Linux router as embedded computer for robots
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Linux router as embedded computer for robots gidesa 01-14-2010
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Posted by John Nagle on January 18, 2010, 2:46 am


Joe Pfeiffer wrote:
>
>> Hello,
>> I am wondering if it is possible to use a device with embedded Linux
>> (as wifi routers, NAS, etc.) as a real embedded computer for a robot.
>> Especially wifi routers today are cheap, often contain an embedded
>> Linux version, and have some I/O ports (Lan and Wifi, of course, plus
>> serial console and Usb sometimes).
>
> The hard part is how to get enough IO -- the routers really don't have
> much.

You have plenty of network bandwidth available, and more motor
controllers are moving to Ethernet. See

http://www.active-robots.com/products/fiveco/ethernet-converters.shtml

But those will cost more than the router.

                John Nagle

Posted by Joe Pfeiffer on January 18, 2010, 9:48 pm



> Joe Pfeiffer wrote:
>>> Hello,
>>> I am wondering if it is possible to use a device with embedded Linux
>>> (as wifi routers, NAS, etc.) as a real embedded computer for a robot.
>>> Especially wifi routers today are cheap, often contain an embedded
>>> Linux version, and have some I/O ports (Lan and Wifi, of course, plus
>>> serial console and Usb sometimes).
>> The hard part is how to get enough IO -- the routers really don't have
>> much.
> You have plenty of network bandwidth available, and more motor
> controllers are moving to Ethernet. See
> http://www.active-robots.com/products/fiveco/ethernet-converters.shtml
> But those will cost more than the router.

A *lot* more, and you've still got the sensor problem. That parallel
USB adapter still seems a better bet....
--
As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously. (Benjamin Franklin)

Posted by BobH on January 18, 2010, 3:19 pm


Joe Pfeiffer wrote:
>
>> Joe Pfeiffer wrote:
>>>> Hello,
>>>> I am wondering if it is possible to use a device with embedded Linux
>>>> (as wifi routers, NAS, etc.) as a real embedded computer for a robot.
>>>> Especially wifi routers today are cheap, often contain an embedded
>>>> Linux version, and have some I/O ports (Lan and Wifi, of course, plus
>>>> serial console and Usb sometimes).
>>> The hard part is how to get enough IO -- the routers really don't have
>>> much.
>> You have plenty of network bandwidth available, and more motor
>> controllers are moving to Ethernet. See
>> http://www.active-robots.com/products/fiveco/ethernet-converters.shtml
>> But those will cost more than the router.
>
> A *lot* more, and you've still got the sensor problem. That parallel
> USB adapter still seems a better bet....

I have used the FTDI chips and associated driver to do parallel I/O. The
latency for USB scheduling and transmission means that 1mS is as fast as
it could get and around 3mS is what I have observed. The platform that I
was running under was windows xp, but I doubt that makes a lot of
difference in the scheduling latency. 480 mBit/second USB II still only
ships a frame per millisecond. This much latency would be fine for
whisker sensors, but you could not close a servo loop for motion control
with it.

I have messed with the Microtic router boards. They have a compact PCI
board interface for up to 3 boards. That seems like the path for I/O to me.

Good Luck,
BobH

Posted by Joe Pfeiffer on January 19, 2010, 12:43 am



> Joe Pfeiffer wrote:
>> A *lot* more, and you've still got the sensor problem. That parallel
>> USB adapter still seems a better bet....
> I have used the FTDI chips and associated driver to do parallel
> I/O. The latency for USB scheduling and transmission means that 1mS is
> as fast as it could get and around 3mS is what I have observed. The
> platform that I was running under was windows xp, but I doubt that
> makes a lot of difference in the scheduling latency. 480 mBit/second
> USB II still only ships a frame per millisecond. This much latency
> would be fine for whisker sensors, but you could not close a servo
> loop for motion control with it.
> I have messed with the Microtic router boards. They have a compact PCI
> board interface for up to 3 boards. That seems like the path for I/O
> to me.

I can't imagine trying to close a servo loop with a processor running a
"real" OS (Linux, XP, or anything else worthy of the name), no matter
what hardware was doing the details of control and sensing. Things like
that are what $1 specialized MCUs are for.
--
As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously. (Benjamin Franklin)

Posted by waynegramlich on January 19, 2010, 12:51 am


Joe Pfeiffer wrote:
>
>> Joe Pfeiffer wrote:
>>> A *lot* more, and you've still got the sensor problem. That parallel
>>> USB adapter still seems a better bet....
>> I have used the FTDI chips and associated driver to do parallel
>> I/O. The latency for USB scheduling and transmission means that 1mS is
>> as fast as it could get and around 3mS is what I have observed. The
>> platform that I was running under was windows xp, but I doubt that
>> makes a lot of difference in the scheduling latency. 480 mBit/second
>> USB II still only ships a frame per millisecond. This much latency
>> would be fine for whisker sensors, but you could not close a servo
>> loop for motion control with it.
>> I have messed with the Microtic router boards. They have a compact PCI
>> board interface for up to 3 boards. That seems like the path for I/O
>> to me.
>
> I can't imagine trying to close a servo loop with a processor running a
> "real" OS (Linux, XP, or anything else worthy of the name), no matter
> what hardware was doing the details of control and sensing. Things like
> that are what $1 specialized MCUs are for.

I basically agree. I am a huge fan of using dedicated MCU's for
tight real-time control. However, the EMC2 project over at:

<http://linuxcnc.org/>

is basically real-time Linux being used to control CNC machines.
This just shows that some people are pushing hard on real-time
Linux.

-Wayne

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