The existing Raspberry Pi 400 almost-all-in-one computer is very, very slick. Fitting in the size of a small portable keyboard, it’s got a Pi 4 processor of the 20% speedier 1.8 GHz variety, 4 GB of RAM, wireless, Ethernet, dual HDMI outputs, and even a 40-pin Raspberry Standard IDE-cable style header on the back. For $70 retail, it’s basically a steal, if it’s the kind of thing you’re looking for because it has $55 dollars worth of Raspberry Pi 4 inside.
In some sense, it’s getting dangerously close to fulfilling the Raspberry Pi Dream. (And it’s got one more trick up it’s sleeve in the form of a huge chunk of aluminum heat-sinked to the CPU that makes us think “overclocking”.)
We remember the founding dream of the Raspberry Pi as if it were just about a decade ago: to build a computer cheap enough that it would be within everyone’s reach, so that every school kid could have one, bringing us into a world of global computer literacy. That’s a damn big goal, and while they succeeded on the first count early on, putting together a $35 single-board computer, the gigantic second part of that master plan is still a work in progress. As ubiquitous as the Raspberry Pi is in our circles, it’s still got a ways to go with the general population.
The Raspberry Pi Model B wasn’t, and isn’t, exactly something that you’d show to my father-in-law without him asking incredulously “That’s a computer?!”. It was a green PCB, and you had to rig up your own beefy 5 V power supply, figure out some kind of enclosure, scrounge up a keyboard and mouse, add in a monitor, and only then did you have a computer. We’ve asked the question a couple of times, can the existing Raspberry Pi 4B be used as a daily-driver desktop, and answered that in the affirmative, certainly in terms of it having adequate performance.
But powerful doesn’t necessarily mean accessible. If you want to build your own cyberdeck, put together an arcade box, screw a computer into the underside of your workbench, or stack together Pi Hats and mount the whole thing on your autonomous vehicle testbed, the Raspberry Pi is just the ticket. But that’s the computer for the Hackaday crowd, not the computer for everybody. It’s just a little bit too involved.
The Raspberry Pi 400, in contrast, is a sleek piece of design. Sure, you still need a power supply, monitor, and mouse, but it’s a lot more of a stand-alone computer than the Pi Model B. It’s made of high-quality plastic, with a decent keyboard. It’s small, it’s light, and frankly, it’s sexy. It’s the kind of thing that would pass the father-in-law test, and we’d suggest that might go a long way toward actually realizing the dream of cheaply available universal (open source) computing. In some sense, it’s the least Hackaday Raspberry Pi. But that’s not saying that you might not want one to slip into your toolbag.
You can’t send Hackaday a piece of gear without us taking it apart. Foolishly, I started by pulling up the sticker, thinking I felt a hidden screw head. Nope, injection molding mark. Then, I pulled off the rubber feet. More molding marks. (Kudos for hiding them so nicely!) Save yourself the trouble; all you have to do to get the Pi 400 open is to pry gently around the edge, releasing each little plastic clip one after the next. It only takes five minutes, and as it says in the motorcycle repair manuals, installation is the reverse of removal.
Inside, there’s a flat-flex that connects the keyboard, and you see that big aluminum heat sink. It’s almost the full size of the keyboard, and it’s thick and heat-taped to the CPU. You know it means business. It’s also right up against the aluminum bottom of the keyboard, suggesting it could get radiative help that way, and maybe keep your fingers warm in the winter. (I didn’t feel any genuine heat, but it’s gotta go somewhere, right? There are also vents in the underside of the case.)
Four PZ1 screws and a little bit of courage to unstick the pad get you underneath the heat spreader to find, surprise!, a Raspberry Pi 4. This was a little anticlimactic, as I’ve just spent a couple weeks looking over the schematics for my review of the new Compute Module 4, and it’s just exactly what you’d expect. It’s a Raspberry Pi 4, with all the ports broken out, inside a nice keyboard, with a beefy heat spreader. Ethernet magnetics sit on one side, and the wireless module sits on the other. That’s it!
How hackable is the Pi 400? Not very. There’s not much room for any kind of foolery in here, because the heat spreader takes up most of the interior volume. Folks who want to replace the USB 3.0 with a PCIe could probably do that, of course, but they’d be better served with a compute module and some DIY. You could try to cram other stuff in here, but with the convenient 40-pin port on the back, you’ll want to connect anything of any size with a cable anyway. It’s not so much that it’s not hackable as I don’t know why you would. (As always, we’re happy to be proven wrong!)
There are two packages for the Raspberry Pi 400: the basic and the full kit, for $70 and $100 respectively. The extra $30 gets you a nice USB C power supply, a Raspberry mouse, a micro-HDMI to regular HDMI cable, a name-brand SD card preloaded with Raspberry Pi OS, and the Official Raspberry Pi Beginner’s Guide. In short, everything you need to get started except a monitor. All of these things are already available, but you can get them bundled in for convenience.
The book is a nice intro that’s basically a guided tour of the great learning content already available on the Raspberry Pi website. The cable, power supply, and mouse are all good to have, and it’s certainly nice not to have to obtain and burn another SD card, but these are more comfort than necessity. Aside from the micro-HDMI cable, I had everything on hand anyway, though if this were a permanent installation, I would probably need to source another USB C wall wart.
I don’t know if it was just for the review model, but it was a nice touch that the SD card was already in the slot. That saved me maybe 10 seconds, but it might have confused someone who is not used to thinking of an SD card as a hard drive.
Convenience, simplicity, and ease of getting set up is exactly the name of the game here, and I think the full kit makes good on that promise. It was about as plug-and-play as possible.
The Pi 400 is the least Hackaday Raspberry Pi. It’s a very slick piece of inexpensive, consumer computing for the masses. The full package is absolutely what I would supply to my father-in-law. And that makes it also the first Raspberry Pi computer to really make good on the accessibility aspect of the founding dream, where they had already hammered the price. Congratulations to the Raspberry Pi folks are in order. This computer, combined with their decade-long investment in producing educational material to guide a newbie along the path, embody that dream.
This may not be the computer you want for a hacker project. That’s what the Model B is for. It’s probably not full of modification possibilities, though we’ll see what you all think. And it’s not, as far as we know, available with the full range of memory options either. If you don’t need the frills of the full package, the $70 price is a small upsell from the $55 of the equivalent Model B, but when you don’t need a keyboard or the nice case, you could put the $15 to use elsewhere.
Still, combine this with a small touch screen, and run it all off of a 5 V power pack, and you’ve got a ton of portable computing in a very small package. If you’re not mousing around all the time anyway, there’s a certain streamlined simplicity here that’s mighty tempting. The 40-pin port on the back makes it easy to add your own gear too, say if you want to use it as a portable logic analyzer, microcontroller programmer, or JTAG platform. I actually prefer the horizontal orientation of this Pi port over the vertical of the Model B — my projects always end up looking like hedgehogs, and gravity wants cables to lie flat. These are small details, but that’s usability.
Finally, I have a Compute Module, a Pi 4 Model B, and now the Pi 400 all sitting on the desk. The Pi 4 is known to throttle when it overheats, which conversely means that it runs faster with a heatsink, even without overclocking. There was mention in the Compute Module datasheet about more efficient processing using less power, and presumably producing less heat. And this big hunk of aluminum inside the Pi 400’s case calls out “overclocking” to me. There’s only one way to figure out what all this means, and that’s empirical testing. Stay tuned.
These last few weeks I’ve been ordering parts for the Hackaday Testbed, a basic quadcopter to be used here at Hackaday. The top question I see when surfing multicopter forums is “What should I buy”. Which frame, motors, props, speed controller, and batteries are best? There aren’t easy answers to these questions with respect to larger quads (300mm or more) . There are a myriad of options, and dozens of vendors to choose from.
Advice was simple in the pre-internet days of R/C planes and helicopters: just head down to your local hobby shop, and see what lines they carry. Hook up with a local club and you’ll have some buddies to teach you to fly. This advice still holds true to a certain extent. Some hobby shops carry the DJI and Blade lines of multicopters. However, their flight control systems are closed source. If you really want to dig in and adjust parameters, you have to either buy a combo package with an open source flight control system, or buy every part separately. Unfortunately, very few local hobby shops can afford to stock individual parts at that level.
In the online world there are several “big” vendors. The classic names in the USA have always been Tower Hobbies and Horizon Hobby. Some new US-based companies are All e RC and ReadyMadeRC. Several Chinese companies, including HobbyKing and RcTimer, maintain warehouses in several parts of the world. I’m only listing a few of the big names here. If I’ve left out your favorite site, drop some info in the comments section.
The killer with many of these companies is supply. A popular component will often go out of stock with no hint as to when it will be available again. When it comes to single parts like batteries, it’s easy to just order a different size. But what about motors or speed controls? These components need to be matched on a multicopter. Changing one for a different model means changing all of them, so it pays to buy a spare or two when ordering! Click past the break for a breakdown of some multicopter parts.
Power systems have been a tough problem since the early days of radio controlled planes. Picking the right power system is a lot like picking the correct microcontroller or op-amp for a circuit design. There are a seemingly endless number of parameters to be taken into account. Once you break it down though, it isn’t too hard.
Motor part numbers are often encoded in terms of stator or can sizes. A DJI 2212 motor means it has a 22mm diameter stator which is 12mm tall. This isn’t a hard and fast rule though, so don’t live by it. The first and foremost parameter in a motor is KV –
Thousands of RPM per Volt. Theoretically, an 800KV motor will turn 800 RPM on a 1V power source. A 14.8V 4S LiPo battery will spin the motor at 11,840 RPM. It’s important to remember that this is a no load rating. The motor’s RPM will drop significantly when it’s spinning a prop.
The next number to look at is the voltage the motor is rated at. Sometimes this value is represented in volts, and sometimes in cells, which usually refers to the 3.7V nominal voltage of LIPO cells. A motor capable of handling a voltage of 4S means it’s good for 4 LiPo cells in series, or 14.8V.
For the Hackaday Testbed, I went with the NTM Prop Drive 28-30S 800KV / 300W motor. These motors are low cost, and should have plenty of power for our quadcopter.
In the old days, R/C plane throttles were controlled by a servo moving a switch. It was full throttle or nothing. Thankfully those days are gone, and we have cheap MOSFETs around to supply us digitally controlled throttles for our brushless motors. Speed controls are generally rated by maximum voltage and current. Figuring out which to buy is simply a matter of matching one to the motor you plan to use. Sometimes manufacturers overstate their speed control’s capabilities. Therefore, it’s often a good idea to leave a bit of overhead, lest you let out the magic smoke.
One more parameter to look at is SimonK firmware. Simon Kirby figured out that many cheap speed controls were running Atmel microcontrollers. He reverse engineered a few boards and wrote his own open source firmware with features like soft start, calibration, and easy parameter updates. Make sure the speed control you choose is compatible with SimonK firmware. Even if it is compatible, check how easy it is to flash the controller. Some controllers have easily accessible testpoints, others require soldering directly to the micrcontroller.
For the Hackaday Testbed, I went with the HobbyKing Blue Series 30Amp controller.
Much like speed controls, batteries will depend on the current and voltage requirements of the prop and motor combination. Lithium Polymer battery packs are sold with three basic parameters: Cell count, capacity, and maximum current. Size and weight are also important – don’t buy a battery so big your quadcopter can’t lift it!
3S and 4S batteries are common in multicopters these days. Maximum current is usually stated in therms of “C”, or the capacity of the battery. A 4000mAh battery with a rating of 45C is stating that it can supply 4 amps for 1 hour, or a maximum current of 180 Amps. It goes without saying that drawing 180 Amps is not a good idea for the overall longevity of the battery.
For the Hackaday Testbed I went with Zippy 35C constant / 45C burst 4S 4500 LiPos.
Multicopter Propellers can confuse even veteran pilots. Props are rated with two numbers. 9×6, 8×4, or 10×4.7 are all common propeller sizes. But what does it all mean?
The first number is diameter. The second number is pitch. Diameter is simple. A 10×4.7 propeller will have a diameter of 10 inches. Pitch is a bit harder. The pitch number of a propeller describes how far the propeller will move forward in a single revolution. If you spin a 10×4.7 propeller it will theoretically pull your plane (or quadcopter) forward 4.7 inches. A 10×6 propeller would pull forward 6 inches. Things get even more complex – how different is a 10×4.7 vs a 9×6? The answer is not much.
For the Hackaday Testbed, I’m going to test several propellers, starting with a conservative 10×4.7.
While propeller and overall drive system performance can be calculated by hand, a computer can be a big help. There are several software packages available to aid with propeller and drive system selection. eCalc is a website based calculator with a free trial and a subscription pay version. Make sure you select the correct calculator, as they have different versions for planes, helicopters, electric ducted fans, and multicopters. A second option is MotoCalc, which is downloadable software. MotoCalc also has a time limited trial. Freeware options are PropCalc and DriveCalc.
Nothing beats real world tests though. Years ago, the Astro Wattmeter created a small revolution in the market. The Wattmeter plugs inline with the battery and measures total current draw and voltage of the drive system. From these values it can calculate power, mAh used/remaining and several other values. One thing to remember is that a propeller will perform differently on a test bench (Static thrust) vs in the air (dynamic thrust). To this end, there are on-board Wattmeter style systems which can either send telemetry data back, or store it for later download.
Multicopter frames come in a multitude of shapes and sizes. The most basic difference between them is the number of motors they carry. Tricopters use three motors in a “Y” formation. A servo tilts the motor at the bottom of the Y to achieve yaw control. One nicety of the tricopter configuration is that all propellers turn in the same direction.This means standard airplane props can be used all around.
Moving up the chain is the quadcopter, which uses four motors and props. Quads (and all sizes beyond tricopters) use matched sets of clockwise and counterclockwise rotating propellers. When all four motors are rotating at the same rate, yaw due to torque effect is canceled out. Increasing throttle to one set of motors while decreasing to throttle on the other set allows for yaw control.
Moving beyond the basic multicopter types, we have the hexacopters and octocopters. The advantage to Hex and Octo format is of course more power! Hexes and Octos can lift more, and in some cases can keep flying if a single motor fails. Hexactopers can be laid out with six arms from a central point, or they can be in the Y-6 formation. Y-6 is essentially a tricopter with stacked counter rotating props at each point of the “Y”. Similarly octocopters can be an 8 pointed star, or an X-8 formation. Y-6 and X-8 formations offer reduced weight due to less arms, however stacked propellers are always somewhat less efficient than two propellers operating in clean air.
Another decision to make is materials. In this case the sky is basically the limit. Multicopter frames can be as simple as a couple of crossed sticks or as complex as interlocking plates with tubes of woven carbon fiber. Kits can be purchased, or designs can be hand made. If you’re scratch building, the local hardware store is often a great source of parts. I’ve seen everything from towel rod to PVC pipe pressed into service as part of a multicopter frame.
The Hackaday Testbed will have a few frames, but I’m starting out with an aluminum and fiberglass model from HobbyKing.
Stay tuned for this one. Flight control and radio control systems will get their own columns. Suffice it to say, we’re going to try several, starting with the MultiWii and the KK2 multicopter boards.
Wow, this turned out to be quite the long post. Until next time, keep on Droning On!
Title Photo by [Alexander Glinz]