My custom home-made short mainshaft project...

[DoubleCH]

...has finally been implemented. I've posted it in my flight log thread but I know this topic may be of interest to those who don't read my flight log thread so that's why I start a new thread about it. I've planned this project long ago but for whatever reason haven't implemented it until now.

Cost is next to nothing with all the materials I have on-hand. If I crash and bend the shaft it'll cost me less than $0.25 to make a replacement. Other than cost, the obvious reason for me is to lower the head. I love the low head in my 450DFC where the height-wise CG is right on the boom. I always wanted to lower the head to reduce the pendulum effect of CG too far below main rotor.

I also like my design because it runs no jesus bolt so no weak point to snap mainshaft in-flight (which I have never experienced anyways). The no-jesus-bolt design also makes it easy to make the custom shaft. I dulled 3 good drill bits even using a drill press to attempt making the upper jesus bolt hole but failed big time. The steel rod is so strong it wouldn't budge. This is actually good because that I changed my original design to run no jesus bolt for the head to using key and keyway to lock the head to the mainshaft. Much easier to make than jesus bolt hole. IMO, if Blade were to design the lower jesus bolt system to run shaft collar instead or to have the jesus bolt hole below the main gear there wouldn't have been any mainshaft-snap issue. I'm surprised no aftermarket mainshaft system including Blade CFX to be designed like that.

Here's my impression so far after flying it 5 packs. The key/keyway system holds up well so far, kind of surprising but good. Flip rate is still governed by BX but initial flip response seems faster almost like my Protos which has super light disc-loading and agility set to really high. Perhaps because of new tight plastic ball ends for the servo linkages cyclic response is much tighter. There's no more wobble or pendulum swing perhaps from the reduced pendulum height. And this is even with my 800+ flight old super sloppy Corona servos that I said I was going to replace with new ones because of the slops. I'll keep running these sloppy old servos and see how many more flights I can squeeze out of them.

Long-term and stress tests are next. Hopefully it holds up well but so far I'm very happy with all aspects of this project. More detailed pics are shown in my flight log thread but it's always good to have a pic handy here... and a flight video... lol:

My Blade 300X Flight #1694 with Custom Low Head (5 min 7 sec)

[Uriah]

That's really interesting. I wonder how hard your steel is compared to steel of the Lynx shafts.



I'm a bit bummed about my 3700RPM 300X. It's hard to prove, but I'm quite sure the Lynx Jesus bolt on the OWB broke in-flight. I've dumb-thumbed many a bird and am not afraid to admit when it's my fault, but I'm quite sure this was part failure. I'm probably going to go back to the stock Jesus bolts just to be sure, especially on my upcoming Lynx Demon since it'll have added stress on the Jesus bolts (I'm going to start with governed 4300RPM and see how it goes - the build should be finished and flight-ready tonight). I like the idea of a failure point at the Jesus bolt, but only if it fails when it's supposed to.

[eddie1983man]

OP, are you using a toothbrush handle for that tail fin?

[DoubleCH]

Was it a threaded bolt or shouldered? Shouldered bolt should be much stronger. Perhaps try Blade main blade grip bolt? I've a feeling they use higher grade steel than the other bolts because they aren't cheap at $4 a pair with nylon nuts. I know my Protos run stronger 12.9 grade bolts on the main grips.

I wonder maybe you have some vibes (hard to tell running CF frame) which weakens the bolt? Cause I've never snapped a shouldered jesus bolt on the head even on the hardest crashes that broke more expensive parts so I put back a threaded jesus bolt for head and on a few crashes they broke which is good saving more expensive parts.

[DoubleCH]

Originally Posted by eddie1983man

OP, are you using a toothbrush handle for that tail fin?

Plastic knife. Another nice and cheap part.

[Uriah]

Originally Posted by DoubleCH

Was it a threaded bolt or shouldered? Shouldered bolt should be much stronger. Perhaps try Blade main blade grip bolt? I've a feeling they use higher grade steel than the other bolts because they aren't cheap at $4 a pair with nylon nuts. I know my Protos run stronger 12.9 grade bolts on the main grips.

I wonder maybe you have some vibes (hard to tell running CF frame) which weakens the bolt? Cause I've never snapped a shouldered jesus bolt on the head even on the hardest crashes that broke more expensive parts so I put back a threaded jesus bolt for head and on a few crashes they broke which is good saving more expensive parts.

It was one of the threaded Jesus bolts that came with the Lynx OWB assembly. They're apparently designed to be a failure point in the event of a crash, but I'm quite sure that's what actually caused the crash. It happened so fast at such a low altitude that it's hard to prove. Either way, I'm going to go back to the stock shouldered ones.

Like you, I'm super picky about vibes. My starting point when building a bird is to do a full run-up with no blades to break the bearings in and make sure it's as smooth as possible with no high frequency vibes going on. On the 300X I dynamically tighten the screws on the tail case. I then move to installing and then dynamically balancing the tail blades. I then install my head and finish her up.

[DoubleCH]

What about the jesus bolt for the head? Is it also threaded? I don't like the idea of threaded jesus bolt for the main gear. I would rather have the head jesus bolt as then the main gear bolt as fuse. The main gear bolt is susceptible to more vibes and mini-impact then the head bolt, which has the 2 follower-arm bolts to help absorb vibes and impact while still be able to break as a fuse. With a shouldered main gear bolt and threaded head bolt, the head bolt should break first like in the couple incidents I had.

[Uriah]

Both were threaded, per Lynx recommendation. I'm still not positive that's what happened, because I was so low to the ground and pushing it so hard that it happened too bloody quick. I told the spectators it was pilot error.



But nevertheless I felt 100% in control when it happened. It just didn't feel like a dumb thumb (or pinch, as in my case). But nevertheless the OWB Jesus bolt is broke and the Jesus bolt at the head is barely bent. I would think the one at the head would have broke first if it was a result of the impact, since they were both threaded and since the head is 7075 alloy. I like the idea of not even having the Jesus bolts.

Here is a video of me vibe testing my upcoming Lynx Demon. The head RPM in this video is somewhere around 4400RPM. The motor is a monster Typhoon 2218H 450H 3450kV, 4s 1000mAH Nano-Tech, 14T Pinion, YEP 40A w/ Governor Store. The drive train is relatively smooth even past 5000RPM (not shown in this video). I'm having trouble finding the ideal startup power. 4% seems too low and 8% seems too high. I'll probably get a better idea on the correct startup power once I have my head and blades on. Any suggestions?

300X Lynx Demon Build - Spoolup @ 4400RPM (1 min 5 sec)

[thruster]

Originally Posted by DoubleCH

And this is even with my 800+ flight old super sloppy Corona servos that I said I was going to replace with new ones because of the slops. I'll keep running these sloppy old servos and see how many more flights I can squeeze out of them.

Are you using the the included brass bushings and rubber isolators to mount your corona aileron servos?

I want to build a DCH 300x replica....but I'll need some new tools maybe.

[Uriah]

The key to a DCH 300X replica is to make it butt ugly, filthy looking, but running absolutely flawless. How you can have all three of those characteristics in one bird is a great mystery.

[thruster]

Originally Posted by Uriah

The key to a DCH 300X replica is to make it butt ugly, filthy looking, but running absolutely flawless. How you can have all three of those characteristics in one bird is a great mystery.

Ha ha.......the silicone lube over time attracts dirt onto the main gear, so I'm careful to never wipe it off. Helps with the 'rat rod' look!

[Uriah]

Silicone lube should dry once it's applied to the belt. I actually soak my belt in WD-40 Silicone in a sandwich bag for 3 or 4 days. Much of the silicone will actually dry inside the bag even when it's sealed. After I take it out of the bag, it's dry within a few hours. If you apply it to the belt while it's installed, I recommend just soaking a q-tip in it and then applying it to the belt at the tail, moving your main rotor to run the belt through the q-tip. If you use the right silicone it should dry on its own. I don't recommend actually spraying it into your boom like some people do because that makes messies. I think the WD-40 silicone has petroleum in it - some say petroleum pre-maturely wears your belt. But I silicone my belt primarily to prevent static buildup so I don't care.

The 300X I crashed a few days ago had about 250 un-crashed flights on it and it was clean as a whistle (that may be why my Jesus bolt broke - I admittedly never checked it). I guess I'm just using non-messy lubricants and keep everything clean.

[DoubleCH]

Originally Posted by thruster

Are you using the the included brass bushings and rubber isolators to mount your corona aileron servos?

No, I just mount the servos like I do stock servos, no isolators. I used the rubber isolators to run my 3D profile plane motor mount vibe isolators. Work great! I used the brass bushings to run the 2mm-3mm sleeve adaptor for my HobbyHot CF blades.

[DoubleCH]

Originally Posted by Uriah

The key to a DCH 300X replica is to make it butt ugly, filthy looking, but running absolutely flawless. How you can have all three of those characteristics in one bird is a great mystery.

That reminds me of my previous-life hobby. I blue-printed my own race car engine, custom home-made my entire air intake system with ITBs (individual throttle bodies, 1 throttle plate per cylinder) including intake airbox folded out of sheet aluminum and a whole lot more home-made mods. Imagine looking at people's faces when I stood beside my car at the National Tour winner circle impound with the hood open for my competitors and everybody else to check for any protential protest items. It was ABSOLUTELY PRICELESS!

[DoubleCH]

Originally Posted by Uriah

I'm having trouble finding the ideal startup power. 4% seems too low and 8% seems too high. I'll probably get a better idea on the correct startup power once I have my head and blades on. Any suggestions?

If you run any of the 3 heli spoolup modes, it shouldn't be too big a problem with too high startup power. That said, the only cases I need to run any startup power bigger than the lowest for any YEP/YGE are

1. the bad YEP30A ESC I got that was faulty and weak and could only do about 80% full power
2. flying my 6S Protos with YGE using my 3S flight pack from my 450.

So, I don't know what to recommend for startup power. You should only tune startup power with all blades on. Run the lowest setting that won't hesitate in any situation. If in doubt, auto setting works good.

[thruster]

So with your bolt-less main shaft, the head block is held on the shaft only by the grip of the follower arm bolts and the steel plate "keys" which are captured within the "keyway" grooves? Correct? Maybe you should apply for a patent.

[Highspeed1964]

Originally Posted by Uriah

The key to a DCH 300X replica is to make it butt ugly, filthy looking, but running absolutely flawless. How you can have all three of those characteristics in one bird is a great mystery.

Helicopters fly because they're so ugly the earth repels them. The uglier the better!

[DoubleCH]

Originally Posted by thruster

So with your bolt-less main shaft, the head block is held on the shaft only by the grip of the follower arm bolts and the steel plate "keys" which are captured within the "keyway" grooves? Correct? Maybe you should apply for a patent.

Haha! I don't think it's unique enough for a patent, which is pretty much a thing for the big companies. Even for a small company, applying for patent would drain your money long before it's ready to gain you anything.

I still need long term tests to see how this system works but so far so good after 10 flights. I love how it flies even more yesterday the 2nd day of the mod. No cyclic wandering more precise and quick flip response but then I don't know how much of it comes from replacing the sloppy hundred-flight-old plastic ball ends in the servo linkages with brand new ones.

[RichKnapp]

Originally Posted by DoubleCH

Haha! I don't think it's unique enough for a patent, which is pretty much a thing for the big companies. Even for a small company, applying for patent would drain your money long before it's ready to gain you anything.

I still need long term tests to see how this system works but so far so good after 10 flights. I love how it flies even more yesterday the 2nd day of the mod. No cyclic wandering more precise and quick flip response but then I don't how much of it comes from replacing the sloppy hundred-flight-old plastic ball end in the servo linkages with brand new ones.

Yep. By time everyone takes their cut in you getting a patent. ( I was going for 3 of them in the past for Diesel tec/metal fabricating tools, but dropped them. )

My great grand kids may have seen a profit. Takes a lot more money than people think to get a patent now days.

THEN you have selling the wrights to companies to sell the product and you only get a small % of each sale because they won't do a full buy out incase it don't pan out.

[Epoweredrc]

Guess i am stupid, what is a keyway and any up close pictures?
So you made a totally new shaft ? you didn't mod a stock one you just found some steel rod and made a hole for the gear to mount but the top your using this system you came up with?
just trying to understand better, I see in the picture the lower head, you was still able to use stock arms and all? how much short is it from stock?
Thanks