A Drone Motor Does E-Bikes

On paper, the motors from both an electric bicycle and a drone can both take about 500 watts or so of power. Of course, their different applications make them anything but equivalent, as the bike motor is designed for high torque at low speed while the drone motor has very little torque but plenty of speed. Can the drone motor do the bike motor’s job? [Pro Know] makes it happen, with a set of speed reducing and torque increasing belts.

The build takes a pretty ordinary bicycle, and replaces the rear brake disk with a large pulley for a toothed belt, which drives a smaller pulley, and through a shaft another set of pulleys to the drone motor. The bracket to hold all this and the very large pulley on the wheel are all 3D printed in PLA-carbon fiber mix.

When it’s assembled, it runs the bike from a small lithium ion pack. That’s not unexpected, but if we’re honest we’d have our doubts as to whether this would survive the open road. It’s evidently a novelty for a YouTube video, and we’d be interested to see how hot the little motor became. However what’s perhaps more interesting is the choice of filament.

Could carbon fibre PLA be strong enough to print a toothed belt pulley? We’d be interested to know more. We saw the same filament combo being tested recently, after all.

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How Much Thrust Is Your Prop Really Making?

The problem of components not conforming to their claimed specification is one that must challenge engineers in all fields, including it seems, that of multi-rotors and remote controlled aircraft. A motor can boast an impressive spec on the website which sells it, but overheat or just not deliver when it’s on your bench. Thus [Valkyrie Workshop] has come up with a simple but ingenious rig to evaluate a motor and propeller combo without breaking the bank.

It tales the form of a L-shaped wooden bracket clamped to a pivot point at its corner with one arm pointing upwards, with motor and propeller in a 3D printed holder on the upwards arm. The other arm extends horizontally and lies on a digital kitchen scale the same distance from the pivot as the motor. The same force as is exerted by the motor is transmitted via the bracket to the kitchen scale, allowing a direct readout of the thrust in grams or kilograms. This is a first version of the rig, further work will move to a load cell and Arduino for more flexibility in measurement.

We’ve featured similar devices here in the past, including one version which can be mounted to an automobile so it can be tested at speed.

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Washing Machine Motors Unlocked

There’s great potential in salvaging a motor from a broken appliance, but so often the part in question is very specific to its application, presenting a puzzle of wires to the experimenter. This was very much the case with older washing machines and other white goods, and while their modern equivalents may have switched to more understandable motors, there are still plenty of the older ones to be had. [Matthias random stuff] sheds a bit of light on how these motors worked, by means of a 1980s Maytag washing machine motor.

Many of us will be used to old-style induction motors, in which two windings were fed out of phase via a large capacitor. This one doesn’t have a capacitor, instead it has a primary winding and a secondary one with a higher resistance. We’re not quite sure the explanation of the resistance contributing to a phase shift holds water, however this winding is connected in for a short time at start-up by a centrifugal switch. Even better, reversing its polarity reverses the direction of the motor.

The result is a mess of wires demystified, and a mains powered motor with a bit of strength for your projects. We’ve let a few of these motors slip through our fingers in the past, perhaps we shouldn’t have been so hasty.

This is a subject that we’ve looked at in the past.

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Double Fed Induction Motors: Clever Motor Control Through Frequency

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.

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

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

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.

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Variable-Nozzle Ducted Fan Provides Fluid Dynamics Lessons

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.

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