Pete850

Hi,

Sorry if this is a dumb question, but when using two elevator servos is it better to plug them directly into the receiver and mix them on the radio or use one channel and a 'Y' lead and reverser?

It's just that I'm using a six channel receiver and if I need independent channels, I'll have to buy a new one.

Will I get more power from the servos by using two independent channels rather than sharing the current from one channel?

Cheers

Pete

hilleyja

My Feedback: (3)

You didn't mention what you had for a TX. If you have a radio like the Futaba 9C you could use their Ailevator function and some mixing and install servos on channels 2 and 5. If you have Hitec digital servos and the Hitec programmer you can reverse one servo with the programmer and install it in a simple "Y" connector with the other on channel 2. These are just some of your options -- again you didn't mention what you had for a TX.

As far as power is concerned: The voltage source to all servos and the RX is the same; it is a parallel setup in your flight pack. (Some giant-scale flyers use powerboxes to separate the servos's power from the RX.) Plugging 2 servos to one channel using a "Y" connector is the same as plugging 2 servos on separate channels. That is why you can plug your battery into any RX channel and even "Y"-connect it with a servo.

Pete850

I have a JR 652 TX and can mix the channels fine - my question is more about 2 servos sharing power from one receiver channel and if I would still get the full power out of each, or is it better to use two separate RX channels.

Thanks

Pete

rajul

My Feedback: (58)

It depends on what size plane you're flying them in, and whether they are digital or analog servos (digital draws more current). You can imagine the single extension wire having to cater for the current demand for two servos. Two separate channels will be better also if you need to do mixing. My 2C

Pete850

We're talking a 72" (27%) Giles 202 using JR NES591 ballraced servos rated at 5.1 Kg each.

The plane will be for general sports flying and "mild" 3D rather than the wild tricks some of you nutters get up to (I save those for the sim - much cheaper!!)

Cheers

Pete

rajul

My Feedback: (58)

Pete, go for independent channels. It will save you from headaches when you're setting up your elevator. Not sure about your Jr radio and rx, but I have a twin elevator plane using a 6-channel futaba rx with a 9c. Cheers

glowplug

My Feedback: (1)

In addition, using a Y-harness will make it very difficult to accurately & independently adjust the throw of each servo to get the elevators to move as if there was one servo controlling them. This could be a potential problem if the pushrods are not exactly the same lengths, and the control horns are not mounted in exactly the same location in relation to the hinge line.

Pete850

Thanks chaps - two channels it is then.

I love this forum..........

Cheers

Pete

famousdave

My Feedback: (61)

Here is my article on setting up split elevators [link=http://www.1tt.biz]HERE[/link]. If properly done you can use a Y with no issues at all. By using the radio to mix out errors in the mechanical setup you will never achieve perfect symmetry.

This is probably no big deal on a sport plane, but if you are flying a pattern or precision giant, it is critical.

Don't use a reverser either (they suck). If you are not using Hitec digitals (which you can program) use a Smart Fly equalizer or a JR matchbox to get a perfect setup.


DP

Pete850

Hi DP,

I've just read your article - some great advice there for mechanical setup, although I do try and set up all my linkages as accurately as I can for all my planes. You would be amazed at some of the horrendous setups I often see at our flying field.

I'll do what I can mechanically, but I don't have digital servos so will have to finish the setup using the radio. I can get things pretty accurate mechanically on single servo setups, but this is my first attempt at two servos for the elevator.

A simple method I was thinking of was to clamp some 12" strips of a fairly ridgid section balsa to either elevator half to act as extensions of the flying surface, and align these by eye first to get them level (radio on). Then move the stick in both directions and check the alignment of the balsa extension strips at both extremes of movement.

Sound feasible to you? (Bearing in mind I'm not a competition flyer)

Pete

RC-Captain

Trim memory eliminates alot of the issues you guys are talking about. If your radio has it use it.....

glowplug

My Feedback: (1)

I don't follow you, Fiend, what does trim memory have to do with it? [sm=confused.gif]

RC-Captain

Lets say you are using two servos for the elvator. Disconnect one then using trim memory for the channel connected to other servo, level the elavator. Before connecting the other servo go to trim memory for that channel and position the arm where you want it then connect it back to rod . If already mixed than you cant adjust the master with out adjusting the slave.

If using Y cord leave both servos connected, observing direction of travel for each servo, use trim memory to level the elavator. No matter where either servo or horn is mounted when trimming, both will move at the same time leveling the elavator.

RC-Captain

I tend to beleive the only benifit for using two servo is for stronger holding on tail ,elevator, or ailerons. I read on RCU where a guy used 4 servos for one aileron and 4 for the other.

As far as current whether Y or mixed the servos will drain the same amount of current.

glowplug

My Feedback: (1)

Fiend, I see what you're saying now......I haven't had that problem mixing the 2 with my 9C though....I'm able to use sub-trim & ATV travel on both the master and slave channels separately, so I can dial in the exact same throws. You've made a good point though, I'm sure there are other radios that have the mixing ability to mix the 2, but lack the ability to adjust them separately.

Ed_Moorman

My Feedback: (1)

If you are using 2 channels and mixing, use a mix that allows trim otherwise when you trim you'll move only 1 elevator.

As for power to each servo, the positive and negative leads for the servos all go to the same power line. They are all connected inside the receiver, so power-wise, it doesn't matter where a servo is plugged in. A normal Y should carry plenty of current for normal servo operation. For multiple digitals on the really big planes, you might need larger leads, but not for regular stuff.

The best reason for using 2 channels, as has been mentioned, is to individually adjust the centers and end points of each side. The same goes for ailerons. Use a flaperon wing type and set the center and end for each side, then set the flaperons for zero travel if you don't want them.

RC-Captain

On my radio this feature only operates for channels that dont have a trim. 3,5-8 There are technically only 4 trims on a radio, so sub trim is used for the rest. There is no trim memory for channel 3 , but to get the low end idling perfect I use the sub trim to close or open the carb.

mglavin

My Feedback: (31)

Utilizing TRIM and or SUB-TRIM may suffice BUT at the expense of precision and linear control movment and or create other problems. Best case setup is to utilize DP's method as referenced above. Mechanical setups that track or operate in unison is of primary importance before anything else is implemented.

The "other problems" are often realized as unequal surface movement at extremes and from neutral realized as a lazy or slower surface as compared to the latter. Match the mechanical setup first to minimize these undesirable results.

Utilizing trims and ATV or end-point will create a NON linear travel curve and or response from the surfaces, again resulting in uneven travel and speeds. Match the mechanical setup to minimize this behavior. Use sub-trim/trim as a last resort.

When implementing trims, mixes and offsets the control signal is favored one direction or is offset, the result is as mentioned previously NON-linear control with respect to stick movement.

RC-Captain

I don't understand what you mean when you say this....I have 2 servos operating my ailerons and I am using them as flaps also and the mix is contolled by the dial or a simple flick of a switch "D" and when the flaps come down they are even , when the flaps are up and are used as ailerons both move an equal amount in the oposite direction. Also when down I can use them as ailerons . So I beleive this is "linear " and I used trim mix and I beleive off sets.

mglavin

My Feedback: (31)

The control signal pulse width at neutral and or center ideally should be 1500us or 1500 micro-seconds and 900-2100us at end points MAXED out.

When trims are used to compensate for a servo that does not center at 90 degrees to the case, the control signal pulse width at neutral may end up at 1530us as an example. Therefore an offset is in place one side of travel center. The TX is unable to compensate for this less an adjustment with End-Point and or ATV. If you were to measure the pulse width of the TX once you had everything dialed in you'd likely see equal travel volume achieved with a pulse width similar to the offset noted at neutral. Subsequently its realized as a NON liner response to stick movement and the travel curve.

Additionally not all TX's are tuned and or mechanically setup to offer the desired 900-1500-2100us parameters. There are several factors at work here, to name a few; mechanical and electro mechanical tolerances and the actual condition of the TX's and its stick components. It very common to measure a TX's output signals and find this to be true...

RC-Captain

when you talk about micro or nano seconds , you are talking about movement that, can or will, not be seen with the naked eye. So if I mix flaps with a switch and then activate the switch, I agree there will absolutely be no way both servos will move at the same speed. If the mix is poorly done, as I have accomplished when I first attempted to set up the flapperons, you can actuallly see one aileron drop before the other.

Using an oscilloscope to adjust the servos for would be most desired, but also would be tedious. The scope could also be used to match any particular servo's movement giving you a better chance of making the set up linear.

mglavin

My Feedback: (31)

It's not the micro-second in of itself; it’s the combined total of same that catches up with you. The sticks recognize center and or neutral at 1500us or at least should. There is nothing you can do short of programming your servo to meet the TX's transmitted pulse signals neutral and end-points, whatever it maybe to alleviate the NON-linear travel arc that’s being transmitted.


Not sure what you’re alluding to with the O-Scope, are you suggesting the TX can be dialed in or that you could observe the control signal pulse width being transmitted?

There are devices available such as Hitec's programmer and other servo testers that dispaly the actual micro-second signal transmitted to control the servo.

RC-Captain

No we are reading the same page.

An oscilliscope is a electronic tool that can measrure Voltage AC/DC, frequency pulses, current, etc . Basically it is the best tool to use to get the best accurate results. Needed? Not really , but if you want to no the true speed of your servos and all other output measures it is the best way to go.

mglavin

My Feedback: (31)

I understand a little about an O-Scope I own an HP 4-channel 100mhz Digital Storage O-Scope and some other gadgets I purchased for playing with our equipment... My latest toy is a programmable electronic load with PC interface.

I was confused by your comments that alluded to utilizing a scope to dial in the servos. thus my inquiry.

RC-Captain

I thought when you started talking about LINEAR and NON-LINEAR I would mention a way to actually see if 2 servos are or not linear.

As far as the tools you have ,I dont have any . I have seen a guy with a program for monitoring batts, charge and discharge but never seen anything for measuring servo specs.