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Posted by Jack Crossfire | Aug 17, 2016 @ 12:40 PM | 1,616 Views
Behind the nonstop H-Rod worshiping, this was built. Liquid methane would have been 1/3 the size. The 1st, cheapest configuration would be 8.3 million lbs of thrust or slightly more than a Saturn V. The SRB's alone would nearly match a Saturn V. This increase would lift 154,324 lbs to LEO or 1/2 the Saturn V capacity. All the increase in thrust to lift less to orbit is government at it's best. The SLS uses 2 stages instead of 3. The 2nd stage has a lot less power because it uses a 1950's pre-Apollo engine to save money. Recycling shuttle components came with a lot of compromise.

The LH & LOX tanks are the 1st things in 50 years purpose built for a manned lunar mission. The tanks are 35% larger than the tanks on the shuttle.
Posted by Jack Crossfire | Aug 15, 2016 @ 10:24 PM | 1,761 Views
The 1st drive with the speakers was manely successful, owing to experience finally forseeing requirements. The weight was manageable. Low frequencies were quite good. They were just loud enough to overcome traffic & deafening in quiet areas. Either the battery faded or the TDA1517 overheated, because they were a lot more clipped near the end.
Posted by Jack Crossfire | Aug 14, 2016 @ 05:56 PM | 1,449 Views
Because every launch has a few tweeks, it's tempting to collect as much trajectory information as possible in 1 table. Kiwipedia has hardly any trajectory information. JCSAT-16 was a GTO instead of a supersynchronous orbit like last time. The separation velocity was a hair lower to allow the single engine landing. Perhaps this means they found more money can be made by more consistent landings than by giving the customer more speed.

Orbcommmm LEO SUCCESS: 2m25s 6012km/h 74km
1st return to land

JASON-3 POLAR FAIL: 6147km/h 66.5km
Failed landing leg

SES-9 supersynchronous FAIL: 8325km/h 64.6km

CRS-8 LEO SUCCESS: 2m34s 6608km/h 71km
barge landing

JCSAT-14 supersynchronous SUCCESS: 2m41s 8355km/h 66.6km
Payload separated at 36276km/h 207km
1st 3 engine landing

THAICOM 8 supersynchronous SUCCESS: 2m40s 8343km/h 65.6km
3 engine landing, bent struts

Eutelsat/ABS supersynchronous FAIL: 2m39s 8361km/h 65.7km
3 engine landing with longer single engine phase. ran out of fuel

CRS-9 LEO SUCCESS: 2m22s 5688km/h 59.6km
1nd return to land

JCSAT-16 GTO SUCCESS: 2m36s 8156km/h 64km
Payload separated at 35240km/h 208km
single engine landing

Doing the math during today's 8.9 miler, it became clear that the BFR will be 13.5million lbs of thrust or 1.8 more powerful than the Saturn V. If thrust was proportional to the LEO mass, it would translate to 500,000 lbs to LEO. Full reuse is converging on 1/4 of the expendable payload, giving 140,000 lbs to LEO. It's probably enough for a capsule full of 100 people. There would have to be another flight full of fuel & supplies. A permanently orbiting booster would take the MCT to Mars. Fortunately, someone is working on the problem.
Posted by Jack Crossfire | Aug 13, 2016 @ 11:11 PM | 1,681 Views
So Dr. Franklyn got some long needed grinding to add more clearance. It had no problems other than rubber hitting plastic where the manufacturing was off by a few mm. Other than that, Dr. Franklyn has a bit of plastic filings around every moving part.

Finished the poor lion's speaker, finally. Due to some kind of accident, it only has 950uF for the mane power when the datasheet said 2000uF. That might explain why it didn't do the full waveform for 4R speakers, but it also might require 14V to support 4R speakers.

So 2 speakers paired to give 8R to a single channel is what it is for the 1st test.
Posted by Jack Crossfire | Aug 13, 2016 @ 01:04 AM | 1,663 Views
1st automated cam success (1 min 46 sec)

The answer is yes. Automated cams work. They're not completely foolproof, but with enough error protection can do a decent job. The 1st automated cam ended up being LIDAR based. The trick with LIDAR was building dense point clouds out of many passes.

All the basic limitations of XV-11 LIDAR apply. It only detects horizontal motion, not vertical. It only works indoors. It can't handle lots of mirrors & windows. It can't detect anything more than 4m away. It can't handle 2 simultaneous sources of motion. It does better at night than daytime with sunlight coming in. The worst case is the camera pans away from the subject.

The less ideal conditions can be handled by classifying more pixels as outliers, but this makes the camera lag more. The room had a small number of windows which still resulted in a usable amount of lag. It tracked for 45 minutes at night without any failures. As the subject moves farther away, the harder it is to get the camera to track with the amount of filtering required for the windows. It's very limiting to not have vertical tracking.

There's still a plan to try a machine vision approach, with its own set of limitations. A thermal cam might do it, but these are extremely expensive.

When the mobile app billionaires finally get automated cams fast enough & reliable enough for the masses, they're going to be a game changer just like brushless gimbals. GPS quad copters won't do it. Cheaper LIDAR is the key.
Posted by Jack Crossfire | Aug 07, 2016 @ 09:10 PM | 3,578 Views
Soldered it in a stereo configuration with a pair of 4R speakers. This went down like a lead weight. Despite the LM324 providing both sides of the waveform thanks to its actively driven virtual ground of 5V, the TDA1517 only put out the bottom half. The TDA1517 didn't even turn on at the vehicle's 8.4V. The input protection diode dropped it to 7.7V & this was below the minimum. It needed 9V to turn on, which the diode dropped to 8.3V.

For some reason, wiring the speakers in series to give 8R got both sides of the waveform. This only amplified a single channel, but seemed to be loud enough to do the job. The circuit needed 0.25A, so a tiny 350mAh cell would boost the vehicle's voltage enough for it to work. The mane problem is enclosing it all in a module suitable for attaching to the vehicle.

It's theorized that the speakers can use the cargo bay as a resonator instead of requiring their own box.
Posted by Jack Crossfire | Aug 06, 2016 @ 01:40 AM | 1,496 Views
If only lions knew 20 years ago what they know now. Of course, there was no way to look up how to connect a TDA1517. Sadly, lions have no interest in building audio amplifiers anymore. If the interest of the 25 year old lion was combined with the knowledge of today, it would have saved a lot of money & grief.

It was an experiment to get more sound reinforcement for less weight, but speaker drivers have to be heavy to be loud. The TDA1517 can get plenty of loudness from large, heavy speakers but the same job can be done by a $10 bluetooth speaker.

An LM324 inverting amplifier with virtual ground can boost the phone output to the 1V peak to peak that the TDA1517 does best with. Key to the preamp is actively driving the virtual ground with a voltage regulator. If the virtual ground is passive or a follower output, the LM324 will only generate the negative side of the waveform.
Posted by Jack Crossfire | Aug 04, 2016 @ 04:30 PM | 2,037 Views
There's no obvious sign of a 16" sink. There are cracks not unlike all the other streets. The windows are a bit closer to the ground than the neighbors, but they're not visually misaligned from the neighbors. The only smoking gun is a wall outlet right next to street level. Either the entire street has sunk or there have been a lot of repairs to keep it looking normal.
Posted by Jack Crossfire | Aug 03, 2016 @ 10:28 PM | 1,917 Views
The metal bearings arrived after 7 days, got installed, & the steering was suddenly rock solid. Months of dicking with PID constants were suddenly proven meaningless. The internet wasn't kidding about plastic bearings being no good. Steering wobble is the mane symptom of worn bearings. The metal bearings should last forever, but the plastic axles also wore down a bit. There's always going to be some wobble.

Went up to 10mph with a shirt payload & didn't get any wobbling. This should get much better video. The new bearings & new differential are much noisier than before. The next step would be a metal differential, so the noise is a fact of durability.
Posted by Jack Crossfire | Aug 03, 2016 @ 12:51 AM | 1,965 Views
So basically, detecting motion via difference keying was a total failure. The noise from the webcam in indoor conditions was too close to the noise from the motion. Furthermore, indoor light sources always overwhelmed any other objects. It couldn't tell whether a subject or the camera was moving because color changes by indoor points of light overwhelmed any global color changes.

The next, super simple idea, was to use the old XV-11 lidar module to detect motion.

Motion detection by LIDAR (2 min 26 sec)

The XV-11 tries to detect a lion walking around the room. A window reflects the LIDAR in 1 place, but doesn't affect its ability to detect motion. The soundings are shown in polar coordinates, then in X-Y coordinates. It does 4.9 revolutions per second. 4 revolutions are stacked to try to reduce the noise, but it doesn't look good for LIDAR motion detection. The lion goes 3m away. Another project is sharing the tripod with the LIDAR.

The problem was once again noise. It would have a hard time differentiating the bubbling of the stationary wall 3.5m away from a slowly moving subject. Of course, there's still a chance common differentiation between the LIDAR plots will prove more robust than feared, but that's another commute away.

The X-Y or the polar plots could be differentiated. The X-Y plot would detect motion tangential to the camera better than motion towards the camera. The polar plot would probably do better in both axes.

Since the camera is stationary, another method is taking a long LIDAR exposure & just subtracting it like a static scene. It would have a hard time with furniture & pillows changing position.
Posted by Jack Crossfire | Jul 31, 2016 @ 10:15 PM | 1,589 Views
So with the Feiyu busted, there's nothing to do than try some other project. The latest idea with the Feiyu was to replace the MOSFETs with some other motor controller which didn't have the reluctance problem. Perhaps it would mean running 9 extra wires outside the gimbal, making it so cumbersome as to defeat the purpose of using a Feiyu in the 1st place. Ideally, there would be replacement MOSFETs with lower deadband, but the same form factor. The means by which the Chinese overcame the reluctance is another great mystery which you just have to forget about in the name of having something work.

It was finally time to go ahead with the motion tracking camera. The motion tracking camera could always have been a very compact Gopro deal, using standard servos. The supply of standard servos is now considered consumable, as the lunchbox destroys them all. The X-Y platform had been around for 3 years with something like this in its future. It was decided to go for the maximum dynamic range of the DSLR.

A webcam would provide the machine vision to the computer, since capturing the DSLR's analog video would take more space. The entire X-Y platform is lighter than the Giotto head, so it was decided to mock it up in place of the tripod head. Designing the mockup & attaching it to the tripod took 2 days.

The mane problem is any motion tracking algorithm depends on a camera that moves to track the motion. It can't detect motion when the camera is moving. There are some ideas for solving this.
Posted by Jack Crossfire | Jul 28, 2016 @ 11:17 PM | 1,582 Views
3 months after landing it.

Landed Falcon 9 First Stage Test Firing (2 min 43 sec)

Now that's something which has never been done before. They didn't say how many engines were the ones which flew on the last mission, but there's always hope it is legit. Also intriguing is how they strap it down from the top, instead of holding it down from the bottom like liftoff.

We all know about the work hardening of metal as it's repeatedly contracted & expanded. It remanes to be seen if the 1st stage can survive all the stresses of a 2nd launch, the aerodynamic stresses of max Q, the vibration, the heating of reentry. Metal contracts & expands quite a bit as it goes from -340F to thousands of degrees.

The shuttle components were reused, but it took years. The mane engines had to be completely disassembled, boroscoped, checked for cracks, tested again. The boosters needed to be completely disassembled, packed with solid propellant & parachutes, transported across the country twice & stacked again. Auxillary power units, landing gear, & wiring usually was only good for 1 mission.

The only way they could launch every 3 months was by processing many components from past launches in parallel. The orbiter had to be rebuilt from scratch using components from many launches.
Posted by Jack Crossfire | Jul 27, 2016 @ 12:37 AM | 1,922 Views
So the front differential was never used since it was converted to 2WD mode. It came out in a single piece suitable for directly inserting in the rear. The mane spur gear was on the right. This got it driving in the right direction again, with no grinding.

The wheel base of the Ruckus is about 1/2 of the Lunchbox, so the Lunchbox wouldn't be a good replacement. The Ruckus is just narrow enough to fit on curbs in the city. The day job probably won't last another 400 miles, so the Lunchbox may still be a suitable replacement wherever the next day job is.

For better stability, a stiffer suspension would be the next idea. Metal gears would solve the differential issues. It's going to need new tires by 800 miles. Helas, the plastic wheel bearings are completely worn out. It can't steer with the current wheel bearings, so like any servicing of an old car, what started as a grinding sound turned into a stream of endless repairs.
Posted by Jack Crossfire | Jul 26, 2016 @ 01:43 PM | 1,861 Views
3 days of dissection between commutes revealed the differential to be stripped. 400 miles in 2WD mode was all it lasted. In 4WD mode, it might have lasted longer. After all the effort to extend the range by converting it to 2WD mode, it never went over 1/2 its range. At least this left a spare differential full of parts. The decision was made to get another 400 miles out of the spare differential parts. With the tires going bald, it'll then be time for another vehicle.

The thought had occurred of using a hoverboard or a boosted board as the next vehicle, but before hoverboards went out of style, they couldn't balance themselves. Boosted boards can't steer themselves. Any other vehicle would require a new motor. The answer most likely is another ECX Ruckus left in 4WD mode to protect the differentials.
Posted by Jack Crossfire | Jul 23, 2016 @ 02:06 AM | 2,013 Views
So SpaceX has been varying the MECO for all of its LEO missions, based on payload. Each mission is customized to get the most reserve for landing, but they might leave margin for engine failures. CRS-9 had the lightest payload, which made a big difference in the burn marks. They could have burned the 2nd stage longer & MECOed sooner, but didn't.

Mane engine cutoff times for the LEO missions:

2m25s 6012km/h 74.3km return to land
6m50s stage 2

2m34s 6658km/h 67.5km return to ocean
7m7s stage 2

2m22s 5688km/h 59.6km return to land
6m29s stage 2

The only trend is they got lower. Speed wasn't on a downward trend. Perhaps they experimentally found lower & lower altitudes where drag could be managed by the 2nd stage, so they could save fuel by accumulating velocity lower in the atmosphere.
Posted by Jack Crossfire | Jul 17, 2016 @ 09:18 PM | 1,904 Views
Revisiting the anticogging table generated a few months ago revealed a bug in its calculation. Measured again the hall sensor readout for a wide range of rotation & found the cogging was fairly consistent around the motor's entire range & power levels. A little manual tweeking just might make a table which defeats the cogging.

Calculated a new table of phase offsets to correct the cogging. This looked a lot more ordered than the previous table. With the new table applied, the rotation was a lot smoother. It still wasn't perfect, but the months had proven any other method would be inferior.

Recursively creating a new anticogging table by testing itself didn't improve the results. A plot of a complete rotation using the anticogging table didn't show any areas where an equal offset could be applied to all parts of the rotation.

Finally, making an anticogging table for the motor's entire rotation rather than a single sine wave period showed some improvement but took too much memory. It means there's some variability in the reluctance or the stiction for different parts of the rotation.

Anticogging a brushless gimbal (0 min 28 sec)

Posted by Jack Crossfire | Jul 03, 2016 @ 05:17 PM | 13,032 Views
It wasn't surprising that a piecewise linear scaling of the PWM could fix the current for all but its least negative point. That was only for a single winding with no rotor. Adding a rotor or changing the angle of the rotor changed the scale factors.

To simultaneously smooth out the 3 sine waves of 3 windings would be a bit harder. The parameters of 1 PWM's linear scaling depend on the linear scaling of the other 2 PWM's. The easiest way was to have the computer shift all 3 sine waves in time so they would play back the desired waveforms. The shift amounts could hopefully be translated into a piecewise linear scaling. With only 2 current sense resistors, there was no way to know the 3rd sine wave or what the positive half looked like. There was only the hope a sensible linear scaling would emerge that could be applied to all the sine waves.

That got 1 sine wave to play back as a sine wave, but not the other 2. The time shifting ended up a messy curve instead of a simple linear scaling.
Posted by Jack Crossfire | Jun 29, 2016 @ 12:01 AM | 3,050 Views
Finally decided to reduce the Feiyu to the simplest possible circuit: a single P MOSFET feeding an N MOSFET through a single motor winding. This gave the same knee graph, current getting less negative as the N MOSFET duty cycle approached the P MOSFET duty cycle, then stalling at around 870. The stall region occupied more of the curve as the deadband increased.

The only way to see all the voltages involved was compositing multiple 2 channel scope views to make 4 channels. On the unknown Feiyu part, the MOSFETs are inverted so they're off if the gate is 0.

Strange physics (0 min 56 sec)

The time of N turning on is ramped from before P turning on to after P turning off. Reverse current happens when both MOSFETs are off, then breaks down when the N off time hits a certain point after P turning on. For later N on times, the behavior is expected. The length of both N & P at 6V increases because there's no place for the charge to go when both MOSFETS are off. The reverse current didn't happen with a purely resistive load.

Basically, the reverse current is a function of the duration of the current flowing from P to N & breaks down accordingly when the P to N is reduced. When N is on with P off, flux in the motor core is trying to send current from N to P, which only flows when N turns off. This is reluctance cogging.
Posted by Jack Crossfire | Jun 26, 2016 @ 07:55 PM | 2,751 Views
The last experiments with The Feiyu involved feeling the amount of torque as the phase changed. This revealed the torque dropping to 0 & the motor stalling exactly where there was a glitch in the current sensed by the resistors. That was where the current of a phase reversed direction or where the PWM on any of the phases crossed halfway.

The next step was holding 1 phase at a constant PWM while ramping a 2nd phase from 0 to the 1st phase. The 3rd phase was disconnected. This started with strongly negative current through the current sense resistor. The current approached 0 as the 2 phases got closer.

This revealed the same glitch when the variable PWM started approaching the fixed PWM & 0 current. It was more clear that the current approached 0 faster than it should have as the PWM increased, then leveled off until it hit 0.

Tried the 2 phase test with different values of the constant PWM. That varied the point of inflection in the variable current to match where the stationary PWM was.