The xMB-8 - RC Groups
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Apr 07, 2010, 11:48 PM
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The xMB-8

== UPDATE: June-10th-2010

The SK-720 is finally installed and tested. It is a great piece of hardware for sure. It is noticeable better than the SK360/Spartan combo it replaces. This weekend if weather holds I'll film a video and lose the X in its name. This will probably be the last entry in the xMB-8 blog since it is no longer a prototype which needs fixing, tuning or new components to fly.


== UPDATE: June-6th-2010

The new components for the xMB-8 have been steadily arriving. By the end of this coming week it should be ready to lose the X and be called as the MB-8. The new SK-720 will be at the heart of the 8th generation, replacing the true and tested SK-360/Spartan combo that powers the two previous generations. A new DELight controller has arrived but it was DOA so I'll have to wait to get a new one.


== UPDATE: May-13th-2010

This is how I hinged the grips on the Century Diamond rotorhead.


== UPDATE: May-12th-2010

Even after the rebalacing of blades, the vibrations kept coming, which made me wonder why I am havng vibrations on a perfectly tracked head (used a laser guide this time) and blades that are balanced to 1/100th of a gram with less than 1 mm CoG difference... so I grounded the xMB-8 for three days to track down where the vibrations were coming from in its airframe form before sticking it back inside the fuselage.

Turns out that the root of the problem was a rigid rotorhead and rigid blades combo. Since the Century head block is not perfectly straight, it has a ~3-5 degree wobble on it (and this is a brand new head BTW), which means that when I rotate it by hand, blade 1 is like 1 cm lower than blade 4. Therefore, since the blades can't flex to follow the rotor disk natural equilibrium position, it causes a very nasty vibration of the blades going up/down. Now, this is probably not a problem for high speed RPM operation but absolutely horrible for a 900 RPM headspeed b/c the centrifugal force is not enough to flex the blades enough to travel at the same plane.

So, what solved this vibration? Hinged grips. I modified the Century head to allow for the grips to pivot ~30 degrees off axis, thus giving each blade the ability to 'flex' or pivot on its own without being drastically affected by the other blades. This also helped a lot in the lead-retreating blade roll tendency when flying forward and it made the heli even quieter. I strongly recommend modifying the head to allow for hinged grips, especially if you plan on flying it without any electronic stabilization.


== UPDATE: May-7th-2010

Went thru the pictures of the arduous work and from the early days to its final inevitable rise to the skies and made a short film about it. Here it is:

The rise of the 8th generation.

The rise of the 8th generation. (4 min 1 sec)

== UPDATE: May-4th-2010

After the fiasco during the funfly I was able to retreat and regroup my forces and deal with all the small issues and today the xMB-8 might very well lose the X prefix. My friend is going to film the flight, which technically its the real maiden flight as a complete helicopter.
Well, success, it flew very well, no more crazy vibrations on the heli anymore!

Here is the video of its first flight in an open area.

XMB-8 (first flight in the open ) Hughes 500D TOW Defender (4 min 21 sec)



== UPDATE: May-3rd-2010

The funfly didn't go well, not even close. I had too many issues to try to tackle them all at the field, too much vibration (poorly balanced blades, yes, my fault...) tracking couldn't get done right with the heavy crosswind and I needed more time, peace and quiet to work these kinks out, none of which was available at the funfly. Certain people kept interrupting me all the time and instead of offering their help, they just simply kept reminding me of the obvious, so to those of you, I want to thank you for your *cough* *cough* "consideration" and hope you have a good life and I am sorry you could't fly your stick banger toy for 3 minutes of your life. So after a few failed attempts to get it in the air, I decided to ground it and let its smaller brother the MB-7/UAV take over the show and as expected, the veteran MB-7 delivered the performance, even with crosswinds. It sure was a sad day for the xMB-8, which hoped to "kiss the sky" and all it did was "bite the dust"


== UPDATE: Apr-29-2010 (3:30AM update)

Success! The xMB-8 flew around the backyard at 2:45 AM for a couple of minutes. Did a circle around the backyard and landed to check and download the datalogs.


== UPDATE: Apr-28-2010

With all of the last minute snags out of the way, the xMB-8 has now a clear path to walk into history, opening a new chapter as the largest, most expensive and most advanced MB helicopter ever built to date. Dwarfing the veteran MB-7/UAV size, the MB-8 builds upon all the success and proven designs of the MB-7/UAV and MB-6D.

This is it, ladies and gentlemen: Tonight *IS* the night that I've been waiting for over 2 years since I started flying helis. Tonight, the night of April 28th of 2010 will be night in which the xMB-8 becomes operational and earns its place amongst the ones who've flown the path before it. Godspeed and hope I don't crash the thing!



== UPDATE: Apr-25-2010

Short of the main 5 blade rotor head the rest of the helicopter is complete. All mechanics are working, lighting system works, everything is mechanically secured and its pretty much ready for maiden when the 5 blade head arrives next week. I've added a picture of the xMB-8 along its smaller siblings the MB-7 and MB-6.

== UPDATE: Apr-22-2010

The xMB-8 is nearing final now, the first maiden candidate will probably go online sometime next week. I am really pushing (and hoping) to have it operational by May 1st so it can debut at the funfly together with its smaller and veteran brothers the MB-7/UAV and the now decomissioned MB-6E, which will be at the funfly too but without any electronics, besides the servos and the motor. Ironically, it was on this very same funfly last year when the MB-6A had its public debut.



Thats right folks, the xMB-8 project has been slowly underway for a little while now. The original xMB-8 planning dates just a month after the xMB-7 was officially started back in September '09 but between the MB-7 exceeding all my expectations, other non-heli projects and life, all have gotten in the way but it is now, finally, getting to a point in which pictures might start to surface any day.

The xMB-8 is a parallel project with the xMB-X and the two helicopters are two completely different projects.

So, then what heli is the xMB-8? Well, lets see, current track record shows three TOW Defenders to date (6,7 and X) so a well educated guess could point to yet another TOW Defender...

More soon.

Last edited by Minibichus; Jun 10, 2010 at 10:46 AM.
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