Total RC Newbie Frustration

[deanoaz]

Sorry, but I'm trying not to go non-linear as I have just spent 45 minutes writing a new topic to have it lost through the sign-in process. Oh, well, life is HELL, then you die.

I will try to shorten this by asking if anyone knows a simulator (or personal recommendations) that you could just put in simple guidelines to get started in defining the on board electronics for a plane (my Guillows Cessna 172)? I have used this process in a past life of high-tech, when a solution was needed, but exact definitions were not available.

Example:
1. I would guess at my plane weight (I don't know it because I am still building it!) and type of flying I would be doing (park model) and I would get some motor guidelines, with limiting parameters (I could then pick a motor out of someone's inventory, only as a guestimate)
2. Those parameters would help define the ESC needed to control that motor and also have some parameters (I would then go pick an ESC from inventory, only as a guestimate)
3. Based on those choices and parameters I could then pick a battery pack as a guestimate. This could also lead to a charger.
4. Through an iterative process, I could reach an end-point solution for on-board electronics.

This could be an iterative process until your parameters and prices satisfied your needs.

Frustrated!

[dirk gently]

Perhaps not the answer you were looking for, but perhaps rather than trying to compute all the gear by yourself, you could simply check what other people have put into the exact same model: http://www.rcgroups.com/forums/showthread.php?t=827861

There are 7 examples of the 172 to choose from.

[deanoaz]

I had already been through that list and found some really good build pic's, which I have been using as I build the 172. But, it is also one of the reason I have posted my "Newbie Frustration" thread as whenever I found electronic equipment, I found a great deal of variation. That is why I was seeking some guidelines. I guess I'll just take a stab and live with the consequences. Thanks.

[dirk gently]

Of course there will be variations, you can put a more powerful motor for better performance, or a smaller one for low wing loading and therefore easier handling. It will also depend on how light you prefer (or are able) to build the model.

For a general parkflyer I tend to find a motor with static thrust more or less equal to the anticipated model weight. This allows you to cruise at half-throttle or so, and leaves some extra power left so that you can escape from a dangerous situation.

For this particular model I would use an Emax 2205 and try to keep the all-up weight under 400g. Matching gear is a 18-20A ESC, 950mAh 2S battery and a 6x3 prop. I would use 9g servos for everything. Total gear weight is 150-200g (depending mainly on the battery) so you have a decent amount of wiggle room with the airframe weight.

[Billy Mc]

When writing a long post to the internet it's a good idea to use a word processor, then copy and paste the text.

[deanoaz]

I have posted a number of things on the Internet and understand what you are saying. But, you know, sometimes you just get into the process before realizing you might get jammed. Did you use a word processor for that one line above? I will for sure do that in the future on this forum for anything more than 20 words.

[deanoaz]

Of course there will be variations, you can put a more powerful motor for better performance, or a smaller one for low wing loading and therefore easier handling. It will also depend on how light you prefer (or are able) to build the model.

For a general parkflyer I tend to find a motor with static thrust more or less equal to the anticipated model weight. This allows you to cruise at half-throttle or so, and leaves some extra power left so that you can escape from a dangerous situation.

For this particular model I would use an Emax 2205 and try to keep the all-up weight under 400g. Matching gear is a 18-20A ESC, 950mAh 2S battery and a 6x3 prop. I would use 9g servos for everything. Total gear weight is 150-200g (depending mainly on the battery) so you have a decent amount of wiggle room with the airframe weight.

I really appreciate your input, as it helps in my trek to find a system for my 172. There are some really good build picture posts on this forum and they have helped me understand some of the areas not clearly explained by the Guillows kit.

[Bill Gaylord]

Of course there will be variations, you can put a more powerful motor for better performance, or a smaller one for low wing loading and therefore easier handling. It will also depend on how light you prefer (or are able) to build the model.

For a general parkflyer I tend to find a motor with static thrust more or less equal to the anticipated model weight. This allows you to cruise at half-throttle or so, and leaves some extra power left so that you can escape from a dangerous situation.

For this particular model I would use an Emax 2205 and try to keep the all-up weight under 400g. Matching gear is a 18-20A ESC, 950mAh 2S battery and a 6x3 prop. I would use 9g servos for everything. Total gear weight is 150-200g (depending mainly on the battery) so you have a decent amount of wiggle room with the airframe weight.

Weight seems about right. The 2205 should work well with a 400gm or less AUW. I haven't heard if he plans on sheeting this model, etc, but one wouldn't want to be heavier than 16. I just finished a Sterling Citabria with comparable motor, but it has an 11oz AUW, giving a bit more leeway. Same setup in my Comet Cherokee, while a bit lighter than 14oz at 12oz, it has plenty of power. One good point was your kv and prop sizing. The 172 per scale won't have a large prop, where larger than 8" will be grinding ground. While a higher kv with 6" isn't as efficient as a lower kv/larger prop setup, it won't be cutting grass either, being a nose wheeled subject. Smaller also will have lower torque effects.

[deanoaz]

That 400g number is the input I was seeking. My "guesstimate" for the total was going to be between 1-2 pounds, which was high compared to that number. I can now move down the road in putting together a list of electronic gear. Thanks!

[dirk gently]

One pound would be pushing it, two pounds, no way it's going to fly.
I have a parkflyer of similar wing area that weighs 165g, or closer to 190 if I choose to put on the landing gear:
http://pfmrc.eu/index.php?/topic/44265- ... Bparkflyer
Yours is a scale plane, so might be difficult to build it quite so light, but 400g should be easily achievable, even 300g is probably possible.

[deanoaz]

Okay, help me correct where my newbie assumptions are wrong:
2 servos/2 wing hold down screws/blocks/hinges/magnets 3 oz
Battery (3S) 5.5 oz
Fuselage (right now, uncovered) 1.0 oz
Wing (guesstimate?) 3.0 oz
Receiver 1.0 oz
Motor 3.0 oz
ESC 1.1 oz
Covering (SWAG ??) 6.0 oz
Total Guesstimate 23.6 oz

I have left off the landing gear (the front gear is going to be steerable) and any added balsa support I might have to put in. By the way, those magnets are for holding up wing struts so that I can pull them off when removing the wing.

[Bill Gaylord]

I've been gradually reducing gear weight, in an effort to build models lighter. For a model like this, a battery weighing 2oz is plenty ample. 2-3s 800-900maH range will provide ample power and balance, if mounted forward. I haven't used a servo larger than 7 grams for ages, in planes up to 40" span. I generally use servos in the 5gm range, and have not yet had a failure. You have to look at the big picture, where motor/battery sizing is based on required power, as well as balancing requirements. I've rarely used much if any ballast for most builds, over a number of years now. I'll mount tail servos against the firewall if necessary, to eliminate ballast. As for remaining gear, a reliable 12A ESC should be ample for a model this size. Microlite covering has been a major weight reducer, used on most of my builds for some years. The weight added is more in the 2-3oz range even when painted, for a model this size. My C172 is 15.5oz AUW, but would probably be a at least an ounce ligher, if built more recently. The model uses Ekonokote covering with a 1/32" sheeted fuse, with Microlite on the ailerons and tail surfaces. More recently I've been using Microlite overall, and painting with lighter results. By rights, a 36" sheeted ducted fan jet should weigh more than the C172, but I recently managed to build and fly one at 15oz AUW, using the minimalist approach.

[dirk gently]

> 2 servos/2 wing hold down screws/blocks/hinges/magnets 3 oz
A 9g servo only weighs 12g (due to additional weight of the cable, plug and horn), so two will put you back less than an ounce. The rest is negligible.

> Battery (3S) 5.5 oz
You only need a 2S battery (with the motor i proposed it's also the only thing you *can* use). A 700mAh battery is 2oz, a 950mAh probably 2.5

> Receiver 1.0 oz
Not sure what radio gear do you use, my receivers weigh between 6 and 12g, so less than 0.5oz

> Motor 3.0 oz
A 3oz motor would be an overkill for this size model. The 2205 I proposed comes in at around 1oz

> ESC 1.1 oz
more like 15-20g

> Covering (SWAG ??) 6.0 oz
I don't think you can come close to that unless you plan to cover with solid concrete. My parflyer that I mentioned had tissue covering, which only added around 10g, film covering will be a bit more, but not much (for example, Oracover is 65g/sq. m., so you can do the math).

BTW, do you have any solid data on the wing area of the model?

[deanoaz]

> 2 servos/2 wing hold down screws/blocks/hinges/magnets 3 oz
A 9g servo only weighs 12g (due to additional weight of the cable, plug and horn), so two will put you back less than an ounce. The rest is negligible.

> Battery (3S) 5.5 oz
You only need a 2S battery (with the motor i proposed it's also the only thing you *can* use). A 700mAh battery is 2oz, a 950mAh probably 2.5

> Receiver 1.0 oz
Not sure what radio gear do you use, my receivers weigh between 6 and 12g, so less than 0.5oz

> Motor 3.0 oz
A 3oz motor would be an overkill for this size model. The 2205 I proposed comes in at around 1oz

> ESC 1.1 oz
more like 15-20g

> Covering (SWAG ??) 6.0 oz
I don't think you can come close to that unless you plan to cover with solid concrete. My parflyer that I mentioned had tissue covering, which only added around 10g, film covering will be a bit more, but not much (for example, Oracover is 65g/sq. m., so you can do the math).

BTW, do you have any solid data on the wing area of the model?

I really appreciate the input. One thing I failed to mention about my electronic gear selection: I am trying to build an electronic equipment "platform" that could be removed and used on another model, so my selection of some of it (i.e. the 3S battery instead of the 2S that would really be adequate) was to leave some leeway for another plane, as yet unknown. I am adding some strengthening in a few places, plus a steerable nose gear, which was why I just rounded that first number to 3 oz. I have the Horizon DX5e/AR610 transmitter/receiver combo, so the receiver weight if from spec's. I don't have a solid wing area....only my estimation from the plans and that is ~180 sq. in. The ESC I used was the 30amp Pro Switch-Mode BEC Brushless with 1+ oz from the spec. sheet. I used the weight of the Park 480 Brushless Outrunner motor for this estimation.....had considered the 2205 at one point and don't now know why I changed. Let me go back and reconsider. I have some Ultracote for covering and don't have a clue how much it weighs per sq. meter, so I will revise that number down to maybe 15g. You have been really helpful.

[deanoaz]

On another one of my posts, a contributor came up with 175 sq. in. for the area of the wing. My estimate from rough measurements was 180, so I guess I'm not far off.