Twist the wires to reduce RF interference?

[tekrunner]

Hey guys,
I just started making and crimping my own servo extensions for my UAV. I was wondering if I should twist them to help reduce Rf interference. Is it true that twisting them would be a good idea?

Thanks,
tekrunner

[rich smith]

Hey guys,
I just started making and crimping my own servo extensions for my UAV. I was wondering if I should twist them to help reduce Rf interference. Is it true that twisting them would be a good idea?

Thanks,
tekrunner

yes

[workshop]

ServoCity sells bulk pre-twisted wire for those not wanting to roll their own.
:)

www.servocity.com

Jeff

[Buzz_Lightyear]

It's complicated if you want to know the reasons why.

But if you want the short answer, probably.

[mecevans]

yes.

[rich smith]

yes.

LOL!

[mecevans]

I just had some troubles with an RF modem as well that seemed to be bleeding over into servos. I figure I'll add on Jeff's list a bit...

- copper foil (or just aluminum foil even) wrapped around the servo lines and servos
- triple check have no ground loops, especially going to the modem (this can be a smoking gun if you find one)
- antenna location and orientation between the radio modem and RC receiver plays a big role too .... if you have coax running to move your radio modem antenna away from the receiver, you may try getting better coax or increasing seperation between the coax and RC antenna
- a counter-poise added to the RC receiver can be a cure-all sometimes too. It is a length of wire the same length as an antenna simply tied to receiver ground and run 90deg to the RC antenna. From what a prof at school told me, it helps reduce RF interference getting to the RC antenna and has worked for me before.
- putting the radio modem in a metal box (faraday cage really) can help if it's not the antenna itself
- reducing the transmit power can help sometimes
- if you have a coax or if your 900MHz antenna is running near a servo or near the receiver itself, try adding more seperation or changing the orientation of the parts to one another. Even if this isn't a final solution, at least you'll know why things are interfering.
- ferrite rings or chokes can work
- you can get an opto-iso box from Jomar if the servos have trouble but the receiver is getting signals okay
- if you have an antenna coax bundled with servo wires, that can cause cross-talking
- ground loops really are my first choice to go looking for. I can explain if you need more, but I'd try wikipedia or google for a diagram. Ground loops can put noise on an RC receiver in a heartbeat

Hope this helps!
If you post some photos of your setup, we may be able to help catch some things we missed in our lists. It always helps to have another few sets of eyes!

Dan

Rich smith,
huh? lol

[smh20502]

any reason you can't use a ferrite ring?

[mecevans]

any reason you can't use a ferrite ring?


you can, they add weight.

[vector_vortex]

Since when do 1-2ms PWM pulses cause RF interference, if your really concerned you should try to reduce the slew rate of the PWM signal, caps at the receiver end. the RF interference coming from the servos will be nothing compared to a high current ESC or telemetery transmitter.

[mecevans]

hes trying to shield everything from each other.

[tekrunner]

hes trying to shield everything from each other.


Yup that explains it. I'm surprised such a simple thread got so many responses. Thanks guys.

[rich smith]

Twisting is done to stop intereference from OTHER sources that cause servos to jitter. My advice don't do anything unless there's a problem. Why look for trouble where there is none?


Since when do 1-2ms PWM pulses cause RF interference, if your really concerned you should try to reduce the slew rate of the PWM signal, caps at the receiver end. the RF interference coming from the servos will be nothing compared to a high current ESC or telemetery transmitter.

[4c3m4n]

I use Teflon insulated shielded wire (MIL-spec) on all my stuff but it depends on how serious your UAV is.

[mecevans]

does anyone know of any good RF/EMI tape or wire shielding?

[4c3m4n]

Get yourself some of these - sure you can find them locally at electronic suppliers.

http://cableorganizer.com/metal-braided-sleeving/

[tekrunner]

Get yourself some of these - sure you can find them locally at electronic suppliers.

http://cableorganizer.com/metal-braided-sleeving/


How effective is that stuff?

[mecevans]

i dont know. im still looking into buying some to try it out. i might find a different type better suited for our application.

[tekrunner]

i dont know. im still looking into buying some to try it out. i might find a different type better suited for our application.


Please let me know if you find anything better.

tekrunner

[airmcn_3]

I think you will be far better off using 3 conductor shielded wire. Go to Belden wire and look up 9451 and 9451D.

Chris

[tekrunner]

http://www.belden.com/pdfs/03Belden_Master_Catalog/04MultiConductor_Cables/04.15.pdf

I'm thinking of going with the 20awg on there? You think that'll be much better then twisted hobby servo wire?

[tekrunner]

Hmmm...I think I need something with a "drain wire" built into the cable. Anyone know more about that?

[airmcn_3]

http://www.belden.com/pdfs/03Belden_Master_Catalog/04MultiConductor_Cables/04.15.pdf

I'm thinking of going with the 20awg on there? You think that'll be much better then twisted hobby servo wire?

Not a bad choice there, I am not 100% sure if they will be better or not, I do know we stuff 80+ 9451 cables into a 3" piece of conduit, this is primarily for microphone cable in large production style applications. We have had no issues with interference.

Chris

[Sherwood]

I have wondered if wrap of Teflon plumbers tape around signal wires might help. I do not know if this would work. Has anyone actually tried it? Teflon is considered to be a good dielectric. Lee Sherwood

[tekrunner]

It would be nice to get to the bottom of this as I think we all have to deal with RF interference.

[mattk0]

Question:
When you're referring to 'twisting' the wires, do you mean literally turning them 360 degrees a few times, or seperating the 3 wires and 'braiding' them? I feel like I've seen both but the 'braiding' would take a bit more work...

[mecevans]

twisting not braiding. google it. twisted servo wire.

[dalbert02]

I use Belden 8771 with good results. Search user DEH6 and "beldon" he mispelled it in one of his posts but has some good info.

Teflon tape because it is a dialectric? I am confused. Air is dialectric too, what is the teflon going to do for you?

-dave

[tekrunner]

I use Belden 8771 with good results. Search user DEH6 and "beldon" he mispelled it in one of his posts but has some good info.

Teflon tape because it is a dialectric? I am confused. Air is dialectric too, what is the teflon going to do for you?

-dave


K thanks I'll try it out. What do you do with the drain wire?

[tekrunner]

Anyone try wrapping servos in copper tape?

[dalbert02]

drain wire is grounded. yes, I wrap my servos with copper tape. I also use spray on sheilding spray. If you do a search here, I am sure you will find all the old posts...

http://www.rcgroups.com/forums/showthread.php?t=735206&highlight=spray+shield

-dave

[tekrunner]

How do you ground the wire, attach it to negative battery line? Oh yeah what airframe are you using? Looks nice.