Gimbal Table
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Hi. Iv undertaken a project which aims to imitate the tracking sensor
on a tank's turret.(scaled down version)The idea is that as my mobile
platform base moves but the sensor table above it stays pointing in
the same orientation. Iv considered using a memsic accelerometer
connected to the base platform and feeding that to my stamp but im
wondering if there's a better way to solve the problem. I cant use a
compass because of the E.M. fields produced by my motors. Has anyone
done a similar project before and found anything which could be
helpful?
Thanks,
Ali Topping
on a tank's turret.(scaled down version)The idea is that as my mobile
platform base moves but the sensor table above it stays pointing in
the same orientation. Iv considered using a memsic accelerometer
connected to the base platform and feeding that to my stamp but im
wondering if there's a better way to solve the problem. I cant use a
compass because of the E.M. fields produced by my motors. Has anyone
done a similar project before and found anything which could be
helpful?
Thanks,
Ali Topping
Comments
relying on outputs of an on-board guidance system (aka "dead reckoning")
becomes inaccurate over time due to accumulated drift in a double
integration of acceleration to position. A digital compass is the
preferred method, so consider shielding an on-board compass from the
motor EMF with mu metal. Other reference methods are possible (GPS
systems use 3 satellites), but are complex and may limit your range
and/or accuracy.
Dennis
Original Message
From: Ali Topping [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=C3pim_-9bUDEPPjb_wdrGC4aI0zmYBgWWPkcfuNBdh6BWIBz3kez3mMDM15BhNMZRItLkvg]ajt1@h...[/url
Sent: Wednesday, May 12, 2004 3:38 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Gimbal Table
Hi. Iv undertaken a project which aims to imitate the tracking sensor
on a tank's turret.(scaled down version)The idea is that as my mobile
platform base moves but the sensor table above it stays pointing in
the same orientation. Iv considered using a memsic accelerometer
connected to the base platform and feeding that to my stamp but im
wondering if there's a better way to solve the problem. I cant use a
compass because of the E.M. fields produced by my motors. Has anyone
done a similar project before and found anything which could be
helpful?
Thanks,
Ali Topping
wrote:
> You need an external absolute position reference of some kind,
because
> relying on outputs of an on-board guidance system (aka "dead
reckoning")
> becomes inaccurate over time due to accumulated drift in a double
> integration of acceleration to position. A digital compass is the
> preferred method, so consider shielding an on-board compass from the
> motor EMF with mu metal. Other reference methods are possible (GPS
> systems use 3 satellites), but are complex and may limit your range
> and/or accuracy.
>
> Dennis
What about a gyro ? that should offer a base that has no external
references ?
Just thinking out loud....
>
>
Original Message
> From: Ali Topping [noparse][[/noparse]mailto:ajt1@h...]
> Sent: Wednesday, May 12, 2004 3:38 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Gimbal Table
>
>
> Hi. Iv undertaken a project which aims to imitate the tracking
sensor
> on a tank's turret.(scaled down version)The idea is that as my
mobile
> platform base moves but the sensor table above it stays pointing in
> the same orientation. Iv considered using a memsic accelerometer
> connected to the base platform and feeding that to my stamp but im
> wondering if there's a better way to solve the problem. I cant use
a
> compass because of the E.M. fields produced by my motors. Has
anyone
> done a similar project before and found anything which could be
> helpful?
>
> Thanks,
>
> Ali Topping
--- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
wrote:
> --- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
> wrote:
> > You need an external absolute position reference of some kind,
> because
> > relying on outputs of an on-board guidance system (aka "dead
> reckoning")
> > becomes inaccurate over time due to accumulated drift in a double
> > integration of acceleration to position. A digital compass is the
> > preferred method, so consider shielding an on-board compass from
the
> > motor EMF with mu metal. Other reference methods are possible
(GPS
> > systems use 3 satellites), but are complex and may limit your
range
> > and/or accuracy.
> >
> > Dennis
>
> What about a gyro ? that should offer a base that has no external
> references ?
>
> Just thinking out loud....
>
>
> >
> >
Original Message
> > From: Ali Topping [noparse][[/noparse]mailto:ajt1@h...]
> > Sent: Wednesday, May 12, 2004 3:38 AM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Gimbal Table
> >
> >
> > Hi. Iv undertaken a project which aims to imitate the tracking
> sensor
> > on a tank's turret.(scaled down version)The idea is that as my
> mobile
> > platform base moves but the sensor table above it stays pointing
in
> > the same orientation. Iv considered using a memsic accelerometer
> > connected to the base platform and feeding that to my stamp but
im
> > wondering if there's a better way to solve the problem. I cant
use
> a
> > compass because of the E.M. fields produced by my motors. Has
> anyone
> > done a similar project before and found anything which could be
> > helpful?
> >
> > Thanks,
> >
> > Ali Topping
Gyro chips that I'm aware of just produce angular velocity, without any
external absolute position reference. Integrating their outputs once to
produce angular position has the same cumulative drift problem as I
mentioned before for accelerometer use.
I don't mean to downplay entirely "dead reckoning." Current GPS-based
car navigation systems use it briefly when the car enters a dead spot
for GPS reception, and then corrects the cumulative drift to an absolute
position reference when the GPS reception is resumed. An article in the
current Scientific American on GPS systems has a good explanation of
correcting GPS errors with use of 3 satellites, but it doesn't mention
this dead reckoning problem.
Dennis
Original Message
From: Dave Mucha [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=FtU-FpmiV_imUq3eW82DHL6_R815C2eQzqiQGl_m4KDH3CV0AQpSgZSlet34PRc3vAH-t1L9TsricCE2]davemucha@j...[/url
Sent: Wednesday, May 12, 2004 10:15 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Gimbal Table
--- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
wrote:
> You need an external absolute position reference of some kind,
because
> relying on outputs of an on-board guidance system (aka "dead
reckoning")
> becomes inaccurate over time due to accumulated drift in a double
> integration of acceleration to position. A digital compass is the
> preferred method, so consider shielding an on-board compass from the
> motor EMF with mu metal. Other reference methods are possible (GPS
> systems use 3 satellites), but are complex and may limit your range
> and/or accuracy.
>
> Dennis
What about a gyro ? that should offer a base that has no external
references ?
Just thinking out loud....
>
>
Original Message
> From: Ali Topping [noparse][[/noparse]mailto:ajt1@h...]
> Sent: Wednesday, May 12, 2004 3:38 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Gimbal Table
>
>
> Hi. Iv undertaken a project which aims to imitate the tracking
sensor
> on a tank's turret.(scaled down version)The idea is that as my
mobile
> platform base moves but the sensor table above it stays pointing in
> the same orientation. Iv considered using a memsic accelerometer
> connected to the base platform and feeding that to my stamp but im
> wondering if there's a better way to solve the problem. I cant use
a
> compass because of the E.M. fields produced by my motors. Has
anyone
> done a similar project before and found anything which could be
> helpful?
>
> Thanks,
>
> Ali Topping
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based on a "coriolis tuning fork principle," producing angular velocity
only -- no absolute position reference.
Dennis
Original Message
From: johncouture [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=jW7CwylWcAHv7aCoCX01D-eTLMtzQvIz32MaMrSLObE0VnxrGnaVYa-vogeWqb2f58HbVNJt0FrridIoFWblMOo]basicstamp@j...[/url
Sent: Wednesday, May 12, 2004 11:03 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Gimbal Table
How about a gyro on a chip: http://www.microsensors.com/gyro.html
> on a tank's turret.(scaled down version)The idea is that as my mobile
> platform base moves but the sensor table above it stays pointing in
> the same orientation. Iv considered using a memsic accelerometer
> connected to the base platform and feeding that to my stamp but im
> wondering if there's a better way to solve the problem. I cant use a
> compass because of the E.M. fields produced by my motors. Has anyone
> done a similar project before and found anything which could be
> helpful?
Google "Angular Rate Sensor":
<http://www.analog.com/Analog_Root/productPage/productHome/0,2121,ADXRS150,0
0.html>
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)