Titan Tricopter Part 1: Design

by Zpack | June 3, 2013 | (12) Posted in Projects

Titan Tricopter Part 1: Design

 

This is my first post on an RC forum- I’ve been into RC off and on pretty much my whole life but none of my friends or family are interested enough to get involved, and I live to far away from any clubs. Anyway I’m hoping that getting involved in this forum will help keep me motivated and informed.

I’ve been flying single rotor helis for about 8 years, but I’ve never gotten very good at it. This is because I crash, a lot, and then have to wait a week for parts to arrive. If you’ve never flown single rotors, they are extremely delicate and complicated. Even a light crash would require me to completely rebuild the rotorhead which usually took about two hours if you include all of the balancing and trimming afterword. Then there’s the fact that most of the parts are all unique to each model of heli so the parts are really expensive for what they are.

I’ve never been very impressed with multirotors, the ones I’d seen up until now have always been slow and not super responsive; but things have come a long way and I think that I can finally make the switch from helis without losing the maneuverability that I’ve gotten used to over the years. I settled on a tricopter because the yaw authority seems to be much better, and maybe because I think they look cooler….

I’m an engineer, and a do-it-yourselfer, so I figured I’d design my tri from scratch. This is the list of features I wanted:

  1. Durability- I want to be able to crash this thing a lot and not have to order parts to get it flying again; my goal is to have a tri that can take a major crash and not have more than a few broken zip ties and may be a busted prop or two. I want 4 out of 5 crashes to be repaired for less than $5.
  2. Maneuverability- I want to be able to do everything I could do with my heli (with the exception of inverted flight of course). This means flips, rolls, spins and fast forward flight.
  3. Cost- This goes back to durability, but I also can’t afford a major initial investment either.

I’ll start by saying that my cost requirement got blown out of the sky when I decided I needed to buy a new radio, but that doesn’t really count toward the cost of the aircraft right? At least that’s what I keep telling my wife…

I spent a couple of weeks researching the designs that were already out there, but they all had little things that I wanted to change. Of course I came across David Windestål’s great design, but there were a couple of issues I had with it:

  • I don’t like how the arms are held in place by friction alone, I want something that will positively position the arms and keep them there, but still fold in a crash
  • I don’t know about you guys, but I almost never crash nose-in, it’s usually tail-in or at some other odd angle. So I decided I wanted the tail boom to be able to rotate in a crash as well, plus I want the forward booms to be able to rotate forward in case I crash side-in.

With this in mind, I got started on the design. I’m really blessed to be working at a place with lots of great tools that I am welcome to use for my own projects. This includes a mill, lathe, laser cutter, and about $100k worth of engineering software.

The type of flying I want to do is mainly aerobatic, so after seeing what Matt Hall could do with his setup ( http://youtu.be/T_qKz16NOXY ), I tried to emulate his hardware specs:

  • 2200 4 cell
  • 1350KVs swinging 8x4.5s (They didn’t have 8x4s in stock, I hope they are close enough)
  • ~12” booms
  • Flashed Hobbyking 30A ESCs

I’m using the Multiwii board because the KK2 was out of stock, but I may end up liking the Multiwii better anyway. I’m really excited about autolevel, I would love to let my friends try flying it- “just let go of the cyclic stick if you get into trouble”; maybe I can get someone hooked on RC!

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Ok now we can finally get to my design. Keeping with the durability theme, I went with 10mm carbon booms with wood cores (more on that later), and all of the parts are laser cut 1/8” thick Acetal (delrin). I spent most of my design time working on the arm retainers. I initially was just going to use zip ties to hold them in place, but I wanted to be able to fold them for storage, and I didn’t want to cut the ties every time. What I settled on was this: