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EMI Suppression Cores

Old 01-08-2004, 08:10 PM
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thanks for the info
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Old 01-08-2004, 08:23 PM
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Glad to help guys



-dave
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Old 01-08-2004, 08:26 PM
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Thanks for the info, even though it confused my brain into remision. Electrical talk sounds like "blah blah blah ginger" to me.
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Old 01-09-2004, 06:22 AM
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dave,

you are mentioned the freqencies that an esc uses verses a servo being about a 2000 fold difference. what frequencies are you comparing? the drive frequency for both units? these pulses that the receiver gives to the servo, are they the same freqency as the xmitter is on? ie. 75MHz etc?

what is actually happening when your servo glitches (or esc for that matter)? ok, that's too broad. i understand the concept of constructive or destructive interference, but what are the two or more sources of the energy that interfere? is the receiver receiving complex rf signals due to reflections, etc from the surroundings the only cause of glitching? or can the signal to the esc or servo be contaminated later down the line by external noise?

this is something i'd like to know alot more about.
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Old 01-09-2004, 10:58 AM
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my assumption is that glitching by:

1) external interference - we can't do anything about that other than changing frequencies

2) inteference created by motor adversely affecting steering servo - assuming such, where should the ferrite go

3) interference between the ESC and the receiver
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Old 01-10-2004, 08:11 PM
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Originally posted by seaball
dave,

you are mentioned the freqencies that an esc uses verses a servo being about a 2000 fold difference. what frequencies are you comparing? the drive frequency for both units? these pulses that the receiver gives to the servo, are they the same freqency as the xmitter is on? ie. 75MHz etc?
2000 was a typo. I meant 200. My original post has been edited to reflect this.
On to your question...
ESCs use a drive frequency between 60 and 20,000Hz. Servos work on a difference algorithm, with "center" being a pulse train with a period of 2mS. 2mS equites to roughly 500kHz (25x), but the span is from 1mS to 3mS (2 +/-1, the ends being the endpoints of servo travel) so the upper limit id actually 1MHz, or 50x the highest ESC frequencies. If you look at average ESCs, their drive frequency is still around 4kHz, which is 250x the high end of servo drive frequencies. The average is probably between 50x and 150x, depending heavily on your ESC, but

what is actually happening when your servo glitches (or esc for that matter)? ok, that's too broad. i understand the concept of constructive or destructive interference, but what are the two or more sources of the energy that interfere? is the receiver receiving complex rf signals due to reflections, etc from the surroundings the only cause of glitching? or can the signal to the esc or servo be contaminated later down the line by external noise?
From what I've been able to measure, servo glitching is caused when the normal pulse train is interrupted, and a pulse is missing due to noise or some other problem. What will happen is that the servo or ESC will suddenly see something very different from what it saw a few pulses ago. It will interpret that as a new command, and try and move to the new position it believes it was commanded to go to (often at one or the other end of it's possible travel). A few cycles later, when the noise is gone, the servo or ESC tries to go back to where it's supposed to be. That radical, and usually very very fast, change is what we see as glitching.

What actually causes the pulse stream to be mangled can be one of any number of things. A large voltage drop at the receiver can make it do unpredictable things, spurious RF noise can corrupt the signal from the transmitter, and noise can be induced directly into the servo wiring (usually by the motor), to name a few.

My personal techniques to avoiding gitching are pretty easy to follow. I leep the wiring from my ESC and servos neat, compact, and as far away from noise sources (the motor) as possible. UI have a XXX-S, so the receiver lead on the ESC is forced to go right next to the motor, but I make sure it's well twisted, since twisted pairs are good at rejecting low frequency interferance (<100kHz, like you'd get from the motor). I keep my brushes in good shape, so that they don't bounce and arc (which releases tons of noise all over the spectrum, from DC to RF), and I don't let my receiver anteanna fold over itself in any way, since that decreases the sensitivity to it's intended frequency (by shortening it's effective length) and increases it's succeptability to noice (since the intended signal isn't as strong as it could be)

-dave
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Old 01-10-2004, 08:22 PM
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Thumbs up oh yes

my love still runs deep for dpaton.

thank you.
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Old 01-10-2004, 08:33 PM
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Default Re: oh yes

Originally posted by seaball
my love still runs deep for dpaton.
Don't tell my girlfriend....

-dave
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