I am in the process of putting together a 35% Yak with a DA 100 to be used primarily for 3D. Just curious if anyone has any opinions about what to use for the throttle. I was thinking about going with just an analog standard servo on the throttle and on the choke. Is the analog standard servo okay or would it be better to use a digital servo? Or, does it not really matter?

Thanks in advance.

I use Futaba S3004 or even S3001 for all my servo applications. No problems yet. It doesn't require the crispness or return to center abilites of a digital. Carburators aren't that precise as to justify one (IMHO). It is the one place to save $. Just be sure to keep it well back of the engine, 10" or more, and connected to the throttle arm with a non-metal linkage like a nylon Gold-n-Rod, especially with EI.

There are various opinions about whether or not to use a digital servo for throttle. At least as of a 2005 posting, Mike McConville believes it's best not to. "Many people do. Its not the best idea though. The power consumption is higher and there is no advantage to a digital on throttle." (http://www.rcuniverse.com/forum/m_27...tm.htm#2729944).

Here's a quote, not from McConville, from a different thread - "Surprizingly, when building an 86" QQ Yak, Quique recommended using a coreless, non-digital servo with enough torque and speed. He says that is what he uses and that he has specific reasons NOT to use digital servo s on throttle." (http://www.rcuniverse.com/forum/m_63...tm.htm#6372027)

On the other side of the discussion, I've heard very experienced pilots say that digital servos are required for throttle in order to maintain a accurate, low idle. You'll find several threads that talk about the topic by doing a search on "throttle servo" in the Giant Scale - Aerobatic forum.

Not trying to pick a fight with you Charlie P. .... Whether or not non-metal linkage is required is a debatable topic. Quite a while ago, I asked Dick Hanson about using a metal pushrod or not and he said using a metal pushrod is fine as long as you isolate it by using plastic connectors on the ends. I use a metal pushrod with plastic ball links and do not have interference problems. I've seen several gassers with the exact same setup.

When looking for the McConville post cited above, I came across this from him - "Also be sure not to have any continuouse metal contact between the engne and linkage, i.e. use a plastic ball link to attach to the carb." (http://www.rcuniverse.com/forum/m_21...tm.htm#2232016)

As with practically anything RC-related, Harleyflyer, there will be opposing viewpoints. Hope the info is helpful.

Dan

I started out with a standard servo on the throttle--swapped out for a high-speed digital and it was really like night and day
Have used metal pushrods with plastic ends with no problems too--

No fight here. There's only so much you can fit in a post. ;-)

The reason, for those interested, is that the electronic ignition, or even the magneto, in gas engines can send "broad-wave" electronic pulses via induction into the servo windings that are then passed to the receiver. This can be glitch city (even with a resistor plug). Isolating the metal with nylon clevises is just another way around the problem. The arm of the servo also isolates it (unless you're using aluminum arms). I use Ny-rods or Gold-N-Rods. Lots of ways to skin a cat.

Aegis is right. There are always opposing viewpoints (even in his own post). The most important thing is to not have any moving metal to metal connections anywhere. (apart from electrical connectors and metal gears in the servos).

Personally I like the use of non digital medium torque standard type servos (such as HiTec HB 425's or 475's)for throttle and nyrods with plastic ball joints on the ends. I'm not a fan of plastic clevises directly onto the throttle arms because they can fail quite easily and the slop can give idling issues. This gives me peace of mind and it works for me

As quoted above, Quique does recommend the use of a fast, high torque, non-digital servos. Specifically, the 4721 and 4735.

I've used the 4721 on several airplanes and it has worked very well for me.

When going to higher voltage, non-regulated systems, such as the A123 batteries, I have to swap this throttle servo with a Hitec servo capable of taking the voltage. Currently experimenting with the HS -5645, which is digital.

i use a hitec hs 81. its small light weight and fast like .09 on 6 volts. as far as a choke i would say any standerd servo should be fine

If I am trying to save weight I use the HS81 also, On my latest 40%er I am using the new hs-5245mg digitals ( http://www.servocity.com/html/hs-524...ital_mini.html ) on my throttle and choke.

For throttle I use cheap light weight standard servos like Futaba S3004 or equivalent.

I'm not aware of a reason why one would use an expensive, heavy, high torque digital servo on the throttle unless you have a terrible installation with lots of drag on the push rod or you forgot to disconnect that powerful return spring from the carb throttle lever.

As for speed, don't you find that servo response on 6 volts is quicker than the engine can respond?

I think it really depends on the application size.

I would not trust a 35% plane with a 100cc engine to a standard low torque servo or a mini.

Saving $40 on such a large investment does not personally sound like proper risk management to me...

Wow! Thanks for all the helpful information! I appreciate everyone's input!