FT Mini Arrow

[lrussi750]

what rate and expo are you guys running?

Mine are usually about 60% rate and 20-30% expo.

 

[CapnBry]

Are people still building these? You bet they are! My first Arrow succumbed to overwhelming structural failure, splitting in half down one wing, then repaired and got another few days out of it before it ripped through on the other side. I decided to extend the box spar between the wings, with a cutout to wedge the receiver in tightly. How many others out there have a build where the receiver is structural?

I needed extra space in the back to fit the flight controller so there's no sides in the bay, all the strength comes from the receiver-spar. Most motor mounts take up too much space so I rolled my own that sticks in the back and is held in place with skewers (4.1g in ABS, PETG would be better). I can pull the skewers out and remove the motor to access the flight controller's USB port and sd slot easily. I needed more space to move the CG forward so I made a little nose so the battery isn't a square on the front. The nose is an N-22 airfoil shape I 3D printed a template for and cut out of doubled foam. After these photos I double-doubled the doublers so the foam board went completely across to get more strength. I also cut a little duct in the cover to blow a little air on the ESC.


The flight controller I 3D printed a little table (0.9g ABS) and used some white gorilla glue to glue it down after removing the paper first. Zipties hold the FC in place. I would have said it is ridiculously secure, but this build is already mostly destroyed (I am writing to you from the FUTURE) and I can say it isn't the worst way to secure it, a few really high-speed crashes can rip it up from the foam. It sort of is a bit wobbly now.


EMAX RS2205 2300KV
EMAX 12A ESC
2x MG90S 9g servos, 3D printed horns, 0.047" music wire pushrods
6x3 Prop
3S 1000mAh battery
Omnibus F4 Pro V2 Flight Controller w/ iNAV 2.0
Beitan BN-180 GPS
364g all-up weight

The 6x3 prop is a bit much for the 12A ESC so I limit the throttle to 80%, which is about 9.6A. A 5035 prop would be better, producing less thrust but we don't really need the 600g of thrust of the 6030 at close to 16A. Hilariously I can just throw it straight up into the air to launch it. I wouldn't recommend this build for anyone though, the nose takes a lot of damage on landing

I've had CG issues with both my arrows though. With it exactly on the CG marks (tested hanging from a thread through the CG marks) it nose dives without a ton of up elevator with perfect elevon reflex set, same as the last arrow I built. If I balance it with the CG about an inch back it glides amazingly but it flying it like that is a heck of a challenge because the pitch rate is off the charts. What's the secret to balancing these things? Get the CG perfect then add reflex until it flies straight?

Motor mount (Thingiverse)

 

[Hai-Lee]

I build, fly and sell a variety of non-FT flying designs. The way I recommend to get the balance spot on is to start with a preset point and test fly it.

Take it to altitude and cut the throttle. try to stall the wing in level flight. if at full up elevator(elevon) it wanders badly from side to side and then drops a wing and stalls the CG is too far aft. If the wing starts bobbing its nose up and down as it enters a stall,recover/stall/recover/and so on profile the CG is too far forward.

Ideally it should just slowly sink, (with at worst a very slight bobbing of the nose). Having determined the current balance land and readjust for optimal balance.

After the balancing re launch and check the throttle responses and if the response is less than neutral you may need to adjust the motor thrust angle.

Just what works for me!

have fun!

 

[CapnBry]

Man this was great advice, thanks @Hai-Lee! I got it to the point where if I cut the power off and hold up elevator it just floats down like a... plane coming in for a landing. It is a little deceptive because now it is harder to tell it is stalling because it is so gentle. Why am I not going up? Oh because you're going too slow dummy.

For posterity, my golden spot was about 5mm back from the standard CG marks and I still needed to add another ~2mm of reflex. Perhaps my design changes for the longer nose adjusted the wing geometry enough to cause that. Definitely much better without nosediving every time I let off the stick.

 

[Mode 1]

Good morning, all.

I'm just finishing up my first Mini. I don't need the complete power pack as i have servos already. However, I am looking for suggestions for engine / esc / battery combos as being new to electrics I don't want to guess and get it wrong. I'm looking for both A and F suggestions. Thanks so much!

~ Dave

 

[BS projects inc.]

I could never really get into the flying wings. I tried to build one but had some trouble with it. I might revisit the project with the arrow.

 

[CapnBry]

I am looking for suggestions for engine / esc / battery combos as being new to electrics I don't want to guess and get it wrong. I'm looking for both A and F suggestions.

Hey Dave, that's a great looking first build, much better looking than my first! I've flown these with a variety of somewhat similar hardware to the A and F packs and here's what I've found.

The A Pack's 6x3 prop and 1806 size 2300KV motor on a 2S and it was crazy weak, like 80% throttle on a fresh battery weak. On 3S it is great but pulls over 12A so that's a bit too much for the ESC. The A pack motor on 2S with a 6x4 prop is much better and stays inside the range for a 12A ESC (8A max, 300g of thrust, 40mph) . For 3S, my favorite is a 5x3.5 prop which comes out about 9A, 400g of thrust, 55mph.

The F pack has a bit larger motor, but roughly the same KV so expect it to eat a little more power and get a little more thrust. An EMAX RS2205 2300KV on a 2S with the 6x4 prop will put out 390g of thrust, 45mph at 11A. On 3S with 5x3.5, you're looking at 480g, 61mph, 12.5A. These are both right at the limit of the ESC which I've heard you want to have like 20% of fudge factor on, so if you're going with the more 2205 size motor, I think an 18A or 20A ESC is a more appropriate fit. Make sure you get one with an integrated BEC for powering the receiver and servos without having to add an external BEC. 1A on the BEC has been fine for me with 9g SG90 servos.

For battery 800-1200mah is as good range as long as you can get it to fit. The arrow's insides are pretty narrow so be sure to check that measurement on the battery you're looking at. 1000mah gives me about 12 minutes of flying around (although I am a pretty tame pilot still).

I would say my go-to setup (and what I have in the Goblin now) is an EMAX RS2205 2300KV, with a 20A ESC with integrated BEC, 3S 1000mAh battery, 5x3.5 or a 5x4 prop (2 blades). There are a ton of combinations that will work just as well though, because there is a ton of overlap in what you get as you mix and match various parts.

 

[Mode 1]

Hey Dave, that's a great looking first build, much better looking than my first! I've flown these with a variety of somewhat similar hardware to the A and F packs and here's what I've found.

The A Pack's 6x3 prop and 1806 size 2300KV motor on a 2S and it was crazy weak, like 80% throttle on a fresh battery weak. On 3S it is great but pulls over 12A so that's a bit too much for the ESC. The A pack motor on 2S with a 6x4 prop is much better and stays inside the range for a 12A ESC (8A max, 300g of thrust, 40mph) . For 3S, my favorite is a 5x3.5 prop which comes out about 9A, 400g of thrust, 55mph.

The F pack has a bit larger motor, but roughly the same KV so expect it to eat a little more power and get a little more thrust. An EMAX RS2205 2300KV on a 2S with the 6x4 prop will put out 390g of thrust, 45mph at 11A. On 3S with 5x3.5, you're looking at 480g, 61mph, 12.5A. These are both right at the limit of the ESC which I've heard you want to have like 20% of fudge factor on, so if you're going with the more 2205 size motor, I think an 18A or 20A ESC is a more appropriate fit. Make sure you get one with an integrated BEC for powering the receiver and servos without having to add an external BEC. 1A on the BEC has been fine for me with 9g SG90 servos.

For battery 800-1200mah is as good range as long as you can get it to fit. The arrow's insides are pretty narrow so be sure to check that measurement on the battery you're looking at. 1000mah gives me about 12 minutes of flying around (although I am a pretty tame pilot still).

I would say my go-to setup (and what I have in the Goblin now) is an EMAX RS2205 2300KV, with a 20A ESC with integrated BEC, 3S 1000mAh battery, 5x3.5 or a 5x4 prop (2 blades). There are a ton of combinations that will work just as well though, because there is a ton of overlap in what you get as you mix and match various parts.

Capn - Thanks so much for the reply. I grew up on nitro, was out of the hobby for nearly 20 years and am back in with both feet. Growing up, my father (who is 80 and stills flies) did all the building so i'm having to learn quickly all the "non flying" bits and pieces of the hobby.

So, coming from nitro all of this electric stuff is a complete mystery to me. I don't know what I don't know and i'm just tying not to make any big, costly, mistakes.

When looking for a motor I'm not sure if all motors are OK for planes or if some are only made for quads. The relationship to between the esc and motor seems critical as well. Gosh, apparently I don't know the proper way to install a receiver as i'm put my bloody wonder VIII in the ground 3 times due to brown-outs. Crazy thing is tough as nails, I've crinkled the front pretty well... a lot of hot glue and she will enjoy another day.. after my new transmitter and receiver arrive on thursday

Anyway.. I really appreciate your detail response. Thank you very much.

oh - that Mini Arrow I built.. It might look nice but what you can't see is I built the wings inside out. It was my very first FT scratch build and I folded the wings the wrong way. Seemed so much easier... I sanded the edges so I have a decent leading edge bit I have no idea if it will fly or not.. i'll be wearing a hard hat just in case. (working on another one now in the event this is a no-go.

 

[CapnBry]

haha well nice save on that inside out Arrow then, it looks great. My first one had one wing noticeably taller than the other and with the max camber in a different place. It still flew ok but needed a little weird elevon trim to not want to always roll.

I also stumbled through all the variables of electric motors so I am happy to help out. There's not really motors that are just made for quads (or at least they're not popular) but smaller brushless motors are usually listed as quad motors because they're too small to be used on regular sized planes. The FT Minis are small enough to not need big motors so they'll work just fine. The good news is that the ESC and motor is only $20-30 combined so worst case scenario you're not blowing hundreds of bucks. Well, unless your plane drops out of the sky directly into a pit of snakes and you lose everything.

Something I found useful trying to understand how all the pieces work was the eCalc prop/motor calculator. It's a pay site but the demo version lets you pick from limited list of components instead of the full set of options. It took me like a month to understand all the options on that page but let me pick up on the generalizations of motor size and kv, what props are appropriate, and how much current it will pull and thrust will be created. You probably already understand props so you're ahead of the game!

 

[Enos Shenk]

I always wanted to try this. I never had any luck with the stock Arrow, I have no idea how people wedge a battery in those things.

So I whipped up an Arrow Twin. Dual Arris motors with Emax Avan props. I absolutely adore these motors and props, they've been powering my Super Bee for quite some time wonderfully. The motor nacelles are cut from the Super Bee template and mounted...Oh, wherever it looked good.

I also on the fly widened the pod by around 2 widths of foam, and extended the rear section of the pod and wings. It actually closes up and balances very nicely with a 1300mah battery.

Hopefully I'll get it out to maiden in the next couple days.

 

[Mode 1]

Hey Dave, that's a great looking first build, much better looking than my first! I've flown these with a variety of somewhat similar hardware to the A and F packs and here's what I've found.

The A Pack's 6x3 prop and 1806 size 2300KV motor on a 2S and it was crazy weak, like 80% throttle on a fresh battery weak. On 3S it is great but pulls over 12A so that's a bit too much for the ESC. The A pack motor on 2S with a 6x4 prop is much better and stays inside the range for a 12A ESC (8A max, 300g of thrust, 40mph) . For 3S, my favorite is a 5x3.5 prop which comes out about 9A, 400g of thrust, 55mph.

The F pack has a bit larger motor, but roughly the same KV so expect it to eat a little more power and get a little more thrust. An EMAX RS2205 2300KV on a 2S with the 6x4 prop will put out 390g of thrust, 45mph at 11A. On 3S with 5x3.5, you're looking at 480g, 61mph, 12.5A. These are both right at the limit of the ESC which I've heard you want to have like 20% of fudge factor on, so if you're going with the more 2205 size motor, I think an 18A or 20A ESC is a more appropriate fit. Make sure you get one with an integrated BEC for powering the receiver and servos without having to add an external BEC. 1A on the BEC has been fine for me with 9g SG90 servos.

For battery 800-1200mah is as good range as long as you can get it to fit. The arrow's insides are pretty narrow so be sure to check that measurement on the battery you're looking at. 1000mah gives me about 12 minutes of flying around (although I am a pretty tame pilot still).

I would say my go-to setup (and what I have in the Goblin now) is an EMAX RS2205 2300KV, with a 20A ESC with integrated BEC, 3S 1000mAh battery, 5x3.5 or a 5x4 prop (2 blades). There are a ton of combinations that will work just as well though, because there is a ton of overlap in what you get as you mix and match various parts.

Capn,

I'm circling back on this thread as I just bought a motor. I kind of... followed your feedback and bought the new Emax RS2205-S 2600kv. I have a spare ESC from the C power Pack (EMax BLHeli 30A ESC) .. will this ESC handle the motor I bought? There are no specs listed for the motor at the store. https://store.flitetest.com/emax-rs2205s-2600kv-brushless-motor-cw-thread-emx-rs2205-s-2600/p542805

Thanks!

 

[Captain Video]

Hi:
My sons and I have three arrows and use those motors with 30 escs with great success. We love those motors and they are pretty durable too.

 

[Mode 1]

Hi:
My sons and I have three arrows and use those motors with 30 escs with great success. We love those motors and they are pretty durable too.

Thanks Captain!

 

[CapnBry]

Multiple Captains!
Yeah that 2600KV version with a 6x3 will pull up to 22.3A / 728g of thrust according to the calculator.
6x4 - 26.5A / 871g
5x3.5 - 15.3A / 584g
5x3 - 13.7A / 519g

All of which are under the 30A load limit. My fully loaded Arrows run about 360g though so even with a 5x3 you've got a ton of thrust-to-weight.

 

[Mode 1]

Multiple captains puts us in rare air indeed!

Thanks for the reply - Happy Flying!

 

[Yayat]

Made slight modification on my arrow, so I can secure HD cam on it

 

[Homey]

Made slight modification on my arrow, so I can secure HD cam on it

Awesome! I have been flying this Mini Arrow since it was released. Fly it every time I go out. Has taught me a ton. Everything from aerobatics to throttle control. Love it.

Peter

 

[Yayat]

Awesome! I have been flying this Mini Arrow since it was released. Fly it every time I go out. Has taught me a ton. Everything from aerobatics to throttle control. Love it.

Peter

Thanks, It does aerobatics nicely

 

[Yayat]

How about put streamer on Arrow?

Sorry if I post to much

 

[CapnBry]

I built another Arrow! The FT Arrow was the first RC airplane I ever built and flew. It didn't last 1 minute. Since then I've made 2 more, both of which didn't last a whole battery without some sort of significant damage. Decided it was time to build a new one since I am A#1 Duke of RC now days. Yes I know my last post with an Arrow was in September; I've grown a lot since then.

Instead of doing the double bevel to form the leading edge, I instead removed the paper one foam-width beyond the fold (which will be the bottom) and the paper on the top back to where the spar is. Using the tip of the hot glue gun, I melted the line where the double bevel would be, then folded the wing. It made a perfect fold without sounding like it was going to explode the paper on the outside edge and didn't even require me to reinforce the leading edge with tape due to it splitting like most my wings do. The leading edge is also more dense than the regular double bevel, since all the original material is still there.

I had this brilliant idea to mix resin dyes with minwax to form a beautiful jewel-toned sealant, but guess what did not work at all? It looks more like someone tried to color it with a crayon and also was a 3 year old child. Gave up on it after two different mixes and just did the bottom in clear and slapped a sticker on it.

Why didn't anyone remind me that there's not a lot of space inside a standard FT Arrow? With my 3S 1400mAh, it didn't all fit, as you can see the electronics door doesn't even close with the battery inside. It does fit, but it puts the CG too far forward so I might try to somehow swap the receiver to the nose and move the battery further back. There's zero room for any FPV gear, which I guess is fine because I'd have to get a smaller battery to keep the CG right. I'm 340g with the battery or 220g without. The cheapie BR2205 2300KV with a 5x3.5 prop puts out 405g 9A at full battery and stays in the air at 50-60% throttle pulling 3A. Even with the extra clearance of my motor mount sticking out an extra ~25mm the Arrow is still pretty loud, you can hear it screaming from across the field.

I have a maiden video but it was pretty unremarkable, and the Arrow disappears once it is 50m away so there's not much to see. I tried to do a lot of close flying but even that seemed far away. Total build time for the project from printing the plans to taking the finished photo was under 4 hours and I was doing other things and drinking wine throughout the process.

A full 15 minutes of flying and not a lick of damage though, a new record! This didn't really scratch the itch I was looking for though. I think I am looking for something small (~300g) and sporty with at least a rudder and ailerons that I can FPV around at ground level and try to avoid some gates I'll set up.