Goliath: One Drone To Rule Them All

We see quadcopter projects all the time here on Hackaday, so it takes something special to get our attention. [Peter McCloud] has done just that with Goliath, a gas powered quadcopter he’s entered in The Hackaday Prize. By gas, we don’t mean a little glow fuel buzzer, We’re talking about a 30 horsepower V-twin lawnmower engine running good old-fashioned gasoline.

Multicopters powered by a single power source present a unique set of problems. Quadcopter propellers need to rotate in opposite directions to avoid the entire craft spinning due to torque action. With individual electric motors that’s as easy as swapping a couple of wires. Not so with a single rotating engine. [Peter] has accomplished this feat with a clever arrangement of single and double-sided belts.

Control is another issue. Generally, central powered multicopters use collective pitch, similar to a helicopter control system. [Peter] has decided to go with high-efficiency fixed pitch blades and a vane system for directional control. Much like hovercraft use vanes to steer, Goliath will use vanes to affect its attitude and yaw.

goliathPropThe propellers are works of art in their own right. [Peter] modeled the propellers in CAD using the principles of blade element theory, then used a Shopbot style CNC to carve them out of pink insulation foam. Styrofoam alone won’t withstand the 60 lbs each propeller will be supporting, so [Peter] plans to laminate the props in composite cloth. This is the similar to the way many full-scale helicopter rotor blades are assembled.

Goliath’s frame is constructed of Dexion style slotted steel angles, and we have to admit, at 240 lbs with engine, it seems like it’s going to be a heavy beast. Big enough to ride at least. Who knows… if the judges like it [Peter] may ride Goliath all the way to space!



SpaceWrencherThe project featured in this post is an entry in The Hackaday Prize. Build something awesome and win a trip to space or hundreds of other prizes.

46 thoughts on “Goliath: One Drone To Rule Them All

  1. “Shopbot style CNC”

    What’s that supposed to mean? Kleenex style tissues?

    Also… that does not look anywhere close to a nominal 30 horsepower engine. That’s like saying you have a 30 HP vacuum or compressor….. that plugs into a 15A 120V receptacle.

    1. Not trying to be rude but I’m guessing they refereed to the Shopbot style cnc so people could gauge what the CNC was like. Bit of a difference between a shapeoko cnc and a shopbot cnc for example.

      Also the engine in question looks like one of these:
      Which I know only specifies up to 27HP but maybe someone over estimated it or simply rounded up. Maybe they did a bit of work to the engine?
      There are some Briggs and Stratons that are 30HP but 27hp vs 30hp is going to be one hell of a quadcopter!

      1. Assuming it’s a 27 “gross” HP model, it’s a 724 cc engine. What does “gross” horsepower even mean? Why not use nominal, indicated, brake, shaft or effective and get real, meaningful numbers?

        1. Sears was (is) a big buyer of these types of engines. They are also known for HP numbers (such as “gross”) that are not obtainable in normal usage. So maybe Briggs uses the Sears numbers, so Sears doesn’t get upset when their buyers see the “real” numbers and get mad.

      1. “Shopbot style” is generally considered a CNC “router”, designed primarily (but not exclusively) for large, 2D workpieces. As opposed to a CNC “mill”, which might have a smaller range of XY motion but is better suited for full 3D work. Pedants, come at me!

  2. Assuming the 240 pounds is not a typo – I wouldn’t want to be anywhere near that brickhouse when it’s tested. Hope the builder has a good lawyer and lots and lots and lots of insurance.

  3. A great looking project. I’ll be really interested in seeing how the vanes work as a means of control. One thing though, the arms look like they might be a bit lacking in torsional rigidity – the last thing you need is the thrust vectors of the props getting out of control. Some diagonal bracing might be needed. But great work so far and I hope it all goes well.

  4. As someone who participates in the RC hobby, I don’t understand why he’s using (as others have pointed out), that particular engine. Given that there are other lighter and more powerful options out there. I have a turbine powered ship using a JetCat turbine, it puts out tremendous power (runs off Jet-A), but pricey. Modern electric motors have equivalent torque/weight curves. Add modern LiPo packs, and it would seem it’s superior to that monster engine choice.

    1. You’re correct that there are other engines out there like the JetCat that have extremely high power to weight ratio. Looking at the specs on the JetCat SPT5 (Turbo Prop), it will deliver 55 lbf from a 5 lbm engine. (11 lbf/lbm vs. approximately 2.4 lbf/lbm for the riding lawn mower engine). But cost was a bigger factor. I wanted something the average maker could come close to affording. The riding lawnmower engine is 1k vs. 21k for 4 JetCat SPT5s. If you’re building a drone for the military and willing to pay a premium for weight, the JetCats are the way to go.
      On the project page I talk a little bit about why I went with this engine.
      The short version is that you have to chose the engine based on the how it fits in the system as a whole. For this application vertical shaft engines have the advantage that lightweight belts can be used instead of a heavy gearbox or drive shafts.

  5. Building large electric multicopters is not difficult at all, you simply add more batteries. This seems to be taking everything that has been learnt and throwing it out the window. I will be surprised if it flies at all.

    If it takes something brainless to stand out from the crowd of people trying to actually make decent useful incremental improvements based on researching what is out there already rather than reinventing the wheel then this whole competition is going to suck.

    1. I don’t think that’s fair. Incremental improvements are great for optimizing existing designs, but I feel this contest is about building something completely novel. Peter definitely has some challenges ahead of him, but if you read through his build logs and comment responses you’ll see he’s applied some basic principles to give his craft a good chance of getting off the ground. Either way, he’s going to learn a whole lot about aerodynamics and control systems, and by sharing everything he’ll make sure we can all learn too.

  6. I’ve seen multirotos that used a big engine for the main prop like a heli. Then used smaller rotors for the steering. It’s not too late for him to go that direction and it will make control easier.

    1. Hm… one central blade for lift, and 4 out on pylons to counter the rotation and control attitude? Maaaaybe… Simplest way might be to use an alternator powered by the engine, and electric motors for the 4 pylon-copters, so you’d have electronic control. Vs doing the whole thing mechanically, which sounds like a nightmare unless you design helicopters for a living.

      Then again I’d guess ANY petrol copter over maybe 10cc would be a massive decapitation hazard. The point of electric ones is they’re safe and easy.

  7. You need to use a 2 cycal engine the can be used upside down and all angels and lighter and less moving parts the 4 cycal engine has to stay level and I know most of the carbs has floats so if it ever turned upside down are steep angles the oil will go into the cylinder and you will flood the engine are starve and kill it just think it in the air and the engine dies and thin it falls to ground ouch

  8. As many have said, a 2 stroke engine is the best option for getting a good enough power to weight ratio.
    I would be surprised if that lump got a foot off the ground.
    Four 2/ engines @ 22cc would be better power to weight ratio, have more control, and rotational speed of upto 12000rpm compared to 3500rpm of the lump shown.

  9. I just don’t see this 4-stroke lawn mower engine having the proper thrust to weight ratio to attain vertical flight, like at all.

    And using all metal structural components just adds to the weight.

    You don’t see many, if any, large scale RC craft using such an engine because they would never get off the ground, and these are planes that only need airspeed across the wings that are generating lift and are mostly made of much lighter balsa/plywood and fiberglass. Even as a “tractor” or “pusher” on a plane, these types of engines don’t work. Too heavy and as someone pointed out already, they have massive flywheels and cranks that want to spin the entire craft.

    I would have used at least an ultralight style motor that is designed for high output power in a stripped down, light weight package. Plus using vanes for thrust vectoring doesn’t sound very effective either in regards to controlling this beast.

    No offense intended here, but this sounds like someone that knows very little about aviation and aviation engineering attempting to do something extremely complex with all the wrong stuff.

    I guess in the end you could put an air skirt around it and have a hovercraft drone, but as far as actually flying…. Good Luck.

    1. I’m reminded of Clarke’s first law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

    2. I agree. Hovercraft sounds like a good idea why not go the whole hog and put the ride on mower blades back on and you’ve got yourself a behemoth of a remote controlled hover mower.

  10. IF power is an issue, he can always modify that engine to produce much more power. Those B&S professional series engines are designed to work hard for long periods of time at peak power, they usually use them for generators. If he goes out to a reputable machine shop and has the rotating assembly lightened and re-balanced as well as insuring a bit more airflow it would not surprise me if the engine makes quite a bit more than 30HP, the torque of those engines come at low rpm as well, which may be beneficial for that sort of aircraft. Brigs engines get raced in cart all over the country, there are speed parts for most of them. If all else fails they do make some micro turbochargers that usually fit 1.2L diesel generators that would be a perfect match for that engine, and it could possibly make over 100hp in short bursts, cooling it will become an issue with that, however if running e85 or straight alcohol it should be plenty sustainable due to the intercooling effects of the fuel, and the turbocharger will make the engine way more efficient at high altitude. As other have said battery power may get the same power to weight ratio, however it wont have the longevity or the repeatability of a god old IC.

    1. Or he could have just bought a proper Rotax engine that was designed from the get go for this sort of thing and probably saved money to boot. I’m just saying lawn mower engines have been around a long, long time, and you don’t see many of them them flying for a reason… Drones and multirotor craft arent exactly new, everybody just treats them as such because they are so affordable and newsworthy these days. And as for saying its “impossible”, no… Likely? Nope. Physics are what they are…

    2. And then there’s good ol’ n-n-n-nitrous! Or nitromethane! The high-explosive fuel of maniacs!

      Actually doing all this to a lawnmower engine, and then powering a helicopter, sounds like some sort of underground hardcore Scrapheap Challenge. I wonder how much weight / power / efficiency trouble he’s suffering with that engine. It’s a nice idea to make something great with what you have on you. I suppose using the correct engine would be a different project altogether.

      Then again there’s the Japanese guy who made his own personal backpack-copter, that only has enough lift for one small Japanese guy. When I saw it on TV, he ran it tethered to the ground rather than risk going up far enough to risk his life.

      I think a man-copter would be a good chance to win The Prize. Certainly would get more attention in the media than some kind of circuit board. I like circuit boards but I like heli-packs more.

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