fast cyclic servos = fast throt servo ?

[aevans692]

hi guys

I am waiting for my new 8717 to come and was thinking , how fast do I need the throt servo to be ? If I am running fast cyclic do I need to match that speed?

Also there is probably a certain amount of lag from the engine, what I mean is if the throt opens from 50% to 100% say in .07 (that's an example) of a second that don't doesn't mean the engine will run from 50% to 100% in that time.. I would of thought that the engine would only reach 100% in a given amount of time no matter how fast the servo was .

( if that makes sense)

So would a 0.18 sec servo be ok ? as I didn't wana spend out for 4 8717's ..

[brgsstm]

Ive seen this debated before and never got a real answer. I think your right however as I would of thought that it is the engine that needs to respond quickly. But there is also the debate as to wether ot not the servo would hunt for the rpm if too slow.

who knows??

im running a S3151 on the throttle anyhow for now!

Tom

[rototiller]

I think most people would be amazed at how fast a nitro motor can change rpm. Listen to a pro driver, driving a 1/8 scale off road buggy. They blip the throttle for traction. Yes there running the fastest, strongest servos they can get there hands on and the motor follows with out any problem.

My throttle curve is at 68% in hover. my upright hover is 75%. By the numbers the throttle needs to travel farther than the cyclic but, I would bet that if you measuer both, the cyclic would have to travel farther to get to wide open. Plus the servo is maintaining rpm, not raising it witch might mean it doesnt have to go wide open to keep up.

DK

[brgsstm]

I think most people would be amazed at how fast a nitro motor can change rpm. Listen to a pro driver, driving a 1/8 scale off road buggy. They blip the throttle for traction. Yes there running the fastest, strongest servos they can get there hands on and the motor follows with out any problem.

My throttle curve is at 68% in hover. my upright hover is 75%. By the numbers the throttle needs to travel farther than the cyclic but, I would bet that if you measuer both, the cyclic would have to travel farther to get to wide open. Plus the servo is maintaining rpm, not raising it witch might mean it doesnt have to go wide open to keep up.

DK

I still dont think a 50 heli engine can change up rpm in less that 0.07secs. It would take longer than that for the extra fuel air mixture to be delivered to the cylinder. A car weighs a lot less than a heli and that only has a few small diameter wheels to turn. On a 600 were talkin not far off 1.5metres of carbon fibre to spin faster!

I agree though that it is probably quicker than one would imagine.

[aevans692]

I under stand that the response of a nitro engine is going to be fast but there is still lag, as mentioned but how much and how fast does a servo need to be to keep ahead of the game.

I would think even a 0.18 servo would open the throt quicker than a 8717 could change the collective moving the same distance, as there is a lot more resistance on a spinning rotor head and their is next to no resistance on the throt.

I would think that a fast throt servo would not be needed.. but I could be wrong, If it was too slow then I think you might get huntting

[rototiller]

I still dont think a 50 heli engine can change up rpm in less that 0.07secs. It would take longer than that for the extra fuel air mixture to be delivered to the cylinder. A car weighs a lot less than a heli and that only has a few small diameter wheels to turn. On a 600 were talkin not far off 1.5metres of carbon fibre to spin faster!

I agree though that it is probably quicker than one would imagine.
1/8 scale buggy is over 8lbs. Yes the heli spins a big rotor but, the cars only have .21's. 40,000 rpm 3.5 hp .21's but, .21 none the less. Pushing all 4 tires

At 16,000 rpms there are 266 rpms/sec. Most run there hypers at 17,000 rpm ???

DK

[miami6]

why not just use another 8717 on the throttle on 8volts

or an 8900g tail servo on 5.1-5.3

or a 9257 tail servo on 5.5-6.0 volts

[aevans692]

I didn't want to get another 8717 to run the throt when it is probably not going to make any diff on the responsiveness of the engine . even if you could open the throt instant there will still be some engine lag, what i really needed to know is that will I see any diff from 0.18 to 0.07 servo..?


Regarding the last posting , I think that 40,000 rpm for an engine don't sound right to me.....?

[lovespicyfood]

Why not get the servo adaptor plate and run a HS81mg? That's what I'm going to do. It's cheap too! :D

[rototiller]

Regarding the last posting , I think that 40,000 rpm for an engine don't sound right to me.....?

http://www.amainhobbies.com/product_info.php/cPath/1_23_31/products_id/6406

You should hear them, they sound like a bunch of bee's on heroin shoved in a jar !!

Specs are at the bottom.

I would think there would be hunt with a too fast servo. Kinda like too much gain on a gyro?

DK

[Street Flyer]

Well I run 8717s all around except for rudder. From my understanding, you want a throttle servo as fast as your cyclic so that's why I have an 8717 on my throttle.

There was a war on here about this a couple months ago.

[jpolidore]

I read that war and the conclusion I think described it best was, the throttle servo was only moving about 20% of it's throw, as opposed to the cyclic moving anywhere from 50 to 75%. Think about it, if you go inverted, which would be the most travel of the cyclic probably over 50%, your throttle may only move 10%, based on the fact that to go inverted you would need a stout curve or a governer. 10% at .15 secs is really fast, then again so is 50% at .06 sec. The Math may be really close. I am putting the hs-81mg on my throttle anyway, cheap and fast.

[Street Flyer]

Your probably right. Originaly I was going to use a 9452 on throttle for $80 but for $20 more I could use the same thing on my cyclic and throttle so I thought why not.

[brgsstm]

I would think there would be hunt with a too fast servo. Kinda like too much gain on a gyro?

DK


Yes i think this is the key here! To be honest i think that this one will never be ironed out and it realy comes down to preference. I myself am happy with a S3151. If I ever get to a level like Szabo i think i will swap it out!! (:rolling)

Tom

[Pinecone]

I read that war and the conclusion I think described it best was, the throttle servo was only moving about 20% of it's throw, as opposed to the cyclic moving anywhere from 50 to 75%. Think about it, if you go inverted, which would be the most travel of the cyclic probably over 50%, your throttle may only move 10%, based on the fact that to go inverted you would need a stout curve or a governer. 10% at .15 secs is really fast, then again so is 50% at .06 sec. The Math may be really close. I am putting the hs-81mg on my throttle anyway, cheap and fast.

10% of travel with 0.15 second servo is 0.015 seconds.

50% of travel with 0.06 second servo is 0.03 seconds.

Throttle wins. :)

HS-81 sounds like the trick to me. Small, light, fast, cheap. Can't beat the 4 way parlay. :)

Or HS-5082 digital if they ever ship.

[aevans692]

Yes but what about the engine lag because the throt opens at that speed that does not mean the engine will . .

I might get that servo adapter . . lol just incase lol..

[brgsstm]

I might get that servo adapter . . lol just incase lol..


Whats this? what does it do?

[rototiller]

I like the hs 81 idea but, I have a 2100 2cell in there and its on the verge of tail heavy. If I lost the weight of the full size servo it would be even more tail heavy.

Before anybody say's it, yes I was planing on getting a bigger pack anyway. :)

DK

[jpolidore]

http://www.readyheli.com/HN6070_Carbon_Fiber_18G_Servo_Adapter_Plate_TREX_6 _p/hn6070.htm

That my dear young man is the Throttle servo adapter plate, allows you to use a mini servo on the throttle like the HS-81mg here are the specs on that:

http://www.servocity.com/html/hs-81mg_micro.html

as you can see the 81mg has a speed of .09 sec and 42oz-in of tourqe and a $23.49 price tag along with the mount of $6.95 you are at a whopping $31 bux with a really fast throttle servo. The only drawback I see is its analog not digital, but then again I could not tell the difference in flight.

[invertmast]

General consensus i give and have been getting from people, is anything under .20 sec. on the throttle is fast enough.

[rototiller]

I just read in the Molti-gov instructions that any thing in the .10 to .16 is great. Digi is a plus.

DK

[aevans692]

I am running 0.18 on throt at the mo, should squeeze that down to 0.15 when i am all 6v ed up ...

[I want it]

I'm running the 9451's on cyclic and throttle do i know if its really fast well uh no but hey i had the sevro laying around and used it. well i got five of the 9451s for my b-day so in go four of them right away.

[fiveoboy01]

I'm running a Futaba S3155 mini with an adapter plate.

I do understand the argument that you're only using the upper half of the throttle throw, so speed ins't so important, but this is NOT always the case.

Let's say you're doing a fast downwards descent, with a lot of negative pitch. The limiter/governor is closing the throttle a LOT to prevent headspeed from going through the roof.

You punch collective at the bottom, and now we're talking about more required barrel movement than if you were doing power sapping maneuvers such as tic-tocs where the barrel is wide open a lot of the time.

I'm not convinced it's required to have something like an 8717 on the throttle but I definintely think it needs to be a fairly "quick" servo.

[ruby903]

I'm thinkin about building a 600 N and I have four (4) 8717's ..... Is there anything wrong with using one on the throttle?