On 09 Mar 2007 04:23:42 -0800, Ryan Autet wrote: >
> Hi
>
> Would any of you gentlemen happen to have source code for the
> QTl Line Sensor from Parallax.
>
> If you wouldn't mind sharing it that would be appreciated.
>
> Thanks
> Ryan
>
>
--
Scott
www.AntiFuel.com
Minds are like parachutes, they only function when they are open.
On 09 Mar 2007 04:23:42 -0800, Ryan Autet wrote: >
> Hi
>
> Would any of you gentlemen happen to have source code for the
> QTl Line Sensor from Parallax.
>
> If you wouldn't mind sharing it that would be appreciated.
>
> Thanks
> Ryan
>
>
--
Scott
www.AntiFuel.com
Minds are like parachutes, they only function when they are open.
Reply by Ryan Autet●March 9, 20072007-03-09
Hi
Would any of you gentlemen happen to have source code for the
QTl Line Sensor from Parallax.
If you wouldn't mind sharing it that would be appreciated.
Thanks
Ryan
Reply by Tom Becker●March 8, 20072007-03-08
> ... any tips on what I could use to shield off the
fields from the motors?
Magnetic "shielding" isn't, really, it is redirection by an intervening
material. You will find it difficult to control the fields from the
motors to create a uniform field around a close-by sensor that
accurately follows Earth.
_Distance_ is your best tool and it is very effective. Again, a
magnetic field decreases quickly as you move away from the source - by
the inverse square, so you'll find a quarter of the magnetic field at
only twice the distance. If you are 20cm from the motors now, you'll
find that 40cm will be four times better, 160cm will be 64 times better,
320cm will be 256 times better than 20cm. Distance is natural,
effective and cheap; look at how magnetometers are mounted to
spacecraft, for example - at the end of a long arm, despite a large
budget. _Distance_ is your tip.
--- In b..., "Tom Becker" wrote: > > It's located 20cm above the 3mm alu plate, on
the opposite side of
> the motors... and I always have everything turned off while measuring... >
> The aluminum won't offer much protection. The motors are just too
> close, I think you'll find.
> Tom
>
any tips on what I could use to shield off the fields from the motors?
I just got hold of a basic stamp, so I'm trying the calibration program
there, but some kind of shielding is probably needed anyhow.
Anders
Reply by Tom Becker●March 7, 20072007-03-07
> It's located 20cm above the 3mm alu plate, on
the opposite side of the motors... and I always have everything turned off while
measuring...
The aluminum won't offer much protection. The motors are just too
close, I think you'll find.
Tom
Reply by toahatt●March 7, 20072007-03-07
--- In b..., Tom Becker wrote: >
> > ... neither compass or, IR or ultrasound is mounted on those pics... >
> The top photo looks like a Parallax HM55B is in the BOE breadboard. > With a drive motor or two only 10cm or 20cm from it,
you will not see > good compass results.
>
> It is not noise that is affecting your results, I suspect, just a heavy > local magnetic bias from the motor magnets, and,
perhaps, a varying > magnetic field from the motor coils as they rotate in
two directions, > driven by a varying current.
>
> A more accurate compass will not improve that. M-metal shielding and > distance will; magnetic fields decrease according to
the inverse of the > squared distance. If you look around online at other
small compassed > robot vehicles, you'll often see the compass
sitting atop a mast of some > considerable height to reduce the bias that the
vehicle produces.
>
> Welcome to compassing.
> Tom
>
probably only there for testing at that moment, or I put it there so
I would not loose it...=)
It's located 20cm above the 3mm alu plate, on the opposite side of
the motors...
and I always have eveything turned off while measuring...
Reply by Tom Becker●March 7, 20072007-03-07
> ... neither compass or, IR or ultrasound is mounted
on those pics...
The top photo looks like a Parallax HM55B is in the BOE breadboard.
With a drive motor or two only 10cm or 20cm from it, you will not see
good compass results.
It is not noise that is affecting your results, I suspect, just a heavy
local magnetic bias from the motor magnets, and, perhaps, a varying
magnetic field from the motor coils as they rotate in two directions,
driven by a varying current.
A more accurate compass will not improve that. M-metal shielding and
distance will; magnetic fields decrease according to the inverse of the
squared distance. If you look around online at other small compassed
robot vehicles, you'll often see the compass sitting atop a mast of some
considerable height to reduce the bias that the vehicle produces.
Welcome to compassing.
Tom
Reply by toahatt●March 7, 20072007-03-07
--- In b..., Tom Becker wrote: >
> > ... I want the calibration program and maybe some guidelines how to > calibrate it.
>
> Tom Handley vanished in late 2005 and his work seems to have vaporized, too. >
> The Hitachi HB55B is similar to other two-axis magnetometers applied to > compassing, so the calibration techniques of other
sensors will guide > you well. I'm currently working with Honeywell
parts and have found > their application notes very helpful. At http://www.magneticsensors.com > (a Honeywell site), find AN214, for example, which
suggests the general > method of rotating the _level_ compass while sampling
to find the
> maximum and minimum of X and Y, which are then plugged into a simple > compassing algorithm. Other methods achieve similar
results by
> interpolating between X/Y magnitude pairs taken and stored in a table > while rotating at a constant rate.
>
> These methods assume that the sensor is level. You will find that tilt > will introduce large errors so, if you are building a
hill- climbing > robot, for example, you must also incorporate tilt
sensors to correct > the compass outputs.
> Tom
> Okay, looked at that datasheet and tried that calibration
approach...but not very succesful...maybe the environment is just to
noisy...
when I turn 90 degrees i eithert get around 70 or 120 on the
compass...but always 360(+- a few) when turning a full circle...
sounded like calibration to be, but I dont know...
anyway, I'll try another module tomorrow...with greater accuracy
here are a few photos of the robot btw.
Autonomus, rescue inpired (send into (burning) building, locate
objects, return with map of building).
This is a Honeywell HMC6352 on a Sparkfun breakout board, mounted to a
brass tube that is held in teflon-plumbing tape in nylon clamps, steered
by a hobby servo via a pair of identical cranks and a carbon-fiber
control rod. The servo is driven by a BX-24 that takes signals from an
ADXL203 accelerometer and an ADXRS401 rate gyro, combined in a
pseudo-Kalman filter, implemented in code. Compass data comes off the
breadboard via the Bluetooth radio near the batteries, whose steel
shells, along with the servo motor magnets, are as far from the compass
as possible, hence the control rod.
For single-axis levelling, this works very well. For two-axes, it
becomes more complicated.
Tom