JR8717 servos

[burke.bill]

This is for the guys who use the JR8717 servos?

I am plan on using them on my 600n, I would like to know what your using on throttle? I will be using the Multi-gov and don't think the JR8717 is needed there? Going for the GY611 and 9256 for tail. Thanks for advice. Bill

[Street Flyer]

Just bought four jr 8717 servos. I will be using one on the throttle, but from what I hear it isn't needed as far as torque. I have heard that you do want a servo simalar in speed to your collective servos.

I bought a multi gov for my 600n and a 611 and 9256.

[kgfly]

You might find this interesting: Mythbuster: Need a fast throttle servo

[burke.bill]

Read the myth good reading kind of knew that. I will be using the Arizona reg and would like a throttle servo that will run on 6V don't know if my Futaba 9252 will handle that. That's one reason I was thinking of useing a good JR servo other than the 8717 any idea's with this in mind?

[kgfly]

No, sorry, don't really know much about servos for 50-size nitros other than what I read, my fleet is all electric.

[Jason Bell]

9252s work fine for throttle, even on 6V. It works on 6V because its regulated, when futaba tests there stuff for 6V, they refer to a 5 cell nicd pack, that when fully charged will go up to like 7.2 Volts.

Futaba 9452, Airtronics 94758z, Jr9000, Jr 8717, even a Futaba 9254 would work great for throttles.

[VegasBob]

Why not just spend $20 more and buy the 8717 for the throttle servo. $20 on a $1500+ machine is background noise. Besides, I'm a Chemical Engineer and I've seen strange things happen in control loops and system controllers when you start mixing stuff of different speeds, electronic configurations, and manufacturers. Why not make your life easier for 20 bucks and buy the 8717?

Bob-Las Vegas

[VegasBob]

Saw Danny Szabo fly his 600N with Futaba BLS451 servos today. Somewhat slow compared to the JR8717s his brother Allen Szabo uses. I think the JR8717 is the new high performance servo... at least for the next few weeks until something faster comes out.

[Jason Bell]

LOL!

Yea nothing can touch the 8717s. Its not only the speed, but its the torque as well.

[george0079]

edited

[kgfly]

Because $20 is $20 and why waste it on an over-spec servo when it could go towards something useful like spare parts or extra fuel or some after-flying refreshment ?

Your vague discomfort with mixing bits is in this case IMO completely misplaced. There is no inappropriate mixing of dissimilar components when you use a throttle servo that differs from the swash servos. If your argument was compelling you would use an 8717 on the tail instead of a more appropriate tail servo.

This is a hobby and folks should do what makes them happy, but IMO there is no particularly good reason to use a more expensive component when a cheaper one is actually better suited to the job.

[VegasBob]

Originally Posted by kgfly

Because $20 is $20 and why waste it on an over-spec servo when it could go towards something useful like spare parts or extra fuel or some after-flying refreshment ?

Your vague discomfort with mixing bits is in this case IMO completely misplaced. There is no inappropriate mixing of dissimilar components when you use a throttle servo that differs from the swash servos. If your argument was compelling you would use an 8717 on the tail instead of a more appropriate tail servo.

This is a hobby and folks should do what makes them happy, but IMO there is no particularly good reason to use a more expensive component when a cheaper one is actually better suited to the job.

Sometimes electronic devices are very complicated and don't work if one component is slower than another.

That said, unless you are highly educated in the field of control systems and have a crystal clear understanding of partial differential equations, ordinary differential equations and elementary calculus, your opinion is anecdotal and unadvised at best.

But if you have no value for your time, save $20 and try to solve some complex differential equation so you can fly your 600N without some sort of throttle collective lag glitch .

I’ll gladly pay the 20 bucks so I’m not bothered with some elaborate partial differential equations feedback loop problem.

My time is worth more than 2 cents an hour.
Maybe yours isn’t.

[kgfly]

"Fun, Learning, Friendship and Mutual Respect"

Bob I did not attack you I simply expressed a different opinion. You are entitled to your opinion as I am to mine.

As it turns out, I have over 20 years experience in engineering working with advanced electronics and a masters degree in control systems, I just don't trumpet it around. So I am not intimidated by your references to science, electronics, engineering, calculus, differential equations or control theory. I understand both the theory and practice of control systems and it is my opinion that you are completely wrong about the potential for feedback control problems by using servos with different characeristics between the throttle and the swash.

For one thing there is no correlation in the either the speed of motion or the range of motion required between the two controls. For another, the control loops involved have very different characteristics involving the different mechanical arrangements, the different programming in the Tx and of course the human part of the feedback system.

With a great deal of work one could perhaps perform model identification on a specific R/C heli and then attempt to solve the equations to determine the optimal performance requirements for the throttle servo, but as you suggest, it is a complex and difficult job and would not be generally applicable to other helis. However most importantly, it would be a complete waste of time and is totally unnecessary.

Apart from any theoretical analysis of the system, there is overwhelming empirical evidence that it works perfectly well. Thousands of nitro heli pilots fly with what you might consider mis-matched servos between throttle and swash and never experience any wild or bizarre control problems as a result. Nor is it a performance issue, so long as an appropriate servo is selected, and you will find many of the world's best pilots flying "mis-matched" setups.

So as I said, before, if it makes you happy then spend $20 extra and use matched servos. That doesn't mean it is the only way or even the best way, just your prefered way. IMO time spent on a hobby should not be measured in dollars/hour or else it's not a hobby.

Happy flying.

[justahobbie]

Wow I like how people use all these big words to try and throw attitude when the guy is just trying to save some money.

To the guy that just needs a question answered... I am a co-owner of a LHS. I have a brand new 600N, 8717 servos, 7703d gyro with the 8900G, Hyper 50, the whole package. I get it at wholesale. And I like the best even though I am by no means a pro heli pilot. I'm using a $14 JR Sport ST47 on my throttle. Partally cause I ran out of 8717's, and I didn't want to use Futaba I had sitting on the shelf(I'm anti Great Planes at the moment. Shop onwer/distributor relations issues. And I know, I used a GP exclusive engine. Oh well.) Not trying to brag, but you just don't need it.

I was kinda worried about it, but remember, when you go from full positive to negative pitch, or vise versa, your using 100% of you control throw. In any mode when your actually flying like that, your throttle curve will be so high I bet your only using about 20% max of the throw on the throttle servo, so the lag will be minimal. Most people I fli with run about a 100-85-100 curve, so thats 15% of the travel. It will seem like it almost matches the collective servos cause it doesn't have as far to go. Unless your in normal mode in a hover and you want to punch full collective (the only time I notice the lag) your not going to notice a slow throttle servo. And given the nature of the question your not a pro so I really wouldn't about it.

And I don't care who you are, what you know, how long you went to school, your salary, or what big words you try to throw at people on the internet to try and make people feel like an idiot. A slow throttle servo working in conjunction with fast collective servos WILL NOT cause RF noise, feedback in a radio system, or inferance of any kind. It will cause nothing more than a slight hesitation in your engine as it tries to rev up under the load of the increased pitch, which will take less than a second anyway.

Go buy a cheap, fast, reliable HiTec or something. That's what I'm ordering in the morning. A 160oz throttle servo is rediculous unless your a good enough pilot to notice the difference.

And don't humor that guy. If his time was really worth more than 2 cents he wouldn't be sitting here trying to egg you on.

[Mercuriell]

Well said Ken - a Futaba 9252 is cheap and sealed against oil ingress - it works fine on regulated 6V - some people have reported bad experience of them as throttle servos - I used a Hitec 6635 as it was cheaper than my cyclic 6965 servos and doesn't need power or blinding speed.

[Pinecone]

And of course he never mentioned trying to adjust engine response (which is really the important parameter) to the collective servo speed.

[Jason Bell]

Also Just remembered that you REALLY DONT need a fast servo. Once in idle up, you are already limiting the throttles range of movement by half or greater, even 1/4 of its travel . 9252, 9452 will do the job just as fine as a 8717, or a 9254, 94758z

[cbdane]

Originally Posted by VegasBob

[SIZE=2]That said, unless you are highly educated in the field of control systems and have a crystal clear understanding of partial differential equations, ordinary differential equations and elementary calculus, your opinion is anecdotal and unadvised at best.

[Finless]

Funny... stuff....
Reminds me of one time when a 30 year real pilot came out with a pretty nice RC airplane. We could tell he was a n00b by his actions so we asked him if he needed any help. With a HUFF he said know I have been a profiessional pilot for 30 years! I am sure I can handle a RC airplane. His flight lasted maybe 15 seconds!

You don't need a fast servo for throttle. Heck the engine does not ramp up near as a fast as even a slow servo and as torkboy says your in idle up etc so you wont be trying to fully open and close the throttle anyway.
I am using a 9252 because I had one handy... Used that on throttle many times on many heli with different govs and no govs.

So feel free to use a cheaper servo just make sure it is heli rated so fuel and vibrations don't kill it

Bob

[VegasBob]

The only point I’m trying to make is that control systems are very complicated and for 20 bucks on a $1500+ system, why take a chance? I like to save money as much as the next guy but from my experience this is not the place to save. I just recently got back into this hobby, (started back in 1979…American Mantis) and know very little about current RC helicopter technology. I’m probably even wrong on this issue. However, I do have many years of experience with process control systems and have spent countless hours trying to make them work. For 20 bucks, I’m not going to take a chance my $1500+ system has some sort of glitch that takes me 40 hours to figure out.

Just my opinion. Do what you want, it doesn’t effect me.