Jack Crossfire's blog View Details
Archive for November, 2014
Posted by Jack Crossfire | Nov 28, 2014 @ 02:54 AM | 6,621 Views
After many years, it finally consumed all the batteries in the apartment, so it was time to fix it.

The label of screw threads was removed forever. It only looked neat, but was never used.

...Continue Reading
Posted by Jack Crossfire | Nov 27, 2014 @ 07:47 PM | 6,962 Views
The 3DR current sensor outputs 0.3V for 5A, 0.1V for 2A, 0.05V for 1A. It was designed for much higher current. It's nonlinear, under 5A. After tearing it down while thinking it over, the decision was made to try a home made shunt resistor.

Based on the internet, the target current is 0-5A. A simple power supply exercise reveals a small piece of wire drops 0.027V at 5A. It would need 122x gain to reach full range. Bench power supplies are quite useful for measuring extremely low resistances.

Then, it was decided a full power regulated system would need to sense current, voltage, gyro, & a voltage representing target power. Then it would need a fixed point multiply. None of the G-buggy circuit could be reused. It would need a higher end microcontroller with the full MP lab build system, finally using the pickit that arrived years ago. The era of the home made programmer with gpasm was over.

Then it was decided making it through hole wasn't worth it. A tried & true surface mount ARM would support bluetooth for phone configuration, 400Mhz for the hand controller, & have real floating point power calculations.

The ancient dspic33fj128mc802 may never be used. It's not worth building a through hole board & bringing up yet another build environment.
Posted by Jack Crossfire | Nov 25, 2014 @ 12:49 AM | 6,626 Views
It was decided the trail was too rutted to get any training effect with the home made rover. After months of passively researching the problem, finally did a sort by price on Horizon, yielding the Tamiya Lunch Box, a 30 year old design. It was the largest thing for its price, big enough to navigate the rutted trail.

Tamiya Lunch Box $105
- working motor included
- plenty of room for gear
- endurance over 1 hour with 5Ah 12V battery
- obsolete 1987 design
- needs bearings

The cheapest hobbyking option was the Quanum Vandal.

Quanum Vandal $64
- modern design
- no motor included There is a 3700kV & 2200kV brushless motor in the apartment.
- probably too low to get up curbs
- unknown endurance
- 142x46x24mm battery

$64 for proportional steering was a lot better than 6 months ago, but the deciding factor was of course

Horizon - free shipping + $10 tax
Hobbyking - $52 shipping, cash only + no tax

The cheapest for the largest size was the lunch box, for all its horror stories. The mane horror stories are the inferior plastic bushings & the chassis bending. There wasn't enough money for any more than the very cheapest thing big enough to get over the curbs.

The funny thing about day jobs is when they're gone, you think you'll spend like no tomorrow when they come back. When they come back, you realize why you never spent like no tomorrow before they were gone. Inherit it, steal it, get lucky on kickstarter, or qualify for bigger loans, but no-one makes money from working.

Step 1 is to determine the current draw of the box & PWM range of the stock ESC.

Step 2 is convert the G-Buggy electronics to a power sensing throttle, outputting real PWM signals for the throttle & steering. The voltage regulator needs to be replaced with a shunt resistor calibrated for the current draw.

With the full headlights, it should be a rolling city on the trail.
Posted by Jack Crossfire | Nov 23, 2014 @ 02:43 AM | 7,102 Views
Capturing HDMI video from an iPad 2 is like going back to the world of 1997. The capture cards are hundreds of dollars. They use PCI. When was the last time something used PCI? They use ancient custom FPGA compression chips to output ancient, horrible quality MPEG-2 compression. The cables are a fortune. The 30 pin connector is 2 generations old. There is no Linux support. There are cheaper grey market items on ebay, but the grey market has never actually shipped anything.

The thing is $50 camcorders have been compressing HD video from image sensors for years. They all use the same $1 Ambarella chip to generate high quality x264 compression. It takes parallel data in the same format from an image sensor as an HDMI decoder would generate. You could hack something out of an FPGA to forward data from an HDMI cable to a stock camcorder. The trick would be the soldering.

The leaders of the cheap market are the Timeleak HD72A & Roxio Game Capture HD. Only the Timeleak can capture HDCP protected content but it has no compression. An intriguing device is the Grabbee HD, which compresses to USB. If the grey market item actually arrived, it would have to be used in Windows. Video capture in Linux is something which has risen & fallen, but it's something that would be rarely used. It would only capture 1 game on the iPad.
Posted by Jack Crossfire | Nov 19, 2014 @ 01:37 AM | 6,949 Views
Posted by Jack Crossfire | Nov 16, 2014 @ 04:44 PM | 6,829 Views
Ultramap finally compiled, after a week. The phone no longer showed a static menu button, so it required a layout change, which required recompiling the program. Adb no longer worked with the new phone & required an upgrade, but Eclipse wouldn't upgrade, so a new version of eclipse was required.

Eclipse wasn't catching all the errors in the version change & running it with constant missing class errors. The xmlns:android="http://schemas.android.com/apk/res/android" line wasn't compiling anymore but wasn't necessary. The phone version was API 19 but Eclipse was compiling 20. Eclipse needed to install API 19 from Window->Android SDK manager. The API number isn't the same as the 4.4 number & there's no easy way to find out what API correlates to the 4.4 number.

All the project.properties files needed to be hand tweeked to say android-19. The AndroidManifest.xml files then needed to say android:targetSdkVersion="19"

Installing Google maps API is a multi step process. You have to download an Eclipse project called Google play services in Window->Android SDK manager, import it as an existing project from the android-sdks/extras directory, & compile it as a library. It has to be linked into your app project, but there are multiple properties dialogs with multiple fields for libraries.

Adding the jar file to Package explorer->Ultramap->properties->project references doesn't work. The entire google play services...Continue Reading
Posted by Jack Crossfire | Nov 15, 2014 @ 05:44 PM | 7,075 Views
The decision was made to convert contact lens agitator #2 to a traditional levitator, since so much work went into it. Would find a cheap thing to hang from it. Instead of reusing the existing electronics, would make a simpler circuit using knowledge gained over 9 years to do a better job. The original circuit had a full H bridge. The new circuit would just pull.

Opening it after 9 years revealed a few critters. It was indeed a steaming pile of dog turd. It was a miracle the original circuit ever worked at all, since it didn't use star grounding, relied on a dog slow LM324, had a lot of unnecessary parts for what seemed to be lowpass filtering. It relied on extreme capacitance to work around the grounding. It was the product of many experiments without an oscilloscope.

The 1st attempt used a MOSFET with full belt & braces snubber diodes. It quickly overheated & destroyed itself. It went back to a tried & true BJT with no snubber diodes.

...Continue Reading
Posted by Jack Crossfire | Nov 07, 2014 @ 11:21 PM | 7,000 Views

It was finally time for a 3rd stab at a contact lens agitator. After years of levitation & home made linear motors, this one would be a tried & true laboratory shaker, using a stepper motor. The linear motor couldn't make enough thrust, was too noisy, & shed metal filings. The levitator had proven completely ineffective but looked neat.

There was hope a computer fan could do the job. Those turned out to use a dead simple half bridge. 1 pin is always 12V. The other 2 pins alternate going to ground. They spin in only 1 direction, no matter the polarity.

The next step was a traditional brushless gimbal motor. A 3 phase motor controller would have been ideal, but completely unaffordable. A pair of BJT's from a burned out lightbulb would do the job. They didn't need spudger diodes like MOSFETs. The same half bridge arrangement of a computer fan actually provided enough of a shaking motion when applied to a brushless gimbal motor.

After much effort, a C program for driving it with PWM wouldn't compile properly. The compiler choked on a counter equality comparison. After redoing it in assembly, PWM was once again a noisy failure. Even at 22khz, it was too noisy because the PIC at 8Mhz couldn't get the timing close enough. A linear regulator would lower the 20V input to control speed, the heat from which would heat the payload.

How to mount a regulator on a CPU heatsink to heat the payload....Continue Reading
Posted by Jack Crossfire | Nov 01, 2014 @ 04:20 AM | 7,010 Views

That was disappointing. They lost 3 in 2007, when an oxidizer tank exploded. Like last time, they'll never release the cause of the accident. This was probably another oxidizer tank failure. The pilots would have been ejected by the blast. The guy in the left seat would have been the unlucky one, knocked by just the right piece of carbon fiber to knock him out.

There comes a point in a space program when enough people have been lost by the same cause that there is a definite safety issue in the management or the system. Hybrid rocket engines just may not be safe enough because they require too much gas under too much pressure for current materials. People have struggled with carbon fiber tanks for decades. They haven't been consistently able to contain a rated pressure.

It's hard to believe they'll be able to make another vehicle without any money coming in from customers. The plan was always to mass produce them, but only after the money was coming in from the 1st one. Dick Branson had slowed funding to a crawl. It's hard to slow it any further without stopping it.

It's yet another story of another guy giving his life in the quest to reach space. As long as space is just 62 miles away, they'll keep reaching for it & some won't come back. Maybe we'll lose 1 per decade. No-one died in the 1990's, when the number of people going up was at its peak. There hasn't been enough money since then. The 2010's are still benign compared to the 2000's.

Virgin Galactic/Scaled was the last to continue the legend of people coming to the high desert of Calif* to ride a vehicle into space, test pilots whose names no-one knew, who rode horses & drank at a run down bar. The legend is really over. Kazakstan ended up being the place for going into space. The new space cowboys drink Vodka & drive trucks with dashcams on the wrong side of the road.