racer8297

My Feedback: (13)

Hi all,

So I got my MX400 set up perfectly (or so I thought). It has an Ultrafly C/13/33 motor and an Electrifly LiPo 1500mah battery and an Ultrafly 25amp speed control.

The problem is, with a fully charged battery, the heli will only hover for about 30 seconds before the battery cutoff voltage is reached and the motor turns off.

All the linkages and swashplate and tail slidder have been checked and are sliding perfectly. There is no binding anywhere. I tried swapping out the servos. No improvement. The pinion on the motor is not binding and the belt drive is not to tight.

Can anyone give my a clue as to what is happening here?

Thanks,
Jim

ewr101

have you tried a different battery?

racer8297

My Feedback: (13)

Good question. I have tried 3 batteries. Also, the battery is not warm when it quits and neither is the motor.


Jim

ewr101

i know it's only 30 sec. but does it seem like it has good power and want to "pop" off the ground when you give it enough throttle to do so?

racer8297

My Feedback: (13)

It has great power. And yes, it does want to pop off the ground. Good head speed and collective response. I fly a Raptor 30 so I do know what it should fly like.

Jim

ewr101

well then i would check the voltage on the battery to see if was close to what you started out with before the 30 sec. hover and if it is i would suspect a bad esc or motor. maybe check the length of the motor mount screws and make sure they aren't causing a short or rubbing on the windings inside the motor. i have never heard of the brand of motor or esc you are using so i'm not familiar with them at all.

racer8297

My Feedback: (13)

Ultrafly and Electrifly are both Great Planes brand. I'll check the voltage later today.

Jim

racer8297

My Feedback: (13)

Alright, I just checked the voltage and now I really don't get it. The voltage at cutoff is 11.56 volts. What should the cutoff voltage be for a 3s Lipo? I am beginning to think that the problem lies with the ESC. Would you agree?

Jim

ewr101

yes i would agree. i have a dragonfly 36 with the walkera brushless and esc and a thunder power 2100 mah li-po. i believe it is set at 9.8 i think. i know that the lhs told me not to discharge it below 3.3 volts per cell so that would be 9.9 volts total. sounds like as soon as you that "topped-off" charge your esc grounds you. like i said i'm not familiar with that set-up so i have no idea how to reprogram the esc. i can't even re program my own. no instructions came with the motor and esc and no one here seems to know either. good luck.

exeter_acres

My Feedback: (2)

I'm betting it is the battery as mentioned....

that battery is only rated to 12A discharge while it looks like that motor can pull 16A or more....

have you measuered the Amps being pulled??
normal cutoff is 9v for a 3 cell lipo.... but if the battery can't supply the juice, it can drop below that VERY quickly.... then once you shut off, it recovers....

I recommend a Watts Up meter to measure it... great tool...

in the meantime, test it with a bigger battery or different gearing

racer8297

My Feedback: (13)

You know exeter, I think you may have hit on it. I think I'll order a battery capable of a higher discharge rate. If that doesn't do it, you will be hearing from me again!

Thanks exeter and ewr.

Jim

ultraviolet

It is not a battery problem. You say that you tried 3 batteries !
The ESC cutoff voltage should be about 10.2 volts ( running down to 9.9 gives you a
short lipo life expectancy). The head speed will drop off at 10.5 volts.

Your ESC is cutting out when the lipo is still holding a solid charge, or your
lipo/motor connectors may be intermittant. Check all the basic stuff before you
start buying more lipo's

racer8297

My Feedback: (13)

Hiya Ultraviolet,

All 3 batteries were the same exact type of battery which have a 12 amp discharge rate. I ordered Lightening battery with a 16 amp discharge rate. If that doesn't do it I will get a new ESC. Which one would you recommend?

Thanks,
Jim

DarkWombat

If you're using a 3S lithium battery, the problem is in your cutoff voltage. As previously stated, the cutoff for a 3S pack should be between 9 and 10 volts. Also, as previously stated, your pack probably can't dish out enough voltage. With the MX400 and the T-Rex helis, I think it's best to shoot for a pack that can discharge constantly at least 18 amps. 20 or more is preferable.

I highly recommend you get a wattmeter too. Or, even get the Hyperion E-Meter, which is a digital voltmeter, tachomter, ammeter and watt meter that you can connect between your battery pack and ESC and use to determine exactly what figures your power system is pulling. You'll definately save in the long run with knowing what amperage the power system is drawing (worst case situation: you're doing a very hard climb-out which causes a big amperage spike in mid-flight, battery conks out and heli crashes! UGLY!). The more you know about your heli on the bench, the more confident you will be in the air knowing that your setup can take whatever comes to it.

racer8297

My Feedback: (13)

Here's an update. Just got my Lightning Lipo in the mail and charged it up. Now the heli hovers for at least 5 minutes if not longer. Thanks all for your help. I guess that the other batteries did not have enough of a discharge rate!

Jim