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Author Topic: how to shield an IMU from motors (mini-tutorial)  (Read 1750 times)

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how to shield an IMU from motors (mini-tutorial)
« on: November 30, 2010, 12:51:28 PM »
The issue with IMUs (and digital compasses) is that they have to be kept far away from motors and wiring and anything else that'll disturb Earths' magnetic field.

Enter Mu-metal.

A coworker and I were experimenting with it today to test how well we can shield our IMU from our magnetically noisy motors. He got some thin sheets, cut it with scissors, and bent it around the servos in a square shape . . .

We were both skeptical, and don't quite understand how it works, but it really makes a huge difference! No robot with a digital compass should go without it.

The only disadvantage of the stuff is that its like 10x more expensive than other metals . . . there are different alloys and thicknesses, but you can expect ~$40 per square foot.

. . . hope this info helps someone ;D

Offline Soeren

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Re: how to shield an IMU from motors (mini-tutorial)
« Reply #1 on: November 30, 2010, 04:53:32 PM »
Hi,

We were both skeptical, and don't quite understand how it works, but it really makes a huge difference! No robot with a digital compass should go without it.

If Ámetal tickles you, try Metglas  ;D
I stumbled over a page comparing several of these mag-shielding alloys recently, but now I cannot find the link :(
Ámetal is very good, but there are several alloys that shields much better than that...
Here is a page selling various types (not as expensive as you seem to think, or as I would have thought) and the page is a good read even if you don't wanna shop.
As far as I've heard, the difference between iron and Ámetal is close to yhe difference between Ámetal and Metglas, so you don't need to add much weight shielding a motor (if you don't mind the bill).


The only disadvantage of the stuff is that its like 10x more expensive than other metals . . . there are different alloys and thicknesses, but you can expect ~$40 per square foot.

The exact reason I didn't brought up the subject of "super" mag-shielding alloys a couple of weeks ago - I would have thought them a bit too expensive for hobby work (although I have to admit that I wasn't a pro back when I first used it, for screening a mains transformer in a sensitive audio pre-amp).
But it seems it's possible to get it and still retain your soul ;D

Just too bad they won't export Metglas  >:(


Btw, I have an old recording studio mixer (all the modules, less the frame) and several of them are wrapped in Ámetal IIRC (except the mike pre's, they're wrapped in silver), but it would be a shame to strip that (and I'd rather find a cheap source for the Metglas locally, if that's possible).
Regards,
S°ren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

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Re: how to shield an IMU from motors (mini-tutorial)
« Reply #2 on: November 30, 2010, 06:35:24 PM »
If Ámetal tickles you, try Metglas  ;D
I stumbled over a page comparing several of these mag-shielding alloys recently, but now I cannot find the link :(
Ámetal is very good, but there are several alloys that shields much better than that...
Here is a page selling various types (not as expensive as you seem to think, or as I would have thought) and the page is a good read even if you don't wanna shop.
As far as I've heard, the difference between iron and Ámetal is close to yhe difference between Ámetal and Metglas, so you don't need to add much weight shielding a motor (if you don't mind the bill).

Yea, I actually found that site earlier today. But I'm having trouble trusting it . . . you know, all those ghost hunting meters they sell and all . . .

Looking around I think I found the source: http://metglas.com/products/page5_1_2.htm

But I guess I'll need to get a quote first . . . money is no big object for me - I work for the US Navy ;D

I'll use a gauss meter on the materials and run some objective experiments to see which is actually better.

Offline Soeren

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Re: how to shield an IMU from motors (mini-tutorial)
« Reply #3 on: December 01, 2010, 11:25:08 AM »
Hi,

As long as their products aren't haunted :D

Looking forward to your results... (And I sure don't mind letting the US Navy fund these inaugural tests ;D)
I think, from what I've read, that you'll get good numbers on it (and in much thinner sheets, so much lighter for a better dampening).
Regards,
S°ren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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