[ODE] Torque settings for simulated servo

[Proyecto de Grado - Construcción de Robots Bípedos]

mmm, I think I got confused and you are right. I don't see any mistake with
the units in your reasoning then. I'm interested in your problem because I'm
thinking of using ODE to do a similar thing. What I don't understand about
servos is that specifications talk only about torque and when you have a
motor output torque depends on speed. Anyway if you get it working let us
know.

Regards,
   Damián Lezama
   Proyecto de Grado - Construcción de Robots Bípedos
   http://www.fing.edu.uy/~pgrobip


> But isn't gravity measured in metres per second squared? Meaning that it
> doesn't matter what the mass units are when calculating your specific
> value of g, only the time and distance units.
>
>
> Ian
>
>
> Proy. Grado Construccion de Robots Bipedos - ENS wrote:
>
> > Hello,
> >
> >    I think your mistake is with the constant "g". Supose you use grams
> > for mass, is "g" still 98,1 ? I think not. My guess is that with your
> > units g=981, so when you multiply by 1 unit of mass you get 981
> > dm.hg/s^2  (dm=decimeter, hg=hectogram). I hope that helps. Why don't
> > you use a standar system ? I use SI.
> >
> > Regards,
> >    Damián Lezama
> >    Proyecto de Grado - Construcción de Robots Bípedos
> >    http://www.fing.edu.uy/~pgrobip
> >
> > Garvin Haslett wrote:
> >
> >> I am using ODE to simulate a robot that I am building.  To model the
> >> servo motors I am using hinges but I seem to be making an error in
> >> setting the servo torque.  I have set gravity to -98.1, thus implying
> >> that one unit of distance is 10cm.  I have chosen my unit of mass to
> >> be 0.1 kg.
> >>
> >> The data sheet for my servo lists the torque as being 4.1 kg cm or
> >> 0.041 kg m.  I convert this to Nm by multiplying by 9.81 giving 0.402
> >> Nm.
> >>
> >> I seem to be getting lost in choosing the correct unit of torque in
> >> simulation.  I've taken the view that a real Newton is the kgm/s^2 so
> >> therefore one of my simulated "Newton" shoud be 0.01 N (0.1m x
> >> 0.1kg).  Continuing this logic my unit for torque should be 0.001Nm
> >> so my the value I set the Max Torque for my servo should be 402.
> >>
> >> However once I do this I find my simulated servo lifting weights the
> >> real one cannot.
> >>
> >> Is there any obvious flaw in my reasoning here?
> >>
> >> Thanks in anticipation of any help,
> >>
> >> Garvin.
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> >>
> >>
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