Jack Crossfire's blog View Details
Archive for September, 2018
Posted by Jack Crossfire | Sep 14, 2018 @ 03:07 AM | 16,242 Views
A little more gamma reveals the blended wing body replaced by much simpler beveled wings & canards. The wings & rudder serve as landing gear. Horizontal surfaces are folding, so they can be flat to provide lift, then be a triangle to serve as landing gear. The folding might also provide aileron functionality. There are a lot more windows & they're tinted. The single piece window of BFR 1 returns. The heat shield is a simpler flat shape.

The engines seem to be the scaled down raptors that were tested 1st, but with vacuum nozzles. He decided to reuse the test engine for the upper stage, while reserving the full size engine for the lower stage. It would speed up development to not delay the ship for the full size engine. A bit disturbing to see ablative nozzles.

A bit puzzling how vacuum nozzles would allow landings on 2 different planets with different air pressures. An overexpanded nozzle is too unstable.

They could also be full sized engines with retracting nozzle extensions.
Posted by Jack Crossfire | Sep 14, 2018 @ 03:06 AM | 16,009 Views
Pay $30 for 4 new servos & the old one will start working again.

Anyways, reflowed the QFN's solder joints, & made a servo exerciser to thrash it all night. Naturally, it would never fail on the bench, but the new servos alone stood a good chance of reviving it. The last order of standard servos was 2001. They were $6 Tower Hobby branded, but shipping was much lower. Those hobbyking servos are now $5, but shipping has followed inflation.

Signs started pointing to a glitching battery connector crashing the microcontroller on the servo. The mane CPU also had glitches, but didn't lock up. The servo may just lock up under certain power glitches. After a cleaning, the $60 servo was revived & didn't crash again. So it's a lot more sensitive to electrical noise than a brushed servo. It must run at a much higher clockspeed.
Posted by Jack Crossfire | Sep 06, 2018 @ 02:42 AM | 24,423 Views
After 400 miles, the $60 brushless servo died & it went into the street. The death was intermittent, as it briefly came on again. Back on the bench, it managed to still have a fault. All the voltages were normal, with no voltage going to the MOSFET gates. Power cycling it a few times in the street didn't bring it back, but it did come back after a power cycle on the bench. Nothing that suffered mechanical wear seemed to be worn out. It was a microcontroller that had become flaky.

It's a Silicon Labs F330, 8051 core. Dave would check all the pins & try to fix it.

After all the servos, there's a real need to build a servo from scratch to last forever. The $60 one has enough useful parts to work again with a custom board, but this would be a significant investment in a rare time when the lion kingdom's time is actually worth more than a servo.

It would be a matter of removing the F330 & soldering a bare ATmega on a separate board to the 6 MOSFETs, PWM, & power. Not sure how the MOSFETs on the underside would be accessed.

Expensive, high performance servos have consistently died much faster than cheap servos. The biggest failure was the Airtronics 94761. https://www.rcgroups.com/forums/show...al#post9953885 A terrible waste from not knowing the importance of PWM frequency in tail rotor actuating.

The longest lasting might be the Tower Hobby brand from 20 years ago. Futabas are in the middle. Servos might have too many moving parts, moving too fast, in too little space.