[HH] Rethinking LinuxPC Robot -- the Linux PI Robot

[Tom Metro]

markw at mohawksoft.com wrote:
> Use the GPIO pins in a distributed way.

Sure, but there may be cases where throwing more Pis at the problem just
to get a few more I/Os really doesn't make sense. And you've previously
said it wasn't economical to add I/O expanders to the Pi.

I'm also betting it is probably easier to do real-time stuff on an
Arduino than a Pi with a full OS stack.

So that's back to mixing technologies. What's the downside? Requiring
the developer to be versed in two different development environments?

Regardless of what is being distributed, taking a distributed approach
lets you make the project more modular, which could be a win for the
project overall, even if it makes the electronics more bulky and
complicated (in the sense that fewer computers are less complicated).

This way you don't need to have the horsepower for vision processing, if
you don't have cameras on your robot. Or you don't need to bother with
having enough I/Os to control an arm, if your bot doesn't have an arm.
Bolt on some new hardware ad plug its specialized controller into the
USB hub.


> I may move motor control to the Arduino, but I still
> need a steady USB communication for the deadman switch.

How does your deadman switch work? The motor controller shuts down if it
no longer hears from your main controller?

You could get away with a signal that repeats over hundreds of
milliseconds for that, so that shouldn't use much bandwidth.


> The PI despite having two USB slots is pretty underpowered. If I
> understand correctly, these is only one USB controller with a built in usb
> hub. The two USB ports and the network interface all go through the USB.

If you want to be able to do stuff like stream live video over WiFi,
then maybe the central controller node needs to be more powerful than a
Pi. Maybe one of these ~$100 multi-core ARM boards would be a better fit.


Federico Lucifredi wrote:
> I would buy a cheap...motherboard and the best sub-150$
> AMD cpu… getting multiple cores at 2+ GHz in the process. This
> seems to beat the pants off a cluster of R.PIs speed wise...

And also use more power. Remember, the bot is battery powered. Though
run-time may not have much practical significance on a hobby project.


> And it is x86.

I know some guys at Canonical that are working hard to make Ubuntu run
seamlessly on ARM CPUs so that distinction will become irrelevant. :-)

 -Tom