Nitro newbie has some questions...

[Ray K.]

Truth be told, I'm not even a newbie... I don't have any nitro birds, or experience, yet.

My questions have to do with servos, though.

I understand that while using a governor on a nitro engine, it's a good idea to use a really fast digital servo. I'm in the process of spec-ing out a TRex 600N, and I'm trying to choose servos. I'm pretty certain at this point that I'm going to use a governor, and probably a mixture regulator too. So....

1- For the throttle servo, I know that it should be fast and digital. Does it have to be particularly powerful, though? I'm having a hard time imagining that the carb takes much muscle to actuate. If it doesn't have to be especially strong, then why go with a super high-end servo? I've seen reviews in magazines where people have used what would normally be a rudder servo.... seems kind of expensive to me. If I don't have to spend $100 on a throttle servo when a $50 servo will do, then I won't. Am I missing anything here?

2- And I guess it's pretty much the same question- for the mixture servo, does that have to be anything special? I figure something light and cheap should be adequate... Again, am I wrong?

3- Any opinions on a CY MP5 vs. Align's .50 pipe?

Thanks for your time, guys!

-Ray

[mondo100]

I use a micro servo which is metal gears, not digital and has a 0.13sec 60' speed with my multigov and it does the job just fine.

[TheBum]

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1- For the throttle servo, I know that it should be fast and digital. Does it have to be particularly powerful, though? I'm having a hard time imagining that the carb takes much muscle to actuate. If it doesn't have to be especially strong, then why go with a super high-end servo? I've seen reviews in magazines where people have used what would normally be a rudder servo.... seems kind of expensive to me. If I don't have to spend $100 on a throttle servo when a $50 servo will do, then I won't. Am I missing anything here?
The speed of the servo depends on your goal. I do all sport flying and have no desire to do hard 3D. I use a Futaba 3151 on throttle and it works great. It's not terribly fast (0.16 sec @ 6V), but it's done the job quite nicely thus far connected through my Multigov.

2- And I guess it's pretty much the same question- for the mixture servo, does that have to be anything special? I figure something light and cheap should be adequate... Again, am I wrong?
A lot of people, myself included, are using an HS65 for mixture control with good results. Since there's very little stress and you're not liable to damage it in a crash, you can cheap out and get the HB model with the Karbonite gears.

[Ray K.]

Very helpful guys, and thank you!

I was at the field this weekend and asked the same questions, and everyone's answers jive. There were, however, a couple folks that were trying to talk me out of a mixture regulator, citing that it's just one more system that can fail. While I understand and endorse that logic, it seems to me that the benefits of a mixture system outweigh the downsides. Improved performance and fuel efficiency and a near-perfectly tuned engine at all times is a very attractive option for me, especially considering that I have no applied experience with nitro engines. I would like to get into at least moderate 3D, and having a powerful and reliable power system is a pretty high priority for me. If such a system adds a few grams to the heli, I can deal with it.

With the progress I've been making with my 450, it'll probably be about this time next year that I'll be dabbling with 3D. I've got all upright orientations down cold, and backwards inverted flight is beginning to get a little more comfortable for me now. I did some pretty decent aerobatics last weekend, too- my first-ever outside loop, a pretty messy death spiral, and some nice loops, rolls, and multiple rotation stall turns. Did some not-so-great stationary rolls and flips too... So it's coming along.

Thanks again for the advice, guys!

-Ray

[Pinecone]

Actually remember, the engine can only respond so fast, so a super fast servo will not increase throttle response.

[Ray K.]

Ah, Pinecone to the rescue again! You've helped me before...

Anyway, I completely understand what you're saying. Do you have any recommendation on what a good speed threshold would be? For example, is anything faster than, say, .12s so fast that it won't make any difference? I intend on using an OS .50 Hyper, if that's any help. I'm still unsure about what pipe I'll be using, but it's likely to be a high-end unit, so I don't think that it should make too much difference on the throttle response.

While we're on the topic of governors, how exactly do they work? I mean, I know that they use a Hall effect sensor and magnets to determine the engine RPM and adjust the throttle accordingly, but do they work simply as a limiter or will they attempt to keep the RPM constant whether it be too fast or too slow? I've never really gotten a straight answer from anyone.

Thanks man!

-Ray

[Espeefan]

Governors keep the engine RPM constant, while the head is loaded and unloaded. Changing the pitch quickly, during 3D flying, continuously loads and unloads the engine, depending how much is used. If you go -8 degrees to +8 degrees, the engine unloads around 0 degrees, and it would have a tendancy to over speed, but a governor will reduce the throttle as it senses this, so the head speed remains more consistant, given you've set it up properly. Basically, setting up a throttle curve in the radio does the same thing. Heli radios have programmable curves so that you can specify how much throttle you want at the far ends of the pitch curve, and everywhere in between. Naturally, as the pitch increases, the engine needs more throttle to maintain the head speed, so that it doesn't bog down. You can fly without a governor, but it takes a little longer to get the throttle curves dialed in. Governors make it a lot quicker and easier, since you more less tell the governor what RPM you want it to maintain, and it does the best it can for you. You should still set-up your throttle curves because if the governor fails in flight, you will then have a back up.

[Pinecone]

I plan on putting an HS-81 or HS-5085 in my Vibe. Should be more than fast enough.

[forjer]

I plan on putting an HS-81 or HS-5085 in my Vibe. Should be more than fast enough.
Good to hear. I've just fit an HS-81 on my 50.