the shell from a styrofoam, but during last year I bought a 3D printer, which came very handy when making these complex shapes. Although at this point I doubt how good idea that was - there is quite a lot of extra weight from that plastic:D We'll see how well it works when it's all assembled again :)
PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Tue Jan 13, 2015 11:29 pm

This is almost complete frame (except "arms"/weapons) and close to complete electronics:




Motion is controlled by RaspberryPi. Uses 22 cheap servos :) There will be extra 6 smaller servos for "arms". Programming in C++, from scratch. It is controlled with PS3 joystick, but there are plans to have some autonomous functionality (face tracking and distance measuring).

One of the unique features of this hexapod is that first joint of each leg (i.e. the one that is mounted on main frame) is mounted at 45deg angle, instead of straight up axis. This creates less mechanical look and more life like gait. Also most hexapods have vertical legs, i.e. first segment going up and second going down. I had to put first segment horizontally and keep it that way all the time in order to make it look like the robot from the movie. That leads to much higher forces on servos, which is not great when you're planning to put all that extra plastic weight on it :))

Another (maybe) unique thing - it tries to take as big steps as possible. Again this is done to make it move like the robot from the movie - it makes it feel heavy/strong. Of course it doesn't look heavy/strong in the YouTube link, because it moves too fast. Honestly, I have no idea how others avoid collisions between legs :) I just wrote custom simulation of legs and estimation/prediction of collision and take steps based on that.
PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby Matt Denton » Sun Jan 18, 2015 6:55 pm

Hi, and welcome to the forum! :)

It have seen the film, and it's a great project! I think that film has inspired many hexapod builders!

Hexapod inspiration post here.

The ball joint you talk of is like the holy grail in robotics, but there are ways of making something behave similar, like a swash plate on a helicopter, we call this a two rod joint in animatronics which uses a universal joint for the pivot point, however, it does not give true ball joint operation.

The 45 degree coxa joints are really nice! I have seen this before on some university hexapods, it makes for a slightly better joint configuration, but more complex build and more complicated IK maths for the leg. I presume your legs are being driven by IK?

As for clashing legs, this very much depends on your gait generator. In my system the legs are driven in such a way that they should never clash, unless you have entered a leg stride length that is outside the normal working zone of the leg. So within my system I do not bother checking for leg clashes!! :o

Got any close up images/video you can share?
Last edited by Matt Denton on Sun Jan 18, 2015 7:01 pm, edited 1 time in total.
Reason: added link
Matt Denton
AKA: Winchy_Matt

micromagic systems ltd
Matt Denton
Site Admin
 
Posts: 1622
Joined: Tue May 20, 2008 9:15 pm
Location: Winchester UK

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Thu Jan 22, 2015 1:33 pm

Matt Denton wrote:The 45 degree coxa joints are really nice! I have seen this before on some university hexapods, it makes for a slightly better joint configuration, but more complex build and more complicated IK maths for the leg. I presume your legs are being driven by IK?


Yes, it's IK driven. I spent a chunk of my career writing animation systems (Battlefield games/Frostbite, Unity game engine, etc), so writing a custom IK system is the easiest part of this project :))

At first I considered even more bizarre setup for legs, i.e. first segment going up and down, second rotating around the axis which goes along the leg segment and third up and down again. Like this (green is rotation axis, red is rotation):
Image
I even had IK implemeted for that:) Main problem with that was that it limits the size of steps that you can take. And building such setup would be more complicated that I would like too :)

Matt Denton wrote:As for clashing legs, this very much depends on your gait generator. In my system the legs are driven in such a way that they should never clash, unless you have entered a leg stride length that is outside the normal working zone of the leg. So within my system I do not bother checking for leg clashes!! :o


Maybe you have some doc (or could point to some paper) describing how gait generator like your works?

I'm not entirely sure why, but I couldn't implement gait generator which doesn't require prediction of leg intersections (and doesn't make tiny steps). Maybe my legs are too close to each other. Or maybe I'm just doing something the other way around. I probably should just read more papers on the hexapod gaits generators :)

A few more shots:

Image
Complete electronics:
  • 2x Raspberry Pi (1st for motion, 2nd for face tracking)
  • 28x Servos (18 for legs, 4 for body, 6 smaller ones for weapons)
  • 1x Camera
  • 3x Servo drivers
  • 2x Lasers (how can you have a robot without lazors??!!! :))
  • 1x Distance sensor
  • 1x PS3 controller
...and some armor.

Another view of hardware:
Image

I don't have better shots right at the moment and can't make new ones, because it is disassembled for 3D printing...
PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Tue Jan 27, 2015 2:37 pm

While other bake cookies for Xmas, I bake robot parts :)

Image

Image
PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby Matt Denton » Tue Jan 27, 2015 2:50 pm

Ohhhh nice! :D
Matt Denton
AKA: Winchy_Matt

micromagic systems ltd
Matt Denton
Site Admin
 
Posts: 1622
Joined: Tue May 20, 2008 9:15 pm
Location: Winchester UK

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Tue Jan 27, 2015 2:50 pm

A short video from testing of arms:

PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby Matt Denton » Tue Jan 27, 2015 2:52 pm

Arms with lasers of course :)
Matt Denton
AKA: Winchy_Matt

micromagic systems ltd
Matt Denton
Site Admin
 
Posts: 1622
Joined: Tue May 20, 2008 9:15 pm
Location: Winchester UK

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby PauliusLiekis » Tue Jan 27, 2015 2:56 pm

You can not achieve world domination plan without lasers :)
PauliusLiekis
 
Posts: 17
Joined: Tue Jan 13, 2015 4:30 pm

Re: T08A2 / R3000 spider lightweight tank (from GITS)

Postby Matt Denton » Tue Jan 27, 2015 3:30 pm

If I had a pound for every youtube comment along the lines of "stick a frickin laser on it man!"...
Matt Denton
AKA: Winchy_Matt

micromagic systems ltd
Matt Denton
Site Admin
 
Posts: 1622
Joined: Tue May 20, 2008 9:15 pm
Location: Winchester UK

Next

Return to Hexapods

Who is online

Users browsing this forum: No registered users and 1 guest

cron