Heli build tutorial.

[thayghetucsb]

Hi guys, i've been puzzled with the electronics to build a new heli. Is it strictly based on the size of heli (450, 500, 500, ect) or some thing else? For example: Exi 450
1. Motor: how would i know the power needed? What Kv means by the way.
2. ESC: i guess this depend on the motor choice. But how would one estimate this?
3. Cycle servo: do i choose based on response time? Torque? Weight? Which is more important over others?
4. Tail servo: what specs do i look at when choosing one for this? Always go with digital or analog is also ok?
5. Gyro: i'm clueless on this too.
I guess i can always copy others' set-up list but i'd like to expand my understanding a little further. In nuttcase video building his EXI squadron, he used 4 of the raiden 12.3g for servo. Then i've seen other used the 9g for cyclic and digital one for tail. How would one decide which is appropriate?

Thanks guys. And it's good to see you guys on this new forum where helping other fellow fliers is top priority, NOT SALES.

[akent]

Hi Thay...:

These are all indeed hard things to figure out!

The motor needs to have enough power to lift the thing, but the rpm's are important, too.
The KV is the relationship in RPM to Volts. A 3,500KV motor for example will turn 3,500rpm per volt. How this is derived, I don't know, as these are driven with PWM (Pulse Width Modulation) in 3 phase from the ESC.
How they come up with power, it has to do with the current draw. So, the more current a motor needs, the more power it will drive the heli with, times the efficiency rating.
Most brushless motors fall into the 80-90% range there.
How that equates to horsepower, I don't know. I have not looked into that, nor seen any charts pertaining to that.

The motor draw determines the size of the ESC that you need. Plain and simple. You need to oversize a bit from the max current a motor can draw.

The cyclic servos don't need to be really fast. They need to have the power to lift the swash together (in an eccpm heli), so this alone cuts the power needed by one third. What I have learned is that if you have a kilo (a couple of pounds) of servo power, this is plenty, and around 1.5 milliseconds for 60 degrees is more than enough.

The tail servo is critical, I have found out. The gyro will compensate very quickly, and if your servo is too slow, it will cause tail wag on you. The consensus seems to be that the tail servo needs to be faster than 0.1 seconds for 60 degrees. The faster the better. The faster this servo is, the more gain you can use with the gyro. The power of the tail servo is also an issue, but alas I don't know what that needs to be. This seems to be an issue with only 3d flyers.

The HH gyro is the key to the tail. There are a million of them out there, and the Futaba 401 seems to be the defacto standard. These run around $150. There is a new clone that costs about $25, but I haven't used one yet. The reviews are excellent though.
I am running an Esky 704B gyro, and it does drift. Drift seems to be the problem with less than good gyros.
Drift example: If I bring my Exi up into a hover, after maybe 5 seconds, it will slowly drift left. I need to then correct. It will hold for another 5 seconds or so. I need to add rudder trim to correct this, but this should not be necessary, as in normal gyro mode, it holds fine!

This is just what I've learned.
I hope someone chimes in with more detailed and/or better info.

Take care,
Kent

[Doozer]

loads and loads of info out there on this, and you'll get many different answers with many different and good reasons why you should use what they say you should. It all comes down to budget and flight style. You can make analog 9g tower pro servos work in anything from a HBFP to a CCPM 450. It really depends on how you are flying or plan to fly. If you are just starting out, seriously I'd go with something that's cheap to replace. The reverse argument to that is, cheaper equipment is more prone to failure and less responsive.

As far as motors go... listen to this podcast media.libsyn.com/media/insideheli/ATTF_79_-_PSC_QA_with_a_side_of_wet_stone.mp3 and this one media.libsyn.com/media/insideheli/ATTF_23_-_JustGoFly_Interview.mp3 I have a JGF motor in my 450 because of this podcast.

I listen to the Allthingsthatfly podcasts religiously now. Tons of info for the beginners and advanced flier as well.

Heres another good website for motor info: www.innov8tivedesigns.com/

Servos: media.libsyn.com/media/insideheli/ATTF_28_-_Servos_and_Trim.mp3 and this one media.libsyn.com/media/insideheli/InsideHeli_44_-_AMA_Show.mp3

ESC's and BEC's - media.libsyn.com/media/insideheli/ATTF_22_-_Castle_Creations_Interview.mp3

I could do more legwork for you if you need me to. But hopefully this will start you off in the right direction. I can read until my eyes bleed and sometimes it makes sense, and sometimes it doesn't. The ATTF podcasts are a godsend to me. All kinds of info, and you can put it on your computer or your ipod and listen whenever you want... on the drive to work, at work, while you're cleaning or working.... whenever.

[akent]

That's great stuff, Doozer!
I had not heard of those podcasts before...
Thanks!

One thing I don't like about the Raiden servos is that they don't have replacement gearsets available for them.

A lot of folks like the Hitec HS-65HB or the HS-65MG (metal gear) version for the cyclic. These are analog. The digital equivalent is the HS-5065MG.
Kent

[thayghetucsb]

First of all, thanks for the great info. Could you enlighten me how the digital servo is better? And is it worth it to spend the extra dollar. In this case is to upgrade from the HS 56 or 65mg to the HS-5025?

[thayghetucsb]

Correction: HS_5065 MG

[McKrackin]

The 5065 is a good servo.
Digi's are really good for the tail.Crisper connections and a little faster reactions.

www.hobbyhorse.com/hitec_hs5065mg.shtml