About to do my first build - Versa wing - got the motor/prop/esc not sure right sized

[Flyswamper]

Hi folks,

A year ago my middle son and I started into the hobby with our first RTF Supercub. Since that time dad (that's me) has gotten a wee bit addicted. We now have 2 Supercubs (one with floats on it), an Apprentice S15e, a Delta Ray, a Blade Nano QX quad, a Blade 120 heli, and for Christmas we added a Blade 350QX. As you can see we've been spending plenty of money on this hobby. I'm a big fan of the guys here at Flitetest and was thinking I really need (and would enjoy) starting down the more economical and interesting road of doing more of the building myself.

So.... taking a baby step, I have ordered and have 2 speedbuild kits for the FT Versa wing that are in the mail to me right now. I also ordered the elements firewall as I hope to build them as pushers.

For the motor, prop, esc, and servos I thought I'd give my local hobby store a bit of my business. So... today I made a trip to the local store in a somewhat unprepared state (meaning I hadn't done all my homework). I pulled up the recommended motor/esc/.... from the website with one of the guys in the shop and looking at their inventory the following is what I walked out of the store with for my power train..

Prop: APC - Composite Propellor - LP 08060EP, 8x6 EP, Thin Electric Pusher prop
Motor: Eflite Park 370 Outrunner Brushless motor - EFLM1205 - 1360 kv with mount and prop adapter
ESC: ElectriFly 25A Brushless ESC (GPMM1820), delivers 25A continuous, 28A surge, 2.0A BEC
Servos: Eflite: S75 Sub-Micro Servo (7.5 g)

Now.... being totally new to this stuff, what I was trying to do was basically just get a very similar setup to what I see the FT guys recommending with the build plans/video. Of course, because I was buying from the inventory of my local hobby store... I didn't get the same stuff.

My question is.... do you guys with WAY more knowledge of this stuff see any trouble with my prop/motor/esc config? I just tried to put what I *think* are all the right numbers into an online calculator (http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en) and it is telling me the following:

•max. current over the limit of the motor. Please verify the limits (current, power, rpm) defined by the manufacturer!
•Your defined Model Weight (incl. Drive) results in a All-up Weight less the sum of all you chosen components (Drive Weight).
Verify your Model Weight and enter either your estimated All-up Weight (incl. Drive) or your basic weight (without Drive).
•The airflow at the propeller blade will stall. Therefore the static thrust and max. current may not be reached. On ground you will measure *Stall Thrust* as maximum.

I'm not sure whether I've entered bad numbers, whether I've really got a combination that might be trouble, or what? Would appreciate any and all words of wisdom that you kind folks might have for me. Bear in mind this is my first foray into this side of RC building.

I've probably got another day or so before my foam speedbuild kits arrive and I start putting stuff together in anger. Just trying to figure out if I ought to make a trip across town back to the local hobby store to exchange/get a slightly different setup or live with what I got.

Thanks,

Flyswamper

P.S. I have a 5.8 Ghz setup arriving in the near future from readymaderc that I hope to eventually put on one of these versa wings. Someday likely to get 1.3 Ghz setup as well (got my ham license earlier this month). So if that matters for the prop/motor config...thought I'd mention it.

 

[lonewolf7717]

Quick review: The prop is the source of most your woes. An 8x6 is heavy in the pitch department and about 3 steps up from what is called for on Park 370 specs. Even just one step up in pitch and drastically change amp draw and may create situation in which motor is exceeding recommended max watts. You really need to try and find a 8x3.8 or for that matter dropping down to a more common 7x4 apc should still give you respectable power while underpropping a bit. Also note you have purchased a pusher prop which will work but will have to run motor reverse from what is normal and changing the normal down/right pitch for a tractor to up/left thrust line.

 

[lonewolf7717]

Quick review: The prop is the source of most your woes. An 8x6 is heavy in the pitch department and about 3 steps up from what is called for on Park 370 specs. Even just one step up in pitch and drastically change amp draw and may create situation in which motor is exceeding recommended max watts. You really need to try and find a 8x3.8 or for that matter dropping down to a more common 7x4 apc should still give you respectable power while underpropping a bit. Also note you have purchased a pusher prop which will work but will have to run motor reverse from what is normal and changing the normal down/right pitch for a tractor to up/left thrust line.

OK...its late and my bedtime. scratch all that about the pusher prop.....the fact this is a versa didn't register. Finding a lower pitch prop does still apply though.

 

[Flyswamper]

Thanks very much for your comments.

When looking at the props and talking to the guy in the shop I was a little confused. I was talking about which way the prop goes with him and he insisted that you put the prop with the letters facing to the rear of the plane if it's a pusher. I distinctly remember listening to the Flitetest guys in a video insist that the lettering on props always looks forward on the plane. what I'm wondering about now is whether the fact that this is a "pusher prop" means that maybe my local hobby shop guys are correct and what I heard in the Flitetest videos applies to "normal" props but not pusher props. Then again.... its all new to me and I need to get some sleep instead of researching more now... so... thanks again... hoping for more enlightenment from the good folks such as you and others on the setup.

If I interpret what you said, sounds like I have two suggested options:

1) get a less aggressive prop. The FT plans (here: http://www.stonekap.net/ftplans/FT-VERSA-TILED-PLANS.pdf) suggest an 8x6 prop which is why I got what I did. You think a 7x4 makes more sense? For the overall plane or because of the motor I bought?

2) get a more capable motor - again FT plans suggest a 1300 kv motor which I think I got a 1360 kv motor..... but I will be first to admit that I haven't read up much on motor sizing. Only enough to know I need to read a lot more on the subject.


My instinct is that *IF* my current equipment isn't quite right that I'd *probably* rather take the motor back and get something more appropriate for the suggested 8x6 prop that the FT guys suggest in the build plans. If I was doing that, is there a simple way to tell me I should get a motor with at least X capacity/capability (just kv rating? or what else)?


Also, getting out the spec sheet for the motor I bought, it shows the following additional details:

Kv: 1360 (rpms per volt)
Io 1.00 A @ 10V 9no load current)
Ri: 0.1 ohms
Continuous current: 12A
Max burst current: 15A
Watts: up to 150
Prop range: 8x6-10x4.7/8x3.8(3 cell)
Brushless ESC: 10-25 amp

 

[lonewolf7717]

I am basing my assumptions on the fact you are using a 3s lipo rather than 2s. The Versa specs do call for a 1300kv which could handle an 8x6 on 3s but since you opted for the 1360kv I would advise you to default to motor spec recommendations which was the 8x3.8. Also not sure if you intend to set up with motor mount in back as many do or per the plan with tractor style in front. The only difference between pusher and standard prop is the direction they rotate. Letters always go forward in either case. I have run a ton of standard props in a pusher configuration but doing so runs the risk of backing off your collet nut and losing your prop in flight....this whole experience will certainly have you brushed up on your "righty tighty, lefty loosy" know how.

Just for fun: your 1360kv motor will be turning 666 more rpm than the 1300kv on the same 11.1v nominal 3s voltage.
Rule of thumb: lower kv = larger props higher kv= smaller props
lower Voltage= larger props higher Voltage=smaller props

Just like the gears in a truck.....low gears (lower kv larger diameter props)= grunt, power, thrust
high gears (higher kv smaller diameter larger pitch props)= less thrust and grunt but far more speed

 

[lonewolf7717]

And somebody is going to come along and suggest you buy a watt meter....guess in this case it's me lol. With a watt meter, motor and a fist full of props you can take the guess work out of most of this.

http://www.valuehobby.com/gt-power-130a-wattmeter.html

 

[Flyswamper]

I am basing my assumptions on the fact you are using a 3s lipo rather than 2s.

Yes, at least a 3s. What I've read and seen in the videos suggest with a pusher configuration (which I'm going for) I'll need plenty of weight up front and a good size battery. Combine that with the fact that I hope to eventually use these as a medium range fpv aircraft (already got my ham license a couple weeks ago) I expect that I'll be going for fairly large battery capacity. Haven't yet figured out what that is, but I'm sure its not a 2s.

The Versa specs do call for a 1300kv which could handle an 8x6 on 3s but since you opted for the 1360kv I would advise you to default to motor spec recommendations which was the 8x3.8.

Here's where my lack of research/educating myself prior to impulse buying steered me wrong. I mistakenly thought the 1360kv motor was better for me. Your auto-gear analogy and now that I see what the units are for this number (rpm per volt) I am realizing that I got a less capable motor rather than a more capable one for the setup.

Also not sure if you intend to set up with motor mount in back as many do or per the plan with tractor style in front. The only difference between pusher and standard prop is the direction they rotate. Letters always go forward in either case.

Yes, I'm planning for a pusher. That is the weird thing at the local shop. I brought this up but didn't want to argue it very long with the guys there. But they insisted that I should put the numbers facing the rear of the plane if it was a pusher. Their justification was that it is easier to quickly read the numbers and know what the prop is...which is pretty lame reasoning I think. I just wondered if the fact that the prop has big bold letters on the packaging that describes it as "Thin Electric Pusher" perhaps meant that the letters really would go to the rear of the plane. Sounds like you are telling me stick with putting them forward the same as the advice that I saw Josh Bixler talk about in some of his videos.

Just for fun: your 1360kv motor will be turning 666 more rpm than the 1300kv on the same 11.1v nominal 3s voltage.
Rule of thumb: lower kv = larger props higher kv= smaller props
lower Voltage= larger props higher Voltage=smaller props

Just like the gears in a truck.....low gears (lower kv larger diameter props)= grunt, power, thrust
high gears (higher kv smaller diameter larger pitch props)= less thrust and grunt but far more speed

Excellent analogy... thanks that was most helpful!

Going to call the local hobby shop and see what other motors they might have in stock. Then if I can find something that I think works I think I'll keep the 8x6 prop and exchange the motor for something more appropriate. Guess I'll need to see if the ESC still works for the revised setup as well.

And somebody is going to come along and suggest you buy a watt meter....guess in this case it's me lol. With a watt meter, motor and a fist full of props you can take the guess work out of most of this.

http://www.valuehobby.com/gt-power-130a-wattmeter.html

Thanks for the suggestion. I will likely do that. I did recently pickup a TM1000 telemetry module. Kinda wondering if I wanted to go a cheap multi-use route if I could buy a sensor for that and just use the TM1000 readings to see the amps, volts and compute the watts from that data.

 

[Flyswamper]

I just called the local hobby store and they have a Park 370 - 1200kv in stock. Plugging that into the calculator causes the warning messages to go away. So... in my still newbie way of seeing al this... this should be a better/appropriate setup I think.

Of course, because I'm doing this a bit haphazardly I suspect my setup won't be as optimum as it could be. So.... if you guys spot anything else please let me know. In particular anything that I could plan on doing with my 2nd versawing build (I bought two...one for me one for my son) that would result in better efficiency setup for medium range fpv flying (i.e. getting longer flight times and using less power so more of it can go to power the fpv gear) I would love to hear the suggestions!

And don't feel like you gotta retype stuff others have said... just guidance that says go look at this http://linkhere.com and read-up would be great.