Testing Brushless Motors with a Scope (or a Meter)

Brushless motors have a lot of advantages over traditional brushed motors. However, testing them can be a bit of a pain. Because the resistance of the motor’s coils is usually very low, a standard resistance check isn’t likely to be useful. Some people use LC meters, but those aren’t as common as a multimeter or oscilloscope. [Nils Rohwer] put out two videos — one two years ago and one recently — showing how to test a brushless motor with a multimeter or scope. Oh, you do need one other thing: a drill.

You don’t have to drill into the motor, instead you use the drill to spin the motor’s shaft. Since a motor and a generator are about the same thing, you can read the voltages produced by the spinning motor and determine if it is good or not. The first video shows the technique and the second, more recent video shows a scope reading a bad motor. You can see both videos, below.

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Electric Longboard with All-New Everything

We love [lolomolo]’s Open Source electric longboard project. Why? Because he completely re-engineered everything while working on the project all through college. He tackled each challenge, be it electronic or mechanical as it came, and ended up making everything himself.

The 48″ x 13″ deck is a rather unique construction utilizing carbon fiber and Baltic birch. In testing the deck, [lolomol] found the deflection was less than an inch with 500 lbs. on the other end. He modified the Caliber II trucks to add four 2250W Turnigy Aerodrive brushless outrunners driving the wheels with the help of belts. The motors are controlled by VESC, an Open Source speed controller. There are a lot of fun details, like the A123 lithium cells equipped with custom battery management system PCBs.

The board sports 5W RGBW headlights that are so bright he can only run them at 10% PWM, plus RGB LED underlighting. All of it is controlled by an onboard Linux box. You can check out [lolomolo]’s GitHub repository for code, schematics, and CAD files. His Instructable for this project also has more design notes and thoughts.

If sweet longboards are your bag, check out the 3D-printed longboard and the long-distance electric longboard we published previously.

Scrap Bin Mods Move Science Forward

A first-time visitor to any bio or chem lab will have many wonders to behold, but few as captivating as the magnetic stirrer. A motor turns a magnet which in turn spins a Teflon-coated stir bar inside the beaker that sits on top. It’s brilliantly simple and so incredibly useful that it leaves one wondering why they’re not included as standard equipment in every kitchen range.

But as ubiquitous as magnetic stirrers are in the lab, they generally come in largish packages. [BantamBasher135] needed a much smaller stir plate to fit inside a spectrophotometer. With zero budget, he retrofitted the instrument with an e-waste, Arduino-controlled magnetic stirrer.

The footprint available for the modification was exceedingly small — a 1 cm square cuvette with a flea-sized micro stir bar. His first stab at the micro-stirrer used a tiny 5-volt laptop fan with the blades cut off and a magnet glued to the hub, but that proved problematic. Later improvements included beefing up the voltage feeding the fan and coming up with a non-standard PWM scheme to turn the motor slow enough to prevent decoupling the stir bar from the magnets.

[BantamBasher135] admits that it’s an ugly solution, but one does what one can to get the science done. While this is a bit specialized, we’ve featured plenty of DIY lab instruments here before. You can make your own peristaltic pump or even a spectrophotometer — with or without the stirrer.

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Brushless HDD Motor Driver from 9V and Painter’s Tape

Hard drives work by spinning platters full of magnetized data while a read/write head very quickly harvests or changes bits as needed. Older (or perhaps cheaper) drives spin at 5400 RPM, better drives spin at 7200 RPM, and elite drives (that mortals like you never shell out for) spin in the 10k-15k RPM range. This spinning is thanks to a sweet combination of a bearing and a brushless DC motor.

Unfortunately you can’t drive a brushless motor without a brushless motor driver. Well, of course that’s not absolutely true — and [Tommy Callaway] has certainly hacked together a crude exception to the rule. He’s using a 9-volt battery and some blue painters tape to drive a brushless motor.

Brushless motors do their thing by placing permanent magnets on the rotor (the part that spins) and placing multiple stationary coils of wire around it. Brushless motor drivers then energize these coils in a vary carefully timed pattern to continuously push the rotor magnets in the same direction.

[Tommy] wired up his 9V to one of these coils and observed that it holds the rotor in position. He then began playing around with different ways automatically break the circuit to de-energize the coil at just the right time. This means using the spinning center of the hard drive as part of the circuit, with blue painter’s tape in alternating patterns to create the timing. Is this a brushless motor driver, or has he just re-invented the brushed motor?

If this workbench trick leaves you wanting for some hardcore BLCD action, you can’t go wrong with this $20 offering to push motors at very high speeds.

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Build Your Own Brushless Motor

Building an electric motor from a coil of wire, some magnets, and some paper clips is a rite of passage for many budding science buffs. These motors are simple brushed motors. That is, the electromagnet spins towards a permanent magnet and the spinning breaks the circuit, allowing the electromagnet to continue spinning from inertia. Eventually, the connection completes again and the cycle starts over. Real brushed motors commutate the DC supply current so that the electromagnet changes polarity midway through the turn. Either way, the basic design is permanent magnets on the outside (the stationary part) and electromagnets on the inside (the rotating part).

Brushless motors flip this inside out. The rotating part (the rotor) has a permanent magnet. The stationary part (the stator) has multiple electromagnets. By controlling the electromagnets, the rotor spins. With no brushes, these motors are often more efficient, they don’t generate as much electrical noise, and there is no danger of brushes wearing out. In addition, the electromagnets staying put make the motor easier to wire and, if needed, easier to cool the electromagnets. The principle of operation is similar to a stepper motor. Steppers are usually optimized for small precise steps. Brushless motors are optimized for spinning, not stepping.

[Axbm] built a clever brushless motor out of little more than PVC pipe, some magnets, wire, and iron rods. The plan is simple: construct a PVC frame, build a rotor out of PVC and magnets, and mount electromagnets on the frame. An Arduino and some FETs drive the coils, although you could drive the motors using any number of methods. You can see the whole thing work in the video below.

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Hacking R/C Brushless Motor Controllers for Use in Big Robots

[professor churlz] wrote in to let us know his results with modifying radio control ESCs (Electronic Speed Controllers) for use in a large (250lb range) BattleBot’s drivetrain. It’s a very long and involved build log entry that is chock-full of details and background.

If you want something spinning hard and fast, brushless is where it’s at. Brushless motors offer much better power-to-weight ratios compared to brushed DC motors, but some applications – like a large robot’s drivetrain – are less straightforward than others. One of the biggest issues is control. Inexpensive brushless motors are promising, but as [professor churlz] puts it, “hobby motor control equipment is not well suited for the task. Usually created for model airplanes, the controllers are lightly built, rated to an inch of the components’ lives using unrealistic methods, and usually do not feature reversing or the ability to maintain torque at low speeds and near-stall conditions, which is where DC motors shine.” Taking into account the inertia of a 243 lb robot is a factor as well – the controller and motor want to start moving immediately, but the heavy robot on the other side of it doesn’t. The answer was a mixture of hardware and firmware tweaking with a lot of testing.

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A Simple And Educational Brushless Motor

Sometimes there is no substitute for a real working model to tinker with when it comes to understanding how something works. Take a brushless motor for example. You may know how they work in principle, but what factors affect their operation and how do those factors interact? Inspired by some recent Hackaday posts on brushless motors, [Matt Venn] has built a simple breadboard motor designed for the curious to investigate these devices.

The rotor and motor bodies are laser-cut ply, and the rotor is designed to support multiple magnet configurations. There is only one solenoid, the position of which relative to the magnets on the rotor can be adjusted. The whole assembly is mounted on the edge of a breadboard, and can be rotated relative to the breadboard to vary the phase angle at which the drive circuit’s Hall-effect sensor is activated by the magnet. The drive circuit in turn can have its gain and time constants adjusted to study their effects on the motor’s running.

[Matt] has made all the design files available in his GitHub repository, and has recorded a comprehensive description of the motor’s operation in the YouTube video below the break. Continue reading “A Simple And Educational Brushless Motor”