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Analog vs. Digital

Old 01-06-2012, 07:22 AM
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panhndl
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Default Analog vs. Digital

I have some Hitec 645mg servos in my KMP T-28c plane. Finally got the electric conversion on my retracts by Down and Locked installed last night. Now my 645mg servos go haywire when working the gear. I find out that analog servos (or maybe more specifically, Hitec analog) are very susceptible to interference from other gear in the plane. Digital servos...nope. No problems.

So, I guess there is at least one more reason to use a digital servo over an analog one. Especially if you're using electric retracts in close proximity to the servos.

By the way, I think the interference is coming from the leads, not the actual motors, themselves. But I could be wrong. I'll know more tonight, but digital servo in the wings, it looks like.
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Old 01-06-2012, 07:34 AM
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Default RE: Analog vs. Digital

Personally, I think digitals are overrated...maybe worth while for 3D, but not for a warbird. If I were you, I wouldn't skirt the problem by just installing digitals, I would correct the problems and then choose a servo. My 2 bits....
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Old 01-06-2012, 07:56 AM
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Default RE: Analog vs. Digital

I could shield the wires, but the hole for the retracts', ailerons', and flaps' leads is smaller than a dime on each side.  They're all going thru there and that hole leads to a cavity near the electric motor on the main retracts.  No way to "fix" the problem other than shielded wires or cutting a fiberglass fuse and built and covered wing.  Even so, not sure it would fix it.  But digital's will fix it.
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Old 01-06-2012, 08:01 AM
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Default RE: Analog vs. Digital

I would use a seperate battery to power the retracts isolating it from the receiver.

Dave N
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Old 01-06-2012, 08:08 AM
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Default RE: Analog vs. Digital

Send an email to down and locked and tell them what's happening. They should have protected their electronics from interfering with other parts of the RC system. It's has nothing to do with digital/analog issues. Before there were digital servos, there were only analog ones for many years. They were always good enough. Dan.
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Old 01-06-2012, 08:30 AM
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Default RE: Analog vs. Digital

I talked with Down and Locked.  He said they have some shielded wires, but suggested digital servos first. 

As far as isolating my battery.  I'm running 2 RX batteries connected to a Miracle Switch connected to a Smart fly Batt Share connected to the RX's.  On Down and Locked's box, there is an option to have a seperate battery powering the retracts, but I didn't opt for it on this set up. 

I talked to Hitec, and they suggested using 1) twisted wire, which I am not, and 2) putting some "ferrite rings" on the wires to help with interference.  I found some on Tower, but they were discontinued.  I'll be ordering the twisted wire, as well.
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Old 01-06-2012, 09:03 AM
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Default RE: Analog vs. Digital

Please let us know what changes have worked out for correcting the problem.

Thanks
Rick
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Old 01-06-2012, 09:05 AM
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Default RE: Analog vs. Digital

I know those down and locked cost a fortune. If they are causing the problem, which they should not, I would not use them. Sorry, but I'm not trying to be a smart *ss. Our planes are just too expensive and hazardous to install something like that in them regardless of the servos you are using. Dan.
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Old 01-06-2012, 09:36 AM
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Default RE: Analog vs. Digital

I have heard of using capacitors across the contacts on the motors to stop electrical interferance.  that may be worth a try. I'm not much on the electrical stuff, so maybe someone will chime in on this.

Dash
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Old 01-06-2012, 09:41 AM
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Default RE: Analog vs. Digital

The digital servos are just masking the electrical interference. It will bite you in the end.
Larry
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Old 01-06-2012, 10:52 AM
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Default RE: Analog vs. Digital


ORIGINAL: larry@coyotenet

The digital servos are just masking the electrical interference. It will bite you in the end.
Larry
Indeed...be warned.

Jeff
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Old 01-06-2012, 11:03 AM
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Default RE: Analog vs. Digital

Use the ferrite rings close to the RX on the retract, flap and aileron leads. You will have to remove the leads from the RX, unplug the wires from the plastic ends so that you will be able to loop the wire through the ferrite ring, replace the plastic ends, plug back into the RX. Then do some testing. You may have to move the rings along the leads until the EMF noise is cleared. The rings should clear it up though. Let us know what you get.
Note.. be sure to loop the wire through the ring, do not just push the wire through so that the ring can slide back and forth, one loop is good enough. You don`t want the ring to move once it is at the right spot.
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Old 01-06-2012, 12:30 PM
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Default RE: Analog vs. Digital


ORIGINAL: panhndl

...I talked to Hitec, and they suggested using 1) twisted wire, which I am not, and 2) putting some ''ferrite rings'' on the wires to help with interference. I found some on Tower, but they were discontinued. I'll be ordering the twisted wire, as well.

I can't believe this kind of problem still exists in today's world. This sounds like 30 years ago. Anyway, you don't have to replace the servo leads, just twist the ones you have. But, As others have said, find the problem, don't just jury-rig a fix. JMHO.
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Old 01-06-2012, 12:33 PM
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Default RE: Analog vs. Digital


ORIGINAL: panhndl

...I talked to Hitec, and they suggested using 1) twisted wire, which I am not, and 2) putting some ''ferrite rings'' on the wires to help with interference. I found some on Tower, but they were discontinued. I'll be ordering the twisted wire, as well.

You don't have to replace the servo wires, just twist the ones you have[8D]. But fix the problem, don't just jury-rig it. JMHO
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Old 01-06-2012, 12:39 PM
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Default RE: Analog vs. Digital

If you insist on using HiTec then you will always have interference problems, the retracts have just highlighted it for you.
Running FPV with a 1watt Tx within 10cm of a HiTec servo and the circuitry burns out. I have had this happen numerous times until I twigged it was the HiTec servos.
Replaced them with JR and Futaba analogue and although the servos twitched they did not burn out.
Replaced them with Hyperion digital and all has been fine.
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Old 01-06-2012, 01:56 PM
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Default RE: Analog vs. Digital

Lots of comments and good information here.

Ok..so digital servos don't actually solve the problem.  They just mask it.  So...how does one actually fix the problem? How can one even determine the interfence is actually gone instead of just masked?

My servo leads are just long enough to reach.  Twisting them would make them too short so I'll just have to replace them.   

Put a capacitor across the points of of the retract motor could possibly fix.  What capacitor?  How would I hook this up? 

What the heck?  Hitec servos get interference?  Other less or not at all.  How come I've never read about this?

I couldn't find much with the "search" feature here.  All seems to stem from reciever interference or some type in cars.  Is there some thread that explains how to detect interference even when you're servos aren't acting up? 
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Old 01-06-2012, 02:37 PM
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Default RE: Analog vs. Digital

you might want to contact Gary Prince aka ram3500rcu and talk with him. he has had a fair amount of experience with D&L. He' currently working on a carf F4u-1 and using D&L for a lot of stuff.
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Old 01-06-2012, 02:56 PM
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Default RE: Analog vs. Digital


ORIGINAL: panhndl

I have some Hitec 645mg servos in my KMP T-28c plane. Finally got the electric conversion on my retracts by Down and Locked installed last night. Now my 645mg servos go haywire when working the gear. I find out that analog servos (or maybe more specifically, Hitec analog) are very susceptible to interference from other gear in the plane. Digital servos...nope. No problems.

So, I guess there is at least one more reason to use a digital servo over an analog one. Especially if you're using electric retracts in close proximity to the servos.

By the way, I think the interference is coming from the leads, not the actual motors, themselves. But I could be wrong. I'll know more tonight, but digital servo in the wings, it looks like.
I have never experienced interference between analogue and digital servo's in my planes. then again I fly futaba servo's

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Old 01-06-2012, 03:03 PM
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Default RE: Analog vs. Digital

Twisting wires is great for phone and network cables.

It does nothing for servo wires.
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Old 01-06-2012, 03:21 PM
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Default RE: Analog vs. Digital

Ring noise suppressors available at radical rc:

http://www.radicalrc.com/category/Ra...ugs-Wire-Etc-7
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Old 01-06-2012, 03:25 PM
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Default RE: Analog vs. Digital

Only try one thing at a time, then if it goes away then you will know.
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Old 01-06-2012, 03:46 PM
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Default RE: Analog vs. Digital

this on your 72mhg, or the newer 2.4?? and dont hitec 645s(of which i have lots, and they all work ACE!) come with a twisted lead?
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Old 01-06-2012, 03:59 PM
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Default RE: Analog vs. Digital


ORIGINAL: All Day Dan

I know those down and locked cost a fortune. If they are causing the problem, which they should not, I would not use them. Sorry, but I'm not trying to be a smart *ss. Our planes are just too expensive and hazardous to install something like that in them regardless of the servos you are using. Dan.
I have to agree here. If they are causing this problem who kinows what else they are interferring with? I watched a big warbird blow up a battery one time because of interference caused by a gas engine. The guy had something fail that put his bird on full throttle so he decided to continue flying it until he ran out of gas. About 10 seconds before he ran out (based on what was in the tank after the crash) his battery blew up a a 9 foot Spitfire went into the field. Being in the avionics field for almost 40 years tells me that you don't screw around with RFI - make Down and Locked fix it!
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Old 01-06-2012, 04:04 PM
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Default RE: Analog vs. Digital

The problem is EMF noise coming from the retract motors. There might be a grounding problem within the mechanism itself, maybe a loose wire. Question,, with all the servos connected, wings on, exactly which servos start to jitter. Is it just the ones in the wing or does the rudder and elevator move also? And where are the other servos in the fuse? Now also do a test by removing the wing and laying along side the fuse, cycle the gears to see if the other servos in the fuse jitter with the same intensity as the ones in the wing now that it is closer. I believe there is also a control module that the retracts plug into, then the module plugs into the RX. The problem may be in this controller also.
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Old 01-06-2012, 05:37 PM
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Default RE: Analog vs. Digital

I'm sorry.  I didn't say earlier.  Only the aileron servo's jitter when the retracts are working. The flap servos are not in yet so I can't comment on them.  The elevator and rudder servos don't have any interference.  Neither does the throttle servo.

I have performed a lot of tests which haven't really told me a lot.  I won't detail all of them, but Just to get an idea, no matter which retract is working, the aileron servos jitter.  It can be any one, two or all three and the aileron servos jitter. It can be the left main and the right aileron and it will jitter.

i can unplug the left aileron servo from the left rx, plug the left rx into the retracts, power each rx with completely seperate switches and battery packs and the right aileron will jitter. 

Not seeing anything consitant.  Oh, except that the digital servo didn't jitter, heh.  I'll keep playing with this.

thanks
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