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Home✈️Aircraft🚁Helicoptere-Elec-Helicopters New or Limited ActivityHeliDirect › Main Shaft Experiments, HDX300
08-02-2007 03:00 AM  13 years ago
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gmcullan

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Southbridge, MA

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Main Shaft Experiments, HDX300
I've had a number of people contact me regarding my main shaft experiments. I thought I'd take a moment and relate my progress.

The HDX300 with the underslung flybar is problematic in that you have a relatively heavy mass spinning at the end of a relatively long 3 mm steel shaft. The slightest imbalance, aggressive maneuvering, or landing with any significant lateral movement is sufficient to bend the stock steel shaft. Several vendors have stepped up to the problem with harder steel shafts. But even the upgraded shafts present problems. Check out my gallery of my "Saga" thread for photos of my recent mishap. I had the mainshaft bend at a 45 degree angle and never even left the floor. This was a "V3" mainshaft.

Some of you know of my experments with carbon-fiber cored mainshafts. This grows out of technologies I use to make slot car axles. With the speed attained by a modern slot car, you can well imagine the impact forces impinged upon the axles when the cars deslot and hit the retaining barriers. A bent axle does not win races!

Sort of the same thing with a R/C heli, in that they just don't fly well, if at all, with a bent mainshaft.

I've been experiementing with scaling-up the slot car axle technology to 3 mm micro heli size. Initial results with a stainless steel/carbon combination have been good. Titanium/carbon fiber has been even stiffer and lighter in weight. The problem is one of excessive wear where the swashplate ball moves up and down the shaft. I have some steel alloy coming in so that I can try carbon steel/carbon fiber combinations. As a benchmark, I also have some injector pins coming in. It's funny, as I'm only 25 miles from the supplier, Plastixs.

I have a test rig that I use that measures the deflection of the mainshafts under load. The load I've chosen is the ready to fly weight of my HDX300. The rig allows me to measure and calculate Modulus of Elasticity (Young's Modulus) which is a measure of the stiffness of the mainshafts.

The goal of the project is to identify suitable material combinations that offer reliable, consistent performance within the expected flight envelop of the HDX300. Good wear characteristics are required so as to minimize wear between the swashplate ball and mainshaft. The resulting shaft also has to be affordable and cost-effective.

The challenges lay with the tube that forms the outer structure of the mainshaft. Not only do I need to settle on an alloy, but it has to be available with consistent dimensional control and surface micro-finish. Some of the test shafts that I've made were of shafts that were center-ground to the desired final OD and polished so as to acheive the desired micro-finish. This degree of hand work might be acceptable for small numbers of test mainshafts, but is unsuitable for volume reproduction that could exceed 100's and go into 1000's us units (Blade/HoneyBee/ and similar helis).

As soon as I have the mainshafts finalized, I will place "beta' test samples with heli pilots more capable than myself for flight evaluation.

As said at the end of the cartoon, "yabbida-dabbita, that's all for now, folks!"
Gerry Cullan,
Gaui 200, 255; T-Rex 250, 450 SE & SA, Mini-Titan, Blade 450
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08-04-2007 09:18 PM  13 years ago
gmcullan

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Southbridge, MA

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More mainshaft musings.
One of the issues with the 3 mm mainshafts are the flat spots or outright grooves cut into them for setscrew retention. Right off the bat, this presents a perfect location to initiat a bend. This is especially so at the midpoint location of the upper retaining collar.

Bear with me, for I'm switching gears here a little. The key to retention is the proper selection of a locking compound. Without mentioning any specific brand, most of us use the "blue" locking compounds to secure screws.

For years I've used "green" locking compound to secure pinion gears on to slot car motor shafts. This "green" formulation is very good at resisting shearing or twisting loads.

Building upon that experience, I started some "heli" experiements.

I've had good results securing main shaft pulleys and heads to my composit shafts without the use of flat spots or grooves. I use a two-stage application of locking compounds. I use a dab of "blue" compound on the threads and a dab of "green" compound on the surface of the set-screw that touches the shaft. This holds the head and pulley on very securely.

I've also used just "green" compound to secure a MicroHeli head onto my modified HoneyBee. That's right, no cross pin nor set-screws. This was an act of faith. But it worked fine. So fine that I had to use the heat from a soldering iron to to heat the head and break the bond between the shaft and center hub.

So the fun and games continue. Until the next installment......
Gerry Cullan,
Gaui 200, 255; T-Rex 250, 450 SE & SA, Mini-Titan, Blade 450
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09-19-2007 04:26 AM  13 years ago
andyk227

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Very interesting stuff. Please keep us posted on your progress with the main shafts.
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09-19-2007 05:36 AM  13 years ago
Cope

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South Lake Tahoe CA

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Yea,Please keep us posted I would love to get one of those shafts!
(Al tho I'm probably not a better pilot than you!)
Thanks Again
Cope44
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09-19-2007 09:53 PM  13 years ago
gmcullan

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Southbridge, MA

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Cope44, you are probably a WAY better heli pilot than I. I hope to have beta units in tester's hands within 6 to 8 weeks. If all goes well, commercial parts fill follow relatively quickly. And don't worry, you ARE one of the people I was going to ask to be a "beta-tester."

I'm still doing some experimenting with shaft length. I've also started some experimenting with the feathering block.

Right now my HDX is flying very well. Hopefully, it will remain so.
Gerry Cullan,
Gaui 200, 255; T-Rex 250, 450 SE & SA, Mini-Titan, Blade 450
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09-19-2007 11:47 PM  13 years ago
Cope

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South Lake Tahoe CA

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Wow GEEEZ I think I'm blushing! I dont know what to say except thanks! I cant wait to see one of your custom shafts. One of my areas of expertise has always been DT testing. (destructive test) Just kidding, Cant wait to hear more.
Thanks again
Cope44

Ps My 300 also now flys well, between bent main shafts ;]
I also used your linkage set up and got much improved geometry.
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09-29-2007 09:39 PM  12 years ago
gmcullan

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Southbridge, MA

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OK, the latest skinny. My source of 3 mm diameter SS thick wall tubing has too much variance in the OD. I get some and it's perfect. Get another and it's slightly too small and the swash and head have a real sloppy fit. Get another and it's just slightly too big so the bearings, swash, and head don't slide on.

Solutions? Looking at getting it slightly oversized and then having it center-ground to the desired OD and surface micro-finish.

Ones and twos are nice, but I bet properly done there is the market for many hundred's of these things.
Gerry Cullan,
Gaui 200, 255; T-Rex 250, 450 SE & SA, Mini-Titan, Blade 450
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10-01-2007 04:02 AM  12 years ago
Cope

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South Lake Tahoe CA

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Oh boy gettin closer it sounds like. Keep up the good work, and of course keep us updated.
Thanks Cope44
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