csm 720 9256 problem at 5.3v regulated

[harmdive]

Hi all

Just had a pretty scary problem with my Titan 50. Here's the story, maybe you can help. I had a maiden flight today having just changed over to fromeco li-ion power. Using reliaswitch and 2600 battery. Went careful for the first couple of flights and then pushed it pretty hard - elevator tic tocs and general 3D. Started doing tail down tic -tocs and then suddenly the tail conpletely lets go - no control until I cut the engine to hopefully get control back. This happened each flight I did this move.

At first I thought the battery was faulty - checked (no problem there). Charged up and then went again. Sport flying first and then hard 3D, tic toc again and same problem. I'm running csm720 gyro with 9256. I've set the voltage to everything at approx 5.3v. Wondering whether this is too much for the servo to handle under excessive load during this manoeuvre. Will drop the voltage fro reg. to 5.0v to try again tomorrow - just wondering if I will be able to save the heli again!! Anybody had the same problem?

[raptorheli2]

well, i have ran 720's at 5.6v on fromeco and i have ran a 9256 at the same time on a 611 however at the same voltage. i would be surprised if it's a voltage issue.

when you say it let go do you mean it let go but continued to work or it let go and it was dead?

cheers

[harmdive]

What I mean is during the tail down tic toc, I will lose tail control for a few seconds until I stop the manouvre. It starts working again when the tail is not under excessive load. I have had an idea passed on to me that it could be the current draw from the 2600mah battery could be tto much or my radio gear cannot deliver enough current to keep the gyro/servo working properly. I don't think it is the voltage as you say. servo hasn't burnt out so this answers that line of thought. Will try it again tomorrow but maybe I will have to get the bigger 5200mah battery?

[Rotorhead]

What tail blades are you using?

Also what amount of pitch and headspeed are you using, and are you using a governor?

If the headspeed bogs then if it gets really low then you could end up just not having enough tail authority to do the job, so the problem may not be the gyro.

[harmdive]

I'm using NHP 95mm tail blades. Headspeed around 1950 - no bogging down. Throttle Jockey governor. I had a 3300mah nimh battery on before and it never had this problem. I also run another raptor 50 with a 3300 nimh with no adverse affects. I think itt has to be with the regulator setup i.e current getting to gyro/servo.

[Rotorhead]

I'm using NHP 95mm tail blades. Headspeed around 1950 - no bogging down. Throttle Jockey governor. I had a 3300mah nimh battery on before and it never had this problem. I also run another raptor 50 with a 3300 nimh with no adverse affects. I think itt has to be with the regulator setup i.e current getting to gyro/servo.

If you had a larger battery then maybe its current draw rather than voltage then, I take it that the nimhs where sub C cells, perhaps the Lipos cant deliver the current the servo needs and its stalling under load, if the total servo load of all the servos is getting close to what the battery can provide then they are all going to slow down, perhaps thats whats going on here?

[harmdive]

Thanks for that. Just been reading some other posts and I'm coming to the conclusion that the 2600 may not be enough when I'm wrenching everything out of the heli. Bit of a nuisance coz I've only just bought the thing and saving the 5200 for my 90 project. Oh well. I'll just have to give the titan a break until I'm confident that this is the problem. Bloody helis!! - I knew I shouldn't have changed something while it was working. I must say though, regulated lipos rock!!

[raptorheli2]

i will be amazed if it's the battery current mate, a duff battery maybe. i run 9255's x3, 9254 thro, 8900 on tail with a revlock 20 and spartan gyro from a fromeco 2600 pack on my 600 nitro and it doesn't do sport flying...works fine.

cheers

[skatefreak]

Hey,
Lets just clarify...
Your running a 7.4 volt regulated system stepped down to 5.3v...
You say you never had this problem on the nimh3k.
Effectivly you can pull on the regulated system and i'm throwing a 600n with 3x9451's, 8900tail/9252throttle at 5.8v on a 720...
I throw this setup around very hard and i have 2 battery packs, one 1700 and one 1900 lipo's.
I would be inclined to say its not the reg system but if the problems have started since you installed it i would recomend reverting back to the last working setup just to be sure...

If i think of anything else i'll give you a shout.

-Jvr

[harmdive]

I am running jr 8715 on cyclics -
pitch - 8711
throttle 810g

looked at jr's website. it says 8715 & 8711 can run @6v. i know 810 is rated for 4.8. i would have thought it would be ok running @ 5.3. The funny thing is, the li-ion has livened up the response of the heli which I like and the tail is now super locked in where it wasn't before during tic tocs. It used to drift to the left with the nimh but now I can see the tail really working hard to keep itself straight when I'm changing pitch like mad. It's when I continue the move really fast for about 10 seconds and THEN i lose tail control. When I stop the tail works fine. I do have another raptor with the nimh still in and no problems but I can really feel the difference in response rate. Does anybody know (if it is a current issue running through my system) what the maximum current is that radio gear can handle. I know the servos I'm using are pretty beefy.

[harmdive]

just been on jrradios.com and they state for 8711 servo:

User Note: Please ensure adequate power supply to your radio system. This servo is capable of high output, thus requires more power than a conventional servo.

Since I have one of these and two 8715's, I'm leaning towards not having enough power for anything else. It's hard to pinpoint as I don't know how hard other pilots push their helis so comparing is difficult. Oh well, off to fly now. Nice and calm day and not raining - that must be a first in the UK:-)

[Ade_Law]

i doubt its the fromeco. they are pretty solid. but to make sure you could use one of these.

http://www.spartan-rc.com/products/voltguard_g3/g3.htm

plug it into the rx and it will tell you if the reg isnt keeping up.

Ade

[Rotorhead]

just been on jrradios.com and they state for 8711 servo:

User Note: Please ensure adequate power supply to your radio system. This servo is capable of high output, thus requires more power than a conventional servo.

Since I have one of these and two 8715's, I'm leaning towards not having enough power for anything else. It's hard to pinpoint as I don't know how hard other pilots push their helis so comparing is difficult. Oh well, off to fly now. Nice and calm day and not raining - that must be a first in the UK:-)

Current then voltage gives you your speed, but you get your torque from the current, and if your battery cant provide the current needed then the servos/motor can't, under load, maintain the speed the voltage has set.

I am currently doing an electrical & electronic engineering course, and my last assignment last year was on multiphase motors, got a distinction, so......

People forget that all these modern super high torque servos are going to draw far more current than the ones we are used to, infact I am surprised that most of these new servos doent come with more beefy wiring, accident waiting to happen if you ask me.

[harmdive]

Current then voltage gives you your speed, but you get your torque from the current, and if your battery cant provide the current needed then the servos/motor can't, under load, maintain the speed the voltage has set.

So are you saying that the 2600 battery cannot suppply enough current to keep everything working properly under load. my nimh 3300 worked with no problem although voltage dropped and I noticed a difference. I'm hoping the 5200 li-ion will solve the problem.

[Rotorhead]

So are you saying that the 2600 battery cannot suppply enough current to keep everything working properly under load. my nimh 3300 worked with no problem although voltage dropped and I noticed a difference. I'm hoping the 5200 li-ion will solve the problem.

I'm not saying it is for definate, but that is what I would suspect having gone down in capacity.

To know for sure you would need to find out the maximum current draw from all the servos and everything else, and if thats close to the lipos maximum current then thats likely the problem, it doesnt have to be over it, but close to, in my experience somewhere close to 70% of the maximum is where you start to see servos slow down, not necessarily stalled, but if its slowing down then the tail could let go.

Its not a case of if the battery can supply say 10A then you are ok drawing 10A, all it means is that be battery can supply that 10A without being damaged, and the closer you get to that the more the under load voltage will drop.

Some of these high torque servos can each be drawing peak currents of amps rather than miliamps.

When that happens the under load voltage can drop significantly, and even go low enough for gyros to reset.

What C rating is that lipo, if its at least 10 then there shouldnt really be a problem, it probably is, but if its not then the 5200 should do the trick (if its the battery that is)

Different battery types have different discharge charictaristics (C rating), NiCds are the best for high current (High C rating), Nimhs are second, and lipos where definatly third, but are probably more equal to Nimhs now.

For instance, if you use NiCds you can use AA size cells for the rx pack, but with Nimhs you have to use Sub C size because the AA size cant supply the same current.

Personally I would think twice about using lots of these super high torque servos without really making sure they can get all they need.