Jack Crossfire's blog - Page 6 - RC Groups
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Posted by Jack Crossfire | Jun 04, 2017 @ 10:15 PM | 3,043 Views
Spacex vs spacex (3 min 22 sec)

You can infer more about the NROL-76 payload by comparing its launch against CRS-11.

The NROL-76 booster went to a much higher altitude but equivalent speed. NROL-76 was a slightly lighter payload, as shown by the faster liftoff. It had to burn a lot more fuel to land the 1st stage from the higher altitude, despite the lighter payload. CRS-11 was a 15,000 lb payload. 9000 of a Dragon mission is the Dragon system alone. The mass of the payload fairing is unknown, so it can't be directly compared to Dragon.

Estimating the mass of NROL-76 requires comparing the time it took to clear the tower to another communication satellite. SES-10 took off ever so slightly slower than NROL-76, so NROL-76 was a hair below 11,000lbs. The difference in speed was only obvious with Dragon launches, showing how the Dragon system was much heavier than a communication satellite with its fairing.

After launch, NROL-76 was detected in a 248mile circular orbit with 50deg inclination. There was no reason to go to the higher altitude besides concealing its orbit.

Falcon 9 nrol76 landing stabilized (3 min 32 sec)
...Continue Reading
Posted by Jack Crossfire | Jun 02, 2017 @ 12:49 AM | 3,101 Views
The lion kingdom's 1st motor was the Gilbert DC-3 motor. It was a marvel for a 5 year old, but it was quite difficult to get the 3V to power it in 1980. Nowadays, low voltages are everywhere, but in those days, everything ran on 120V unless it was expensive.

The motor collection has grown, over many vehicles. They're a lot more efficient than the DC-3. There are a few more little motors. Without a purpose, they're doomed.
Posted by Jack Crossfire | Jun 01, 2017 @ 01:11 AM | 3,801 Views

After 6 years of fabrication, the stratocruiser finally came out of the hanger for a fueling test. It was made out of used 747 parts, millions of fiberglass layups, & billions of latex gloves. It must be the largest piece of fiberglass in the world. Whether it's an ITS or a stratocruiser, the trend in space travel is bigger things.

In another twist, instead of marketing towards launching a single, large rocket, the plan is to launch multiple smaller rockets in a single flight. This model should allow it to avoid bad weather & reach different orbits in a single flight, but it's limited to low Earth orbit & very small payloads. The problem is they're still throwing away the rocket when a fully reusable rocket is coming increasingly closer to reality. By their forecasted 1st launch in the next 2 decades, a falcon heavy could technically achieve full reuse for small LEO payloads. The need for a gigantic airplane launching expendable rockets for these payloads would instantly end.
Posted by Jack Crossfire | May 31, 2017 @ 01:01 AM | 2,870 Views
So a solution to the car mp3 player presented itself, eventually. It should be a very simple bluetooth DAC with its own volume control. It shouldn't use the standard bluetooth speaker protocol, since that volume control is erratic. Both a non deterministic neural network in the Android operating system & different settings for different bluetooth speakers make it worthless. There should be a volume control just for cars, which is fixed.

The phone should constantly listen for this bluetooth DAC's advertisements. When it connects, it should resume playback from a playlist that spans multiple directories. When it disconnects, it should pause playback. After a certain time disconnected, it should rewind a few seconds. That way a glitch doesn't make it rewind.

It should be simple enough to not be a disaster when it's stolen.

This should give the desired auto start when the engine starts. The lion kingdom isn't aware of an existing solution. They either pair the car as a standard bluetooth speaker or require plugging the phone into a USB port to access the files on it, every single time you get in.

Of course, Calif* doesn't allow touching a phone while driving, at all. The simple DAC would need buttons for skipping songs. It quickly grows into the original Android Auto vision of a head unit which mirrors a phone. It would instantly get stolen. The Goog has since abandoned that vision in favor of just another phone app which uses your car as a bluetooth speaker.
Posted by Jack Crossfire | May 29, 2017 @ 11:51 PM | 3,342 Views
Falcon 9 nrol76 landing stabilized (3 min 32 sec)

Finally got this stabilized, but it was still lousy. The problem is the motion tracker couldn't lock on to the constantly changing flame & gas exhaust. It probably still brings out more detail than the raw footage. The 2nd stage nozzle is more visible. There are no photos of a fully assembled 2nd stage, but the nozzle appears to be the largest possible diameter that would fit.

The ground based cam was a thrill. Seeing something that large hurling towards the ground at 1000mph with no power, with the air currents swirling by, shows how precarious the landing maneuver is. It's hard to believe the engines will ever start on time & it looks right at the limit of physics, right next to black holes colliding & pulsars. Navigating this narrow window in the laws of physics is what all rockets are going to have to do.
Posted by Jack Crossfire | May 28, 2017 @ 04:50 PM | 2,735 Views
The H King finally did a 6 mile drive without any gremlins. Compressing the springs just 1/2" & narrowing just the bottom was enough to keep it from bottoming out with 8oz of payload for 3 miles. This took 1800mAh.

It took 1800mAh to go 8 miles in the hills at 9:30/mile with a shirt for part of that.
Posted by Jack Crossfire | May 27, 2017 @ 05:52 PM | 3,078 Views
The lunchbox worked quite well for 21 miles in the city. The 1 downside was it was harder to get around people. The many upsides were it had a much easier time navigating curbs & uneven pavement. It could carry useful cargo. The tires would last much longer than the smaller vehicles. The tires are the biggest consumables, after the steering servo & differential have been sized up enough.

There are ideas to lower the CG of the lunchbox by making the suspension rigid & lowering the cargo down to the wheels. It might have been a better deal than the H King.
Posted by Jack Crossfire | May 27, 2017 @ 05:30 PM | 3,055 Views
In another effort to have the H King functional by Tuesday, it was all about fixing the suspension. It was bottoming out badly & grinding its screws. Tried making hot glue bumpers. Hot glue came off easily & would have been ground away instantly. The final solution was bolting on a plastic sheet using more easily sourced bolts than the stock screws.

Tried raising the suspension, but the shocks couldn't be moved any closer without interfering with the zip ties holdling the cargo on. The only option was stiffening the springs with some home made C rings.

It got a headlight switch to squeeze out the last bit of battery power.
Posted by Jack Crossfire | May 25, 2017 @ 12:44 AM | 2,754 Views
Kind of disappointing to see Musk diverting so much money away from the original Mars colonization effort to terrestrial problems like hyperloop, boring machines, & AI, exactly the same way government budgets do. It's like how most programmers don't have enough focus to finish their original idea without a boss telling them what to do.
Posted by Jack Crossfire | May 24, 2017 @ 03:56 AM | 2,854 Views
The 11 year old ACN 16/15/4 was a direct replacement for the H King motor. The ACN has 2100kV, a 3.2mm shaft, & optional wider bolt spacing. It alone cost as much as the complete H King. 2100KV must have been right near the minimum for inrunners.

Opening the H King revealed a completely dry gear. The H King motor was the kind which can't be opened & rewound. The motor bolted into soft plastic without washers. The best gear alignment was pretty bad. The MEGA has wider bolt holes but there's not enough room to drill more plastic.

The downhill runaways were fixed by dramatically decreasing the PID gains & limiting the minimum throttle to a value which brakes less. The minimum should be set more precisely to a level that just turns the motor. Also, the ACN motor had much higher cogging which led to nihilistic braking.

On the 1st drive with this motor, it used 880mAh to go 4.5 miles at 9 min/mile. There was no payload & the LEDs were on. That's 195mAh per mile, slightly lower than the Ruckus. Driven to destruction, its 4Ah 8.4V battery would go 20 miles. It's tempting to install a headlight switch.

Based on the blog history https://www.rcgroups.com/forums/show...Ruckus-testing, the Ruckus had a 4Ah 8.4V but it only went 10 miles until destruction while carrying a shirt.

It's strange that when using the 4200KV motor, the H King burned through 800mAh per mile. It must have been right above stalling.
Posted by Jack Crossfire | May 21, 2017 @ 10:09 PM | 3,300 Views
Hussled the fabrication quite a bit, in the slight chance it would actually work in time for overload week, but the 1st drive quickly showed it had a long way to go. It was clear that the lunchbox would be the weekday driver.

It was decided that there was still no way the electronics could go on the chassis, so back on the container they went. The electronics were covered in rubber from an exercise band. All the voltage regulators went on 1 side, in a power farm. There was no way to keep that from sticking out, because it would melt plastic.

The ESC went into the H King's original battery compartment. Another creative battery tray was developed. The integrated vehicle was a menagerie of duct tape, packing tape, scotch tape, & hot glue.

The tachometer detected a lot more revs to hit the same speed. Braking was ineffective at low speed, though still functional at high speeds. Steering servo didn't have as much throw as the Ruckus. The slightest downhill made it freewheel, at which point the tachometer didn't detect an RPM & it oversped. Suspension was still a bit soft. The plan is to make it rigid. It was a lot more stable than the Ruckus while carrying the shirt, phone, & heavy speaker. Motor stalled quite often when starting & when hitting bumps.

Finally, the battery died after only 5 miles. A lower KV motor with larger pinion is the leading candidate. At least, it was incredibly quiet compared to any previous vehicle.

Now the speed test:

# dist sec min/mile
1 404 156 10:20
2 407 106 7:6
3 408 106 7:4
4 405 105 7:2
5 400 107 7:5
6 207 45 5:55
7 207 45 5:50
Posted by Jack Crossfire | May 21, 2017 @ 02:10 AM | 3,197 Views
After much conceptualizing of how to make the handle/camera mount out of carbon fiber, it was decided to just extend the coroplastic.

While the coroplastic on the Ruckus came from storage boxes from 17 years ago which had long been discontinued, it turned out Home Depot still had coroplastic sheets. It cost $14, a lot more than it did 17 years ago. After much experimenting with string & adhesives to bond it, OSH turned out to still have reusable zip ties. All the coroplastic would be held together by zip ties.

After many agonizing measurements, the new cargo container was done. Every effort was made to document the relative sizes of the 3 vehicles before the Ruckus was torn down. At 10" x 7" x 5", the lunchbox has 315-350 sq in, roughly equal to the H King. The H King can't haul as much mass as the lunchbox.

While the H King looks much bigger than the Ruckus, it's only 1" wider & can't be filled any higher than the Ruckus. The extra material is manely the handles & more durable bumpers. Experience proved the container constantly runs into things & people, so it needs strong bumpers.

The new coroplastic was 4mm thick while the old coroplastic was 3.1mm thick. It's so much more massive, the bumpers may be replaced by plastic sheets.

Since the Ruckus had a dying servo & differential, the decision was made to tear it down & reuse its electronics in the H King. There were a lot of memories in the 17...Continue Reading
Posted by Jack Crossfire | May 20, 2017 @ 03:03 AM | 3,354 Views
The H King wheels from edge to edge came in at 8.25" x 12.5". The Ruckus wheels from edge to edge were 7.5" x 10"

It was only slightly bigger than the Ruckus despite going from 1/16 to 1/12. Being 2 wheel drive, there was no shaft down the middle, freeing up a large space. The wheels were all on ball bearings. It was such a better value than the Ruckus, 2015 feels like the dark ages.

Applying lessons learned, there would only be a cargo container & a handle/camera mount with no material over the wheels. The LEDs & radios would all go on top of the cargo walls. The electronics would go under the battery. The cargo would expand from 244 cubic in to 318 cubic in. The old cargo was 15" x 5" x 3.25". It would increase to 4.25" wide.

The handle/camera mount is key. Designing this feature is the great challenge & going to keep the Ruckus on the road for much longer. The scale is big enough to get the camera a little higher, but this requires reinforcing the side panels.

Since cargo is increasing from 3.25" to 4.25" wide, the camera platform either needs to get wider or the handle needs to bend when the camera is on it.
Posted by Jack Crossfire | May 18, 2017 @ 01:29 AM | 2,742 Views
Now the long since deleted interview from the New York University Astronomy Society. You might think it strange to hear so many female voices in an interview about rocket engines, but it was an astronomy meeting, not an engineering meeting. Nothing has changed in the female preference for basic sciences that lead to teaching careers, even 20 years after the lion kingdom witnessed the same dynamic.

Tom Mueller interview (52 min 16 sec)

Tom Mueller is probably just as important to the Falcon 9's development as Musk. Musk consulted him on at least 1 idea & it makes one wonder who originally started the discussion about propulsive landing. It's hard to imagine coming up with the idea of a staged shutdown to reduce the number of valves on the engine. He said it was done on smaller engines but never scaled up. There are no goog search results on what a staged shutdown is.

There were a few other nuggets of information, like how something as small as the injector was a big factor in the engine's total efficiency & how they got the injector efficiency as high as possible. You would think blowing up hardware on the test stand is only what NASA & Blue Origin do, but for the 1st time, Muell revealed SpaceX blew up a lot of hardware in getting staged shutdown to work. We can infer combustion is still too complicated for even the latest advancements in computer modeling to simulate.

There was also the nugget about Goog proposing satellites for internet back haul. The reason is the latency is too long for user interfaces, but mirroring large amounts of data for a data center wouldn't need short latency & it's still faster to mail very large amounts of data than send it through the ground.

Posted by Jack Crossfire | May 16, 2017 @ 12:55 AM | 3,027 Views
Insprucker dropped a few knowledge nuggets during today's launch. They pushed the oxygen loading back to 35 minutes before launch & fuel loading to 60 minutes before launch. When he said that, the race was on to see if it would explode again, but there were notes on the internet about them putting in an extra helium tank & lowering the pressure from the rocket which exploded.

After stage separation, the audience was cheering about something followed by "1st stage lost at sea". It might have been an attempt to soft land the 1st stage in the ocean.
Now that Musk released a video of the fairing steering itself, we know not all the recovery hardware was omitted. Based on the cheering, it must have landed right before the 1st stage crashed. They're not showing complete fairing videos because of BEZOS.
Posted by Jack Crossfire | May 13, 2017 @ 08:39 PM | 2,811 Views
It was disappointing to read the SLS had encountered similar failures as the X-33. According to kiwipedia, the hydrogen tank for the X-33 failed pressure tests shortly before it was canceled. The oxygen tank for the SLS similarly failed weld tests before ever reaching pressure testing. More specifically, the oxygen tank required a thicker wall than any previous friction stir weld & they weren't able to develop a suitable welding tool.

Probably the final nail in the coffin was the LOX dome being dropped by incompetence & damaging tooling. The delay will give bean counters more time to kill it. NASA has a strange mandate to pursue cutting edge methods in some places like the welding, yet stick to age old propellants like hydrogen.

Ironically, it may be the conservative use of aluminum that kills the SLS. In the 20 years since X-33, progress on composite tanks continued at a snail's pace. They could have probably done it more easily with composites than aluminum, now. The powers that be gave Earth the bare minimum amount of materials so if we worked right at the limit of physics & did it absolutely perfectly, we could just barely colonize another planet.

Unfortunately, the room temperature layups with vacuum bags of your hobby project aren't perfect enough to do the job. The carbon fiber needs to be heated & evacuated in an autoclave to reach the perfect mass required. Then, the entire tank needs to be built in 1 piece.

In the 8 Mike Griffin years, they managed to produce 1 new vehicle, an Ares I test article. In the 8 Charlie Bolden years, they produced absolutely nothing. Even in that time span, without counting the moon program, the trend was down. Also noteworthy, 50 years after building the Saturn V, they were completely unable to build an equivalent rocket.
Posted by Jack Crossfire | May 13, 2017 @ 06:41 PM | 3,077 Views
It would be worth releasing the lion kingdom's fully functional BLE stack for the RPZW as open source, but it would make rent go up again when a CEO sold a startup based on it. The mane idea is it starts a shell using Popen, then feeds the input characteristic to stdin while feeding stdout to the notification handle. Stderr is dumped to the console. This restricts the python to just a bluetooth layer. The shell must be started as 'bash' not 'bash -i' or it'll generate SIGINT.

The system is based on modifying bluez/test/example-advertisement & bluez/test/example-gatt-server
1st, you have to run example-advertisement once. This runs continuously as connections come & go. Then, you have to run example-gatt-server to wait for a connection. After the connection ends, it has to be restarted.

There is no callback in the bluez dbus interfact to detect when it's connected or disconnected. Instead, 99% of the time, you get a StartNotify when it's connected. StopNotify callback when it's disconnected. When that doesn't happen, you always get a StartNotify callback when it's reconnected.

When StartNotify is called twice in a row, issue os.system('killall -9 python3') to cause the python script & Popen subprocess to die. This won't kill a subprocess started by the Popen subprocess. That requires giving another process name to killall. An outer loop can restart it, where StartNotify then calls Popen. Besides this method, your BLE client can always send codes to the characteristic when it connects. There are many tricks to redirecting I/O from the subprocess.

There are still problems when starting it from /etc/rc.local instead of ssh. Having more than 1 characteristic also doesn't work.
Posted by Jack Crossfire | May 12, 2017 @ 12:10 AM | 3,618 Views
When last we visited the LED backlight replacement, it needed a more precise way to control brightness than varying the DIM pin voltage. The proper way to use the FB pin voltage requires 2 voltage regulators: 1 to provide 5V to DIM & 1 to provide variable voltage to FB. The decision was made to try dividing the 5V with a 1k pot.

This worked quite well. The current drawn by FB was low enough that the pot accessed the full range of brightness by outputting 1.4V to 4.6V. It was much finer control than the DIM pin. The brightness was also more independant of input voltage, though not completely. So the proper way of using the DF6113 is 5V on the DIM pin/ENA wire & dividing the 5V with a 1k pot for the FB pin/DIM wire.

1/16" balsa was hot glued in to get the LEDs to press against the glass. It needed slightly more than 1/16" of filler.

It's now much brighter than even a modern phone. What a bobby dazzler, like the lion kingdom bought one. There's no artifacting from the LEDs. It's finally bright enough to use minimum waveform intensity. Soldered to the power switch, since that cuts off the 14V. The 15V connector on the back is always on & is really 14.7V. The power switch has 14V. The manes voltage is always on. Tweeked the pot so the 3 LEDs in series got 8.7V.
Posted by Jack Crossfire | May 04, 2017 @ 06:44 PM | 2,936 Views
The ECX Ruckus blew its 2nd differential in 15 months & the servo started jittering. Time to desperately look for more expensive vehicles. Managed to get in 1.5 super fast miles.

# dist sec min/mile
1 211 46 6:6
2 201 46 6:0
3 202 46 6:0
4 212 47 6:9
5 210 45 6:1
6 208 48 6:9
7 201 45 5:57
8 210 48 6:7
9 202 51 6:40
10 201 46 6:5
11 201 46 6:4
12 201 46 6:8
13 207 53 6:52
Posted by Jack Crossfire | May 03, 2017 @ 02:26 AM | 3,246 Views
In the very old days, every LCD display including every laptop had plain old, miniature fluorescent lights for backlighting, right down to the traditional fluorescent light glasswork & mercury. If you're lucky enough to have a piece of 20 year old vintage equipment, they'll need replacement. They slide into the LCD panel for easy replacement. Since this LCD panel is $300, it's a good idea to replace just the tubes.

New fluorescent tubes would be over $50 today, so an even better idea is to get an LED replacement kit from China for $8 delivered. The LEDs would be brighter. After 3 weeks, the LED replacement arrived.

They're nothing remarkable for an LED afficionado. The LEDs are packed as close as possible. The important note is the strips must be shortened for the display. The LEDs are wired in groups of 3 which have clearly visible traces joining each group of 3. They must be cut between the groups.

This driver board is a simple buck converter based on the DF6113. It takes 10-24V & outputs a fixed current. It amounts to a maximum voltage of 3V per LED. Input current at full power, for the full 24" strips is 1A at 10V.

Very important: When the strips are cut, the brightness increases because it's a constant current regulator. Also, the constant current varies based on the input voltage until it hits the maximum current. Then it becomes fixed for all input voltages.

The board is wired according to the "ENA+DIM inverted analog...Continue Reading