[Kedumba]

Hi All,
I'm looking at what I need for the OV-10 Bronco EP that I got off Kieran and I've become a little confused about the choice of motors and props. The instruction manual is no help in this area as it simple states that I need 2 brushless motors and props to suit or 2 x 0.15 cu in glow motors.

After googling around the closest model that contains any info that I can find is here at www.Nitroplanes.com.au. I know it's not identical but it seems really close. That website recommends 2 x 400T motors and 8x6 props.

Does anyone know what would the be hobbyking equivilant of a 400t motor or how I can work out which one is the equiv? I had a look at hobbyking and the choice of motors is a little overwhelming.

Secondly, I was thinking maybe of using a 3 bladed prop to look more closer to the real one. Any idea on what an equivilant 3 bladed prop might be? Also, any idea where I can get them from as all the 3 bladed props at hobbyking seem to be on backorder.

Finally, I'm gonna need 6 servos. Any suggesiton for a digital servo that is any good but I'm not gonna have to take out a second morgage or sell my first born child to afford half-a-dozen of them?

Thanks all in advance
Mick

[kizza42]

I meant to have a chat with you about this.
My original vision was to pick a 3 bladed prop diameter that looked good and scale and work the whole power train back from that. I never got around to getting exact sizes but HK definitley have a few 3 bladed props in the ballpark (Even reverse props for counter rotating blades as well).

Start here: http://www.s4a.ch/eflight/motorcalc_e.htm and find a motor setup to suit the speed/amp levels you desire.

I was anticipating it would end up around a 35-30 or 35-36 of some description and no more than 60 amps per side. That would have given it some speed but kept battery size/flight time manageable. High on the agenda was using finer pitch blades and making up speed with high rpm (kv) to get a sound closer to what the real ones sound like.

Was going to run the standard HK Digital Metal Gear servo's all around and was also looking at putting in retracts.

[gbanger]

Hi Mick
Just to continue from Kierans input.
The recommended glow 15 engines have a number of electric counterparts designed specifically to replace said glow engine. The simplest are the G series from HK, these are given a number that relates directly to the output of their petrol cousins. This one is worth a look.
http://www.hobbyking.com/hobbyking/store...duct=14402
This will give you an idea of the motor size, kv etc you need if you want to look at similar motors.
Once you have worked out what motors, ESC's and batteries you are going to use you can work out you flight weight. Flight weight is one of the most critical things you need to know so you can work out what props you need for the performance you desire.
When you have worked all that out post again and we will work out exactly what props you need.
Hope this helps.
Gazz

[Kedumba]

Bugger, this is gonna be far more complicated than I first thought. I like Kierans idea of scale props with the higher kv but I'm not sure how to work it all out.

I'm not sure I want to go up to 60amps as per kierans suggestion. It seems a little extreme for me especially at my skill level. I don't want hyper speed either, just a nice scale cruising speed with maybe a little bit extra in reserve will keep me happy. I can always upgrade later if I want to go breaking any speed records!

So, my first pass at guessing what I'd need:
Prop: GWS HD8040 3 Blade
or possibly
GWS HD9050 3 Blade Prop

Pity thay seem to be on backorder. Maybe they'll coem into stock by the time I'm ready to place an order.

Motor: Turnigy TR 35-30A 1700kv
ESC: TURNIGY Plush 30amp

How does that look?


Also, do I need to get a normal and a counter rotating prop? I always though the motors were supposed to turn in the smae direction, or is it set up so one turns clockwise and one turns counter-clockwise?

Thanks
Mick

[gbanger]

Dont forget you've got 2 motors Mick
Are U running separate ESC's or both off the one.
30 amps sounds like it might be OK if you have 2 of the suckers.
I would do a ball park flying weight mate or you may end up with an under powered bucket of puss that has cost more than a few dollars. It dosn't take much effort to get a ball park figure and then you know where you stand with power and props etc.

[smuzz]

You'll have to get two ESCs, can't run two BL motors off one.
Gazz is right with the emphasis on AUW Mick, what does the documentation say?
If it's something like 1500g to 2000g then a pair of 3530's would be close to the mark.

Have a search through RCGroups too, you might find a thread on that particular model.

[Drew]

Here's some accumulated info I've gathered in building some of my crazy plans.

The attached PDF walks through this (simple) process. It waas written when brushed motors and NiCd batteries were king.
- Calculate the wing loading or desired wing loading.
- Work out approximate horsepower (Watts as input power) needs based on weight for your flying style.
- blah blah blah
- Decide on the prop to get the right amount of thrust and airspeed. The stall speed depends largely on the wing loading and you should aim for a capability of 2-3 times the stall speed.

Power Selection calculations.pdf Size: 55.09 KB  Downloads: 175

Since that seems like a bit of a chore, the wizards at RCGroups have got together and built a web page that does just this .

http://www.rcgroups.com/forums/showthread.php?t=254742&page=2

Of course, motocalc, etc also have valuable databases of stuff but you need to have a ballpark of what you're looking for.

The last (and possibly best) guide is to find others who have successfully flown the same or similar size/weight/dimension models and find out what they used.

If none of that works, try sacrificing your newborn at first light of a full moon with some eye of newt - I think that's still in stock @ hobby king .

[Kedumba]

Dont forget you've got 2 motors Mick
Are U running separate ESC's or both off the one

I was planning on 2 ESC's, one for each motor and running them via a Y harness to the RX. Not sure if this is the correct way of doing it but it seems to make sense to me.

Gazz is right with the emphasis on AUW Mick, what does the documentation say?
If it's something like 1500g to 2000g then a pair of 3530's would be close to the mark

Umm, the instructions don't! I've trawled RCGRoups and I've found a thread here that talks about a Bronco that looks similar, at least nearly identical wingspan and other specs. The weights I've gleaned from skimming through the first 10 pages or so seem to range from 1300 grams up to 2267 grams (5lbs). I'll have a go at weighing the box of bits tomorrow and maybe guestimating the weight of the other bits (servo's motors batts etc) and try get a ballpark, but for now, I'm gonna go with the heaviest from RCgroups and add a little and say it's gonna be around 2300 grams.

The last (and possibly best) guide is to find others who have successfully flown the same or similar size/weight/dimension models and find out what they used

Uh, yeah, the first guy used:
Mega 1615-4 - $131 each
2nd guy used BP 2908-10 - $178 each
3rd guy used Mega 22/30/3 - $150 each

Gave up looking after that. Obviously these guys have no wives to answer to and can see no problem in spending $300 plus on just the motors. I was hoping for something in a more family friendly price bracket, otherwise I just may have to have an "OMG I can see why Kieran sold it" sale

I'll have a look at that WeboCalc thingy and see if I can make heads or tails of it.
Mick

[kizza42]

Don't lose faith mate, those motors are all from the stone age of around 2005-2006.

Take the 2908-10 for eg... Take a look at what powers this...
http://www.hobbyking.com/hobbyking/store...oduct=6331

They're all piddly motors....

Try this on for size:
2x 8x6x3 Master Airscrews (Not in stock at HK but plenty of other places to get them/Available in both directions)
2x NTM Series 35-36B 1400Kv / 495W http://www.hobbyking.com/hobbyking/store...duct=14093
1x Turnigy 3300mAh 3S 30C Lipo Pack http://www.hobbyking.com/hobbyking/store...oduct=9500
2x 30amp ESC http://www.hobbyking.com/hobbyking/store...oduct=2164

   

Cut the est flight time in two and you still have a modest endurance and top speed.

$80ish

[Kedumba]

Don't lose faith mate, those motors are all from the stone age of around 2005-2006.

Your right!! I was so busy reading the posts that I didn't even check the dates that the posts were made!

What you suggested Kieran sounds really good. Is it worth going for 2 x 2200mAh for a total of 4400mAh at an extra 100 grams of weight? I guess that really depends on what the final weight of the plane is i suppose.

Is the 3 blade 8x6 prop too high a pitch? or does that depend on the motor?

Do I need to have one motor counter rotating? Is that to balance the torque?

Thanks
Mick

[kizza42]

[quote='Kedumba' pid='6196' dateline='1306276733']
[quote]Don't lose faith mate, those motors are all from the stone age of around 2005-2006.[/quote]
Your right!! I was so busy reading the posts that I didn't even check the dates that the posts were made!
[quote]
What you suggested Kieran sounds really good. Is it worth going for 2 x 2200mAh for a total of 4400mAh at an extra 100 grams of weight? I guess that really depends on what the final weight of the plane is i suppose.
[/quote]
The eternal question for a twin electric... Twice the redundancy or twice the chance of failure!?! I'd personally prefer the motors to hit low voltage cutoff together with one power source than at different times. You could still use 2 of your existing 3s 2200's but wire them up in parallel

[quote]
Is the 3 blade 8x6 prop too high a pitch? or does that depend on the motor?
[/quote]
Its what they have available. Note the pitch speed calculation, its not exactly out of the park screaming.

[quote]
Do I need to have one motor counter rotating? Is that to balance the torque?
[/quote]
You don't but why wouldn't you, thats half the fun!

[robair]

Gday Mick

I have been down a identical road with my Twinstar, Kieran's suggested parts list looks good stuff.
I am going to hold off posting the specific specs for the moment as Kieran is going to do a final look over for me later this week before the maiden.
If he's happy I'll post the specs.
If you don't go 3 blade counter rotating you will never forgive yourself, it looks and sounds the goods.


Cheers
Rob B

[robair]

Gday Mick

I am assuming you have this all sorted however the twinstar runs on the following set up.

Each side runs a 2650 nanotech via turnigy plush 60 to a turnigy aerodrive xp 35-36 1400kv motor. Props are 3 blade 9*7.

Kieran kindly gave her a final engineering and airworthiness look over last night and pronounced all well for the maiden.

We did decide that the power output may be overkill for the Bronco however 3 blade 8 inch props would prob fit the bill.

I have the twinstar flight ready for tomorrow, can't wait to see how she goes!

Cheers
Rob B

[Kedumba]

Hi all,
Does anyone have a spare XT-60 Female plug that they could donate or sell to a worth cause?

I need to make a Deans to Xt-60 adapter for batteries. I have the Deans plugs but no XT60's. I've got an order in with Hobbyking but it'll take a while to come and I just need one to get me outta trouble quick..

Thanks
Mick

[Drew]

Mick,

I do and I probably even have a spare adapter built to suit your need. Unfortunately, I'm at Putney and not likely to be at the field this w/end. If you're really keen and don't have a better offer, you're welcome to come by and grab it.

[smuzz]

I've probably got some here Mick.
With the field being unsuitable for most fixed-wing planes, I don't think I'll be there at all this weekend but let me know if/when you're going to be there and I'll drop by.
Cheers,
Steve

[chrism]

Hi Mick,
I have some and will be at the field tomorrow from around 9-00am. I don't intend staying all morning though, probalbly till 11-00am.

Chris M

[Kedumba]

Wow, Thanks everyone with all the offers.. .. Thanks heaps Chris, I'll pop down the field tomorrow morning and grab it off you if thats ok. Might bring my wing down and give it a chuck as well as I don't think anything else I've got will get off the ground and spend some time watching the Heli guys throwing their machines around the skies.....

Thanks
Mick

[Kedumba]

Was going to run the standard HK Digital Metal Gear servo's all around and was also looking at putting in retracts.

Kieran (or anyone),
Do you have a link for the Servo's that you would recommend for the bronco? Preferably ones that are reasonably priced as I have to get 6 of them. Once I have the servo's I can start building and I can then start to think about the power needed to get it off the ground.

Also, did you have any idea of what kind of retracts you had in mind? Will the retracts have any problem with our strip and the longish grass? Don't wanna have them rip off the first time I try landing.....

Each side runs a 2650 nanotech via turnigy plush 60 to a turnigy aerodrive xp 35-36 1400kv motor. Props are 3 blade 9*7.
Kieran kindly gave her a final engineering and airworthiness look over last night and pronounced all well for the maiden.
We did decide that the power output may be overkill for the Bronco however 3 blade 8 inch props would prob fit the bill.

Does this mean you have a different idea for the powertrain or just go for smaller props? Hobbyking only seems to have the 9 inch props, not that they are in stock ....

[kizza42]

This is my servo of choice, just about everything I fly has them:
http://www.hobbyking.com/hobbyking/store...oduct=6314

Unfortunately stock is out at the moment.

Rob is saying we used the same philosophy when deciding on our power trains. All you need to do is scale it down to the scale of the plane which means 8" props etc.

For both the props and servo's. Have a look at http://www.himodel.com/ HK aren't the only boys in the game

[Kedumba]

They don't have a wide choice of 8 inch props, however what do you think about giving these a try: GWS 8 x 4 3-blade Propeller GWPR002S3D

Also, Do you think these Servos would be ok? CORONA 12.5g/ 2.5kg/ .14 sec Metal Gear Micro Servo CS-939MG

Thanks heaps for putting up with my annoying questions..
Mick

[kizza42]

They're ok, definitley see if you can source some digitals though, will make getting a plane with that many servos much easier to setup/trim.

I wouldn't risk gws props, have a look around the net for some master airscrews in pusher and puller configs. You'll find them.

[Kedumba]

They're ok, definitley see if you can source some digitals though,

Oh, I thought they were.... read a line, skip a line... maybe I'll just stick to the HK ones, will be a couple of weeks before I can afford to order them anyways, with luck they'll be in stock by then.

I wouldn't risk gws props, have a look around the net for some master airscrews in pusher and puller configs. You'll find them.

Okies, I'll try do some searching..... Thanks Kieran

[kizza42]

Servo's instock go go go!
http://www.hobbyking.com/hobbyking/store...oduct=6314

[Kedumba]

Servo's instock go go go!
http://www.hobbyking.com/hobbyking/store...oduct=6314

Bugger, gotta wait till payday... still 3 days away....

[kizza42]

How many you want, I'll do a group order tonight

[Kedumba]

How many you want, I'll do a group order tonight

The manual says I need 6 of them.

[Kedumba]

Hi All,
Just a simple one. If I know the current draw of my plane and the capacity of the battery, is there a simple way to calculate flight time?

eg My plane draws 16amps, and I have a 1800mah battery, how can I calcualte how much flight time I would get?
Thanks
Mick

[Drew]

That's easy. You will get exactly until the ESC cuts out due to low voltage! .

Seriously, it does depend on the day and flying style. If you get 16A WOT, you probably won't be flying at WOT for the whole time. If you are flying on a windy day, you will possibly be flying at a higher throttle setting than cruising around on a calm day. If the aircraft is a floating trainer or glider, you might spend some of the fligh time on idle. Obviously a 3D craft will work harder.

Having said all that, I figure a 50-60% throttle guess is reasonable. So assume that you'll be drawing 16A for take off and a couple of emergency spurts and 8A for the rest of the flight.

Not for the real info - an 1800mAh battery can sullply 1.8A for 1 hour, 3.6A for 30 minutes, 7.2A for 15 minutes or 15.4A for 7.5 minutes and be completely exhuasted.

You don't want to exhaust the battery - only go to 75% of those figures, maybe 60% for safety. Based on the average expected draw, plan you flight time from there.

Finally, start conservative with a few short test flights and measure how much is taken out then plot the threshold from there.

[popeyepete]

Copy of FlightTime.xls Size: 15.5 KB  Downloads: 172

Kizza posted this once before.