Can a Robot Traverse a Twisting Square Tube?

[sbstn]

Hello, I was wondering if I could get some advice on how to build a robot that can traverse the inside of a twisting square tube, whilst staying at its centre.
Heres an image of the kind of tube it will be:

Its probably doable with a rollercoaster style design but it seems like an expensive and complicated task to put in the rails.
Would a robot with wheels on opposite sides of the wall just jam?
Ideally I wouldn't be constructing anything on the surface of the tube but perhaps lining the edge with gear teeth would help simplify things in terms of slippage etc.
Bit of a strange problem I know: building it for a film prop, it will look cool when its done ;)

 

[Simon Bridge]

Give the robot two sets of four wheels on legs arranged so the wheels fit in the corners of the tube.
If the tube crossection area changes, you'd want to spring load the legs.
Choose the right wheels and you don't need to modify the tube surface.

Note: you can do it with two sets of three if you are careful - the wheels still fit in the corners.

The other approach is to make a flying robot that is much smaller than the width of the tube.

 

[sbstn]

Great thanks very much, can I ask why the corners?

 

[billblack]

if you put the wheels in the corners that would serve to keep the vehicle centered in the tube. That would make things much easier when traversing the inside of the tube. You might look @ http://www.inuktunusa.com/crawler-vehicles/ as well...Inuktun does this job very well.

 

[Simon Bridge]

Thanks billblack - the idea is that the corners will act as rails keeping the vehicle on track, yeah.
I'd also want to put a joint of some kind in the middle to allow the robot to twist with the pipe.
A lot will depend on the dimensions.

I've attached a couple of concept sketches for one approach.
That would be pretty solid - there are other solutions depending on the dimensions of the pipe, what sort of dramatic effect you wanted etc. You may prefer more spindly and insectoid.

However, this should show how you need the wheels to go - you can also use tracks or rows of small wheel a-la rollerblades, but you want them to fit to the corner. This arrangement should be able to plausibly handle cylindrical pipes at varying grades up to vertical.

Some sort of silicone tyres for stiction - but if there was trouble you'd probably get away with cheating it will a strip of fabric gaffer-tape down the corners.

 

[sbstn]

Oh cheers Simon thanks for going to so much trouble! Definitely a great help.
The way the pipe is being constructed means it's effectively a loft/extrusion of a rectangle with rotation over time, meaning the cross section will maintain its dimensions - that should help to simplify things a bit.
And thanks for the link billblack, seems like a good reference for the chassis.
Time to make some mockups :)