The Current Advances of PCB Motors

There’s something to be said about the falling costs of printed circuit boards over the last decade. It’s opened up the world of PCB art, yes, but it’s also allowed for some experimentation with laying down fine copper wires inside a laminate of fiberglass and epoxy. We can design our own capacitive touch sensors. If you’re really clever, you can put coils inside four-layer PCBs. If you’re exceptionally clever, you can add a few magnets and build a brushless motor out of a PCB.

We first saw [Carl]’s PCB motor at the beginning of the year, but since then we’ve started the Hackaday Prize, [Carl] entered this project in the Prize, and this project already made it to the final round. It’s really that awesome. Since the last update, [Carl] has been working on improving the efficiency and cost of this tiny PCB motor. Part of this comes from new magnets. Instead of a quartet of round magnets, [Carl] found some magnets that divide the rotor into four equal pieces. This gives the rotor a more uniform magnetic field across its entire area, and hopefully more power.

The first version of this 3D printed PCB motor used press-fit bushings and a metallic shaft. While this worked, an extra piece of metal will just drive up the cost of the completed motor. [Carl] has redesigned the shaft of the rotor to get rid of the metallic axle and replace it with a cleverly designed, 3D printed axle. That’s some very nice 3D printing going on here, and something that will make this motor very, very cheap.

Right now, [Carl] has a motor that can be made at any board house that can do four-layer PCBs, and he’s got a rotor that can be easily made with injection molding. The next step is closed-loop control of this motor. This is a challenge because the back-EMF generated by four layers of windings is a little weak. This could also be accomplished with a hall sensor, but for now, [Carl] has a working PCB motor. There’s really only one thing to do now — get the power output up so we can have real quadcopter badges without mucking around with tiny brushed motors.

[Carl] has put up a few videos describing how his PCB motor works; you can check those out below.
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3000W Unicycle’s Only Limitation Is “Personal Courage”

Electric vehicles are fertile ground for innovation because the availability of suitable motors, controllers, and power sources makes experimentation accessible even to hobbyists. Even so, [John Dingley] has been working on such vehicles since about 2009, and his latest self-balancing electric unicycle really raises the bar by multiple notches. It sports a monstrous 3000 Watt brushless hub motor intended for an electric motorcycle, and [John] was able to add numerous touches such as voice feedback and 1950’s styling using surplus aircraft and motorcycle parts. To steer, the frame changes shape slightly with help of the handlebars to allow the driver’s center of gravity to shift towards one or the other outer rims of the wheel. In a test drive at a deserted beach, [John] tells us that the bike never went above 20% power; the device’s limitations are entirely by personal courage. Watch the video of the test, embedded below.

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Here’s Why Hoverboard Motors Might Belong In Robots

[madcowswe] starts by pointing out that the entire premise of ODrive (an open-source brushless motor driver board) is to make use of inexpensive brushless motors in industrial-type applications. This usually means using hobby electric aircraft motors, but robotic applications sometimes need more torque than those motors can provide. Adding a gearbox is one option, but there is another: so-called “hoverboard” motors are common and offer a frankly outstanding torque-to-price ratio.

A teardown showed that the necessary mechanical and electrical interfacing look to be worth a try, so prototyping has begun. These motors are really designed for spinning a tire on the ground instead of driving other loads, but [madcowswe] believes that by adding an encoder and the right fixtures, these motors could form the basis of an excellent robot arm. The ODrive project was a contender for the 2016 Hackaday Prize and we can’t wait to see where this ends up.

Travel in Style on an Electric Air Sled

What do you do during the winter months in Ohio? Sledding of course! Sledding normally takes place on hills, but [Peter Sripol] is no slave to the terrain. He’s built an air sled to conquer the barren wastelands of unplowed parking lots. Air sleds aren’t as outlandish as you might think — the Soviet Union had decades of success with them.

The project starts with toboggan style plastic sled. [Peter] built a frame into the plastic using an aluminum square. The frame is used to support a motor pod at the back of the sled. The motor, of course, comes from his DIY electric plane project. Don’t worry — [Peter] didn’t cannibalize his plane. The plane’s motors are being upgraded, and this is one of the originals.

The motor itself is quite a beast. It’s a 150cc equivalent brushless outrunner motor from HobbyKing. It’s not cheap either at around $450 USD.  The motor is controlled by an equally beefy brushless controller wired into a standard R/C car receiver. A pistol grip transmitter makes a great wireless throttle for the system.

Steering is a much more mechanical affair. The sled’s rudder is controlled much like that of an airplane. A steel cable pull-pull system is connected to a stick mounted in front of the pilot. The unreinforced styrofoam rudder turned out to be a weak point in the build — check out the video after the break to see the full story.

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Low-Power Motor Can Run for Years on a Coin Cell

Can you run an electric motor for two years on a single lithium coin cell? [IamWe] figured out how to do it, and even though his donut motor doesn’t look like any motor we’ve ever seen before, it’s a pretty solid lesson in low-current design.

The donut motor is really just a brushless DC motor with a sign-pole stator and a multi-pole rotor. The frame of the motor is built from a styrofoam donut, hence the motor’s name. The rotor is a styrofoam sphere with neodymium magnets embedded around its equator. A sharpened bicycle spoke serves as an axle, and clever magnetic bearings provide near-zero friction rotation. The stator coil comes from an old solenoid and is driven by a very simple two-transistor oscillator. [IamWe]’s calculations show that the single CR2032 coin cell should power this motor for over two years. This one looks easy enough to whip up that it might make a nice project for a long winter’s night. Watch it spin in the video below.

This one seems like a perfect entry for the Coin Cell Challenge contest. Sure, it may not be a coin cell jump starter for your car, but our guess is this motor will still be spinning in 2020, and that’s no mean feat.

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Rewire Your Own Brushless Motors

Hackaday likes the idea of fine-tuning existing hardware rather than buying new stuff. [fishpepper] wrote up a tutorial on rewinding brushless motors, using the Racerstar BR1103B as the example. The BR1103B comes in 8000 Kv and 10000 Kv sizes,  but [fishpepper] wanted to rewind the stock motor and make 6500 Kv and 4500 Kv varieties — or as close to it as he could get.

Kv is the ratio of the motor’s RPM to the voltage that’s required to get it there. This naturally depends on the magnet coils that it uses. The tutorial goes into theory with the difference between Wye-terminated and Star-terminated winding schemes, and how to compute the number of winds to achieve what voltage — for his project he ended up going with 12 turns, yielding 6700 Kv and 17 turns for 4700 Kv. His tutorial assumes the same gauge wire as the Racerstar.

Just as important as the theory, however, the tutorial also covers the physical process of opening up the motor and unwinding the copper wire, cleaning the glue off the stator, and then rewinding to get the required stats.

[fishpepper]’s handle has graced Hackaday before: he created what he calls the world’s lightest brushless FPV quadcopter. In addition to motors and drones, he also rocks a mean fidget spinner.

 

Open Source Motor Controller Makes Smooth Moves with Anti-Cogging

Almost two years ago, a research team showed that it was possible to get fine motor control from cheap, brushless DC motors. Normally this is not feasible because the motors are built-in such a way that the torque applied is not uniform for every position of the motor, a phenomenon known as “cogging”. This is fine for something that doesn’t need low-speed control like a fan motor, but for robotics it’s a little more important. Since that team published their results, though, we are starting to see others implement their own low-speed brushless motor controllers.

The new method of implementing anti-cogging maps out the holding torque required for any position of the motor’s shaft so this information can be used later on. Of course this requires a fair amount of calibration; [madcowswe] reports that this method requires around 5-10 minutes of calibration. [madcowswe] also did analysis of his motors to show how much harmonic content is contained in these waveforms, which helps to understand how this phenomenon arises and how to help eliminate it.

While [madcowswe] plans to add more features to this motor control algorithm such as reverse-mapping, scaling based on speed, and better memory usage, it’s a good implementation that has visible improvements over the stock motors. The original research is also worth investigating if a cheaper, better motor is something you need.