[Gghc-discuss] Proposed initial purchase - too much?

[Erich Heine]

See responses inline. The tl;dr here is I won't order anything until someone
else chimes in, as there seem to be some pretty big differences of opinion
here.

On Thu, Mar 31, 2011 at 8:37 AM, <jmanton at illinois.edu> wrote:

> > *  3 arduinos
> > * 3 XBee sheilds
> > * 2 XBee Explorer USB
> > * 5 XBee radios
>
> This is $359.05, plus shipping (assuming SparkFun, $27.16 overnight for
> Friday, $14.44 2-day for Monday).  Also a huge chunk of our initial
> outlay.
>

My expense objection was about stuff that may not be needed, given that with
a short period of time we can shave a lot of money off of the outlay for a
prototype. I propose there is a difference here, in that the arduinos and
XBees are:

* core components that will be the basis of the project
* not something we can do ourselves in a week
* something we will be using in all cases, not just a one-off prototype

I also think it should be pointed out that my suggestion includes more 2
more XBees than before, so we can have computer->arduino wireless for 2
developers. This is a big chunk of money in the cost above. Further, some of
the stuff is available from Amazon and we get free 2-day shipping with my
Amazon Prime membership. I also have to point out: if I order today, we can
get stuff on Saturday, as 2-day shipping  through UPS and FedEx include
saturday delivery.


> With this option we don't have motors, a base, batteries, or a motor
> controller.  I don't like the idea of spending that much money and leaving
> out the entire drivetrain and power subsystem.  Our first robot milestone
> is supposed to be driving in a figure-8.  We can't do that with this
> option.  You also can't disconnect the arduino/XBee from your laptop, as
> it won't have power, so doing range tests with the XBees will be a pain.
>
>
I think that perhaps then, it would be reasonable to use the time on other
milestones, like communicating between  computers and Arduinos over XBee. I
also think it would be reasonable to do the figure-8 next week, instead of
focusing on the communications during that time. Those things are not
dependent on each other.

The power situation can also be solved by taking an extension cord, a
wall-wart cellphone USB charger, and a USB cable, combining them, and
powering the Arduino that way.

The robot stuff: you are absolutely correct, we won't have the robot. This
is sort of core of my proposal: The actual robot kit is pretty expensive,
and I am wondering if we can come up with something for much cheaper with a
weekend of deep planning work. The more I look into this, the more I find
that it is not very hard to drive a couple of motors with an arduino, our
robot seems very simple, but maybe I'm missing something. I'd really
appreciate some input on it -- what are the problems with this?, what are
the hidden complexities?, and so on.



> That said, at this point I feel we need to order *something*, or else we
> lose an entire week.  I would prefer to have drivetrain components to work
> with this weekend, but if it gets us to an agreement faster then go ahead
> and get this list (don't forget USB cables and the 8-pin and 6-pin headers
> - the XBee Shield does NOT come with headers to plug it into the
> arduino!).  We can worry about the drivetrain and power later I guess.
>
>
Good catch on the XBee headers, that is such a weird gotcha -- why would
they sell it that way? :/

Mini USB connectors are plentiful. I have at least 4 of them on my desk. We
don't need to buy them at a 4x cost + 2-day delivery.

Finally, about this idea of a "lost weekend":  I don't think anything is
lost. We can spend some time designing and researching parts this weekend,
instead of a future weekend, and we have the robot available next weekend
instead of this weekend. All amounts of work are conserved, the schedule is
just rearranged, plus we may save money and get to learn some electronics in
the process.

 Aside from that, I have dedicated a big amount of time to this project --
this includes all of Tuesday evening, parts of wednesday, thursday, and
friday evenings, and some time on weekends, so if some of these options
require grunt-work/time-consuming stuff, let me do it, as I am available and
willing. I appreciate that several of us have very limited time, but we
shouldn't spend and design as if there was no time to do this at all.

Overall, it would be nice to have someone else weigh in on this, since there
are several group members who have not responded at all.

Regards,
Erich
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