We’ve been keeping a close eye on [Nick Rehm]’s cool spinning drone project, which basically eschews a rigid airframe for a set of three airfoils joined to a central hub. The collective pitch of the blades can be controlled via a servo in the hub, and the whole thing can be made to rotate and provide lift thanks to the thrust of tip-mounted motors and props. We’ve seen [Nick] manage to get this contraption airborne, and hovering is pretty straightforward. The video below covers the next step: getting pitch, roll, and yaw control over the spinning blades of doom.
The problem isn’t trivial. First off, [Nick] had to decide what the front of a spinning aircraft even means. Through the clever uses of LED strips mounted to the airfoils and some POV magic, he was able to visually indicate a reference axis. From there he was able to come up with a scheme to vary the power to each motor as it moves relative to the reference axis, modulating it in either a sine or cosine function to achieve roll and pitch control. This basically imitates the cyclic pitch control of a classic helicopter — a sort of virtual swashplate.
The results of all this are impressive, if a bit terrifying. [Nick] clearly has control of the aircraft even though it’s spinning at 250 RPM, but even cooler is the bit where he kills first one then two motors. It struggles, but it’s still controllable enough for a bumpy but safe landing.
Spacecraft rocket engines come in a variety of forms and use a variety of fuels, but most rely on chemical reactions to blast propellants out of a nozzle, with the reaction force driving the spacecraft in the opposite direction. These rockets offer high thrust, but they are relatively fuel inefficient and thus, if you want a large change in velocity, you need to carry a lot of heavy fuel. Getting that fuel into orbit is costly, too!
Ion thrusters, in their various forms, offer an alternative solution – miniscule thrust, but high fuel efficiency. This tiny push won’t get you off the ground on Earth. However, when applied over a great deal of time in the vacuum of space, it can lead to a huge change in velocity, or delta V.
This manner of operation means that an ion thruster and a small mass of fuel can theoretically create a much larger delta-V than chemical rockets, perfect for long-range space missions to Mars and other applications, too. Let’s take a look at how ion thrusters work, and some of their interesting applications in the world of spacecraft!
It’s often said that getting into orbit is less about going up, and more about going sideways very fast. So in that sense, the recent launch conducted by aerospace startup Astra could be seen as the vehicle simply getting the order of operations wrong. Instead of going up and then burning towards the horizon, it made an exceptionally unusual sideways flight before finally moving skyward.
As you might expect, the booster didn’t make it to orbit. But not for lack of trying. In fact, that the 11.6 meter (38 feet) vehicle was able to navigate through its unprecedented lateral maneuver and largely correct its flight-path is a testament to the engineering prowess of the team at the Alameda, California based company. It’s worth noting that it was the ground controller’s decision to cut the rocket’s engines once it had flown high and far enough away to not endanger anyone on the ground that ultimately ended the flight; the booster itself was still fighting to reach space until the very last moment.
There’s a certain irony to the fact that this flight, the third Astra has attempted since their founding in 2016, was the first to be live streamed to YouTube. Had the company not pulled back their usual veil of secrecy, we likely wouldn’t have such glorious high-resolution footage of what will forever be remembered as one of the most bizarre rocket mishaps in history. The surreal image of the rocket smoothly sliding out of frame as if it was trying to avoid the camera’s gaze has already become a meme online, arguably reaching a larger and more diverse audience than would have resulted from a successful launch. As they say, there’s no such thing as bad press.
Naturally, the viral clip has spurred some questions. You don’t have to be a space expert to know that the pointy end of the rocket is usually supposed to go up, but considering how smooth the maneuver looks, some have even wondered if it wasn’t somehow intentional. With so much attention on this unusual event, it seems like the perfect time to take a close look at how Astra’s latest rocket launch went, quite literally, sideways.
A group of students at Boston University recently made a successful test of a powerful rocket engine intended for 100km suborbital flights. Known as the Iron Lotus (although made out of mild steel rather than iron), this test allowed them to perfect the timing and perfect their engine design (also posted to Reddit) which they hope will eventually make them the first collegiate group to send a rocket to space.
Unlike solid rocket fuel designs, this engine is powered by liquid fuel which comes with a ton of challenges to overcome. It is a pressure-fed engine design which involves a pressurized unreactive gas forcing the propellants, in this case isopropanol and N2O, into the combustion chamber. The team used this design to produce 2,553 lb*ft of thrust during this test, which seems to be enough to make this a class P rocket motor. For scale, the highest class in use by amateurs is class S. Their test used mild steel rather than stainless to keep the costs down, but they plan to use a more durable material in the final product.
It seems as though every week we see something that clearly shows we’re living in the future. The components we routinely incorporate into our projects would have seemed like science fiction only a few short years ago, but now we buy them online and have them shipped to us for pennies. And what can say we’ve arrived in the future more than off-the-shelf plasma thrusters for the DIY microsatellite market?
Although [Michael Bretti] does tell us that he plans to sell these thrusters eventually, they’re not quite ready for the market yet. The AIS-gPPT3-1C series that’s currently under testing is designed for the micro-est of satellites, the PocketQube, a format with a unit size only 5 cm on a side – an eighth the size of a 1U CubeSat. The thrusters are solid-fueled, with blocks of Teflon, PEEK, or Ultem that are ablated by a stream of plasma. The gaseous exhaust is accelerated and shaped by a magnetic nozzle that’s integrated right into the thruster. The thruster is mounted directly to a PCB containing the high-voltage supplies and control electronics to interface with the PocketQube’s systems. The 34-gram thrusters have enough fuel for perhaps 500 firings, although that and the specifics of performance are yet to be tested.
We’re not entirely sure what to call this one. It’s got the usual trappings of a drone, but with only a single rotor it clearly can’t be called by any of the standard multicopter names. Helicopter? Close, but not quite, since the rotor blades are fixed-pitch. We’ll just go with “monocopter” for now and sort out the details later for this ducted-fan, thrust-vectored UAV.
Whatever we choose to call it — builder [tesla500] dubbed it the simultaneously optimistic and fatalistic “Ikarus” — it’s really unique. The monocopter is built around a 90-mm electric ducted fan mounted vertically on a 3D-printed shroud. The shroud serves as a mounting point for the landing legs and for four servos that swivel vanes within the rotor wash. The vanes deflect the airstream and provide the thrust vectoring that gives this little machine its control.
Coming to the correct control method was not easy, though. Thanks mainly to the strong gyroscopic force exerted by the rotor, [tesla500] had a hard time getting the flight controller to cooperate. He built a gimballed test stand to work the problem through, and eventually rewrote LibrePilot to deal with the unique forces on the craft and tuned the PID loops accordingly. Check out the results in the video below.
Some attempts to reduce the number of rotors work better than others, of course, but this worked out great, and we’re looking forward to the promised improvements to come.
You’d be hard pressed to find an aircraft that wasn’t designed and tested without extensive use of simulation. Whether it’s the classic approach of using a scale model in a wind tunnel or more modern techniques such as computational fluid dynamics, a lot of testing happens before any actual hardware gets bolted together. But at some point the real deal needs to get a shakedown flight, and historically a favorite testing ground has been the massive dry lake beds in the Western United States. The weather is always clear, the ground is smooth, and there’s nobody for miles around.
Thanks to [James] and [Tyler] at Propwashed, that same classic lake bed approach to real-world testing has now been brought to the world of high performance quadcopter gear. By mounting a computer controlled thrust stand to the back of their pickup truck and driving through the El Mirage dry lake bed in the Mojave Desert, they were able to conduct realistic tests on how different propellers operate during flight. The data collected provides an interesting illustration of the inverse relationship airspeed has with generated thrust, but also shows that not all props are created equal.
The first post in the series goes over their testing set-up and overall procedure. On a tower in the truck’s bed a EFAW 2407 2500kV motor was mounted on a Series 1520 thrust stand by RCBenchmark. This stand connects to the computer and offers a scripted environment which can be used to not only control the motor but monitor variables like power consumption, RPM, and of course thrust. While there was some thought given to powering the rig from the truck’s electrical system, in the end they used Turnigy 6000mAh 4S battery packs to keep things simple.
A script was written for the thrust stand which would ramp the throttle from 0% up to 70% over 30 seconds, and then hold it at that level for 5 seconds. This script was run when the truck was at a standstill, and then repeated with the truck travelling at increasingly faster speeds up to 90 MPH. This procedure was repeated for each of the 15 props tested, and the resulting data graphed to compare how they performed.
The end result was that lower pitch props with fewer blades seemed to be the best overall performers. This isn’t a huge surprise given what the community has found through trial and error, but it’s always good to have hard data to back up anecdotal findings. There were however a few standout props which performed better at high speeds than others, which might be worth looking into if you’re really trying to push the envelope in terms of airspeed.