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Author Topic: Selecting a magnetic compass  (Read 1794 times)

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Offline knossosTopic starter

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Selecting a magnetic compass
« on: October 21, 2010, 01:09:23 PM »
I am looking through my options for a compass.  This is for a personal project that does not have any strict parameters, although the robot will be loaded with sensors so the type of interface will make a difference.  I am thinking I will probably go with I2C since I will already be using a Wii Motion+ and Nunchuck but am willing to consider other options.  I will eventually be adding GPS as well.  This will be on a chassis with wheelchair motors, most likely mounted on a plastic mast approx 12" above the metal frame (approx 18" above the motors).  In addition it will have 2 forms of wireless comm, one of which will likely be WiFi amplified to about 1w (mentioned in case of known issues with noise).

So far I am looking at this Devantech with tilt compensation:


Any recommendations?
"Never regret thy fall,
O Icarus of the fearless flight
For the greatest tragedy of them all
Is never to feel the burning light."
 
Oscar Wilde

Offline madsci1016

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Re: Selecting a magnetic compass
« Reply #1 on: October 21, 2010, 01:17:51 PM »
I have used both the HMC6352 and the HMC6343 on my SAGAR robot. The HMC6343 also gives roll and tilt data via it's 3 axis accelerometer.

On my robot, it surfers vibrational noise from the movement, and electromagnetic noise from the motors.

Watch the 3D render of the orientation in this video:

SAGAR Autonomous Robot Waypoint Mission Interface and Vehicle Video


I doubt in my application the Devantech would be any different, as it's the application, not the compass that's causing problems. I could mount it up on a mast, but would rather not. Instead, I'm going to add a 3 axis gyro as well and combine that data to filter out the noise.

It's not shown in this video, but is works well when I move SAGAR by hand, and the motors aren't running.

« Last Edit: October 21, 2010, 01:20:47 PM by madsci1016 »

Offline DUKELancelot

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Re: Selecting a magnetic compass
« Reply #2 on: October 21, 2010, 01:18:23 PM »
I like the parallax one. http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/compass/List/0/SortField/4/ProductID/98/Default.aspx

($29.95)

The one madsci1016 recommended  is also sold by parallax at a reduce price.

Also about the wifi. Have you considered a router on the robot.
The one in the pic is a Linksys WRT54GL router. It's very hacker-friendly in that it runs Linux.
« Last Edit: October 21, 2010, 01:21:58 PM by DUKELancelot »
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Offline knossosTopic starter

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Re: Selecting a magnetic compass
« Reply #3 on: October 24, 2010, 08:25:43 PM »
@DUKELancelot
I would probably prefer a wifi module as opposed to the router, but haven't found one with an SMA connector that I can attach my amp to.  If I don't find something I like, I have considered using one of my routers instead.

@madsci1016
I assume you upgraded to the HMC6343 for the added tilt compensation.  The one I was looking at has 3-4 degree accuracy instead of 2 degrees like yours.  From your experience, do you think the extra accuracy makes a significant enough of a difference?

As for mounting my compass, I was considering the mast method to avoid motor noise, but I hadn't really thought about vibrational noise which the mast may well amplify.  Also the mast may prove problematic depending on how I mount my pan assembly on top of the robot.
"Never regret thy fall,
O Icarus of the fearless flight
For the greatest tragedy of them all
Is never to feel the burning light."
 
Oscar Wilde

Offline madsci1016

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Re: Selecting a magnetic compass
« Reply #4 on: October 25, 2010, 07:35:01 AM »
@madsci1016
I assume you upgraded to the HMC6343 for the added tilt compensation.  The one I was looking at has 3-4 degree accuracy instead of 2 degrees like yours.  From your experience, do you think the extra accuracy makes a significant enough of a difference?

Held flat, not really. But when i tilted the cheaper one more then 10 degrees, it's reading would go crazy. Also my application didn't really need an compass that was super accurate.

 


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