Archive for the 'Emergency Quadrotor' Category

 

A Slightly Less Sculpture-Like Quadrotor

Jul 20, 2011 in Emergency Quadrotor, Project Build Reports

Greetings, Internets. What’s the deal this time, I can’t even finish something before it goes live?! Anyways, to answer pretty much all questions about why the thing may or may not work, here’s a nice little video.

That’s right, it wiggles. Having no left-handed fans (ball is in your court, Hobbyking!), I could either use movable vanes or fixed angularly mounted fans to cancel the resultant torque from everything spinning in one direction. And by Robot Jesus if I’m going to have to mount something cockeyed or make something motorized and adjustable, I’m gonna do both of it at once. Hence, 1 dimensional thrust vectoring. Would that be like, thrust scalaring or something? The controlled wiggling should also let the vehicle translate and rotate without requiring thrust differential – it’s pointing the exhaust opposite the direction it wants to move the most in. This is the riskiest part of the whole project, and I am itching to see if it even makes sense.

As the video shows, the electrical system is now fully wired up and ready. I spent the evening coding up a storm, getting some basic running code completed that lets me test the  servos and determine their correct directions, and also calibrate the Turnigy S100A-HV controllers in software (as opposed to me twiddling a stick).

This is the primary wiring for one side. I ended up ditching the switch-in-the-middle idea after determining that the channels of the HK Quattro battery charger which charged the “high side” battery pack would also be mistakenly supplying power to the controllers. To eliminate this problem, I’d either have to add a second switch (pointless) or isolate all the battery charger channels from each other.

Turning the Quattro from a single 4-channel charger into four isolated one-channel chargers takes a little bit of trace-cutting and the result needs 4 independent isolated power supplies, like laptop or monitor brick adapters. It’s been done before on the Jedboard project, with a different model, but the Quattro isn’t that different. I’ll throw up some details on it later after my aforementioned laptop power bricks arrive.

Once I decided to go with the four channel isolated charger route, I wired up the power normally – the master switch governs the positive battery rail only. There are two switches on my switch panel, and the little one is a “precharge bypass” for the larger. Flipping this switch on before the larger key switch powers on the logic and also connects the controllers to the battery through a 10 ohm power resistor, letting the capacitance fill up slowly (instead of stepping from zero to 40 volts instantly, which would theoretically result in infinity amps). I decided there was enough bus capacitance involved in this whole system to warrant a precharge circuit.

I whipped up a quick charger panel with Deans connectors. The “isolation required” notice is just to make sure I never try shoving all the leads into eachother. There are no cell balance connectors here, though the packs have them; I’m going to balance the cells on a need basis only.

There was really no “signal wiring” to speak of for this build – the signals just plugged into eachother. In the center of the show is a 2.007 Arduino Nano incubator board, which was custom-made, custom-paid, and cuuuuustom-fitted for the 2.007 class.

Each circuit has a 5v BEC module that feeds into the carrier board. This gives me a degree of redundancy in the logic power and also relieves the stress of feeding four (or more?) unhappy servos from one BEC. The BECs are the entry-level Hobbyking HV 3 amp unit.

There’s nothing left but the software. Or is there?

A Quadrotor-shaped Sculpture, and the Continued Tragic Goals Reduction of the Land-Bear-Shark

Jul 17, 2011 in Emergency Quadrotor, Land-Bear-Shark, Project Build Reports

Hello Internets! If you want the latest about what’s going on with this design (since this post is kind of an awkward in-the-middle post where nothing is working yet), see the EQ category here.

-ChArLeSg, 19 July 2011

No, it doesn’t fly yet. Quit asking.

I basically spent the better part of a day putting together the entire frame and placing the components. Given that everything was rods-and-joiners, this process did not take long at all. The hard part was actually making sure things came out square (or 45 degrees in the case of that X). I also made a center coupler for the X that also mounts the flight controls. The coupler increases the torsional rigidity of the frame signifiantly by forcing the crossing rods to be a constant distance apart.

INSTANT QUADROTOR!!

Not really. In this picture, I’ve slipped the 4 fans on and aligned them pretty exactly according to the models. I cut the rods pretty exactly to length – tolerances of maybe +/- 1/16″, so overall the thing is very square.

The weight of the fans is causing a bit of upwards bow visible in the carbon fiber rod. That will be fixed once the ‘upper level’ is added.

Here are the cute little corner landing legs, still incomplete. Ultimately they’ll just have a section of carbon fiber tubing embedded in the hollow conical point, upon which will be impaled a nerf ball or similar squishy ball-shaped thing (no, not Ballcopter)

The second ‘level’ has been added, including the battery hangers, so now the frame is much stiffer. It’s still lacking in the torsional rigidity department (i.e. if I grapped each end with 2 fans and twisted), but that’s a given since the upper and lower rails aren’t really joined at all, and the CF tube is still somewhat flexible. Since this thing should never be picking itself up by 1 corner, I don’t think it’s problematic. I have, however, considered just cutting out a long balsa or lite-ply plate which bridges the long center gap between the tubes.

I really like my battery mounts here. They’re Velcro cinch straps from McMaster, and are perfect for things like hanging a not-too-heavy battery in a not-too-solid manner. Little flat 3d printed feet give the battery packs a surface to be aligned on, and also hold the nylon straps from falling off sideways.

Most important of all, they’re adjustable side to side and the rail itself is adjustable front-to-back. I’ll need it when I’m trying to balance this thing.

And here it is, with appended Arduino carrier board and a Razor 6DOF IMU appended on top of that. What’s missing? Well… everything else. The heavy power wiring needs to be added still, and then oh god the software.  The total weight in this picture is exactly 8 kilograms.

I probably just made some Aero/Astro folks cry there, but with all four fans hauling, I have 8 more kilograms to go.  (Okay, so realistically like 3 or 4!)

Can you spot the tiny quadrotor?

A visitor from Physical Sciences Inc. dropped by MITERS with that cute little thing in the center. It’s adorable…and exceptionally stable for something so small. I hope this contraption works…

failshark

So let’s see, what have I actually built compared to what I wanted the Land-Bear-Shark to be?

  1. Brushless drive, wireless dual-channel wrist-controlled, reversible, with electronic braking
  2. Brushed drive, wireless dual-channel wrist-controlled, reversible, with electronic braking
  3. Brushed drive, handheld radio controlled, forward-only, with electronic braking

I am proud (…?) to say that now it has been reduced to forward-only with coasting. And radio controlled…..barely.

After the last update, LBS kept blowing through motor controllers (sound familiar? Only all of my vehicles ever do that). For some reason, the signal-side and gate drive problems were never resolved, and the gate drive chips kept failing short. Their inputs simply became low impedance for some reason, causing the microcontroller pin voltages to no longer change sufficiently to indicate a shift in logic state. The outputs would also some times randomly die, but there was never a power semiconductor failure. That means I’m getting somewhere, right?

In any case, LBS was going to premier at the last Swapfest in June. Literally the morning of, I tried riding it to the event….and made it about 50 feet out of MITERS before the left side drivers gave out. Dragging that 70 pound brick back to the shop was unpleasant.  Then in late June, along with my partner in engineering malfeasance Amy, I replaced the drivers (again) for a joint “demo event” to staff in the Mechanical Engineering department. This time, I made it all the way onto campus and around some building. But once again, in the middle of blasting around in the hallways, the right side quit this time.

Derp. At least I had a pushcart to transport it back this time, because I was just going to leave it in someone’s office otherwise.

After that failure, LBS sort of sat on a stand at MITERS, taking up space until last week…

Clearly, I just needed a new start on the motor controllers. I didn’t care any more about regenerative braking, reversibility (standing on the thing while spinning in place is actually really hard and taxing on the motors), efficiency, brushlessness, or anything. I was just going to rig up a single-quadrant forward-and-coast-only controller. The most bone-simple thing you can build that can control any reasonable amount of power at all. This controller has been called Beast-it-troller because it’s time to just beast something.

This controller is a single low-side pull-down configuration. The reason there are “upper side” FETs is because they have been coerced into acting as diodes by bridging the gate and source leads. This acts as a flyback diode for the motor. The single low-side configuration is vulnerable to uncontrollable latchup failure.

Now, doesn’t that make you comfortable? Regardless, it’s dead simple and ran LOLrioKart for almost a year.

I designed it in about one hour and had the board files immediately sent to Advanced Circuits for fabrication. Their quick-turnaround basic service is reasonably cheap and great when you need a board…………….right about now.

I decided to totally gut the system wiring and start over, too. While I had all the components dismounted and unwired, I decided to do a full bench test on a current limited power supply. The code was knocked down to the barest functionality needed to go forward or do nothing. The dummy loads here are some adorable small Minertia servomotors picked up off a free stuff list.

A board designed in an hour probably has bugs and numbskull errors, and this was no different. Like every controller I’ve ever built (ever), it needed a Little Blue Wire hack. I neglected to actually route the MOSFET source pin (power side ground) to the gate drive IC’s gate return pin (signal side ground). While the grounds are in fact connected elsewhere, so it wasn’t the end of the world, having the gate drive return current come through a few extra feet of wire would have introduced noise into the system.

After that, it just kind of worked. It’s hard to get this type of controller wrong.

I also discovered that this thing has a very unique and convenient self-balancing service position.

The downside of the fowrard-or-bust control is that turning with a short radius is less predictable and more finicky, depending strongly on the available drag on the slower tread. It’s also almost impossible to turn in place unless I shift way back and keep most of my weight on the ball tail. However, larger radii and sweeping turns are no problem.

Guess what? July Swapfest is tomorrow!

Declaring Emergency (Quadrotor)

Jul 13, 2011 in Emergency Quadrotor, Project Build Reports

So I have been quietly working on quadrotor business for the past week and a half after Ballcoptering from 3000 miles away. All four of the thrust modules are done, due in part to Make-a-Bot logging something like 70 or more hours of cumulative operation during that time alone. There was also a little bit of work done shortly before I left, so this post will recap all of that. I’m fairly confident I can get this thing making an ungodly racket by the weekend (those fans are LOUD) if not a controlled and scientific one.

Speaking of science, I actually got the chance to put one of the tailcone-equipped fans onto the Fankart Rail for a real honest-to-robot-Jesus instrumentation session. I was curious to see how addition of the smooth cone surface would affect the thrust output of the fan – since without it, the motor ends bluntly. Given the exhaust velocity of ducted fans, I was expecting a difference of a few ounces at full throttle.

I think my expectations were in line. Using the same 10S lithium pack as last time, I got a maximum sustained 2.97 to 3.0 kgf of thrust. The pack dipped to 31.5 volts during this time. The results do closely match last times – 31.1v minimum and 2.85 kgf.  I didn’t get a RPM reading this time, however, and that extra 0.4 volts might well account for the difference.

But if that is not the case, the tailcone appears to net me back around 100 grams or so. Not that significant, but regardless it adds to my aero/astro cred, right?

It turned out that one of the stock 5mm adapters that I had reamed to 6mm was still way out of round. That’s how horrible they were to begin with. I didn’t have a small enough boring bar (that went deep enough, anyway) so I had to make do with a 6mm reamer. It probably just followed the path of least resistance anyway -  I didn’t mark the parts to distinguish them, but one of them was distinctly rushed.

To resolve this, I elected to just duplicate the most important dimensions on the stock part and make one myself from scratch. It worked well – while I couldn’t find a lathe which could turn metric threads (and did not have a 10mm x 1) die, 26 threads per inch is close enough to 25.4 (1mm pitch) that the prop nut was able to thread on enough.

I also managed to destroy one of them instantly when I forgot that I couldn’t thread at 600 RPM.

Oops. Luckily, I only needed one.

However, ultimately the effort was for nought – the one that I didn’t destroy was improperly reamed out to 0.238 instead of 0.236 (6mm). The other one was left at 15/64″ (0.234″) and it turned out to be a snug fit on the motor shaft. For some reason, I went for the loose oversize fit on the second because there wasn’t a 6mm reamer. That 0.002″ of radial play translates into OH GOD WHY DID I EVEN BOTHER at the end of the prop adapter once everything was tightened down.

So discovering that I can no longer Course 2 properly, I borrowed Shane’s prop adapter.  :<

After many hours of scraping 3d printer droppings, here are all 4 thrust pods completed!

The upper left controller is zip tied on since during my trip away, someone knocked the module off my shelf, breaking it into a few pieces, some of which was the Turnigy controller’s mounting flanges. I had spares of the wood parts, but still. Not smooth, bro. Not smooth at all.

At least they piled the wreckage very neatly back on my shelf and proceeded to not tell anyone.

I had to print a total of 32 of these little corner joiner things, in batches of 9. Pretty easy, right? Yeah, each batch took 4 hours and I had to make 3 more sets after discovering that some were done in the wrong orientation (where the lamellae of 3d printing are stressed in their weakest direction). Oh, and one set died mid-print, so that’s one more.

While I was staring idly at the printer, I whipped up these switch panels. They’ll attach in between the upper and lower set of frame rods. This thing will have a front and back power system, since otherwise I’d be facing very long wiring runs. This setup doesn’t necessarily weigh less (in fact, the Hella switches are about 4 ounces each), but it simplifies the wiring somewhat. Each battery feeds 2 controllers directly instead of all battery wires coming together and then branching off again. I also get the benefit of redundant 5v BECs, one from each battery. The small switches are designed for precharge circuitry, allowing the logic to be powered without main power application (and also not beating the controllers in the face with all 40-odd volts of the battery at once).

I’m actually going to try a very unconventional arrangement for the master power switch. Because the Hobbyking 10S batteries are actually 2 discrete 5S packs with a middle “bridge” connector, I’m going to wire these switches such that they open and close that middle bridge. This should, in theory, split the battery into those 5S packs with an isolated center, allowing me to charge them with a single 4-channel charger. I have yet to work out all the implications of this, but it SHOULD work.

So here’s what a batch of parts looks like fresh off MaB’s print bed. It’s covered in stringers, little noodles, and support lattices which are also extruded ABS, so some degree of knifework and sanding is required to clean the parts up afterwards. These are the joists for the center truss.

But this is what they look like after they’re cleaned up!

With these important pieces complete, I could start cutting carbon fiber tube to length. The right angle pieces also shown here are the (+37) Rails of Battery Mounting, which are actually made using square CF tubing.

I couldn’t assemble the entire frame, however. I didn’t design any means of landing this thing safely yet, and putting the frame together would have meant that the motors were sitting on the tailcones. Probably not good news, and definitely not good if I want a remotely aligned frame.

So I made a frameholding jig for the time being. Its only purpose right now is to create a place I can safely put the quadrotor down on.  This is not landing gear, though it’s of the right shape and not very heavy, so maybe it could be pressed into the task. This little thing is made from laser cut 1/4″ cheap plywood. The V grooves seat the carbon fiber frame tubes, and the distance between towers is also exactly the distance between the joists of the truss.

To come: Putting it all together!

I already received the ultrasonic distance sensors and the IMU, so after frame assembly I should be able to move quickly onto master power wiring. Otherwise, this thing is mostly plug-and-(program-and-test-and-)play.

More Thrust Vectoring

Jul 07, 2011 in Emergency Quadrotor, Project Build Reports

I’m back.

Wait, where did I go for like 2 weeks? I’ll explain that later, as well as detail what Shit Went Down™, but I was finally able to run the Emergency Quadrotor fan with thrust vectoring on a full 36 volts:

Yeah, I just kind of grabbed it. No thrust measurements except “wow, my arm is sore from holding onto that”, but I wouldn’t expect it to be more than 4 kilograms as recorded legitimately before.

This test confirmed the servos as being strong enough to muscle around the fans, even at full speed. I was concerned that gyroscopic forces would mean the servos would act too slowly to control the vehicle, but they are still responsive. There is visually discernible lag if I manually “step” the servo position from limit to limit, but it’s not enough to concern me: the fans should never be split-second actuating from lock to lock.

The test also (fortunately) showed that the structure is strong enough to hold back the full force of the fan. There’s no reason itwouldn’t be, but still.

Next step: Make 3 more. Poor Make-a-Bot.

The Emergency Monorotor?!

Jun 22, 2011 in Emergency Quadrotor

The thrust vectoring module seen in the previous update has become a working object. So what I have now can potentially be turned into a midair single axis Segway, but I don’t think it quite works like that.  This module has been a physical refinement of the construction process – I’ve already made several changes and additions to the design which will be reflected in the rest of the modules. This one probably won’t make it onto the vehicle itself given its role as the guinea pig of the experiment.

The loose cage has now been assembled. Because the gaps here are so large from experimenting with laser cutter kerf, I used massive puddles of wood flour filled epoxy to assemble the joints. Most of them are filleted in addition to have epoxy between surfaces, and I clamped the entire thing down for a day (read: pile a large lead acid battery on top of) so it could set properly. The result is quite stiff, except at the corners where there is only 1/8″ lite plywood. It’s quite flexible there, and in the interest of not making a quadrotor with the torsional rigidity of thin sheets of plywood, I made an additional “corner thickener” for the outer corner which will bear the load of the frame tubes through those sidewalls. It’s attached through thick CA glue.

Next, notice that I’ve made a new controller mount. That flange is simply too floppy for me to want to mount anything to it, so that part will be “supplemented” with the 1/4″ thick part behind the cage. It will bolt through the 1/8″ wood and into the trunions below.

The rest of the modules will be built with the extra corner thickener and the bigger controller mount.

Those little plastic blocks to the left were made by my ever hard-working but rarely mentioned 3d printer:

 

Pictured are all the frame joiners, the pivot for the EDFs, and the smaller half of each trunion. MaB is sort of my unsung hero project – making alot of things easier, but always just kind of working so I never write anything about it. Unlike my other crap which breaks every time I think about staring at it wrong.

After cleaning the little nubs off with some selective sanding and knifing, the parts are ready for use.

Now, I don’t trust a 1/2″ nub of plastic with holding back 28,000 RPMs of ducted fan, so those nubs have center holes that reach almost all the way to the fan flange so I can glue something in which has meaningful shear strength – like chunks of the carbon fiber frame tubes.

I also printed off this cute little tailcone for the motor. It has 1mm walls and is vented so the motor can still flow cooling air through the center. Not having a blunt edge at the back will probably gain me back another ounce of thrust or something.

Here’s the servo linkage all hooked up. I actually reprinted one of the pivots to have a built in servo horn of sorts so I could use my stock of ball links. This arrangement worked well. The 2-56 threaded rod link allows me to fine tune the angle of the fan with respect to servo neutral.

(You know you’re in the future when you can say “I reprinted it and…”)

Here’s the rig readied for testing with the Controller Mounting Extension attached. The board bolting into the fan trunions is much stiffer than a chunk of wood hanging off of the main structure, and it also makes for more economical laser cutting since a huge tab like that doesn’t tesselate well at all.

Downside of printing with light fill to make things print quickly: They’re not structural really, at all. I think this was on 25% fill or something, but it exploded as soon as I applied meaningful bolt tension. I’ll clearly be doing these small parts in near-solid.

Here’s a short test video with me running the fan on 3S lipos…and a very discharged lipo at that. So there were maybe 10 volts going into this thing, period. It was still enough to shuffle the thing across a table with a 20AH lead acid battery on top of it.

MIT Tech TV

There you have it. I have yet to do a full power test on 10S lipos, but that needs to happen in order for me to see if the cage is structural enough…and if the servo can even wrestle the fan around at those speeds.

Oh yeah, here’s the biggest lipo I’ve ever seen. Seriously, how did this not set the plane on fire again?