[Rock-dev] Proposal for adding velocity information in base::actuators::Status

[Sylvain Joyeux]

On 04/05/2012 02:11 PM, Javier Hidalgo Carrió wrote:
> Velocity can be derivate from position, but we would get bigger error in
> velocity if we do it a rock level.
> FPGAs in each joint computes the velocity using the encoder (position)
> information at much faster frequency.
> The derivation step is smaller at the FPGA. Monster reports this
> information only every 40 ms.
>
> I would say is better to use the velocity coming from the joint/FPGA
Well. Depends what you call "velocity" here (and this is the underlying 
reason why we need to have a much broader discussion here).

If it is instantaneous velocity at the time where the status is 
generated, then you are right, but it is going to be (1) a very 
quantified and noisy value since it is highly dependent on the precision 
of your encoder and of the sampling time of your FPGA and (2) would not 
give you the big picture about what your system does (since you have 
this instantaneous velocity only once every 40ms).

If it is average velocity over the 40ms, then there is no difference 
between the two methods.

I do not want appear to say that your use case is useless, I want to 
point out that we will need to have a richer representation anyways if 
we want to support every use case.
-- 
Sylvain Joyeux (Dr.Ing.)
Space & Security Robotics

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