Double Fed Induction Motors: Clever Motor Control Through Frequency

February 18, 2024 by Jenny List 27 Comments

Somewhere in most engineering educations, there’s a class on induction motors. Students learn about shaded-pole motors, two-phase and three-phase motors, squirrel cage motors, and DC-excited motors. It’s a pre-requisite for then learning about motor controllers and so-called brushless DC motors. [Jim Pytel] takes this a step further in a series of videos, in which he introduces the doubly fed induction motor. If a conventional three-phase motor can have its coils in either rotor or stator, here’s a motor with both. The special tricks with this motor come in feeding both rotor and stator with separate frequencies, at which point their interactions have useful effects on the motor speed.

There are two videos, both of which we’ve put below the break. Understanding the complex interaction of the two sets of magnetic fields is enough to make anyone’s brain hurt, but the interesting part for us is that the motor can run faster than either of the two drive frequencies.

Sadly we’re not aware of any easily available motors using this configuration, so we don’t think it will be possible to easily experiment. But if you want to amaze your friends with an in-depth knowledge of motors, take a look at the videos below.

Continue reading “Double Fed Induction Motors: Clever Motor Control Through Frequency” →

Brushless ESC Becomes Dual-Motor Brushed ESC With A Few Changes

February 15, 2024 by Lewin Day 15 Comments

What is a brushless ESC, really? Well, generally, it’s usually a microcontroller with a whole lot of power transistors hanging off it to drive three phases of brushless motor coils. [Frank Zhao] realised that with a little reprogramming, you could simply use a brushless ESC to independently run two brushed motors. Thus, he whipped up a custom firmware for various AM32-compatible ESCs to do just that.

The idea of the project is to enable a single lightweight ESC to run two brushed motors for combat robots. Dual-motor brushed ESCs can be hard to find and expensive, whereas single-motor brushless ESCs are readily available. The trick is to wire up the two brushed motors such that each motor gets one phase wire of its own, and the two motors share the middle phase wire. This allows independent control of both motors via the brushless ESC’s three half-bridges, by setting the middle wire to half voltage. Depending on how you set it up, the system can be configured in a variety of ways to suit different situations.

[Frank’s] firmware is available on Github for the curious. He lists compatible ESCs there, and notes that you’ll need to install the AM32 ESC firmware before flashing his version to make everything work correctly.

The VESC project has long supported brushed motor operation, too, though not in a tandem configuration. Meanwhile, if you’ve got your own neat ESC hacks, don’t hesitate to hit us up on the tipsline!

The Chocolate Must Flow This Holiday Season

December 7, 2023 by Kristina Panos 8 Comments

After a long December of hand-coating chocolates for relatives last year, [Chaz] decided that enough was enough and built a chocolate enrobing machine to do the dirty work for him. As a side project, he built a rotary tumbler to chocolate-coat things like wasabi peas, which we assume are designated for [Chaz]’s enemies.

This build started with an off-the-shelf chocolate fountain for which [Chaz] designed and printed a new nozzle in PLA. He also knocked off the flutes that make it fountain on the band saw and removed the rest of the material on the lathe.

The conveying bit comes from a conveyor toaster oven that [Chaz] had lying around — he removed the conveyor and hooked it up to a motor from his collection using a slightly modified flex coupler.

With the chocolate enrober complete, [Chaz] moved on building to the rotary tumbler, which is made from two thrift store pans hammered together at the edges and connects up to the front of a KitchenAid mixer. The final verdict was that this did not work as well as the enrober, but it wasn’t a complete bust — wasabi peas (and most of the kitchen) got coated in chocolate.

While we’re not sure we’d use that PLA chocolate pump more than once, we sure would like to enrobe some things in chocolate, and this seems like a good way to get it done. Check out the build video after the break.

Chocolate is good for more than coating everything in sight. Speaking of sight, check out these chocolate optics.

Continue reading “The Chocolate Must Flow This Holiday Season” →

Variable-Nozzle Ducted Fan Provides Fluid Dynamics Lessons

October 19, 2023 by Bryan Cockfield 15 Comments

Any student new to the principles of fluid dynamics will be familiar with Bernoulli’s principle and the Venturi effect, where the speed of a liquid or gas increases when the size of the conduit it flows through decreases. When applying this principle to real-world applications, though, it can get a bit more complex than a student may learn about at first, mostly due to the shortcomings of tangible objects when compared to their textbook ideals. [Mech Ninja] discovered this while developing a ducted fan based around an RC motor.

The ducted fan is meant to be a stand-in for a model jet engine, based around a high-powered motor generally designed for drone racing. Most of the build is 3D printed including duct system, but in order to improve the efficiency and thrust beyond simple ducting, [Mech Ninja] designed and built a variable nozzle to more finely control the “exhaust” of his engine. This system is also 3D printed and can restrict or open up the outflow of the ducted fan, much like a real jet engine would. It uses two servos connected to collars on the outside of the engine. When the servos move the collars, a set of flaps linked to the collars can choke or expand the opening at the rear of the engine.

This is where some of the complexity of real-life designs comes into play, though. After testing the system with a load cell under a few different scenarios, the efficiency and thrust weren’t always better than the original design without the variable nozzle. [Mech Ninja] suspects that this is due to the gaps between the flaps, allowing air to escape and disrupting the efficient laminar flow of the air leaving the fan, and plans to build an improved version in the future. Fluid dynamics can be a fairly complex arena to design within, sometimes going in surprising directions like this ducted fan that turned out better than the theory would have predicted, at least until they accounted for all the variables in the design.

Continue reading “Variable-Nozzle Ducted Fan Provides Fluid Dynamics Lessons” →

New Electric Motor Tech Spins With No Magnets

September 10, 2023 by Al Williams 58 Comments

When you think of electric motors, you usually think of magnets. But magnets are heavy, and good magnets can pose problems when you need lots of them. A technology called SESM (separately excited synchronous motors) requires no magnets, but now ZF — a German company — claims to have a different scheme using inductive excitation. Motors that employ SESM tend to be larger and require a direct current to turn the rotor. This DC is often supplied by slip rings or an AC induction with a rectifier. The innovation here is that the inductive excitation is built completely into the shaft, which the company claims makes the motor both compact and powerful.

This kind of motor is usually destined for electric vehicles. The company claims the motor reduces losses by about 15% over conventional techniques. To maximize efficiency, conventional SESM uses slip rings or brushes to transmit power to the shaft. However, ZF claims their inductive improvements are even more efficient and can reduce axial size by around 90 mm.

Another advantage of the technology is that there is no need to provide a dry space for slip rings. That means fewer seals and the ability to cool the rotor with oil as you would with a motor containing permanent magnets. The company plans to offer a 400 V version of the motor and an 800 V that uses silicon carbide electronics.

If you build your own motors, have you tried anything like this? Usually, we don’t see motors this big, of course. We have, however, seen builds of reluctance motors that don’t use magnets.

Hands-Free Compass Uses Haptic Feedback

September 5, 2023 by Bryan Cockfield 15 Comments

If you’ve never experienced it before, getting turned around on a cloudy day in the woods or getting lost during an event like a snowstorm can be extremely disorienting and stressful — not to mention dangerous. In situations where travel goes outside the beaten path, it’s a good idea to have some survival gear around, including a good compass. But if you need your hands for other things, or simply don’t want to have to stop often to check a compass, you might want to try out something like this belt-mounted haptic feedback compass.

The compass is based around a Raspberry Pi Pico microcontroller and uses a ULN2803a transistor array chip to control a series of motors. The motors are mounted all along a belt using custom 3D printed clips with wires woven to each through the holes in the belt. The firmware running on the belt communicates with an Android app via USB to control each of the motor’s vibration based on the direction the wearer is traveling and their desired heading. With certain patterns, the wearer can get their correct heading based on the vibrations they feel through the belt.

While it does rely on having a functioning phone, a modern smartphone’s built-in compass doesn’t require a signal to work. We would still recommend having a good simple compass in your pack as backup if you’re going to be far off the beaten path, though. There are other ways of navigation besides by compass, map, or GPS too. Have a shot at inertial navigation if you want a challenge.

Thanks to [Peter] for the tip!

You Can 3D Print A 12,500 RPM Brushless Motor

June 28, 2023 by Lewin Day 18 Comments

Typically, when most of us need a motor, we jump online to order one from a catalogue. [Levi Janssen] recently had to build his own for a college project, however, and learned a lot along the way.

[Levi] whipped up his brushless DC motor design in OnShape. The motor has six coils in the stator, with the rotor carrying eight neodymium magnets. It’s an axial flux design, with the rotor’s magnets sitting above the coils. This makes construction very easy using 3D printed components. Axial flux motors also have benefits when it comes to power density and cooling, though optimization is outside the scope of [Levi]’s work here.

[Levi]’s video covers both the development of the motor itself as well as the drive circuit, too. The latter is of key value if you’re interested in the vagaries of driving these motors, which is far more complex than running a simple brushed motor. He even gets his motor up to 12,500 rpm with his homebrewed drive circuit.

Making your own motors can help you solve some difficult engineering challenges, like building motorized rollerblades. Alternatively, if winding coils sounds too slow and too hard, you can just use off-the-shelf gear and hack it to make it work. Here, we support both methods.

Continue reading “You Can 3D Print A 12,500 RPM Brushless Motor” →