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Mini tail sitter VTOL wing.

#1
Hi all! First time actually posting here.

TL;DR It currently looks like this:
IMG_0368.JPG


So a after a few years of flying helis and multirotors, I've gotten myself sucked into all things Flite Test. After building some of the basic designs like the Nutball, Delta and Bloody Wonder, I decided it was time to try something off the wall. I've seen tail sitting VTOLs before and thought that was pretty cool to have a plane that can land like a heli. I've also wanted to make something with differential thrust, and FT keeps featuring the X-Vert in their videos... so I figured I'd try to make something like that!

After looking through some numbers and some random guessing, I decided to go with dual 1306 3300kv EMAX red bottoms with 3x3x3 props. My first choice was going to be 1806s, but it seems like they are going out of style, and I didn't want to shop around forever. I used a Ready Made RC Seriously Dodo flight controller running iNav 1.7. The first version of the plane might best be described as "stuff poorly attached to an old warped piece of left over foam". I didin't really know what I was doing, so I made a 15x10" rectangle, with a 25% cg and 20% control surface.

IMG_0323.JPG

I was mostly interesed in experimenting with how much control surface I would need to hover. While this rough crappy version never hovered, I was able to get it to fly pretty well, and it was _fast_. Since the foam I used for it was warped, it was really squirrely, and always tried to roll heavily to the right. It started delaminating near my crappy motor mounts, and I figured I was pushing my luck that it hadn't already disintegrated mid-flight. So I moved on to making a v2 with a little more thought into the design and construction.

IMG_0355.JPG

I swept the wing a little to help move the cg forward, increased the control suface area and gave it a KF step airfoil. I mounted the motors out in front of the wing on a square poplar dowel to give them access to a nice smooth airstream. The first plane I had before building FT planes had a pusher prop and had a fair amount of trouble with wing turbulence hitting the prop. This time I used some leftover Elmers foam. Heavy stuff, but reasonably durable.

IMG_0356.JPG

Well, it turns out that poplar dowel wasn't strong enough, and it broke pretty easily on the first battery after a couple rough landings. I was just starting to get a feel for how much control throw it needed too. With a little glue, it was back up in the air... then the ground... and then back on the bench. That clearly wasn't going to last, so I turned the motors around and put them inside the wing. Even though they were just held on by a couple dabs of hot glue, they were well protected by the wing and vertical stabilizers and didn't break again.

IMG_0366.JPG

At this point I was pretty happy with how it flew. It was definitely less efficient than the first prototype, but I didn't really care about extreme flight time or efficiency anyway. iNav doesn't support VTOLs directly, so to experiment with hovering, I rotated the board setting and all of my motor/servor mixes to make it fly like a multi-rotor. After a bit of turning, I got it to hover quite nicely! (I should record a video...) It's not as stable as a quad, especially in the pitch direction so it's hard to fly well in acroo made. Angle mode is a breeze however. iNav's PIFF controller works perfecetly for this. Unfortunately hovering draws a lot of current, and my 35C 450 mah Gremlin batteries are not quite up to the challenge. Pulling 10-15 amps, they peter out in less than two minutes. The voltage drop at full throttle is at least 0.3 volts! Unfortunately there is no way to switch back and forth between forward flight mode and hover without pasting some commands into the iNav command line. Vertical takeoffs work fine in forward flight mode since it accelerates pretty quickly.

IMG_0368.JPG

Over the weekend I made v3. The wing structure is better reinforced and made with FT foam so it's about 30 grams lighter. I made the wing a little deeper, and trimmed in the edges of the elevons to make it less twitchy in forward flight. I also made a cylindrical nose for it. The AUW is ~220 grams with a 450 battery now. The nose definitely helps it to fly more smoothly, but seems to increase the drag quite a bit. Maybe it will get better once I add panels to cover the back too.

I think my next step is to dig into the iNav code and see how hard it will be to make a mode switch to swap the profile settings so I can actually swap between the forward flight and hover settings. It could be a true VTOL at that point. Adding support for rotating the controls and self leveling would be icing on the cake.

Will post more as I make progress. :D
 
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#3
It's a Ready Made RC Seriously Dodo flight controller running iNav 1.7. So not meant for VTOL, but I'm looking forward to tinkering with that too as I'm a programmer by trade, and have some mild control systems experience.
 
#4
I really need to get somebody to record me flying it more.

I've been able to fine tune the COG a bit better. There's a pretty good sweet spot where I can flip it nicely, or pitch it up into a hover. Shift it back by 5mm, and it's very unstable. Shift it forward by 5mm and it requires a lot of elevator to keep it level. That makes it kinda hard to experiment with battery size. It can hover with a 3s 1500mah, but really only as a novelty. 450mah works well, but I'm killing my batteries (35C is not enough). An 850mah works ok, but it definitely feels heavier in the air. Also annoying to switch sizes since my counterweight is nickels taped to the back of the fins.
 

LitterBug

Troll Spammer
#5
If you are using 3" props, it is really hard to beat the RotorX RX3040T (and now 3044T) props in weight and efficiency. Those motors should be able to handle 4S. I've been running the 4000kv variant on my FlexRC Owl quad frames on 4S for over a year and never had any issues. Mentioned it over in my thread, and will say it here too. I have two KK2 boards that I'll send you if you want them. They came with a used tricopter I bought and am rebuilding with an F3 DTFc controller.

Cheers!
LitterBug
 
#6
Well, thrust isn't really the problem. The noise is like running a vacuum cleaner, and I think the high RPMs is wasting a lot of battery vs a larger slower prop. I might try and scale it up with 2204s next spring though.

A KK2 board is tempting for running OpenAeroVTOL, but I think I'd need to buy an AVR programmer for it anyway. I don't suppose they have 36x36mm mounting holes such that I could just swap it in without having to modify my frame?
 

JimCR120

Got Lobstah?
Site Moderator
#7
Hello slembcke. Wow, what a first post and wow what a build! It certainly flies well. I am looking forward to videos of the vertical take and landing capability iif you are able to achieve it. Even if not, it's a nice build.

I did pop over to your "About Me" tab. You are informative and thorough. The one thing is I don't know how to say the name you've chosen. Could you explain it and tell us how to say it and/or offer your regular name?

Welcome to the forum and please do keep us posted.
—Jim
 
#8
Oh it mostly is my regular name. ;D Scott Lembcke (lem-key)

On an on topic note, I've been looking through the OpenAeroVTOL code, and the transition mixing is much simpler than I had thought. Could be an interesting project to try and hack it on top of iNav without being overwhelming. The iNav dev wants to support VTOL eventually anyway so maybe I can be of some help.
 

LitterBug

Troll Spammer
#9
A KK2 board is tempting for running OpenAeroVTOL, but I think I'd need to buy an AVR programmer for it anyway. I don't suppose they have 36x36mm mounting holes such that I could just swap it in without having to modify my frame?
Yeah, I thought about playing with them for half a day but decided it wasn't worth the time and effort since there are newer better options readily available. It is a bit larger than the modern 30.5x30.5 mounting used these days too. Offer stands. PM me if you are interested.

Cheers!
LitterBug
 

bjjn

New member
#10
Change kv motors

Well, thrust isn't really the problem. The noise is like running a vacuum cleaner, and I think the high RPMs is wasting a lot of battery vs a larger slower prop. I might try and scale it up with 2204s next spring though.

A KK2 board is tempting for running OpenAeroVTOL, but I think I'd need to buy an AVR programmer for it anyway. I don't suppose they have 36x36mm mounting holes such that I could just swap it in without having to modify my frame?
Why not change the kv motors.
 
#11
Unless I switch from 1306 to 1806 motors, I couldn't find anything with a lower kv. I did try running them with 4" bullnose on 3s, but they drew too many amps. Maybe possible if I had a better selection of 2s batteries. Dunno.
 
#13
Has any progress been made on this? I have a dual tractor spear that I want to do VTOL with. It currently has inav and was thinking of swapping for a pixhawk but would like to stick with inav if I can. Thanks for the hard work.
 
#14
I was looking in the forum here for VTOL designs. I saw your design slembcke. I like it. I was wondering if you will be getting back to it?

I drew up a version of it in Sketchup. I am going to build this this weekend with DTFB. Two wooden spars buried in the KF step and wing. Probably #D printed motor mounts. I plan on using a KK 2.1.5 Mini flashed with Open Aero2VTOL. I will be using a XM+ RX. It will have EMAX 1806 motors with 5" X 3" or possibly 5" X 4" props. Most likely 6 gram servos. Planning on a 3S, possibly 4S 800 to 1300ma battery. I have made a try at making it 3D Printer ready but not very successful so far. The posted .STL could possibly be broken down into a print. As a 3D print it would be better to have a real wing cross section.

I do hope you find the time to return to this. The flight video was great. I would have liked to see it hover on the mid wing mounted motors.

I know this is an older post but I thought it needed another look! Hope you agree.
 

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#15
Started cutting out pieces yesterday. Haven't scratch built in a few years so going slow. It looks like two of these VTOL's could be built from one board with careful cuts. Looking for my compass so I can round the pod front. Once I get it tested I will try to make some plans. Need to add assembly tabs in many places. Right now everything will be "butt" glued. It's coming along but I am slow.
 

Attachments

#17
It can't (more detail above). I was going to try and make some iNav modifications, but I got sucked into making homebrew games for the NES instead...

I simply had two separate config settings, one for hover and one for flight. I had to hook it up to the computer to switch them. It proved that I could make it hover, but that was all the farther I got.