Demonstrating The Mars Rover Pendulum Problem With A Drone On Earth

The sky crane system used on the Perseverance and Curiosity Mars rovers is a challenging control system problem that piqued [Nicholas Rehm]’s curiosity. Constrained to Earth, he decided to investigate the problem using a drone and a rock.

The setup and the tests are simple, but clearly illustrate the problem faced by NASA engineers. [Nicholas] attached a winch mechanism to the bottom of a racing-type quadcopter, and tied a mass to the end of the winch line. At first, he built a foam model of the rover, but it proved to be unstable in the wake of the quadcopter’s propellers, so he used a rock instead. The tests start with the quadcopter taking off with the rock completely retracted, which is then slowly lowered in flight until it reaches the end of the line and drops free. As soon as the rock was lowered, it started swinging like a pendulum, which only got worse as the line got longer. [Nicholas] attempted to reduce the oscillations with manual control inputs, but this only made it worse. The quadcopter is also running [Nicholas]’s own dRehmFlight flight controller that handles stabilization, but it does not account for the swinging mass.

[Nicholas] goes into detail on the dynamics of this system, which is basically a two-body pendulum. The challenges of accurately controlling a two-body pendulum are one of the main reasons the sky crane concept was shelved when first proposed in 1999. Any horizontal movement of either the drone or the rock exerts a force on the other body and will cause a pendulum motion to start, which the control system will not be able to recover from if it does not account for it. The real sky crane probably has some sort of angle sensing on the tether which can be used to compensate for any motion of the suspended rover. Continue reading “Demonstrating The Mars Rover Pendulum Problem With A Drone On Earth”

Hackaday Links: February 21, 2021

Well, that was quite a show! The Perseverance rover arrived on Mars Thursday. Don’t tell the boss, but we spent the afternoon watching the coverage in the house on the big TV rather than slaving away in the office. It was worth it; for someone who grew up watching Jules Bergman and Frank Reynolds cover the Apollo program and the sometimes cheesy animations provided by NASA, the current coverage is pretty intense. A replay of the coverage is available – skip to about the 1:15:00 mark to avoid all the filler and fluff preceding the “Seven Minutes of Terror” main event. And not only did they safely deliver the package, but they absolutely nailed the landing. Perseverance is only about 2 km away from the ancient river delta it was sent to explore for signs of life. Nice shooting!

We’re also being treated to early images from Jezero crater. The first lowish-rez shots, from the fore and after hazard cameras, popped up just a few seconds after landing — the dust hadn’t even settled yet! Some wags complained about the image quality, apparently without thinking that the really good camera gear was stowed away and a couple of quick check images with engineering cameras would be a good idea while the rover still had contact with the Mars Reconnaissance Orbiter. Speaking of which, the HiRISE camera on the MRO managed to catch a stunning view of Perseverance’s descent under its parachute; the taking of that photo is an engineering feat all by itself. But all of this pales in comparison to a shot from one of the down-looking cameras in the descent stage, show Perseverance dangling from the skycrane just before touchdown. It was a really good day for engineering.

Would that our Earthly supply chains were as well-engineered as our Martian delivery systems. We’ve been hearing of issues all along the electronics supply chain, impacting a wide range of industries. Some of the problems are related to COVID-19, which has sickened workers staffing production and shipping lines. Some, though, like a fire at the AKM semiconductor plant in Japan, have introduced another pinch point in an already strained system. The fire was in October, but the impact on the manufacturer depending on the plant’s large-scale integration (LSI) and temperature-compensated crystal oscillators (TCXO) products is only just now being felt in the amateur radio market. The impact is likely not limited to that market, though — TCXOs pop up lots of gear, and the AKM plant made LSI chips for all kinds of applications.

What do you get when you combine a 3D-printer, a laser cutter, a CNC router, and a pick-and-place robot? Drones that fly right off the build plate, apparently. Aptly enough, it’s called LaserFactory, and it comes from MITs Computer Science and Artificial Intelligence Lab. By making different “bolt-on” tools for a laser cutter, the CSAIL team has combined multiple next-generation manufacturing methods in one platform. The video below shows a drone frame being laser-cut from acrylic, to which conductive silver paste is added by an extruder. A pick-and-place head puts components on the silver goo, solders everything together with a laser, and away it goes. They also show off ways of building up 3D structures, both by stacking up flat pieces of acrylic and by cutting and bending acrylic in situ. It’s obviously still just a proof of concept, but we really like the ideas presented here.

And finally, as proof that astronomers can both admit when they’re wrong and have fun while doing so, the most remote object in the Solar System has finally received a name. The object, a 400-km diameter object in a highly elliptical orbit that takes it from inside the orbit of Neptune to as far as 175 astronomical units (AU) from the Sun, is officially known as 2018 AG37. Having whimsically dubbed the previous furthest-known object “Farout,” astronomers kept with the theme and named its wayward sister “Farfarout.” Given the rapid gains in technology, chances are good that Farfarout won’t stay the Sun’s remotest outpost for long, and we fear the (Far)nout trend will eventually collapse under its own weight. We therefore modestly propose a more sensible naming scheme, perhaps something along the lines of “Farthest McFaraway.” It may not scale well, but at least it’s stupid.

Hackaday Links: February 16, 2021

This is it; after a relatively short transit time of eight months, the Mars 2020 mission carrying the Perseverance rover has almost reached the Red Planet. The passage has been pretty calm, but that’s all about to end on Thursday as the Entry Descent and Landing phase begins. The “Seven Minutes of Terror”, which includes a supersonic parachute deployment, machine-vision-assisted landing site navigation, and a “sky-crane” to touch the rover down gently in Jezero crater, will all transpire autonomously 480 million km away. We’ll only learn about how it goes after the eleven-minute propagation delay between Mars and Earth, but we’ll be glued to the NASA YouTube live stream nonetheless. Coverage starts on February 18, 2021 at 11:15 AM Pacific Standard Time (UTC-8). We’ve created a handy time zone converter and countdown so you don’t miss the show.

As amazing as the engineering on display Thursday will be, it looks like the US Navy has plans to unveil technology that will make NASA as relevant as a buggy-whip company was at the turn of the last century. That is, if you believe the “UFO Patents” are for real. The inventor listed on these patents, Dr. Salvatore Pais, apparently really exists; he’s had peer-reviewed papers published in mainstream journals as recently as 2019. Patents listed to Dr. Pais stretch back to 2004, when he invented a laser augmented turbojet propulsion system, which was assigned to defense contractor Northrup Grumman. The rest of the patents are more recent, all seemingly assigned to the US Navy, and cover things like a “high-frequency gravitational wave generator” and a “craft using an inertial mass-reduction device”. There’s also a patent that seems to cover a compact fusion generator. If any of this is remotely true, and we remain highly skeptical, the good news is that maybe we’ll get things like the Epstein Drive. Of course, that didn’t end well for Solomon Epstein. Or for Manéo Jung-Espinoza.

Of course, if you’re going to capitalize on all these alien patents, you’re going to need some funding. If you missed out on the GME short squeeze megabucks, fret not — there’s still plenty of speculative froth to go around. You might want to try your hand at cryptocurrency mining, but with GPUs becoming near-unobtainium, you’ll have to get creative, like throwing together a crypto mining farm with a bunch of laptops. It looks like the Weibo user who posted the photos has laptops propped up on every available surface of their apartment, and there’s also a short video showing a more industrial setup with rack after rack of laptops. These aren’t exactly throw-aways from some grade school, either — they appear to be brand new laptops that retail for like $1,300 a pop. The ironic part is that the miner says this is better than the sweatshop he used to work in. Pretty sure with all that power being dissipated in his house, it’ll still be a sweatshop come summer.

A lot of people have recently learned the hard lesson that when the service is free, you’re the product, and that what Google giveth, Google can taketh away in a heartbeat, and for no discernable reason. Indie game studio Re-Logic and its lead developer Andrew Spinks found that out last week when a vaguely worded terms-of-service violation notice arrived from Google. The developer of the popular game Terraria was at a loss to understand the TOS violation, which resulted in a loss of access to all the company’s Google services. He spent three weeks going down the hell hole of Google’s automated support system, getting nothing but canned messages that were either irrelevant to his case or technically impossible; kinda hard to check your Gmail account when Google has shut it down. The lesson here is that building a business around services that can be taken away on a whim is perhaps not the best business plan.

And finally, we watched with great interest Big Clive’s secrets to getting those crisp, clean macro shots that he uses to reverse-engineer PCBs. We’ve always wondered how he accomplished that, and figured it involved some fancy ring-lights around the camera lens or a specialized lightbox. Either way, we figured Clive had to plow a bunch of that sweet YouTube cash into the setup, but we were surprised to learn that in true hacker fashion, it’s really just a translucent food container ringed with an LED strip, with a hole cut in the top for his cellphone camera. It may be simple, but you can’t argue with the results.

Continue reading “Hackaday Links: February 16, 2021”