Aerial Robotics Hack Chat

Into the third dimension

Wednesday, June 8, 2022 12:00 pm PDT Local time zone:
Hack Chat
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Nick Rehm will host the Hack Chat on Wednesday, June 8 at noon Pacific.

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When it comes to robots, especially ones that need to achieve some degree of autonomy, the more constrained the environment they work in, the easier it is for them to deal with the world. An industrial arm tethered next to a production line, for example, only has to worry about positioning its tool within its work envelope. The problems mount up for something like an autonomous car, though, which needs to deal with the world in two -- or perhaps two and a half -- dimensions.

But what about adding a third dimension? That's the realm that aerial robots have to live and work in, and it's where the problems get really interesting. Not only are there hardly any constraints to movement, there are also the problems of aerodynamic forces to deal with, navigation in space, and control systems that need to respond to the slightest of perturbations without overcompensating.

The atmosphere is a tough place to make a living, and dealing with the problems of aerial robotics has kept Nick Rehm occupied for many years as a hobbyist, and more recently as a full-time aerospace engineer. Nick has spent his time away from the office solving the problems of autonomous flight, including detection and avoidance of mid-air collisions, development of vertical take-off and landing (VTOL) and fixed-wing aircraft, and even ground-effect aircraft. He'll drop by the Hack Chat to discuss the problems of aerial robots and the challenges of unconventional aviation, and help us figure out how to deal with the third dimension. 

  • Hack Chat Transcript, Part 2

    Dan Maloney06/08/2022 at 20:10 0 comments

    Joe Stavitsky12:45 PM
    @Nick Rehm couldn't you just use some form of current sensing? You know the current pretty well and also the shape of the conductor

    Nick Rehm12:46 PM
    @Joe Stavitsky I actually don't know of too many opensource software options for rotor design. Most stuff I've worked with was proprietary/in-house. Simple momentum analysis can get you a surprisingly long way though

    Thomas Shaddack12:46 PM
    @pascal.fust Yup. Homogenous, no fusing lines, 100% fill factor. Heard something about increase of fracture toughness by graphene or nanotubes.

    Joe Stavitsky12:46 PM
    @Nick Rehm So you have used commercial software? Which did you like?

    Nick Rehm12:47 PM
    One option for "3D Printed" rotors I've been thinking about is just using the 3d print as a mold for a cast epoxy/glass final product

    Joe Stavitsky12:48 PM
    I mean, who really cares about durability of 3d prints? At that price, the fragility is kind of the point. As long as it lasts the entire flight, and collisions will ground you no matter what your rotors are made of

    Joe Stavitsky12:49 PM
    @Nick Rehm also, do you recommend any kind of "wind tunnel arrangement" to test propellers, to control for temperature, humidity, etc?

    Myself12:49 PM
    Casting forfeits the advantage of being able to place infill where it's needed for strength but otherwise conserve lightness, which I think is a big deal in 3DP. Just need that second extruder with a carbon fiber strand that it can smush into the still-warm top layer before extruding more plastic over it ;)

    pascal.fust12:50 PM
    @Thomas Shaddack I mean, we are talking about tip speeds of 200-300km/h or more, depending on the design

    Nick Rehm12:50 PM
    If it's big enough, could even print out a channel to slot in a carbon spar after the fact. I've done that with tiny LW-PLA blades with a 2mm carbon spar

    Nick Rehm12:51 PM
    Yea I guess the big question is how big of a rotor are we talking?

    Myself12:52 PM
    Yeah, for land-based stuff I print 1/4-20-threaded hollows in a lot of my larger parts and add some all-thread when it's done printing. Something like that for CF tube would make a lot of sense.

    pascal.fust12:52 PM
    I think that size does not really matter as smaller size implies higher rotation speed, resulting in higher forces

    Nick Rehm12:53 PM
    @Joe Stavitsky re: wind tunnels: just be sure to keep your reynolds number constant

    Nick Rehm12:54 PM
    Fc = mv^2/r

    Joe Stavitsky12:54 PM
    @Nick Rehm cool makes total sense

    Sam Boardman joined  the room.12:55 PM

    pascal.fust12:55 PM
    And, rotational force is only part of the game.... don't talk about about torsion

    Nick Rehm12:55 PM
    Fun fact: only reason heli blades don't break despite being so flimsy is that the centripetal force literally pulls them tight

    Joe Stavitsky12:56 PM
    @Nick Rehm We heart Physics =P

    Myself12:56 PM
    makes sense, also why they wobble so much as they go around their circle

    Joe Stavitsky12:57 PM


    Nick Rehm12:57 PM

    Myself12:57 PM
    oh now I'm gonna have the Airwolf theme in my head

    Joe Stavitsky12:57 PM
    Underrated movie

    Nick Rehm12:58 PM
    Did I miss any questions/topics? Sorry tried my best to keep up. I can hang around for a few more minutes

    Myself12:58 PM
    Are you open to followup contact?

    pascal.fust12:59 PM
    Wobble is maybe not a problem, but twisting might destroy the nicest pitch

    Joe Stavitsky12:59 PM
    @Nick Rehm yeah I'd be really stoked if you had time to look at my props once I get started

    Nick Rehm12:59 PM
    Sure, ya'll can email me at Very happy to nerd out over projects or answer and deep questions about drones/helis/autonomy

    Thomas Shaddack1:00 PM
    @pascal.fust Aeroelasticity for the rescue?

    Nick Rehm1:00 PM
    Or I guess direct message me here; I don't check hackaday messages as often tho

    pascal.fust1:00 PM
    hmmm... if well predicted, it can work out

    Nick Rehm1:01 PM
    Keep the chord-wise structural center of your blade ahead of the lift center and most twisting problems...

    Read more »

  • Hack Chat Transcript, Part 1

    Dan Maloney06/08/2022 at 20:10 0 comments

    Dan Maloney12:00 PM
    Welcome to the Hack Chat everyone, let's get started. I'm Dan, I'll be modding today along with Dusan (I think) as we welcome Nick Rehm to talk about Aerial Robotics.

    Dusan Petrovic12:00 PM
    Hi Dan!

    Nick Rehm12:00 PM
    Hey everybody, can you hear me?

    Dusan Petrovic12:00 PM
    Welcome everyone!

    Joe Stavitsky12:00 PM
    No but we can see you :)

    Boian Mitov12:00 PM
    Hi @Dan Maloney and @Nick Rehm :-)

    Dan Maloney12:00 PM
    Hi Nick, thanks for coming on today. can you start us off with a little about yourself?

    pascal.fust12:00 PM
    nothing to hear, but I can read you

    Johan von Konow joined  the room.12:01 PM

    Dusan Petrovic12:01 PM

    Nick Rehm12:01 PM
    Sure Dan

    garrettmagma joined  the room.12:01 PM

    Nick Rehm12:02 PM
    I've been into radio control aircraft for about 14 years, so it was really fun to see the drone revolution happen in front of my eyes growing up. Graduated from University of Maryland in 2019 with BS in aero engineering, then went on to masters of aero/rotorcraft with a focus in aerial robotics/dynamics/control

    Nick Rehm12:02 PM
    My favorite era of aerial robots / done was the multi-wii flight controller days where I had to convince my mom that I needed to tear apart the wii controller to build a drone

    Joe Stavitsky12:03 PM
    Heh, I screwed around with that briefly

    Dan Maloney12:03 PM
    Did she buy it?

    Nick Rehm12:04 PM
    It finally clicked for her when she saw a wooden tricopter floating around the front yard haha

    Joe Stavitsky12:04 PM

    Dan Maloney12:04 PM
    Better to ask forgiveness than seek permission, right?

    anfractuosity12:04 PM
    was the wii controller used to control the drone, or in the drone out of interest

    Myself12:04 PM
    With an accompanying triumphant scream of "IT'S ALIIIiiiiiive!", I presume?

    Nick Rehm12:05 PM
    I think my parents loved the idea of RC because it kept me both in my room and away from video games

    RichardCollins12:05 PM
    @Nick Rehm Was your masters at University of Maryland? (College Park years were some of the best)

    Nick Rehm12:05 PM
    We used the IMU from the wii motion plus back before IMUs were cheap as heck

    anfractuosity12:05 PM
    cool :)

    pascal.fust12:06 PM
    nice hack

    Joe Stavitsky12:06 PM
    @Nick Rehm do you mind saying where you work?

    Nick Rehm12:06 PM
    Ahh yes, masters from maryland as well--I went straight from BS to my MS program because I was already well acquainted with the rotorcraft center team

    Nick Rehm12:07 PM
    I'm at JHU APL working as an aero engineer

    Nick Rehm12:07 PM
    I'll leave it at that, but obviously there is some overlap in hobby/job skills

    Joe Stavitsky12:07 PM
    @Nick Rehm awesome

    Cliff W joined  the room.12:07 PM

    Sheridan-Tech12:08 PM
    Could you tell us which kind of projects you have worked on

    Sheridan-Tech12:08 PM

    pascal.fust12:08 PM
    @Nick Rehm What do you think about the optimization of aircrafts for VTOL/fixed wing UAV ?

    Nick Rehm12:09 PM
    Sure, one project I have out there is an open-source flight controller which I use on every single flying thing I make:

    pascal.fust12:09 PM
    good stuff

    Nick Rehm12:09 PM
    It is meant as a teaching tool for people who aren't too familiar with software dev

    Yohan Hadji12:10 PM
    Hey Nick, what is in your opinion the next big challenge in the domain of small autonomous flying robots?

    Nick Rehm12:12 PM
    @pascal.fust I think optimization is extremely hard until the system constraints are defined really really well. For example, "we need a vtol that can fly for a long time".... Can that vtol transition and fly on a wing? Are there loitering constraints? Funny enough most problems not involving the need for a loitering camera can be solved with a regular fixed wing

    Joe Stavitsky12:13 PM
    @Nick Rehm I mean, in that formulation if you can circle small enough you can call it "loitering" I think?

    Nick Rehm12:13 PM
    @Yohan Hadji I think the big challenge always has been and will continue to be onboard state estimation. It's getting better with better sensors and lighter...

    Read more »

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