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.

3D Printed Hovercraft Takes to the Air

Instructables user [John_Hagy] and some classmates built an RC hovercraft as their final project in the Robotics Education Lab at NC State University. It’s a foam slab with a Hovership H2204X 2300Kv brushless motor inflating a skirt made out of ripstop nylon. Nylon is great here because it has a low friction coefficient and is nonporous to keep the air in. A second motor propels the craft, with a servo turning the whole motor assembly to steer. The team designed and 3D-printed fan holders which also help channel the air to where it’s supposed to go. Control is via a typical radio-control transmitter and receiver combo.

The project writeup includes a lot of fun detail like previous versions of the hovercraft as well as the research they undertook to learn how to configure the craft — clearly it’s their final paper put on the internet, and well done guys.

Needless to say, we at Hackaday can’t get enough of this sort of thing, as evidenced by this cool-looking hovercraft, this hovercraft made on a budget and this solar-powered ‘craft.

Smooth and Steady Cuts with an Improvised Power Feeder

Some woodworking operations require stock to be fed at a smooth, steady rate, for which purpose a power feeder is usually employed. They’re expensive bits of gear, though, and their cost can usually be borne only by high-output production shops. But when you need one, you need one, and hacking a power feeder from a drill and a skate wheel is a viable option.

It should come as no surprise that this woodshop hack comes to us from [Matthias Wandel], who never seems to let a woodworking challenge pass him by. His first two versions of expedient power feeders were tasked with making a lot of baseboard moldings in his new house. Version three, presented in the video below, allows him to feed stock diagonally across his table saw, resulting in custom cove moldings. The completed power feeder may look simple — it’s just a brushless drill in a wooden jig driving a skate wheel — but the iterative design process [Matthias] walks us through is pretty fascinating. We also appreciate the hacks within hacks that always find their way into his videos. No lathe? No problem! Improvise with a drill and a bandsaw.

Surprised that [Matthias] didn’t use some of his famous wooden gears in this build? We’re not. A brushless motor is perfect for this application, with constant torque at low speeds. Want to learn more about BLDC motors? Get the basics with a giant demo brushless motor.

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