[ODE] notes on the quickstep method

[Russ Smith]

> I'm using ode for precisely this kind of thing - motorized legged 
> creatures and whatnot..  Can these quickstep issues be overcome
> through increased iterations, smaller steps, etc, or is this always a
> problem?  

there are ways to help overcome these problems for quickstep:

  * increase CFM a bit.
  * reduce the number of contacts in your system (e.g. use the minimum
    number of contacts for the feet).
  * don't use excessive friction in the contacts.
  * use contact slip if appropriate
  * avoid kinematic loops (actually, kinematic loops are inevitable in
    legged creatures, so you can't avoid them)
  * don't use excessive motor strength (fmax).

increasing the number of iterations may help a little bit, but if your
system is really near singular then it wont help at all. the nature of
the SOR method for near-singular systems is that it will converge
quickly to an approximate solution then converge extremely slowly to the
'real' solution.

> Does stepfast suffer from similar issues or is that even worth 
> considering anymore?

i've not used it much, but i'm sure it has similar issues.

russ.

-- 
Russell Smith
http://www.q12.org