Throttle Servo location ?
 

I was wondering why lots of folks seem to place the throttle servo close to the engine ? It seems that this violates the practice of providing separation between the engine and radio and provides an electrical path for noise to get back to the rest of the radio components.

Wouldnt it be better to use a non-conductive pushrod (like a nyrod) and place the servo aft with the other radio gear?

Just curious -

Thanks, Eric

RE: Throttle Servo location ?
 

Yes, it would be safer to place the servo farther away from the engine and ignition box.

But, people put their servo next to the engines all the time and get away with it. I can't get away with it. I've had 2 instances where having 9" or 10" of seperation was not enough to get a good range check. Seperating the components to more than 12" solved the issue.

I think it's one of those things where you take your chances. I've got to the point where I won't do anything less than 12" seperation. It just doesn't work for me to try and get things any closer. I get mad when I put a servo or switch too close to an igntion piece and then end up with RF problems. I have to tear something apart and do it over. [:@] So, I don't set myself up to fail anymore. 12" rule applies to everything now.

It's not always easy to get 12" either.

RE: Throttle Servo location ?
 

I agree with the 12 inch rule but in some situations you just cannot get 12 inches. So what you do is use Ferrite chokes (H9 calls them RF filters) within 4 inches of the receiver and that will solve the problem. I use Ferrite chokes on all my gas powered planes where having a power box that does it's own filtering just is not called for.

Comp-Arf planes are famous for having the throttle servo mounted on the "engine dome" (what they call it) either inside the dome or underneath. Heck the 2.3M Extra has the ignition battery on one side of the mototr dome along with it's battery on a mount that puts it right behind the front of the cowl and the receiver battery on the other side of the motor dome on the same type of mount along with the throttle servo inside the motor dome. You now have at least 2 places to get RF back to the receiver (servo and battery pack). It's the only way to make it balance using the recommended engine setup.

The Gp Super Stearman is another example of there is no way you are going to get 12 inches seperation

RE: Throttle Servo location ?
 

Going to the Hangar 9 site and entering RF Filter in the search window brought me to nothing. On the other hand, Horizon Hobbies listed two such RF Filters, both made by JR. Looks good. Sooo, do you use one of these per servo lead? Thanks for the heads up on this!

RE: Throttle Servo location ?
 

I apologize, they are JR not H9.

http://www.horizonhobby.com/Products...ProdID=JRPA029

Yes, you use one per connection. You will need to wrap the wire around it a minimum of 3 times so add roughly 4 to 6 inches to the length of any extensions you need

If you want to see an example. Download this manual and look at the radio installation section on page 26

http://www.composite-arf.com.hk/arf/images/1080823178661-2.3_Extra_manual_(v1.0).pdf

RE: Throttle Servo location ?
 

The 12" rule is a good one, but better radios, better ignition caps, weight and balance, and linkage geometry frequently takes precidence over the rule. As one that nearly always has the throttle servo well within 12" of the engine or ignition system I know it works, but solid range checks determine whether or not it flys that way. The use of Nyrods for throttle linkage worked well most of the time when the amount of exposed and unsupported Nyrod was only a couple of inches, But gassers often have the linkage quite a bit farther out than the Nyrod can be supported. Rigid linkage also provides more accuracy in throttle trims and motion and does not easily bend under linkage loads.

Use the method that best suits the installation and that provides a clean range check with the engine running.

RE: Throttle Servo location ?
 

Good sanity check - thanks guys !

RE: Throttle Servo location ?
 

Any of these look familiar? Horizon only charges ya $8 apiece. :eek:

http://www.allelectronics.com/cgi-bi.../Ferrites.html

[sm=thumbup.gif]





I've bought these before, but it's just not worth the money when you can buy the same thing for $1.50 each from www.allelectronics.com
http://www.horizonhobby.com/Search/D...JRPA028&CatId=

RE: Throttle Servo location ?
 

That surprises you ?;)

RE: Throttle Servo location ?
 

Horizon ripping modelers off? Nope. Not a bit surprised. [:@]

I'm always on the hunt for cheaper stuff thats the same thing. I made a couple orders from that electronic place in my previous post. They treated me good. Delivered it when promised. Emailed the tracking info to me. Emailed the order # and info to me after I placed it. I'll be shopping there more often.

RE: Throttle Servo location ?
 

I think I'll be placing an order at the electronics shop instead. I use quite a bit of these due to intermittent RF issues beyond our control where I fly at. Once I went to using the rings, all my problems went bye-bye

Thanks for the link Rcpilet, that really helps

RE: Throttle Servo location ?
 

For those long unsupported Nyrod installations I have inserted the outer Nyrod housing in close-fitting aluminum tubing. You can go a long way between suppports with this arrangement. I have one in an open cockpit model that looks pretty decent.

Bedford

RE: Throttle Servo location ?
 

RCPilet--Thanks for the link on the RF. Looks like they have several--do you have a preference? Thanks

RE: Throttle Servo location ?
 

Guess I've been lucky;), I usually place my batteries, ignition and throttle servo all within a couple of inches of each other and have yet to have a problem. No chokes filters, magic boxes, etc. Always have excellent range checks to boot. I use CF rods with ball links, very positive and they never change my trim settings d/t expansion like some ny rods. All equipment used is of high quality and I imagine that is a contributing factor also.
That being said, please follow the manufacturers recommendations for separation.

RE: Throttle Servo location ?
 

I like the grey one near the bottom of the page. It looks exactly like the one from Horizon.

http://www.allelectronics.com/cgi-bin/item/FB-46/235/FERRITE_SNAP_BEAD_0.36%22#34;ID,0.87"#34;OD_X_0.66 "#34;L_.html

RE: Throttle Servo location ?
 

Has anyone actually connected a servo directly to the throttle? That is, coupling the rotating servo shaft to the throttle shaft without a translational linkage. This approach would be akin to the couplers used in the RDS system for controlliing surfaces with torque tubes instead of conventional linkages. John

RE: Throttle Servo location ?
 

Not that I'm aware of, but I know of numerous instances where a metal servo mount was made that replaced the diaphram cover on a gasser carb, thereby driving the carb lwith inkage only an inch long....

RE: Throttle Servo location ?
 

Yes, it used to be called a snake drive. Basically it was a speedometer cable attached to the servo out put shaft and butterfly shaft.

RE: Throttle Servo location ?
 

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The old saying, "Ignorance is Bliss" comes to mind.

For those not electronically educated folks, the obvious solution would be to mount your gear wherever you wanted and then use a PCM receiver to sort it out.

Being electronically ignorant, they are not aware of missed/masked frames, etc. To them, in their trouble-free world, the model flies just fine. They are unaware that their model is flying on far less than the normal amount of control inputs. They laugh at we worry warts - after all, aren't they having perfect results?

Their smiles will quickly disappear if someone sues them after an accident with serious injury or a fatality. The prosecution will reveal their incompetence to the jury and blah-blah-blah...


Ed Cregger

RE: Throttle Servo location ?
 

If it will pass a proper range check, it will work. period.

RE: Throttle Servo location ?
 

We get some OUTSTANDING range checks with our throttle servo arrangement[8D]

RE: Throttle Servo location ?
 

I hope I am not showing too much ignorance here. I have experience with glow and electronics, but not with gassers.

Do you have any pictures of the set up you use with the servo mounted on the carb? And related to that, some of the carburetors I have seen have fairly strong return springs. With such a low-slop coupling to the servo, can the springs be exchanged for springs with lower tension or even removed? Thus, one could use a smaller, but still high-quality servo.

RE: Throttle Servo location ?
 

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Without a frame counter in line with the servo outputs, you don't know if all of the baseline pulses are there or missing.

As was mentioned in a previous article, we live in an analog world, not a digital yes or no world. PCM is not able to decide diddily, but if you are not high performance aware enough to miss the control input frames yourself, you could be flying on less than fifty percent of the inputs you are making and just blaming it on yourself for getting old(er).

To avoid situations such as these, move up to 2.4 GHz. Their much wider modulation envelope will minimize the effect of audio frequency interference (engine ignition noise) and will relegate the artifacts to a much lower power domain.


Ed Cregger

RE: Throttle Servo location ?
 

ED, for several years of flying my B-17 I've never had range or percieved dropout issues with my 10x on PCM. There may be some frame dropouts here and there but I've never known it. Not having a glitch counter on board, it'd be silly of me to say that it's not an issue but I'm confident that after well over 200 flights with this setup at many different flying sites I feel safe.
What's most unusual however is the fact that each G-23 gas engine has it's own throttle servo mounted <ON> the engine and connected to the receiver through a "Matchbox" and about 12 feet of wiring. The only glitching I ever had was when, during routine maintenance I inadvertently pinched a servo wire under an engine mount and broke the insulation. The aileron servos twitched intermittently....that was the only indication that something was wrong. Fortunately the problem showed up during preflight.
Mitch

RE: Throttle Servo location ?
 

I'm not sure if you want pics of servos mounted "on the engine" as the post about that was after your question, if it's pics of servos mounted close the the engine then here you go... ;)

The first pic is the throttle servo mounted in the Hangar 9 provided location with the servo arm inside the engine box and the control rod comes through the firewall for the throttle. The second pic is the choke servo mounted on the bottom of the engine box.