Which embedded system would you use?

A research,

Which digital and wired communication system would you use for the
following robotic system.

A system composed by a PC/104+ (it is just a very compact standard PC)
with Xenomai (or maybe RTAI), and some sensor nodes (something like
12, but could vary a lot). These sensor nodes are basically composed
by a DSP/MCU/DSC (not the same one on every node) and some sensors and
actuators. The sensors can be anything so i will not give any fixed
description, but a good example would be a Brushless motor (with the
control routine inside the MCU/DSC), and 4 to 5 sensors with a max
sample rate of 2ksps. Basicaly the PC/104+ should get all the data
from sensor nodes (the MCU will handle the communication on the node
side) perform some processing and send back some reference to the
actuators control routine. The whole system should work with a 500us
period. The max acceptable latency between the PC/104 ask for the data
and the reception should be 100us, and the maximum latency for the
actuators command should be 70us (bewtween teh pc104 send and the node
receive). From all the commercial standard availables, all i could
find was Ethercat and Firewire, that have a chance to handle this
communication..Any idea? Just a final comment. The system should have
the minimum amount of cables possible and the max distance between the
PC104 and the nodes is 3m.

Thanks!!

On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
> A research,
>
> Which digital and wired communication system would you use for the
> following robotic system.
>
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.
>
> Thanks!!


As for reducing cables, look into Zigbee.

www.winsystems.com and other makers offer boards with Zigbee.

Otherwise, I think ethernet might be a good choice. Or USB 3 perhaps.
Much depends on the 'horsepower' in the node/sensor units I guess.

On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
> A research,
>
> Which digital and wired communication system would you use for the
> following robotic system.
>
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.
>
> Thanks!!

As for reducing cables, look into Zigbee.

www.winsystems.com and other makers offer boards with Zigbee.

likely, it's data rate is way too slow, it claims low latency, but
that might also be to slow for you.

Otherwise, I think ethernet might be a good choice. And power over
ethernet (POE) could be a way to reduce cabling - at least power
cables)
Much depends on the 'horsepower' in the node/sensor units I guess.

On May 4, 7:36=A0am, Sink0 <sin...@gmail.com> wrote:
> Which digital and wired communication system would you use for the
> following robotic system.

If you have an industrial background and want something that works
better than spec'ed, go for CAN BUS.

If you're an academic and just experimenting and most probably do some
very different things with the same boards next year, go for
ethernet.  Possibly start with raw ethernet frames or static UDP this
year (for the latency), and go ARP + TCP next year.  Or skip the first
step for convenience.  Porting UIP or LWIP is a good place to start.

Best regards

Sink0 wrote:

> A research,
> 
> Which digital and wired communication system would you use for the
> following robotic system.
> 
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.
> 
> Thanks!!

What SIL level is this robotic system required to have? ... (based on the 
Hazard Analysis and Risk Assessment work you have obviously already done. 
You have done that haven't you?).

-- 
********************************************************************
Paul E. Bennett...............<email://Paul_E.Bennett@topmail.co.uk>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-510979
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

Not yet becouse we are going to work on a research enviroment and its
all very experimental. The robotic system its for rehabilitation
purposes, and human motion analisys, so we are going to need high rel
on this.. but we dont need any certification for now. Thats the rules
here (i am not from US). We are not really worried about that for now
as there are lots of safety requirements implemented mecanicaly, so,
on the worst case scenario the system would not work properly, but
would not cause any harm to any person. All the actuators are very low
power (100W or less) due to some security restrictions, and all them
got a properly placed mechanical lock.

Any way, i am developing myself a system with these requirements from
the scratch using FPGA, and i am already on a intermediate stage, but
i always like to check new ideas as i dont want reinvent the wheel.

Marc, CAN would be perfect, but it is too slow, and i cant belive the
arbitration scheme used on CAN could be used on a 50-100Mbps
communication system. Ethernet, is fast for big packages, but VEEERY
slow for small and distribuited ones (thats the reason for the
existency of EtherCAT) due to a big latency between packages.

Thank you!

On May 4, 2:38=A0pm, "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk>
wrote:
> Sink0 wrote:
> > A research,
>
> > Which digital and wired communication system would you use for the
> > following robotic system.
>
> > A system composed by a PC/104+ (it is just a very compact standard PC)
> > with Xenomai (or maybe RTAI), and some sensor nodes (something like
> > 12, but could vary a lot). These sensor nodes are basically composed
> > by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> > actuators. The sensors can be anything so i will not give any fixed
> > description, but a good example would be a Brushless motor (with the
> > control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> > sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> > from sensor nodes (the MCU will handle the communication on the node
> > side) perform some processing and send back some reference to the
> > actuators control routine. The whole system should work with a 500us
> > period. The max acceptable latency between the PC/104 ask for the data
> > and the reception should be 100us, and the maximum latency for the
> > actuators command should be 70us (bewtween teh pc104 send and the node
> > receive). From all the commercial standard availables, all i could
> > find was Ethercat and Firewire, that have a chance to handle this
> > communication..Any idea? Just a final comment. The system should have
> > the minimum amount of cables possible and the max distance between the
> > PC104 and the nodes is 3m.
>
> > Thanks!!
>
> What SIL level is this robotic system required to have? ... (based on the
> Hazard Analysis and Risk Assessment work you have obviously already done.
> You have done that haven't you?).
>
> --
> ********************************************************************
> Paul E. Bennett...............<email://Paul_E.Benn...@topmail.co.uk>
> Forth based HIDECS Consultancy
> Mob: +44 (0)7811-639972
> Tel: +44 (0)1235-510979
> Going Forth Safely ..... EBA.www.electric-boat-association.org.uk..
> ********************************************************************- Hid=
e quoted text -
>
> - Show quoted text -

On 05/04/2011 04:36 AM, Sink0 wrote:
> A research,
>
> Which digital and wired communication system would you use for the
> following robotic system.
>
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.

I think you've got a tough row to hoe, and I can't think of a strong 
reason to favor one over the other.  I _suspect_ that you'll end up with 
Ethernet, either running one of the real-time Ethernet protocols and 
most specifically not using TCP/IP, or running your own home-rolled 
Ethernet protocol.  I also think you'll be spending some amount of your 
time and energy dissuading the OS on the PC-104 side from ever sending 
anything long.

Look at high-speed USB, too.  I don't think you want it, but it has 
speeds to rival the practical FireWire versions.

Finally, I rather suspect that you'll never hit bandwidths that would 
really require that sort of speed -- if you've got some robotic 
contraption with cable lengths of three meters, then I doubt that you'll 
have any loop bandwidths greater than 100Hz.  That's getting down to 
allowable sampling rates of 1kHz or even 500 if you push on it, and 
_that's_ getting down to speeds where the CAN bus starts making lots of 
sense.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
> A research,
>
> Which digital and wired communication system would you use for the
> following robotic system.
>
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.
>
> Thanks!!



You might also look at Token Ring. It's architecture 'might' be a
little better for your app than ethernet. Though I have no idea about
cost/availability of components.

On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
> A research,
>
> Which digital and wired communication system would you use for the
> following robotic system.
>
> A system composed by a PC/104+ (it is just a very compact standard PC)
> with Xenomai (or maybe RTAI), and some sensor nodes (something like
> 12, but could vary a lot). These sensor nodes are basically composed
> by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> actuators. The sensors can be anything so i will not give any fixed
> description, but a good example would be a Brushless motor (with the
> control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> from sensor nodes (the MCU will handle the communication on the node
> side) perform some processing and send back some reference to the
> actuators control routine. The whole system should work with a 500us
> period. The max acceptable latency between the PC/104 ask for the data
> and the reception should be 100us, and the maximum latency for the
> actuators command should be 70us (bewtween teh pc104 send and the node
> receive). From all the commercial standard availables, all i could
> find was Ethercat and Firewire, that have a chance to handle this
> communication..Any idea? Just a final comment. The system should have
> the minimum amount of cables possible and the max distance between the
> PC104 and the nodes is 3m.
>
> Thanks!!

Token Ring/ARCnet might work well for robotics, but it seems nothing
has been done since about 2001 and I doubt components are available.

On May 4, 2:42=A0pm, 1 Lucky Texan <alcky...@swbell.net> wrote:
> On May 4, 6:36=A0am, Sink0 <sin...@gmail.com> wrote:
>
>
>
>
>
>
>
>
>
> > A research,
>
> > Which digital and wired communication system would you use for the
> > following robotic system.
>
> > A system composed by a PC/104+ (it is just a very compact standard PC)
> > with Xenomai (or maybe RTAI), and some sensor nodes (something like
> > 12, but could vary a lot). These sensor nodes are basically composed
> > by a DSP/MCU/DSC (not the same one on every node) and some sensors and
> > actuators. The sensors can be anything so i will not give any fixed
> > description, but a good example would be a Brushless motor (with the
> > control routine inside the MCU/DSC), and 4 to 5 sensors with a max
> > sample rate of 2ksps. Basicaly the PC/104+ should get all the data
> > from sensor nodes (the MCU will handle the communication on the node
> > side) perform some processing and send back some reference to the
> > actuators control routine. The whole system should work with a 500us
> > period. The max acceptable latency between the PC/104 ask for the data
> > and the reception should be 100us, and the maximum latency for the
> > actuators command should be 70us (bewtween teh pc104 send and the node
> > receive). From all the commercial standard availables, all i could
> > find was Ethercat and Firewire, that have a chance to handle this
> > communication..Any idea? Just a final comment. The system should have
> > the minimum amount of cables possible and the max distance between the
> > PC104 and the nodes is 3m.
>
> > Thanks!!
>
> Token Ring/ARCnet might work well for robotics, but it seems nothing
> has been done since about 2001 and I doubt components are available.



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