Automating RC Motor Efficiency Testing

Small brushless motors and LiPo batteries are one of the most impressive bits of technology popularized in recent years. Just a few years ago, RC aircraft were powered by either anemic brushed motors or gas. Quadcopters were rare. Now, with brushless motors, flying has never been easier, building electric longboards is simple, and electric bicycles are common.

Of course, if you’re going to make anything fly with a brushless motor, you’ll probably want to know the efficiency of your motor and prop setup. That’s the idea behind [Michal]’s Automated RC Motor Efficiency Tester, his entry to the 2016 Hackaday Prize.

[Michal]’s project is not a dynamometer, the device you should use if you’re measuring the torque or power of a motor. That’s not really what you want if you’re testing brushless motors and prop configurations, anyway; similarly sized props can have very different thrust profiles. Instead of building a dyno for a brushless motor, [Michal] is simply testing the thrust of a motor and prop combination.

The device is very similar to a device sold at Hobby King, and includes a motor mount, microcontroller and display, and a force sensor to graph the thrust generated by a motor and prop. Data can be saved to an SD card, and the device can be connected to a computer for automatic generation of pretty graphs.

Brushless motors are finding a lot of uses in everything from RC planes and quadcopters, to robotics and personal transportation devices. You usually don’t get much of a data sheet with these motors, so any device that can test these motors will be very useful.

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Bike Power Meter with Crank-mounted WiFi Strain Gauges

In any motorsport, the more you know about how the engine is performing, the better a driver is likely to do in a race. That holds for bicycles, too, where the driver just happens to also be the engine. There are plenty of cheap bike computers on the market, but the high-end meters that measure power output are a bit pricey. [chiprobot] is looking to change that with a home-brew, low-cost bike power meter.

The project still appears to be in the proof-of-concept phase, but it’s an interesting concept for sure. The stock crank arms are carefully fitted with two pairs of tiny strain gauges. The gauges are wired in a Wheatstone bridge arrangement, with one gauge in each pair mounted perpendicular to the force on the crank to serve as a static reference. Output from the bridge is fed to an HX711 instrumentation amplifier. The demo video below shows how sensitive the bridge and 24-bit amp are.

The goal is to send crank data to a handlebar-mounted UI via WiFi with a pair of ESP8266 modules. We like the idea of a bicycle area network, but [chiprobot] has his work cut out for him in terms of ruggedizing and weatherproofing all this gear. We’ll be sure to keep an eye on this project. In the meantime, there’s plenty to learn from this bike power meter project we covered last year.

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TrainLight: Transit Info At A Glance

In a world of sensory overload, sometimes it’s nice to get the information you need without a bunch of clutter. [Savage] has created an attractive and minimalist system to display the current wait times for specific trains in his San Francisco neighborhood.

trainlight-legendIt’s basically a Spark Core and a 60 LED-per-meter strip of WS2812Bs. A 1000µF cap filters the power coming in from a switching adapter and a resistor limits the level-shifted logic going to the LEDs. Eight barriers made from card stock keep the light zones from bleeding together. The sides of the square canvas panel indicate cardinal directions and are oriented to [Savage]’s southern-facing house.

The server gets prediction data every 30 seconds using the RESTbus JSON API. [Savage] added in a bit of time for walking down the stairs, putting shoes on, and walking to each stop. TrainLight receives these times over WiFi and lights the LEDs accordingly. If a section isn’t lit at all, the wait time for that line is greater than 10 minutes. Dark green means you have 5-10 minutes to get there, and pale green means 2-5 minutes. If the LEDs are yellow, you’d better put on your running shoes.

This is a fairly simple build with a focus on subtlety. Even before guests in his house understand what they’re looking at, [Savage]’s TrainLight makes for an interesting conversational piece of blinkenlights and doubles as illumination for the stairs. There’s a slightly sped-up demo after the break.

Want to make your own? [Savage] has a tutorial page and his code is up on the gits. Blinky lights are also good for telling you whether the trains are running at all.

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Electric Skateboard Reaches Neck-Breaking Speeds

[Mischo Erban], a Canadian speed-freak, just broke a world record on an electric skateboard. 59.55mph! That’s almost 100km/h.

We’ve covered a lot of electric skateboards over the years, as well as some commercial versions — like the Boosted Board, one of the few actual Kickstarter success stories — and of course, people have hacked them as well. But this board from Next Generation Vehicles (NGV), seems to have taken speed to the next level.

Made by a Slovenian tech startup, the board features direct drive motors built into custom wheels. The article is a bit light on details, but we imagine they must be a few kW each in order to reach those speeds. No mention of a range (we can’t imagine it’d be very far at those speeds), but it is just a prototype.

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Rescuing The World’s First Preserved Railway

Preserved railways are now an established part of the tourist itinerary. It doesn’t matter if you call it a railroad, railway, chemin de fer, Eisenbahn or whatever, the chances are that somewhere near you there will be a line rescued from dereliction on which you can spend a Saturday afternoon in vintage rolling stock being hauled by a locomotive long ago withdrawn from regular service. They are established enough to have become an industry in their own right, with the full range of support services to maintain hundred-year-old machinery and even build entire new locomotives.

So we’ve become used to seeing preserved railways in a state of polished perfection. Sometimes a little too perfect, there was a wry observation in a recent BBC documentary on the subject that a typical British preserved railway represents an average day in the 1950s when the Queen was about to visit. Anyone who lived through that era will tell you the reality was a little different, how run down the system was after World War II and just how dirty everything became when exposed to decades of continuous coal smoke.

A particularly worn-out section of railway in those days could be found at Tywyn, on the Welsh coast. A 2’3″ narrow-gauge line built in the 1860s to serve a slate quarry and provide a passenger service to local communities, the Tal-y-Llyn Railway (Welsh pronunciation help) had been in continuous decline for decades and on the death of its owner in 1950 faced closure. With only one of its two locomotives operational and its track in a parlous state it attracted the attention of the author Tom Rolt, already famous for kick-starting the preservation of Britain’s inland waterway system. A preservation society was formed, and in a joint enterprise with the former owner’s estate the line was saved. The world’s first preserved railway had commenced operations.

"Lawnmower" Locomotive in 1952 [Source: talyllyn.co.uk]
“Lawnmower” Locomotive in 1952 [Source: talyllyn.co.uk]
In a country reeling from the economic effects of fighting a world war there was no infrastructure for a group of enthusiasts rescuing a near-derelict railway. Nobody had ever done this before, there was no body of expertise and certainly no handy suppliers to call when parts were required. To rebuild their line the Tal-y-Llyn volunteers had to reach into their own well of initiative gained over the “Make do and Mend” war years and build their own way out of any challenges they encountered. In case you were wondering what the relevance to Hackaday readers has been in the last few paragraphs there’s your answer: what would you do if you were handed seven and a quarter miles of run-down track and a single barely serviceable locomotive that is one of the oldest in the world still running?

We are fortunate that in 1953 an American film maker, Carson “Kit” Davidson, visited the line, and through his affectionate short film we have a portrayal of the railway’s state in the early stages of preservation. When the footage was shot they had secured a second serviceable locomotive courtesy of the nearby and recently closed Corris Railway, but had yet to replace the majority of the worn-out and overgrown track. It’s a treat to watch, and sets the stage very well for the home-made machinery that is to follow.

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Broken Promises of the Wankel Engine

Through the history of internal combustion engines, there has been plenty of evolution, but few revolutions. Talk of radically different designs always leads to a single name – Wankel. The Wankel rotary engine, most notably used in automobiles by Mazda, has been around since the late 1950’s. The Wankel rotary is an example of a design which makes sense on paper. However, practical problems cause it to underperform in the real world.

Invention and History

felixwankelFelix Wankel’s engine was conceived during a dream. In it, 17-year-old Felix was driving his car to a concert. When he arrived, he bragged to his friends that his car used a new type of engine – half turbine, half reciprocating. “It is my invention!” he told his friends. Upon waking up, Wankel became dedicated to building his engine. Though he never received a formal degree (or a driver’s license), Wankel was a gifted engineer.

Young Wankel’s checkered history includes membership in several anti-semitic groups in the 1920’s. He was also involved with the founding of the Nazi party. His conflicting views on the direction of the party lead to his arrest in 1933. Eventually released through action of Hitler himself, Wankel joined the SS in 1940. The end of the war saw Wankel spending several months in a French prison for his wartime involvement.

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Converting an Electric Scooter to Lithium Batteries and Disabling the Safeties

There’s a bunch of different electric scooters available nowadays, including those hoverboards that keep catching fire. [TK] had an older Razor E300 that uses lead acid batteries. After getting tired of the low speeds and 12 hour charge times, [TK] decided it was time to swap for lithium batteries.

The new batteries were sourced from a Ryobi drill. Each provides 18 V, giving 36 V in series. The original batteries only ran at 24 V, which caused some issues with the motor controller. It refused to start up with the higher voltage. The solution: disable the safety shutdown relay on the motor controller by bridging it with a wire.

With the voltage issue sorted out, it was time for the current limit to be modified. This motor controller uses a TI TL494 to generate the PWM waveforms that drive a MOSFET to provide variable power to the motor. Cutting the trace to the TL494’s current sense pin removed the current limit all together.

We’re not saying it’s advisable to disable all current and voltage limits on your scooter, but it seems to be working out for [TK]. The $200 scooter now does 28 km/h, up from 22 km/h and charges much faster. With gearing mods, he’s hoping to eke out some more performance.

After the break, the full conversion video.

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