Electric vehicles are getting more traction these days, but this trend is rolling towards us in more ways than just passenger vehicles. More and more bikes are being electrified too, since the cost of batteries has come down and people realize that they can get around town easily without having to pay the exorbitant price to own, fuel, and maintain a car. Of course there are turnkey ebikes, but those don’t interest us much around here. This ebike from [Andy] is a master class in how to build your own ebike.
Due to some health issues, [Andy] needed a little bit of assistance from an electric motor on his bike, but found out that the one he wanted wouldn’t fit his current bike quite right. He bought a frame from eBay with the right dimensions and assembled the bike from scratch. Not only that, but when it was time to put the battery together he sourced individual 18650 cells and built a custom battery for the bike. His build goes into great detail on how to do all of these things, so even if you need a lithium battery for another project this build might be worth a read.
If you’ve never been on an electric bike before, they’re a lot of fun to ride. They’re also extremely economical, and a good project too if you’re looking for an excuse to go buy a kit and get to work. You can get creative with the drivetrain too if you’d like to do something out of the box, such as this bike that was powered by AA batteries and a supercapacitor.
The geared DC motor has become the bread-and-butter of the modern-day beginner project. Unfortunately, with the advent of vast online catalogs peddling a wide assortment of these mechanical marvels, validating the claim that one DC motor will outperform the others is a challenge.
Such is the dilemma that our own [Gerrit Coetzee] faced as he set out to buy these geared motors in bulk. In his initial teardown, he quickly compares the change in design, from the original which possess the two-part clutch that extends on overloading, to the clones with the feature disabled altogether.
He then goes on to research methods of measuring the motor’s output where he discovers the Prony Brake which leads to the Rope Brake Dynamometer. This is where things get interesting and [Gerrit Coetzee] goes on to hack his own version of the machine. The idea is to have a rope wound to the wheel that is powered by the motor. With one end of the cord attached to a spring scale and the other end to a suspended weight, the motor speed affects the force on the spring scale. This change in force measured by the scale can be used to calculate the power output by the motor.
[Gerrit Coetzee] goes on to replace the weight with springs and the scale with an electronic load cell while using a stepper motor to stretch the cord thereby adding the requisite tension to the string. We thought this was a very elegant solution where the entire experiment could be controlled electronically.
This is a work in progress through the writeup is an excellent example of how to tailor a traditional experiment to the modern times. We have seen similar investigations for larger salvaged motors and dynamometers with lots of sensors.
The simple DC brushed motor is at the heart of many a robotics project. For making little toy bots that zip around the house, you can’t beat the price and simplicity of a pair of brushed motors. They’re also easy to control; you could roll your own H-bridge out of discrete transistors, or pick up one of the commonly used ICs like the L298N or L9110S.
But what if you want an all-in-one solution? Something that will deliver enough current for most applications, drive dual motors, and deal with a wide range of input voltages. Most importantly, something that will talk to any kind of input source. For his Hackaday prize entry, [Praveen Kumar] is creating a dual brushed motor controller which can handle a multitude of input types. Whether you’re using an IR remote, a Pi communicating over I2C, an analog output or Bluetooth receiver, this driver can handle them all and will automatically select the correct input source.
The board has an ATmega328p brain, so Arduino compatibility is there for easy reprogramming if needed. The mounting holes and header locations are also positioned to allow easy stacking with a Pi, and there’s a status LED too. It’s a great module that could easily find a place in a lot of builds.
If you need even more control over your brushed motor, you can soup up its capabilities by adding a PID loop for extra smarts.
Buying surplus equipment lends a frisson of excitement as you eagerly await the package or crate containing your purchase. Did you buy a hidden treasure, or has some shyster succeeded in unloading a pile of garbage onto you, their mark? [Professor Churls] shelled out $49.99 for a military surplus bomb hoist which definitely falls into the former category. His teardown reveals it to be a beautifully over-engineered piece of Cold-War-era American hardware.
As the package with its extremely heavy contents is first inspected, he reminds us just what a bomb hoist does, it is clipped to an aircraft by ground crew and serves as a small but extremely powerful crane to lift up to a 6000-pound piece of ordnance onto the wing pylon of an aircraft. This particular example dates from the 1960s, and features a 28-volt DC motor coupled to a bulky gearbox assembly on a swivel mount for attachment.
His teardown is extremely detailed, but such is the engineering and complexity of the device you’ll want to read every part of it. The motor is a fairly traditional separately-excited brushed DC design such as you’d expect from that era, but with unusual features such as brushes on pivots rather than a slide. The multiple sets of gears are packed in aged and phenolic-smelling grease, and have unusual features such as stub-form teeth for high torque at low durations. There is even an entirely separate gear train for the hex drive provided so that crews could keep the bombers rolling even when the power was out.
He leaves us with the tantalising information that there is a project awaiting this device, but doesn’t tell us what that might be. We hope we’ll get to see it, whatever it is. Meanwhile it’s great to see that this kind of item can still be found from military surplus suppliers, where this is being written they have degenerated into little more than stockists of camouflage-printed camping gear. Our colleague [Brandon Dunson] lamented in 2015 on the slow decline of the electronic surplus business in his location.
If you’re a fan of endurance racing motor vehicles, there’s one that puts the 24 Hours of Le Mans, the Dakar Rally, and the Baja 1000 to shame, and the race doesn’t even involve cars. Indeed, the vehicles used for this massive trek from France to China are electric bicycles, powered only by solar panels. This is the epic Sun Trip endurance race, and one of its competitors built a unique tandem bike that is powered both by pedaling, rowing, and the solar panels.
The tandem bike is interesting on its own since the atypical design uses a back-to-back layout which means one person is facing backward, but the storage space is dramatically increased over the normal forward-facing layout. The person in the rear doesn’t pedal, though. [Justin_le] built an upper-body-powered rowing station for that spot so that the person riding back there can rest their legs but still help propel the vehicle. Of course, there’s also a solar panel roof so the two riders can pedal and row in the shade, which includes MPPT and solar tracking which drives a small electric motor on board as well.
This race started in June but is still going on. There’s a live GPS feed so you can keep up with the teams, and if you get really inspired you can go ahead and sign up for the 2019 race as well. This particular bike was also featured on Radio Canada as well if you’d like to learn more about it.
Thanks to [Arthur] for the tip!
When it comes to production, fast is good! But right the first time is better. Anything that helps prevent rework down the line is worth investing in. Some of the best tools to catch problems are good test fixtures. The folks at Tertill (a solar-powered robot for killing weeds that kickstarted last year) took the time to share two brief videos of DIY test fixtures they use to test components before assembly.
The videos are short, but they demonstrate all the things that make a good test: on the motor tester there are no connectors or wires to fiddle with, the test starts automatically, and there is clear feedback via prominent LEDs. The UI board tester also starts automatically and has unambiguous LED feedback, and sports a custom board holder with a recess just the right shape for the PCB. Once the board is in, the sled is pushed like a drawer to make contact with the test hardware and begin the test. The perfectly formed recesses in both units serve another function as well; they act as a go/no-go test for the physical shape of the components and contacts being tested.
Both videos are embedded below; and while there isn’t much detail on the actual test hardware, we do spy a Raspberry Pi and at least two Adafruit logos among other hacker-familiar elements like laser-cut acrylic, 3D printed plastic, pogo pins, and a PVC junction box.
Continue reading “A Peek Into a Weed-Eating Robot’s Test Fixtures”
Beds! They don’t move around enough, so the young people say. They need more motors, more horsepower, more self-driving smarts – right? Honestly, we’re not sure, but if that’s the question being asked, [randofo] has the answer.
Aptly named, Bedfellow is an art project that sought to create a bed that could explore and socialise with occupants aboard. The core principle was not just to create a bed that could move under its own power, but one that could intelligently drive around and avoid obstacles, too. This is achieved through the use of ultrasonic sensors, with an Arduino Mega as the brains. The bed chooses a random direction in which to move, checking for obstacles on the way. It’s pretty basic as far as “self-driving” technology goes, but it gets the job done.
Far from being a lightweight artistic statement, the bed has some serious performance credentials. The drivetrain is a couple of 4 horsepower DC motors with speed controllers cribbed from a golf cart. These are fed through a 20:1 gear reduction to boost torque and avoid the bed moving too quickly. [Randofo] reports it can comfortably haul 12 people without slowing down, and we don’t doubt it. With that much power, your average flatback bed would be ripped to pieces, but never fear for this one – there’s plenty of heavy engineering holding it together.
It’s refreshing to see an art project executed with both elegant aesthetics and brutally powerful hardware. Sure, it might not be much good for sleeping unless you live in a loft with a concrete floor, but hey – they’re awfully popular these days. Now all it needs are some ground effects.