View Full Version : Short Shafted A Mod.

01-06-2009, 09:56 PM
As a general disclaimer, I am new to RC Helis, but I can't help but experiment. Looking at the main shaft, I could only think that the further the ends are from the bearings, the more likely it is to vibrate. And further the blades are apart, the more they can fight with each other.

So, I cut about an piece out of the main shaft. It is now a half inch from the lower blade to the upper blade (at the shaft) I remembered to move the upper bearing.

I was nervous, but she flies very stable afterwards. She makes a slight buzzing sound now, Probably due to the lower blade moving through more turbulant air from the upper blade. I understand I am more vunerable to flybar-lower blade strikes, my next mod will be to help compensate for this.

At least with parts being avalable and relativly cheep, I can reverse it if neccary.

Anyone ever tryed anything like this?


01-06-2009, 10:44 PM
Haven't seen that before...I'll be interested in seeing how you compensate for blade strikes. Good luck!

01-07-2009, 11:05 AM
I've gotten pretty bold with my flying and blade strikes are bad enough as it is, especially if I changed directions really quickly while zipping across the room. I can just imagine how bad it would be with the blades any closer together. Would your mod happen to involve reducing the amount of travel the flybar would have? If so, it seems it would reduce your amount of maneuverability and/or responsiveness.

01-07-2009, 01:43 PM
I have never had a blade strike a blade, I don't think they have enough travel. but as far as the flybar goes, I am debating doing a flybar shrinking mod, which, it sounds like, is often done to increase response. As I have said, this is no high idea plan, just some experimentation based on some ideas and intuition. I am hoping to smooth out vibrations and the 'bounce' at the end of movements as the heli is righted by the top blade. Who knows what will happen.

01-07-2009, 04:16 PM
Yeah, I've never had a blade strike a blade, I'm talking about the flybar hitting the lower blade. I'll have to check into the flybar mod though...

01-08-2009, 10:35 PM
Having shortened the flybar, I can now let loose with it. Wether through the shortened fly bar, or the upper blade having less leverage on the heli, my forward speed seems improved. If fact, it is moving more that fast enough for this Noob in a small apartment.

I am also wondering if I am getting some Co axial prop action. (the second blade reduces tangential air flow.)

Also, climbing slightly while moving forward, you can really get some speed. Watch the walls.

01-09-2009, 02:29 AM
Do you have any pictures of the mod ? how did you do it ?
Thank you

01-10-2009, 10:16 PM
I would assume just cut the carbon outer shaft down to size.. fit hte inner shaft to it, mark the bottom of the gear and cut off at the mark right? might have to try this one. my MCX has been doing the toilet bowl thing lately

01-10-2009, 10:44 PM
That is what I did. I did remove the upper bearing and housing and replace it after the cut. You really have to cut down the fly bar down if you do this. I did this by cutting the bar next to the weights, drilling the CF out of the weights with a pin vice and tiny drill bit, and super glue the weights back on. (measuring the distance to make it even).

Make sure you file the cut inner shaft smooth, the bearings are a tight fit and it will not fit if there are any burs.

But a warning, I don't have a lot of experience with this, I am just experimenting. I like the way my mCX flies with this done to it, but proceed at your own risk.

01-11-2009, 04:40 PM
i jsut did your mod today, It works great :) first step after getting the inner and outer shafts out is to remove the top cap form the outer shaft. then I cut about 1/2 a cm off the TOP of the outer shaft (this way all the screw holes and the recess for the gear are still intact). I used a dremmel with a cut off wheel and sanded it to be flat. Put the top cap back on and install the outer shaft back on the bird. then put the inner shaft on, and put the inner shaft gear on... mark a few mm below that gear and cut it off with a dremmel. sand the burrs off, re install and your done. took me about 15 min :) thanks for the great idea! it completely got rid of any wobbeling my bird had.

01-11-2009, 05:01 PM
I am glad to hear that it worked good for you. Just watch for flybar/blade strikes. You moved yours a bit less than I moved mine, do you get a slight hum when yours flies?

01-11-2009, 05:05 PM
nope, no new humming at least. but check to make sure the two white gears are spinning right. I had the lower one on a bit crooked at first and that did make some humming. I also shortened the flybars a few days ago so flybar strikes are less of a possibility. I can land on top of a soup can now :P couldnt do that before this mod.

*edit* i also sprayed silicone in all the bearings and on the inner shaft, that proubally also cut down on the noise a bit

02-04-2009, 11:32 PM
I have been able to remove a tad more from the shaft by lowering the lower blade. Just so that the original holes in the shaft appear above the lower blade holder. I had to move the control rods to the lowest holes on the servos, extend the slot in the swashplate guide, and trim the shaft retaining ring to accomidate this. It seems to help a lot with the vibration, and the banking.

05-22-2009, 11:41 PM
Just about to do this with mine. Thought id jump on this forum first to get some ideas on how far to go. SQRT2 you went the full monty. i have done the flybar shortening mod which would compliment this mod a lot..., this can be done easily by heating the weight with a soldering iron (you will be surprised how quick and easy this is) just dont have your head over what your doing the CA stinks and burns your eyes somewhat...:lolol

Just did this mod. ended up cutting 10mm from the outer shaft and re shortening my flybar. Flybar total length now 80mm. Heaps more response no more flybar strikes (im trying)...

05-25-2009, 09:30 PM
Glad to hear it works good for you. make shure that you file the new flat parts on the inner shaft (where the gear screws engage it) nice and strait. If they are at an angle it can be hard to get the lower gear level.
I have worked even more on this mod. I have lowered the lower blade as far as I can see it being done. I don't have control rods anymore between the swash and blade. The swash has bumps on it I have added that ride directly upon the blades. Small rubberbands, the ones that hold the canopy on, hold the swash and the blade together.


05-26-2009, 09:14 AM
Think i went too far with the flybar. I have bad TBE now no stable hover. SQRT2 your flybar seems to be a lot longer than mine. I hope its the flybar and not the outer shaft mod. I do have a slight humming sound now with the blades closer but nothing that worries me. Sounds a bit cool anyway. Need to fix the TBE though...

05-26-2009, 01:51 PM
TBE? try double weighting the flybar. Glue some weights from a broken flybar on the end of your flybar. It helps a lot.

05-27-2009, 10:57 PM
yep tbe. I cant hold it steady in a hover it just does stupid little circles like its hanging from a string and swinging.:thumbdown::thumbdown: Ill mess with the flybar when i get home in couple of weeks...