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Thursday, July 30, 2015

Laser Crash Testing

Well, no. We don't actually crash test the planes on purpose.  Enough of that goes on that you really don't put any additional effort into it. It's better that crash testing happens naturally and organically. Otherwise you mess with Mother Zen and all, which isn't very nice.
Occasionally we have a problem and capture it on video. In instances such as this, I post the footage to show you how tough these planes are. They are not designed to be treated this way, and I certainly suggest you don't. However, in the rare event you slap your EXP off the ground, it is good to know the plane is built so well.
I was testing an off brand of ESC and it simply failed. To make matters worse, I used a parachute maneuver to kill the altitude and speed. With no power to rely on the plane surprised me by how much lift it blew off in the rotation. Simply put, she was a dead duck, falling about 40 feet, right on the cowl and main wheels. You can hear how sickening the sound was in the video.
Astonishingly the plane was undamaged except for a few scratches on the cowling. It didn't even hurt the wheel pants. One of the SFGs was cracked, but I shot CA  onto the break with a hypodermic needle right through the covering. All I had to do was wipe it off and you would never be able to tell.
I looked the plane over extremely carefully. After a shot like that it is hard to believe nothing broke, but it appears the plane was not even fazed by all of this. Astonishing, actually.
 The second video in this article was from the very next day, and all I really had to do to it was change out the bad ESC and fix the SFGs. I think that impact would have outright killed a lot of other planes.
Again, please don't try this with your EXP. 

ESC and BEC Set Up
I was lucky this time because I could have very easily destroyed the plane. If the BEC in the ESC had fried I would have lost control of the radio too, so I'm not letting this upset me and am taking it as a good lesson, which is, don't try new stuff on a plane you can't afford to wreck.
It was also such a surprise that it destroyed my confidence, but the best way to get that back was to use another ESC that has never failed me... the Airboss Elite 45.
Fortunately I had one that I cut the switch off a while back, so I simply soldered a Castle 10 amp BEC (set to 7.4 volts) to the deans plug on the ESC.  Remember, this Laser uses HS5070MH and 5087MH high voltage servos, so I needed bigger power than the Airboss' currently has, For now I have resigned myself to running a separate BEC so I can keep using the Airboss.
This is how I always mount my Airboss in an EXP, so you might think this is nothing different until you turn the plane over. I mounted the Castle BEC on the bottom of the motorbox, right in the airflow coming in the lower cooling hole. Hopefully this will keep the BEC cool and happy.
I hate running separate BECs because of the additional wiring, complexity and having more potential failure points. However, this is the only way to do it with an Airboss ESC right now. After this recent experience using something else, I am never again using anything but an Airboss ESC. For now, I will just hold my nose and run a separate BEC.
My soldering is actually pretty decent, but on things like this I am loathe to trust my own work. I managed to keep this installation reasonably tidy, and this is how I will do it on all my 7.4 volt planes until/if we get a 7.4 volt Airboss.
Servo Update:
This is the same plane as featured in January's "Laser In High Voltage" blog article. astute readers will remember this plane features Hitec's HS5070MH servos on the ailerons and rudder, and an HS5087MH on the elevator, all run on 7.4 volts. You can actually run them on 8 volts, but they were a little faster than I liked. At 7.4 volts they are still very quick and pack more torque than I can use.
This, along with my recently departed 48" Yak, has been my primary plane since December, so it has seen a lot of hard use. The servos have stayed tight, center strongly, and do everything I ask from them. I am very pleased with them.
This plane gets flown fast a lot because the servos make it so crisp at high speed. We were getting a slight degree of stalling and blowback on the 6 volt servos, but at the time it was the best thing we had. We sort of lived with the because we didn't know any better, that is, until we tried MH series servos. They have so much speed that I had to turn the voltage down to keep up with them, and so much torque that I had to turn my low rate ailerons back because it was rolling too fast.
Stalling and blowback can score the potentiometer, weaken amplifiers and burn servo motors up outright. Once you damage a servo from stalling, it becomes weaker and even more prone to stalling an even more damage. It is a self perpetuating cycle that you can put a stop to with MH series servos.
Since the MH series  servos have so much torque, they are better suited for the harsh environment of extreme aerobatics. With stalling and blowback eliminated, so is a source of potential reliability issues, and I expect this will result in the servos having a much longer lifespan than their 6 volt counterparts.
I plan to use up the HS65MGs that I already have, but any new 48" plane I build will get HS70MH and HS5087MH servos.
The servos are performing brilliantly, but I am worried that the last impact may have damaged some of the gears. This is not the servos fault because you aren't supposed to crash them! Since I am planning a new Laser I will just send them in to Hitec service for inspection. Hitec usually doesn't charge for servicing a servo outside of the cost of replacing metal gears. That's cheap considering they will come back with new gears and freshly serviced in like-new condition.
This Laser is working out especially well. Since January I have been flying it as my primary plane, which means abut 25 flights a week or so. Here you can see I recovered the SFGs in yellow so they would be more visible. the white roundel is from the red 48" Yak EXP.
Above you can see I have been tinkering around with the racing wing tips from the 48" MXS. They bolt right on and make the plane much more groovy at high speed. Smoothness at high speed is ridiculous. You give up a little tumbling ability with the tips, but over all the plane seems a little better with them. Anything that adds stability is a good thing. That, and they look so cool I am leaving them on.
Here camera guy Mad Marty prepares for the next shoot steadyng his nerves with a stiff shot of nicotine.
Just in the last two or three flights with the tips I have become really, really comfortable using them. I always liked the extra stability, but now I am figuring out how to get the plane to snap more violently in spite of that. As you can see, it's pretty lively



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