How Current Shunts Work

Current. Too little of it, and you can’t get where you’re going, too much and your hardware’s on fire. In many projects, it’s desirable to know just how much current is being drawn, and even more desirable to limit it to avoid catastrophic destruction. The humble current shunt is an excellent way to do just that.

Ohm’s Law.

To understand current, it’s important to understand Ohm’s Law, which defines the relationship between current, voltage, and resistance. If we know two out of the three, we can calculate the unknown. This is the underlying principle behind the current shunt. A current flows through a resistor, and the voltage drop across the resistor is measured. If the resistance also is known, the current can be calculated with the equation I=V/R.

This simple fact can be used to great effect. As an example, consider a microcontroller used to control a DC motor with a transistor controlled by a PWM output. A known resistance is placed inline with the motor and, the voltage drop across it measured with the onboard analog-to-digital converter. With a few lines of code, it’s simple for the microcontroller to calculate the current flowing to the motor. Armed with this knowledge, code can be crafted to limit the motor current draw for such purposes as avoiding overheating the motor, or to protect the drive transistors from failure.

In fact, such strategies can be used in a wide variety of applications. In microcontroller projects you can measure as many currents as you have spare ADC channels and time. Whether you’re driving high power LEDs or trying to build protection into a power supply, current shunts are key to doing this.

Continue reading “How Current Shunts Work”

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.

Gorgeous Engineering Inside Wheels of a Robotic Trail Buddy

Robots are great in general, and [taylor] is currently working on something a bit unusual: a 3D printed explorer robot to autonomously follow outdoor trails, named Rover. Rover is still under development, and [taylor] recently completed the drive system and body designs, all shared via OnShape.

Rover has 3D printed 4.3:1 reduction planetary gearboxes embedded into each wheel, with off the shelf bearings and brushless motors. A Raspberry Pi sits in the driver’s seat, and the goal is to use a version of NVIDA’s TrailNet framework for GPS-free navigation of paths. As a result, [taylor] hopes to end up with a robotic “trail buddy” that can be made with off-the-shelf components and 3D printed parts.

Moving the motors and gearboxes into the wheels themselves makes for a very small main body to the robot, and it’s more than a bit strange to see the wheel spinning opposite to the wheel’s hub. Check out the video showcasing the latest development of the wheels, embedded below.

Continue reading “Gorgeous Engineering Inside Wheels of a Robotic Trail Buddy”

Hoverboard Reborn For Electric Rollerblading

Rollerblading is fun, but who needs all that pesky exercise? Wouldn’t strapping on the blades be so much more tempting if you had an electric pusher motor to propel you along your way?

We have to admit that we raised a wary eyebrow as we first watched [MakerMan]’s video below. We thought it was going to be just another hoverboard hack at first, but as we watched, there were some pretty impressive fabrication skills on display. Yes, the project does start with tearing into a defunct hoverboard for parts, primarily one wheel motor and the battery pack. But after that, [MakerMan] took off on a metalworking tear. Parts of the hoverboard chassis were attached to a frame built from solid bar stock — we’ll admit never having seen curves fabricated in quite that way before. The dead 18650 in the battery pack was identified and replaced, and a controller from an e-bike was wired up. Fitted with a thumb throttle and with a bit of padding on the crossbar, it’s almost a ride-upon but not quite. It seems to move along at quite a clip, even making allowances for the time-compression on the video.

We’ve seen lots of transportation hacks before, from collapsible longboards to steam-powered bicycles, but this one is pretty unique.

Continue reading “Hoverboard Reborn For Electric Rollerblading”

Open Source High Power EV Motor Controller

For anyone with interest in electric vehicles, especially drives and control systems for EV’s, the Endless-Sphere forum is the place to frequent. It’s full of some amazing projects covering electric skateboards to cars and everything in between. [Marcos Chaparro] recently posted details of his controller project — the VESC-controller, an open source controller capable of driving motors up to 200 hp.

[Marcos]’s controller is a fork of the VESC by [Benjamin Vedder] who has an almost cult following among the forum for “creating something that all DIY electric skateboard builders have been longing for, an open source, highly programmable, high voltage, reliable speed controller to use in DIY eboard projects”. We’ve covered several VESC projects here at Hackaday.

While [Vedder]’s controller is aimed at low power applications such as skate board motors, [Marcos]’s version amps it up several notches. It uses 600 V 600 A IGBT modules and 460 A current sensors capable of powering BLDC motors up to 150 kW. Since the control logic is seperated from the gate drivers and IGBT’s, it’s possible to adapt it for high power applications. All design files are available on the Github repository. The feature list of this amazing build is so long, it’s best to head over to the forum to check out the nitty-gritty details. And [Marcos] is already thinking about removing all the analog sensing in favour of using voltage and current sensors with digital outputs for the next revision. He reckons using a FPGA plus flash memory can replace a big chunk of the analog parts from the bill of materials. This would eliminate tolerance, drift and noise issues associated with the analog parts.

[Marcos] is also working on refining a reference design for a power interface board that includes gate drivers, power mosfets, DC link and differential voltage/current sensing. Design files for this interface board are available from his GitHub repo too. According to [Marcos], with better sensors and a beefier power stage, the same control board should work for motors in excess of 500 hp. Check out the video after the break showing the VESC-controller being put through its paces for an initial trial.

Continue reading “Open Source High Power EV Motor Controller”

Simple Electric Bike Conversion from 3D-Printed Parts

Challenge: Perform an electric conversion on a bicycle. Problem: No significant metal working skills or equipment. Solution: 3D print everything needed to electrify the bike.

At least that’s the approach that [Tom Stanton] took to his electric bike build. Having caught the electric locomotion bug on a recent longboard build, [Tom] undertook the upgrade of a cheap “fixie,” or fixed-gear bike. His delta printer was big enough for the motor mount and weather-resistant ESC enclosure, but he needed to print the drive pulley in four quadrants that were later glued together. We can’t say we hold much faith in the zip ties that transmit all the torque through the rear wheel’s spokes, but as a proof of concept it seems sturdy enough. With a throttle from an electric scooter and a battery in a saddle bag, the bike turns in pretty decent performance — at least after a minor gearing change. And everything blends in or accents the black frame of the bike, so it’s a good-looking build to boot.

Want to catch the cheap electric personal transportation bug too? Check out this electric longboard, or this all-terrain hoverboard.

Continue reading “Simple Electric Bike Conversion from 3D-Printed Parts”

Propeller Backpack for Lazy Skiers

At first glance, it looks eerily similar to Inspector Gadget’s Propeller Cap, except it’s a backpack. [Samm Sheperd] built a Propeller Backpack (video, embedded after the break) which started off as a fun project but almost ended up setting him on fire.

Finding himself snowed in during a spell of cold weather, he found enough spare RC and ‘copter parts to put his crazy idea in action. He built a wooden frame, fixed the big Rimfire 50CC outrunner motor and prop to it, slapped on a battery pack and ESC, and zip-tied it all on to the carcass of an old backpack.

Remote control in hand, and donning a pair of Ski’s, he did a few successful trial runs. It looks pretty exciting watching him zip by in the snowy wilderness. Well, winter passed by, and he soon found himself in sunny California. The Ski’s gave way to a bike, and a local airfield served as a test track. He even manages to put in some exciting runs on the beach. But the 10S 4000 mAH batteries seem to be a tad underpowered to his liking, and the motor could do with a larger propeller. He managed to source a 12S 10,000 mAH battery pack, but that promptly blew out his Aerostar ESC during the very first static trial.

He then decided to rebuild it from ground up. A ten week welding course that he took to gain some college credits proved quite handy. He built a new TiG welded Aluminium frame which was stronger and more lightweight than the earlier wooden one. He even thoughtfully added a propeller safety guard after some of his followers got worried, although it doesn’t look very effective to us. A bigger propeller was added and the old burnt out ESC was replaced with a new one. It was time for another static trial before heading out in to the wide open snow again. And that’s when things immediately went south. [Samm] was completely unaware as the new ESC gloriously burst in to flames (8:00 into the third video), and it took a while for him to realize why his video recording friend was screaming at him. Check out the three part video series after the break to follow the story of this hack. For a bonus, check out the 90 year old gent who stops by for a chat on planes and flying (8:25 in the third video).

But [Samm] isn’t letting this setback pin him down. He’s promised to take this to a logical finish and build a reliable, functional Propeller Backpack some time soon. This isn’t his first rodeo building oddball hacks. Check out his experiment on Flying Planes With Squirrel Cages.

We seem to be catching a wave of wind-powered transportation hacks these days. Hackaday’s own [James Hobson] spent time in December on a similar, arguably safer, concept. He attached ducted fans to the back of a snowboard. We like this choice since flailing limbs won’t get caught in these types of fans.

Continue reading “Propeller Backpack for Lazy Skiers”