Extreme Repair of a Burnt PCB

[xsdb] had a real problem. His JBL L8400P 600 watt subwoofer went up in flames – literally. Four of the large capacitors on the board had bulged and leaked. The electrolyte then caused a short in the mains AC section of the board, resulting in a flare up. Thankfully the flames were contained to the amplifier board. [xsdb's] house, possessions, and subwoofer enclosure were all safe. The amplifier board however, had seen better days. Most of us would have cut our losses and bought a new setup. Not [xsdb] he took on the most extreme PCB repair we’ve seen in a long time.

After removing the offending caps and a few other components, [xsdb] got a good look at the damage. the PCB was burned through. Charred PCB is conductive, so anything black had to be cut out. The result was a rather large hole in the middle of an otherwise serviceable board. [xsdb] had the service manual for the JBL sub. Amazingly, the manual included a board layout with traces. Some careful Photoshop work resulted in an image of the section of PCB to be repaired. [Xsdb] used this image to etch a small patch board.

The amplifier and patch were milled and sanded to match up nearly perfectly. Incredibly, all the traces aligned. [Xdsb] soldered the traces across the join with small sections of wire and solder wick. After soldering in some new high quality capacitors, the amplifier was back in action!

If you’re a big fan of burned PCB’s, check out Hackaday Prize Judge Dave Jones latest EEVblog video, where he works on a Ness home alarm panel with a similarly cooked section of FR4.

[Thanks for the link JohnS_AZ!]

Hackaday Prize Judge Elecia White Writes Tell-All Blog Post

The awarding of The Hackaday Prize is nearly upon us!  With just over a day left to go, Launch Judge Elecia White has decided to spill the beans and write a blog post about which of the five finalists she thinks should win. We don’t want to spoil the surprise… but what the heck, she wants them ALL to win.

ChipWhisperer because it brings high-end hardware security tools to the masses.

SatNOGS because it brings space to your back yard,

PortableSDR because of its great waterfall display,

ramanPi because come on, it’s a freaking spectrometer!

Open Source Science Tricorder because it uses sensors to help us see the science in the world around us.

Elecia knows how much time, effort, and passion went into these projects, and how each one embodies the open and connected spirit of The Hackaday Prize. Only one day remains before the big event in Munich, and the announcement of the winner.

An Interview with Tesla Battery Hacker [wk057]

We covered [wk057] and his Tesla Model S battery teardown back in September. Since then we had some time to catch up with him, and ask a few questions.

You’ve mentioned that you have a (non hacked) Tesla Model S. What do you think of the car?

It’s the best car I’ve ever driven or owned, period. Not to get too into it, but, I love it. I’ve put almost 20,000 miles on it already in under a year and I have no real complaints. Software feature requests… but no complaints. After almost a year, multiple 1700-miles-in-a-weekend trips, and an overall great experience… I can never go back to a gas vehicle after this. It would be like going back to horses and buggies.

A salvage Tesla Lithium battery had to be expensive compared to a Lead Acid setup. What made you go with the Tesla?

Actually, if you consider that the Model S battery is already pre-setup as a high-capacity pack, contains the wiring to do so, and the modules are much more energy and power dense than any lead acid battery bank, it’s actually almost cheaper than a comparable lead acid bank and all the trimmings.

I haven’t officially weighed them, but the modules from the Model S battery are roughly 80 lbs. 80 lbs for a 5.3 kWh battery is around 15 lbs per kWh, which is impressive. For comparison, a decent lead acid battery will have a little over 1 kWh (of low-rate discharge capacity) and weigh almost the same.

Also, the Tesla pack is much more powerful than a lead acid bank of the same capacity.
Generally a lead acid battery bank would have a capacity that would only be realized with slow discharges, so, 1/20C. Much over that and you sacrifice capacity for power. 1/20C for an 85kWh pack is only 4.25kW, barely enough for a central air unit and some lights without losing capacity.

Now the Tesla pack can be discharged (based on how it does so in the vehicle) at up to 3.75C for short periods, and at 1/2C continuously without really affecting the overall capacity of the pack. That means I can run 10x more power than lead acid without a loss in overall charge capacity. Leads to a much more flexible battery solution since the loads will, in reality, always be so low that this will not even come into play with the Tesla pack, but would almost always be a factor with lead acid.

Charging is also somewhat better with the Tesla battery. Charge a lead acid battery at a 1/2C and it will boil. Charge the Tesla pack at 1/2C (42kW) and it might warm up a few degrees. Oh, and the charging losses at high rates are much less than lead acid also.
Overall, without continuing to yack about the technical aspects, it’s just a much better battery, takes up less space, weighs less, and has more power available.

There are likely decent arguments for other solutions, but the rest aside, this one won out because it was definitely more interesting.

Click past the break to read the rest of our interview with [wk057]!

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Tiny R/C P-51D Mustang Tips the Scales at 3 Grams

Commercial R/C aircraft have been getting smaller and smaller with each passing year. In the early 2000′s, a palm-sized plane or helicopter was the dream of many an R/C enthusiast. Today, you can pick them up for around $20 USD at the local mall. The smallest models however, are still built by an elite group of modelers. Weighing in at a mere 3 grams, [Martin Newell's] P-51D mustang model certainly puts him into that group. While the P-51′s 11.6 cm wingspan may not make it the smallest plane in the world, its many functions make it incredible.

The Mustang is an 8 channel affair, with elevator, throttle, rudder, ailerons, flaps, navigation lights, working retracts, and flashing cannon lights. That’s Wright, we did say retracts, as in retractable landing gear on a 3 gram model.

All the Mustang’s flight surfaces feature fully proportional control. However, there are no closed loop servos involved. The flight surfaces use magnetic actuators, consisting of a tiny neodymium magnet surrounded by a coil of magnet wire. We’re not sure if the signals to these actuators is straight PWM or if [Martin] is varying the frequency, but the system works. The retracts use heat-sensitive Nitinol “muscle wire” along with a bellcrank system to make sure the landing gear is up and locked after takeoff, and comes down again before a landing.

We don’t have any in-flight video of the Mustang, but we do have footage of an even smaller 1.2 gram plane [Martin] has been flying lately. Click past the break to check it out!

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Forkless Motorcycle Tears up the Track

The bike above may look like a pristine Yamaha prototype, but it’s actually the work of [Julian Farnam], a motorcycle hacker of the highest level. We caught his Yamaha A-N-D FFE 350 on OddBike, and you can read [Julian's] own description of the bike on his Slideshare link.

The FFE 350 started life as a Yamaha 1990′s RZ350 two-stroke racer. From there, [Julian] gave it his own Forkless Front End (FFE) treatment. Gone is the front fork, which while common in motorcycle and bicycle design, has some problems. Fore-aft flex is one – two thin tubes will never make for a rigid front end. Changing geometry is another issue. Since forks are angled forward, the front wheel moves up and to the rear as the shocks compress. This changes the motorcycle’s trail, as well.

Forkless designs may not have these issues, but they bring in a set of their own. A forkless design must have linkages and bellcranks which are often the source of slop and vibration. [Julian's] design uses two sets of linkages in tension. The tension between the two linkages removes most of the slop and provides that directly connected feel riders associate with forks.

The FFE 350 wasn’t just a garage queen either – it laid down some serious laps at local tracks in Southern California. Unfortunately, the forkless design was too radical to catch on as a commercial venture, and the FFE has spent the last few years in storage. [Julian] is hard at work bringing it back to its 1998 glory, as can be seen on his restoration thread over on the Custom Fighters forum.

Wax Motors Add Motion to Your Projects

[electronicsNmore] has uploaded a great teardown and tutorial video (YouTube link) about wax motors. Electric wax motors aren’t common in hobby electronics, but they are common in the appliance industry, which means the motors can be often be obtained cheaply or for free from discarded appliances. Non-electric wax motors have been used as automotive coolant thermostats for years.  Who knows, this may be just what the doctor ordered for your next project.

As [electronicsNmore] explains, wax motors are rather simple devices. A small block of wax is sealed in a metal container with a movable piston. When heated, the wax expands and pushes the piston out. Once the wax cools, a spring helps to pull the piston back in.

The real trick is creating a motor which will heat up without cooking itself. This is done with a Positive Temperature Coefficient (PTC) thermistor. As the name implies, a PTC thermistor’s resistance increases as it heats up. This is the exact opposite of the Negative Temperature Coefficient (NTC) thermistors we often use as temperature sensors. PTC’s are often found in places like power supplies to limit in rush current, or small heating systems, as we have in our wax motor.

As the PTC heats up, its resistance increases until it stops heating. At the same time, the wax is being warmed, which drives out the piston. As you might expect, wax motors aren’t exactly efficient devices. The motor in  [electronicsNmore's] video runs on 120 volts AC. They do have some advantages over solenoid, though. Wax motors provide smooth, slow operation. Since they are resistive devices, they also don’t require flyback diodes, or create the RF noise that a solenoid would.

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