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

[Javier Hidalgo Carrió]

On 04/05/2012 02:23 PM, Sylvain Joyeux wrote:
> 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.

Yes, I totally agree. We need to investigate more Sherpa use case.