Re: Abominations, schedule & Euler angles

Hi all,

I completely agree with Mike Jost on his viewpoint to make the simulated 
physics match the actual hardware. My aim is not to change the rules to 
drive the contest into a specific arbitrary direction, like avoiding the 
diving strategy, but rather to make the model of the robots and the 
world more realistic so that the control programs could eventually be 
ported to real robots et become really useful.

However, as noted by Frans, the rules in every sport are always evolving 
and I also try to maintain some coherent and interesting rules so that 
this robotics sport can evolve to address interesting robotics 
challenges. But I believe that the current sport rules are pretty fine 
and well defined and I don't want to change them too often and too 
drastically. Rather, I believe we should only change the physics to get 
closer to real robots as proposed by Mike.

Moreover, I really appreciate the work of Mike, providing us with 
numerical values for physics parameters drawn from the Pino robot and 
SDR4X data.

Mike Jost wrote:

>I agree the self collision detection should be implemented, however the
>robot servo torque should not be limited only because many competitors
>have found a way to stand-up unless the movements violate self-collision or
>violate commercially available servos.  I have no problem with robots diving
>either.
>  
>
I completely agree with that.

>The engineer in me asked the question "Is the current model valid?".
>
>Since this is a model of the Sony SDR-4X, it should be limited to the
>capabilities of that design.
>I tried to find the servo specs of the SDR-4X but, the best I could do was
>to estimate the specs based on a comparison with the PINO open source
>robot design.  http://www.symbio.jst.go.jp/PINO/
>The PINO is a humanoid robot similar to SDR-4X.
>
>Comparison:
>The SDR-4X weighs 6.5 kg, from
>http://www.sony.net/SonyInfo/News/Press/200203/02-0319E/
>The PINO robot weighs 4.5 kg.
>The PINO robot uses servos with a torque of 2.06 N*m for the leg, waist and
>shoulder servos.
>The Judoka robot weighs 0.725 kg. (Note: physics density could be changed to
>900 kg/m3 to better match the SDR-4X weight).
>
>Scaling the servos torque, based on weight, from the PINO robot to the
>Judoka and SDR-4X robot gives a torque for the servos equal to 1.03 N*m.
>1.03 = (4.5 * 0.725) / 6.5
>
>Results:
>I set all the servo torques to 1.0 N*m in my Judoka robot and it was still
>able to stand-up using the "splits" method of correction.
>My Judoka robot failed to stand-up when the torques were set lower than 0.7
>N*m.
>My Judoka robot failed to walk when the torques were set lower than 0.5 N*m
>(Due to collapsing of joints from inertia).
>
>So, it would appear doing the "splits" to stand-up is a valid method for the
>PINO and SDR-4X robots.  Also a few humans, ballet dancers, olympic
>ice skaters, can use the "splits" method to stand-up (not me).
>
>Recommended Changes to Webots:
>1.  Physics density = 900 kg/m3
>2.  Maximum torque of servos = 9 N*m
>  
>
According to your previous results, I assume you mean 0.9 N*m (or 1 N*m)

>3.  stopping self-collision
>  
>
I will implement these changes. I will also add joint limits in the model.

>Notes:
>Servo manufacturers use a torque unit of kg*cm instead of N*m as this unit
>is more user friendly.  A kg*cm is the torque required for the servo
>to lift a 1 kg mass on earth with a torque arm of 1 cm.  The conversion from
>kg*cm to N*m is *= 9.807/100.
>Webots uses N*m for torque.
>  
>
Thanks for pointing that out. However, Webots uses only metric system 
units everywhere (to avoid entering the debates between physicists, 
mechanical engineers and others). I will add this note in the servo 
documentation of Webots.

>Judoka mass Excel worksheet:
>http://www.mikejost.com/cyberbotics/JudokaModel/JudokaMass.xls
>
>Movies of SDR-4X:
>goto bottom of this page   http://www.droidlogic.com/
>
>  
>
Many thanks for all these information! I really appreciate your valuable 
contribution!

I will submit a new version of the judo.wbt world for testing to 
everyone for one week. After I get some feedback on the performance of 
your robot on this world, we may modify it or introduce it as the new 
official world for the contest.

Happy new year,

-Olivier


 

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