Jack Crossfire's blog View Details
Posted by Jack Crossfire | Jul 30, 2020 @ 02:19 AM | 3,802 Views
The repaired steering linkage in


finally broke for the last time. It was the 1st time a teflon repair broke. It managed to drive 3 miles with only 1 wheel turning. It couldn't turn sharply, but it could go in straight lines & turn slowly through the miracle of computer aided steering.

The lion kingdom ordered enough aluminum steering linkages last year to replace them all, but never bothered replacing them until necessary. No vehicle being driven as much as these is perfect. They're all destroying themselves with high mileage & manetaned just enough to get by.

As usual, there were discoveries during the repair. It ran into some kind of animal excrement. A very sticky brown material with the rubbery smell of bile was covering a steering linkage which had to be replaced. It was truly awful. Couldn't clean it all off. Just threw away as many parts as possible & returned the remaneing, slightly coated parts.

Lions are usually careful about avoiding excrement. It may have really been some kind of plant matter.
Posted by Jack Crossfire | Jul 03, 2020 @ 03:12 PM | 4,284 Views
In the face of worn nylon straps, another phase of tire coatings began. Aquarium sealer was the absolute toughest adhesive lions ever saw. Vibram rubber showed similar wear to nylon. There was a trend with nylon where impregnating it with E6000 made it more robust. To save money, later nylon straps weren't impregnated with E6000, which may have made it wear out faster. Using 1" wide straps is definitely better.

The news last covered the Mars rover tire wear in 2019. After traveling 13 miles, it was much more beat up than lion tires after 100 miles. Lions can get hundreds of miles out of tires by frequently replacing nylon straps, but the idea is to reduce the manetenance.
Posted by Jack Crossfire | Jun 19, 2020 @ 01:15 AM | 10,175 Views

Interesting review of the Skydio 2 & Mavic Air 2.  DJI has so many mavic's, the meaning of any of the product names has all become quite meaningless.  It might as well be the DJI X AE A-XII.

As before, the Sky Diddyo isn't intended to be flown in any manual way, but be a fully autonomous tracking cam.  They emphasized it doesn't come with a stick controller, but a lot of quad copters have relied on pure phone controllers before.  Casey Neistat was disappointed in the 1st Sky Diddy's lack of any artistic rules & composition, but he was also sponsored by DJI.  The new Sky Diddy continues to be brute force technology without artistic composition.  

The big change with the SkyDiddy is the introduction of a GPS beacon for the tracking instead of being purely machine vision.  They didn't say if the GPS beacon completely replaces machine vision for the tracking or just aids it.  It's kind of a throwback to 2010 when everyone used GPS.  Maybe there's a lesson for the rest of us tracking cam afficionados.

The tracking is still relatively far away, little improved from the very best of the GPS trackers 10 years ago.  It wouldn't be useful for portraits.  They were impressed by the evolution of the Diddy's obstacle avoidance & considered it uncrashable in any environment, but the way it avoided crashes was manely by just stopping when it couldn't find a route rather than being more creative than the Skydiddy 1.  An...Continue Reading
Posted by Jack Crossfire | Jun 11, 2020 @ 01:48 AM | 15,508 Views
2 years in storage made the tires change color & get harder. We'll see which side wears out faster. The last 2 tires had asymmetric wear & rotating them made no difference. It may be the same phenomenon that rubber erasers go through.

The old tires eventually started slipping, despite never being removed from the hubs. They just stretched & got looser over time, so even though they're real tight now, they still got the rubber cement.
Posted by Jack Crossfire | May 17, 2020 @ 02:39 AM | 10,334 Views
Automated cam 3 (2 min 33 sec)

It was a 4 year process to finally get this level of tilt & pan tracking of a lion. The mane limitation was money, followed by long commutes. Not having to commute for 2 months finally opened a window to focus on it. There will always be tweeks to do, to try to improve the composition, but the algorithm is pretty finalized.

Tracking cams require very fast autofocus & low light sensitivity. It took a long time for cameras to achieve the required performance at an affordable price. The EOS RP does it real well & it was all lions could afford. Then, an affordable laptop with the required computing power had to come along, since it has to be portable.

It's hard to believe this process began with a fully functioning lidar system, went to a 180 degree security cam & evolved to purely machine vision through the viewfinder.
Posted by Jack Crossfire | May 03, 2020 @ 11:05 PM | 6,958 Views
Not often you see them with a 35mm movie cam. This one was in Star Wars IX. No in-camera stabilization for this one. They didn't use any of the quad copter footage.
Posted by Jack Crossfire | Mar 14, 2020 @ 10:51 PM | 9,953 Views
What a lion actually looks like with his dog.
Posted by Jack Crossfire | Mar 14, 2020 @ 10:48 PM | 9,900 Views
Was hoping it just cracked acrylic, but the lunchbox cracked too. Tried separating threadlock from plastic with a washer, but the threadlock most have gone right through. Just a matter of applying threadlock after tightening the nut.

There should be enough friction from the washer to keep it together, but if it ever has to be taken apart, it's going to need a reinforcing layer of teflon. The chassis is extremely rare on ebay or a $130 tag, in today's money.
Posted by Jack Crossfire | Feb 09, 2020 @ 12:02 AM | 6,759 Views
It didn't take long for the lion kingdom to realize it was running hundreds of miles in silence. The Anker was no louder than a phone speaker. There are 2 ways to make a bluetooth speaker louder. They all currently have a separate radio & amplifier. The HT8692 amplifier in the Anker has a gain adjustment resistor, but it has a very low maximum gain. Anything below 65k made no difference.
The next step was putting an op-amp between the ATS2815 radio & amplifier. All it took was a bare LF353 with a gain pot. The Anker provides a virtual ground & dividing resistors to combine the 2 channels.

The maximum gain of this circuit was limited by the input offset voltage of the op-amp. Above the maximum gain, the DC offset of the output mutes the signal. The lion kingdom tuned it just below the maximum gain & relied on the phone volume to limit distortion. It's amazing how much power these speakers have put out, over the last 5 years, without blowing up.
Posted by Jack Crossfire | Jan 16, 2020 @ 12:40 AM | 8,841 Views
After literally years of looking for a compact way to power a bluetooth speaker from the mane battery, the reason why they never worked was finally found. It wasn't the large filter capacitor or the ripple but the $1 car chargers only handling 1 Amp. When they were upgraded to 2A, the speakers started working with no changes. 1A is not enough to power a speaker, despite all the current measurements coming in below 1A.

The easiest solution was always to not hack anything but stick an original speaker in with a plane old USB cable & car charger. The hacking apart of car chargers & speakers was to make them more compact & lighter. Now the convenience of only having to charge the mane battery & transmitter battery, with no beeping after 10 miles, is finally known.
Posted by Jack Crossfire | Jan 09, 2020 @ 01:13 AM | 5,430 Views
The answer is no. You can't power a bluetooth speaker from a $1 car charger. The $1 car chargers are only useful for charging because they make too much ripple. Only a very large filter capacitor can reduce the ripple enough, in which case a battery is smaller. A giant filter capacitor is still more convenient than a battery. After years of taking 3 batteries out of the vehicle for charging, it's so convenient to only have to worry about 2.

The car chargers can be tested with an 8ohm load. The ripple is affected by output capacitance & battery impedance. Newer batteries can power bluetooth speakers more easily. The Rudung creates 100mV of ripple. The 10000uF output capacitor + 1R resistor reduces it to 50mV. The 10000uF with a new battery produces no ripple. An inductor on the output makes no difference.
Posted by Jack Crossfire | Jan 07, 2020 @ 12:48 AM | 7,493 Views
The $1 buck converters now go up to 2A, fixed voltage of course. Almost worth building a dummy load to see how long they really handle 2A before blowing up.
Posted by Jack Crossfire | Jan 04, 2020 @ 04:21 AM | 9,544 Views
$1 car USB chargers were a good substitute for expensive voltage converters for many years. Just replace the feedback resistors with a pot & they could make any voltage at 1A.
Of course, if you didn't already have a bag of pots & caps, they would be a lot more than $1.

They were useless in their intended role as car chargers because the caps exploded in the heat.

The party ended when the Chinese finally moved to fixed voltage regulators. Any application would need to run on 5V now.
Posted by Jack Crossfire | Jan 03, 2020 @ 12:28 AM | 6,926 Views
Don't plug a 4.2V speaker into 12V or it'll let out the magic smoke. Fortunately, it only blew up the amplifier chip, a HT6871. The radio & leds were still intact. It would take 1 month to order a new amplifier chip from China, so went ahead & got a new speaker. With this experience, it was decided to put in different connectors for 12V than 4.2V.

It was such a good speaker during its 3 year lifespan, the lion kingdom put in a different amplifier chip & revived it. There were some amplifier chips from a terrible speaker with the same pinout. The new speaker arrived anyway & was a better deal.


Manely, the newest speaker turns on right when power is applied instead of requiring holding a button after applying power. It's all a matter of luck, but money buys a lot more online with the 1 week delay than locally.

The sub $25 can speakers have been the right size for robots.

The new amplifier chip uses a boost converter to make 7V. It would be simpler just to use a speaker with higher impedance or a battery with higher voltage to get the same power, but apparently it's cheaper to use higher voltage with standard speakers & a battery voltage which doesn't require a boost converter for charging.
Posted by Jack Crossfire | Dec 18, 2019 @ 12:33 AM | 11,826 Views
The decorations keep getting better, with the discovery of brown pipe cleaners at Hobby Lobby & the order of giant red LEDs for the LED animation.
Posted by Jack Crossfire | Oct 22, 2019 @ 02:33 AM | 5,281 Views
A scooter ran a red light at 25mph & smashed straight into it. Miraculously, only the wheel was smashed. He broadsided it & dragged it a few feet, but manely took out the food it was carrying. Scooters & bikes are in the grey area of not having red light rules enforced & not having speed limits.

In regular use, the lion kingdom has had 1 wreck every 2 years & all in crosswalks or sidewalks. The 1st wreck was an SUV turning right, destroying the cargo area, damaging the chassis & 1 wheel.

Ground vehicles which coexist in the road network have similar expenses as flying, but instead of impacts with the ground, it's impacts with full sized vehicles. Fortunately, they don't damage the other vehicles or cause injuries, but when cars impact robots, car insurance doesn't cover it & it's pretty much the robot owner's expense.

They're quick with the sorry's & the excuses but no driver is willing to pay for it. Lions don't pressure anyone for money because of what happened to quad copters. If there's any hint of liability, they'll regulate the ground robots into the stone ages. They're already banned in almost as many areas as quad copters.

The mane problem is they're harder to see than humans. Near misses with cars happen every month, usually when cars make right turns. High acceleration & planning for it is key. The lion kingdom usually has the robot drive ahead, in order to bait cars. If the car keeps going, there's a good chance they don't see the lion.

There were a few right turns that would have impacted lion instead of robot. The robots are all intended to be expendable, but there's still a desire to prevent one from becoming a total $500 loss, in today's money.
Posted by Jack Crossfire | Oct 20, 2019 @ 11:32 PM | 6,942 Views
The lion kingdom can remember no time when it needed 2 power supplies simultaneously. They were only used for remembering different settings or having different connectors. Manely, they were hoping for a future need that never came.

A Rudung was sacrificed. The new butter surprise created a stable 9V from a 12V battery. It had a 0.5V dropout.

Subjectively, the results were more realistic than without a regulated voltage. There was a steep drop in PWM for the 1st turns, then a leveling off. Finer precision was still a matter of complete drives & measuring charge.

The alignment affected downhill drives more than uphill. It might have been because more weight was on the front wheels when going downhill.

The 1st 9.2 mile drive burned 246mAh/mile.
Posted by Jack Crossfire | Oct 19, 2019 @ 06:41 PM | 6,828 Views
It broke after only 6 months. Knocking the wheels the right way, rather than old age, is how they break. The only replacement part is the fabled Tamiya Shaft Bag 58347, long out of production. There are aluminum ones in China with a 6 week waiting time.

Lacking any replacement parts, the lion kingdom attempted a teflon repair. The bolt isn't long enough to reach through the teflon. Teflon is softer than the original nylon.

During this process, it became clear the steering rods could be 1 hole shorter, so the wheels would have to be realigned for the teflon repair & aligned again next year when the China shipment arrived. All this wheel alignment had the lion kingdom searching for a better way. Lions traditionally aligned the wheels by driving a mile, recharging the battery, & measuring the charge. The charge depended on the wheel alignment as well as the battery temperature, & how charged it was yesterday.

The ideal way is to drive a certain distance & record the PWM, but this requires a constant battery voltage. A Rudeng/RIDEN voltage regulator is still the ideal solution for getting a portable, constant voltage. Getting one is another 6 week China shipment.

It was while searching for a voltage regulator that lion kingdom realized this was what Sparkfun sold, 15 years ago. What did Sparkfun sell nowadays? Manely dumbed down educational kits for large schools, big ticket items for corporations, & some standard connectors. Their power supply offerings where now the laptop bricks office supply stores sold 20 years ago instead of the bare boards they used to sell.

Exotic parts for starving college students & programmers are now only available in China. The next option is building a fixed voltage buck converter out of digikey parts, the same way lions would have done it 20 years ago.

There may just be no money to be made in exotic parts just for building other things. They'd rather buy something prebuilt.