gmcullan
Veteran
Location: Southbridge, MA
| 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,
HB CP2, T-Rex 450 SE & SA, HDX300, MicroHeli Monster, Mini-Titan, Blade 400 |
