Need help guys: Big Lama

menakit1 · Posted: Sun Mar 28, 2010 11:11 pm Post subject: Need help guys: Big Lama

Ok, I'll explain the full situation:
For weeks now, I've noticed that the big lama has been inclined to rudder right on it's own. I've however, gotten really good controlling this heli though so it was never a huge problem for me. Already had the prop lever on the mixer cranked all the way in the other direction - just in case you'll advise that.. never worked. Because it never worked I decided that the problem HAD to be that the main motor was kinda spinning a little rough, not smooth like the other motor, and was simply gettin' worn down. Yesterday, I decided.. ok, even though I don't NEED to, I'm just gonna fix this problem for the hell of it. Slapped two brand new motors in and made sure they were smooth before I put'em in. Broke them in and then hovered the heli to readjust the prop lever. The heli was PERFECT.. no rudder at all without my command. After setting it up I set the heli aside 'til this morning. Got up, started flying, and the exact same problem I'd had before has raised it's ugly head on the first battery. It seems when the battery is at full power, everything is even keel, but as the battery starts dying, the heli spins to the right (slowly, not out of control).
Soo.. I've given detail.. hopefully someone skilled in the arts of coaxials can advise me on what to do.
Thanks.

pjdog · Posted: Sun Mar 28, 2010 11:36 pm Post subject:

Hi menakit1. I had the same problem only I didn't replace the motors.

If you look at the 4 in 1 receiver you notice there are two pots. One is 'gain' the other is 'proportional'. The proportional is the pot that will adjust the mix between the motors. One motor is getting more battery power or one motor just runs better than the other. This is normal.

unplug the battery. With the plactic screw driver that came with your Lama, adjust the pot left or right just a little. Plug in the battery in and try a flight to see what it does. If you went the wrong way unplug the battery and adjust the other way. Keep up the process until you get the helicopter stable. Aways unplug the battery as the effect will not happen unless the battery is unpluged. When you plug the battery in is when the actual adjust takes effect.

Good luck.

PS: post your location in your profile. Thanks.

menakit1 · Posted: Sun Mar 28, 2010 11:54 pm Post subject:

pjdog,
the prop that i was referring to is the proportional pot... i've already tried readjusting it countless times. This is not the problem. need another idea.

pjdog · Posted: Mon Mar 29, 2010 12:18 am Post subject:

I guess I'm at a lost now. I thought for sure that was your problem. If you can't get it out with the proportional pot than I would think that there mush be a bind somewhere in the drive train causing a load on one motor. After a run is one motor hotter than the other?

Only thing I can think of?

menakit1 · Posted: Mon Mar 29, 2010 12:25 am Post subject:

ya you may have something there. later on today, i'll take it for a run and see if one's hotter than the other. but I think either way, i'm takin' the bird apart today either today or this week and oiling every moving part. if that doesn't work then i'm gonna say something's wrong with the mixer probably. what do you think?

pjdog · Posted: Mon Mar 29, 2010 2:08 am Post subject:

Sometimes I go to another forum and preach about oiling the gears and gear end of the motor. Swatch plate, bearings, shafts and all parts the rub.

One guy always gets on me about oil being a dust magnet. He is right but that's what cleaning stuff is for. Helicopter maintenance is part of the game. I want to get the maximum life out of my stuff. So I use oil. Silicon and light machine oil. It does works. Today I just completed my 91 flight on the main brushed motor on a Falcon 40 V2. Libration. Is the only way you can prolong the life of a any motor.

I did get some dirt in the bottom gear of the Big Lama that cause some problems Wednesday. I cleaned it up and oiled the gear and went flying again. All was well.

Are you sure that you don't have a gear slipping on your Lama. You said you took it apart. The Grub screw on the gears has to be sitting on the flat spot of the rotor shaft. Both gears and both shafts. Check that also. That could cause rotation but normally it's more severe.

tombo242 · Posted: Mon Mar 29, 2010 4:51 am Post subject:

Hi menakit1,

This is a fairly mormal problem with a co-axial. My little indoor heli does exactly the same and the rotation varies even battery to battery. Unless you have exactly the same charge level and battery internal resistance the heli will rotate..

However, the "Proportional" pot should not be at its max setting, usually all that is required is a few clicks rudder trim to keep it happy. The fact that you need more than this does indicate a problem somewhere in the system. As you have eliminated the mechanical side there only remains the electronics. Can you measure the voltage to each motor? This could well be the problem. As your batteries must have rested some during the motor change, they could still be at fault. Other than that it is the Rx and ESCs to the motors that you will have to look to.

St Bosse · Hopping Maniac Joined: 06 Sep 2011 Posts: 24 Location: RSA

My Big Lama does exactly the same. At full charge, rudder trim sits centre and after a minute or two, starts drifting to the right resulting in a trim adjustment to the left. It's then stable for quite a while but then as it comes closer the battery end, will need some more trim adjustment to the left.

I also adjusted the proportional but that only moved the trim range more to the centre, i.e. trim will now sit more to the right of centre position and will be adjusted over the centre to the left until battery flat. In my opinion this will not come right until one get matched motors, internal resistance wise, to ensure constant voltage levels in both motors throughout the flight from full battery to end.

On the other hand, flying in a light breeze, the stick input is quite big and the trim errors become totally insignificant.