JRjunkie

I just pulled my Corona out of the closet. Its been there about a year. I remember feeling like it need more sorting out when I was flying before, but I was just learing to hover and was also thinking that it was my lack of talent.

So, I cycled the packs, radio check, and went for a whirl. The tail was wagging but the tail also seems overly sensitive to changes in the throttle. Unless I make the smallest throttle adjustment, the tail moves approximatly 30º in each direction. So anytime I adjust the throttle for a wind change the tail swings. This presents me with a problem. Turn the gyro down to stop the wagging but increase the throttle swings.

I have the GWS gyro that only has a gain screw and a center screw.

I also noticed that the head appears to have about 15º of backlash (best term I could think of). If you hold the Main gear still, then you can hold the head and rotate it. I am guessing there is too much clean between the bolt and the notch in the main shaft as the main shaft remains stationary. Is this anyone else experince or do I need to get a bigger bolt in order to seat properly with the notch in the shaft?

Could the backlash be the source of the throttle induced swings? Or could gear meashing of the tail linkage? Or is the tail pitch mechanism too tight?


Finally, I a have a battery pack that is misbehaving. It is a 7 cell Ni-Cd (8.4v) pack that is rated, i think, at 2700 mah. My peak charger will only put ~8.7 volts and 3.5 amps to the pack. If I remeber that pack should charge at 1.5 volts per cell so that is 10.5 volts. (My second pack charges at approx 10 V and maxes the the charger out at 5.5A). Is it a dead cell? Any advice to attempting a recovery?

Thanks in advance,

Lucas

JRjunkie

Hello?! Any ideas?

FlyingFish

My Feedback: (17)

I fly and repair Corona 120's all day, Sounds like your corona needs a slight make over! As far as the backlash were, you can hold the main gear and move the rotor head, THAT'S NORMAL, Leave it! As far as your gyro, their sensitive and can go bad! I have just expeienced this same problem a day ago and solved it! I had a Gyro that would fly great after you adjust it, then after about 3 flights the tail swang again! It had to keep getting reset, and i knew when the gyro went bad cause I would turn the heli slightly then the heli would be facing right at me regaurdless of settings, NOT GOOD! If your tight for money then try increasing the gain on your gyro more so that turning is held more ridgid to stop tail swings! If you keep adding more gain and it still swings wildly I would get a new gyro, thats what I did, I got a Heli Max Gyro, it's a simple gyro and works well. Also Lots of People have their gyros mounted at the nose of the Corona, that's ok, but when I got my new gyro, I placed it right behind the main rotor shaft, double face tape right on the crutch and it works much, much better Now! After all thats the axes point that the gyro needs to correct for, NOT AT THE NOSE! As far as that battery pack of yours is concerned, I would throw it out and replace it with a lipo battery, 11.1V 3 cell 2100 mAh (If you have a Brushless motor) Otherwise replace it with a another NiCad......!

Hope This Helps!

JRjunkie

Thanks for the tips! I swapped the screw in the head and no change so I was hopping someone would comment on the backlash.

Since my last post, I wrapped the tail rotor in some weeds and after it stopped spinning sitting in flat grass, I elected to disassemble the whole boom section and rebuild it. During the rebuild, I sorted out a few things, re-aligned the pushrod and the rotor/servo neutral positions. I now have the gain cranked up to ~80% with no wagging. The tail seems a little dead, but thats fine with me for now.

The more I mess with the Corona, the more I think that the little GWS gyro just isn't that hot (it was nice and cheap though!!!!!!). I have been messing with the revolution mixes in my JR 8103 and have found them help to alleviate the problem. On the other hand, I am wondering if the tail authority in the Corona just isn't enough to overcome quick changes in the throttle / rotor torque.

I have been cycling the crap out of the bad pack in an effort to revive the waining cell and it seems to be working, the pack starts out charging at lower voltage, but then increase to around 10v by the end of cycle. It still seems a little weaker in the Corona than my other pack, but delivers adequate performance for hovering practice and tail sorting.

gadget01

I just "finished" the initial build of my Corona 120 electro. I'm using a MultiPlex 480/4D brushless with a MultiPlex controller, HiTec 81MGs, Kokam 2000mAh LiPo. For my initial run-ups, the Corona just wants to do 360's to the left. When I try to correct this motion with the tail rotor, or even just try to hold the nose straight, the tail rotor actually slows down giving me very little yaw authority. The bearing in the tail rotor gearbox tends to slip out, and I found that I can quite easily spin the tail rotor all while the drive wire is static.

The problem as I see it, is the tail rotor hub is slipping around the shaft since there isn't any set screw or anything to keep it from slipping. My initial thought was this was designed that way to make it more "crash friendly" for tail strikes and some slippage ability was desirable. All it does is slip once you spin everything up try and use the tail rotor to control yaw.

How is this remedied?

FlyingFish

My Feedback: (17)

OH NO MY FRIEND! YOU SHOULD NOT BE ABLE TO ROTATE THE TAIL ROTOR WHILE HOLDING THE MAIN ROTOR STILL!
NO SLIPPING IS ACCEPTABLE !!!!!!!!!!!!!!!!!![X(]

Get your CORONA CONSTRUCTION MANUAL and go to page 9-2 see Figure 9-2 See the set screws 4-40x5/8" Setscrew at the top drawing, they are inside the tail rotor blades, thoses set screws must be tight!

gadget01

Ok, those set screws are tightened down now and I'm getting good yaw control. Thanks for the tip--

After adjusting this and that.....

I have hover! Stable and controllable. Like Hannibal says, I love it when a plan comes together. I can see now that a gyro is absolutely necessary for a fixed-pitch helo, as any throttle changes to adjust power have a big torque effect. I mounted my gyro just behind the main rotor shaft at the top of the frame and it seems to be doing its job- better than I expected. I'm going to have to get a 2nd LiPo very soon, as waiting for pack to recharge is wasted hovering opportunity. I'm using a 2000mAh Kokam pack now... any suggestions on batteries?

FlyingFish

My Feedback: (17)

Sorry I didn't get back to you sooner but for some reason R/C Universe dosen't always Drop me an e-mail to tell me that theirs been a response to a thread even though I've checked the "Notify me Box", Anyway, I use a Kokam 3 Cell 11.1volt 2000 mAh Lithium polymer (lipoly for short) Battery with a 15C Discharge rate for my brushless Corona 120's. If you want longer run time then get the same battery with a higher mAh, for example a 2100 mAh would run the motor a bit longer than a 2000 mAh and a lot longer than a 1500 mAh battery pack!. But you must keep the same 11.1 Volts and a 15C rating is better than 10 or 12 C rate! What I like about Lipolys is that I keep them charged, then when Im ready to fly, even if it's a week after I charged them, the Lipoly is still fully charged and I just take the heli out the minute I decide to fly, rather than charging it for an hour before I go out with the heli, like I use to do with the NiCads. By the time the battery charges, usually a wind kicks up and I cant fly. So I charge my Lipolys on days I dont Fly and then just take out the fully charged heli at a moments notice on the days I do fly......

GYRO TIPS:

1) When taking your heli outside, if their is a big differance in temperature from outside to the temperature of were your heli is stored, Then allow about 10 - 12 minutes for the gyro to adjust to the outside temperature! If your heli is in a nice air conditioned room at 72 degrees,and then you take it outside were the temp might be 92 degrees your heli might not respond right or act funny for a while while flying it. The same goes for taking your heli outside in the cold after keeping it in a warm room[X(]

2) Dont carry or hold your heli while you turn it on or when turning on the gyro. The gyro needs to be placed on a flat surface, then turn it on and leave it undisturbed for at least 15 seconds so that the gyro can initiate itself and give you the proper performance![X(]

These are two factors that can cause a helicopter or a helicopter's gyro to act stupid or cause the gyro to not do it's job of holding the helicopter stable![:@]

gadget01

Thanks again for the tips. I understand that there are 2 types of gyros- piezo and heading lock, where heading lock is better. Is this correct?

Also, there doesn't seem to be any good component choice advice for newbies. It's kinda like you have to buy a bunch of expensive gear to learn the hard way what and what not to get for your setup. I'm not reinventing the rotor blade here, I just want my helo to hover and manouver for a good 15 minutes or so before the batteries give out. Oh, and here's another dorky thing about my the speed controller, which totally sucks.... when the battery drops below the limit, the motor completely shuts off dropping my Corona like a rock. I thought that when your battery starts getting low in an electric helo, you just gradually have less and less power, which gives you the opportunity to land in a controlled manner since you would notice the power loss when you are flying.

I thought I would jump into a higher performance option for longer run times by getting brushless motor and LiPo batteries. This Muliplex Permax BL-480 4D brushless motor that I got, as recommended by www.helihobby.com, says in the instruction manual that it can only take a 2 cell LiPo! What kind of crap recommendation is that? This motor along with the ESC cost me $150 plus shipping. Now I think I need a different motor that is compatible with more cells so I can longer run times.

What motor/LiPo battery do you recommend for a 15-minute run time, along with an ESC that won't drop my Corona like a rock as soon as the voltage drops? I hear that Hacker motors are nice, but they are a little spendy. I usually prefer opting for the higher-end hardware to start with, but it really helps to know how to pick the right stuff so you don't end up wasting cash on the wrong equipment.

So far this ride is satisfying, yet very frustrating. I hovered it for the first time last Thursday.

FlyingFish

My Feedback: (17)

Yes, heading lock Gyro is better, but here's my Brushless set up! I have a Mega 15/16/3 brushless motor with a pheonix 35 speed control combo! No Dropping out of the sky with this Baby on Board! Follow this link to buy that combo -----> http://www.dynamoelectrics.com/detail.aspx?ID=708

I can get up to 20 minute Flight times with (2) two Kokam 11.1volt 2000 mAh 3 Cell Battery packs on board, wired in Parallel Circuits! That Combo gives me about 20 minutes of flight because the battery packs in Parallel circuits gives me the same safe 11.1 volt and 4,000 mAh,That's double the mAh and Doubled the time! So long as the weight of my heli is kept at around 42 ounces it flys great! You can buy a Parallel circuit connector that will allow you to wire two packs together in such a way as to keep your voltage the same but increase your mAh to increase flight duration!

If you want to run longer times and can only use 2 cell battery packs (helihobby reccomendation) then keep that combo you got and get 2 cells lipo packs with more mAh. you can find them at hobby lobby, Follow this link-------> http://www.hobby-lobby.com/kokam.htm Remember the more mAh, the longer the run time! but if you can't find 2 cells that give enough mAh, then maybe you can put two (2 cells) together, but I'm not sure about that, I might just buy a brushless motor and speedcontrol combo that takes 3 cell lipos! your motor & ESC combo from helihobby can only take 2 cells cause it runs on 7.4 volts not 11.1 volts!