DPRG mailing list archives: [DPRG] DPRG Outdoor Challenge Lessons Learned

Fri May 16 22:59:28 CDT 2008

Hi Kenneth,

The "Road Rage" tires currently on jBot are 5.25 inches diameter.
I also have some "Rock Crawler" tires that are 7 inches but I don't
run them very much, they don't seem to work as well, and have
too much friction in "scrubbing" or sideways movement.

I just went out and measured the curb in front of my house and
the best I can tell the rise is 7 (or 8) inches and the run in 4 inches,
looks like they were hand sculpted with a concave curve at the
bottom and convex curve at the top.

If you look in the background of this picture of Erik strolling with
his robot:

<http://geology.heroy.smu.edu/~dpa-www/robots/dprg/outdoor/photos/DSCF5690.JPG>

you can see the curbs I was referring to in the post (they're red)
which I assume are the same as the curbs in front of my house,
but don't know that for sure.

best,
dpa

Kenneth Maxon wrote:
> David, or anyone else involved in the outdoor competitions there in Texas...
>
> How tall are the curbs we are talking about?
>
> ProtoBot has significantly larger tires that jBot and ProtoBot is not
> particularly fond of "hopping curbs".
>
> Okay, sure ProtoBot was designed with hard suspension on purpose because it
> is a quick prototype to test out things that work and don't work and to get
> and up and running outdoor entry running while the Sojourner is the longer
> term 2++ year development with full blown suspension.
>
> Help me out here but I thought jBot had the 4in(ish) tires rather than the
> 6in(ish) scale tires?  Am I loosing my brains here?
>
> The reason I asked anyone to answer rather than only David (David feel free
> to chime in too), is the real question here isn't what size tires jBot has,
> but rather are the curbs in Texas shorter than the curbs out here
> "in-the-middle"?   I am beginning to suspect that they may be.   Possibly
> this is related to the consistent and massive downpours that turn the roads
> into rivers here, although I suspect Dallas gets its fair share of
> torrential down pours also, soooo...   Are the curbs sloped?  Cupped?
> Possibly shorter?
>
> BTW, ProtoBot has 10" dia tires that make short work of grass clods in a
> medium wild field and easy climbing of relatively clean dirt piles in the
> construction spot behind the back 40...
>
> -Thanks, Kenneth
>
> -----Original Message-----
> From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
> Behalf Of David
> Sent: Friday, May 16, 2008 10:13 AM
> To: dprglist at dprg.org; jabshier at kc.rr.com
> Subject: [DPRG] DPRG Outdoor Challenge Lessons Learned
>
>
> Howdy,
>
> John, thanks for the feedback and analysis of your DPRG ORC robot
> entry "This line left intentionally blank," which, for those not
> there, took first place in challenge #2, the 100 foot Borenstein
> square.
>
> I didn't think of it at the time but I wish we had aimed your robot
> to run over the curb to the west onto the meadow next to the parking
> lot, and back, to see how moving across a 3D surface would have
> effected your 2D navigation technique.  Have you ever tried this?
>
> Here's a video (6M mpg) of an early version of jBot doing an
> out-and-back over two curbs for testing.  My suspicion is that
> your robot might do just as well, with the compass errors
> canceling each other out:
>
> <http://www.geology.smu.edu/~dpa-www/robo/jbot/jbot_2curbs.mpg>
>
> I think the compass + rate gyro scheme that you mention below might
> also do pretty well on uneven ground, but this is all conjecture at
> this point.  Would be really nice to have some actual experience to
> back that up one way or the other.
>
> If it turns out that an full axis IMU really is required, Robert Scheer
> has a team in Portland working on a home brew device which hopefully
> they will sell to folks outside their club when finished,  I believe
> the target price is well under $300 but again, this is all conjecture.
>
> As a final note, the Microstrain IMU comes with all sorts of possible
> adjustments to improve factory performance for a particular use.  My
> experience is that any adjustments I've attempted only made the thing
> work worse than the factory defaults.  I offer this as a single data
> point (me) that tuning a 27 parameter 9 axis IMU is not a trivial task.
>
> A question on your steering algorithm, do you run into any sort of
> overshoot or oscillation of the steering by using a P-only control?
> Does the robot have a deadband or other means of reducing or damping
> the steering control?  Same question for velocity control.
>
> Congratulations on your win last weekend, looks like you are (or soon
> will be) ready to move on to the more difficult challenges!
>
> best regards,
> dpa
>
>
> J