[ODE] Rotation troubles

[Ignacio García Fernández]

On Sat, Dec 27, 2003 at 04:41:35PM +0100, Nicholas Francis wrote:
> Thanks for the tip. I played around with spring/damping, and they work  
> quite nice, except for:
> 
> * Du to the low force applied when the target is 'close' to being  
> right, it takes a very long time to get the last 2-3 degrees of  
> rotation right
> * On the flip side of the above, the rotations get very fast if the  
> target direction is far away (as the spring gets very strong).
> 
> Correcting the spring/damper constants to fix one of the above problems  
> naturally made the other one worse. I tried adding a falloff to the 1-d  
> (by raising it to, say, 0.5) in order to compensate, but it did not  
> solve the problem.
> 
> We're already using sping/dampers for the camera control, and for that  
> it works great. However, here the varying strength of the spring makes  
> the object being rotated look either too heavy or too light. I think  
> the reason it works for cameras, but not helicopters is that  
> helicopters have a certain mass (to say the least), hence when they  
> turn too fast it feels wrong in a way a camera never will. At the same  
> time, an experienced pilot will certainly 'drive' the helicopter just  
> as hard when 10 degrees away from a correct shot as when 90 degrees  
> away.

What you intend to do is to «control» the direction of the
helicopter. An here I mean control in the Control Theory sense.

The problem is that you're using a low order control system. You
should consider a higher order control system that involves, not only
the direction, but also de velocity or even the acceleration of the
direction.

> 
> Any other suggestions, or do I need to get up to speed on my math  
> skills?

Use a higher order control... which involves some new math skills,
indeed :-)

Or, probably better, try with a controller that acts on the
constants. This is the idea you have already tried, but there exist
methods that tune them dynamically very fine.

Look for 'second order control' and for the string "P+D"

I don't know too much these systems, but I'll help with whtever I can.

Regards


-- 
May the source be with you
--------------------------------------------------------------------
Ignacio García Fernández                       Instituto de Robótica
ignacio.garcia_at_uv.es                      Universidad de Valencia
http://robotica.uv.es/~ignacio/                     Tlf. 96 354 3564