ZAGI 400-X ; power cutting out to motor after flying at full throttle - RC Groups
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Jul 12, 2001, 12:52 AM
Registered User

ZAGI 400-X ; power cutting out to motor after flying at full throttle

I have had a zagi 400-x for 1 month+ now and I have encountered an weird intermittent problem that I haven't been able to figure out. THANKS IN ADVANCE!

The problem did not appear during my first flights. But then the motor began to suddenly cut out after flying around at full throttle for ten minutes or so. The control surfaces would remain active so I could just bring it in for a landing with not so much difficulty in most cases.

I concluded that this was the speed control. ANY THOUGHTS?

So one day I made the mistake of letting my friend try to just glide it. The idea was that i would throw it and he would glide it in for a quick landing. Well somehow we had some miscommunication and he turned on full throttle and luckily crashed it very quickly. He later claimed that the plane lost total control and that that was what caused the crash. I was doubtful, but I had experienced the throttle cutting out condition described above in the preceding flight (I had just finished flying and the battery was running out, but by no means dead).

Anyway, the next time I tried to fly, the plane was dead. First I sent the speed control back to ZAGI, and they were very nice and sent me back a new one. The plane still didn't work. So then I sent my receiver back to HITEC (the three channel one that came with my skyscooter). The crash had been nose first, but the received was not visibly damaged. (I will be reinstalling the receiver in the wing when I get it back - the nose is a really stupid place to put it) They returned it to me with a receipt that said there was no problem found. However, when I reinstalled it the plane worked like new.

Unfortunately, on my first flight I again encountered the throttle cutting out problem. Again this usually occurs after prolonged full throttle flying. Even worse still, on my second flight (the next day) the plane was again exhibiting the throttle problem after ten minutes or so of flying. The engine would cut out, I would land with control surfaces operational, I would go get the plane, the throttle would then respond again, so I would fly some more until the engine cuts out again. The problem is that finally everything cut out and the plane crashed hard (The battery was still going strong, 95% or so). The sytem was nonresponsive and the transmitter smashed so I sent it back to hitec for possible repair.

I still can't figure this out tho. Any ideas???

My guess is that it is the speed control. Anyone else with similar experiences. I am using the stock 400-x battery and stock engine that came with my 400-x, so I have trouble blaming it on the ESC. I would think that zagi would supply a speed control that is adequate.

Thanks for any help.

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Jul 12, 2001, 08:03 AM
Registered User
Larry Dudeck's Avatar
It sounds like the ESC is overheating. It is an AVEOX unit that should be good for 15 amps or so.

A couple of things to check...
Is your ESC getting enough cooling?

A real dumb question...did you open the cooling vent holes in the canopy?

Did you mount the ESC directly on the battery? If so, the heat from the battery could be conducting into the ESC, contributing to the ESC heating.

Are you using the push-on prop that came with the kit? Different props will drag more or less current.

I have 48 flights on my ZAGI X with no indication of this type of trouble. But I don't use full throttle except on launch
Jul 12, 2001, 08:59 AM
AMA 697691 / FAA 13675
Hi Kristian,

Larry has some good suggestions.

I would add the following:
  • After launching and obtaining a decent height, reduce throttle to 3/4
  • When motor quits, do the servos still work?

If your motor or servos are drawing excessive current, this may cause problems.

First determine if full length flights are achieved with 3/4 throttle. Remember that the Zagi can glide for loooooong periods on a very low 1/4 throttle.

Second, determine if just your motor cuts out or all the servos cut out like your buddy suggested.

Please tell us what prop you are using.
Latest blog entry: Greg's Web Hangar
Jul 12, 2001, 10:39 AM
Stress Be Gone
GBR2's Avatar
Kind of seems obvious. He is flying for 10 minutes at full throttle and the motor then starts and stops. The ESC is cutting off the motor circuit because the battery voltage is to low but the servos still function because the voltage level still allows the BEC circuit to function. All of this is normal. As to the rest of the problems he had from his "crash", who knows.
Jul 12, 2001, 02:51 PM
Registered User
i don't know the 400x kit parts specifically, but it sounds like normal BEC cutoff.

i.e. when the battery is ALMOST discharged, the speed control intentionally turns off motor power.
this is to reserve power for the radio...

that is your cue to land...
BTW, if you throttle down and then back up, you should be able to have some power again... it will not cut off if you go up to say 50% throttle, enough to hold altitude and come around for a landing...

it all makes sense-- if it let you fly until the battery was dead, you would lose radio control. better to have no motor than no control, right?

and flying full throttle all the time on a zagi seems wasteful to me-- the airframe is by its nature not fast... the real speed difference between 75% and 100% throttle is pretty low if you ask me...

try flying low, slow and accurately some time-- that's almost as much fun, sometimes more...

anyway, back to the me this sounds like hardly an emergency warranting desperate pleas for help :-)
and you propbably have a speed control that's doing the right thing, no need to upgrade...

just my opinion of course.
welcome to e-zagi-flight. ...maybe research a bit before the next urgent problem?

mike in PA
Jul 12, 2001, 07:33 PM
Tacoma, WA, USA
William A's Avatar
Originally posted by Joe-z:

The problem did not appear during my first flights. But then the motor began to suddenly cut out after flying around at full throttle for ten minutes or so.
In your first flights, did it cutout at all ?, cause it should have.

And when it does cutout, will it come back on if you kill your throttle for a second, then throttle back up ?, also normal.

10 min is about what you get at full throttle with that battery.

Have you tried another battery ?.
Jul 12, 2001, 08:06 PM
Registered User
1. When it cuts out I immediately go into emergency landing mode. It always catches me off guard and I only have about 10 flights or so under my belt with this zagi. One time I tried once to lower the throttle to off position and turn it back to full and nothing happened. However, without fail, operation begins again after a couple of minutes, usually by the time I make it over to the landing spot. At this point, I have to turn the throttle off and back on(if I haven't already) to get a response.

2. I don't remember it cutting out in the first flights, but I really have a bad memory for these kind of things as they don't really seem very important at the time.

3. I have two other batteries - converted rs 1700s that I converted myself. I used them in a rotation the first few times I flew, but have grown tired of them as they somehow do not have as much power as the zagi one - another area of confusion for me that I would apppreciate comment on as they are both 1700 mah.

4. Prior to this zagi I had a skyscooter, and it never exhibited this behavior, despite repeated full throttle flights. Like I said, this cutting out is occuring while the battery is still going strong. That just doesn't make sense. It cuts out and then I can just pick the plane up when I get to it and fly at full throttle again. My understanding of the cut-out feature is for protection in very low battery situations, which these clearly are not.

5. I guess it looks like the consensus is that this is a esc problem. I am considering a motor upgrade to multiplex 450 turbo. Any ideas on a good upgrade esc?

6. Sorry about the pleas for help. Although this is not an urgent situation, my level of frustration is quite high, and I researched around in this group extensively prior to posting.

Jul 12, 2001, 09:52 PM
Registered User
The RS1700s are probably NiMH cells which provide a lower voltage under load than the equivalent capacity NiCD battery. Also, due to their higher internal electrical resistance, NiMH aren't usually capable (especially in small sizes) of keeping up with high amp loads. 1700mAh sized NiMHs shouldn't be too much of a problem for a stock Zagi, but you will notice decreased performance compared to a NiCD pack. Of course, if they are not NiMH cells, this would not be the case... Rather poor cell quality would be to blame.

Something is not being communicated correctly here. Are you saying that you fly at full throttle for 10 mins, switch to a fresh pack, and then the problem occurs? Or are you having the cut-out problem with the same pack you've been flying with for 10 mins?

If it's the first then it could be your ESC overheating. If you've had the ESC replaced and it acts the same way, while it's unlikely to be solely an ESC problem, it might be. Otherwise, you're plane could be pulling too many amps. Do your batteries heat up substantially? If they do, then too much power is being drawn through the system. Since you seem to be using the stock Zagi 400X power system, it's unlikely to be the prop. The motor could be the culprit, or the cells themselves.

If you've been running the same battery for 10 mins at full throttle you are definitely hitting low voltage cut-off. There's no way you still have 100-95% power left. If your Sky Scooter was pulling less amperage than the Zagi, then you will obviously have longer flight times. Cycling to zero throttle briefly (up to 5 secs depending on battery state) will reset the cutoff and allow you to fly at part throttle, full throttle, or whenever the circuit senses another low voltage situation. In your situation, if you land and wait for the motor to come back, can you then go on and fly for a few more minutes at full throttle?

Regarding you 450 Turbo upgrade. You probably know this already, but you will definitely have to go with higher current capacity cells for it, 800AR at a minimum.

There's a slim possibility that your batteries are to blame in conjunction with the ESC, but that's getting weird.

Jul 12, 2001, 10:02 PM
Registered User
I don't think the boy is even listening

It's not a bad ESC !

You don't run a 400 sp motor full throttle for 10 minutes and still have 100 % power left ! Maybe you are trying to melt your poor ESC by putting it on top of the batteries and running the plane full throttle for 10 minutes !

Sounds like 100% pilot error here !

[This message has been edited by Feodosia Flyer (edited 07-12-2001).]
Jul 12, 2001, 10:15 PM
Registered User
1. I am saying that I fly at full throttle for tem minutes or so...prob. less than 10 min., then the throttle cuts out. The wierd thing is that this doesn't always occur. It seems like the esc gets hot and then it thinks the battery is about to run out. After it cuts out I must land and then when I walk over to the plane I can pick it up and fly at full throttle for a minute or two and then it cuts out again. The other day I did this four times and finally I lost total power and crashed.

2. The battery gets pretty hot, but not nearly as hot as it did in the skyscooter where it was insulated in foam, and I did not encounter this with the skyscooter. However, I was using a gear box with the skyscooter so the motor rpm was much lower, but I don't know what the result of that is.

3. Would a sanyo 1400 ae work with the 450 turbo motor? What would happen if I used the 1700 with it?
Jul 12, 2001, 11:40 PM
Registered User

I don't see much of a problem. Let's assume 8A for 10 min. 8Ax10A/60min/hr.=1330mAh. Running at 10Amps would be 1670mAh. Are you using the Zagi '1700AE' pack, which are actually 1700AAU? If so, it is not surprising to see the voltage drop below the BEC cutoff after 10 min full power. But by the time you walk over to your plane, the cells have cooled recovered a bit, and can supply voltage for a bit longer. Have you tested the pack voltage after cutoff, under load?

Jul 12, 2001, 11:55 PM
Registered User
1. I have no means of testing pack voltage.

2. I am having trouble making one of my points. Forgive me. When I say that the battery has 95% power, maybe 90% would be more realistic....however, the plane is still flying around fast...the reduction in speed from lauch (minute one) is barely noticable. If this esc is going to cut off my engine when the plane is still flying around fast, that is not the esc for me, and I should just get a different one. I would use the esc from my skyscooter if it weren't for the fact that I landed it in a small stream one my last flight.

3. Also, I am not timing my flights. I guess some peole, actually do that, but I can see no reason...I mean to say its not important to when I say ten minutes that is just a rough approximation.

4. Like I said, I researched around in this group considerably before posting my problem, I have found some users who claim to have 15 minute full throttle flights. I am not making this up.

5. Also, I am not a boy....I'm a little girl. Don't try to email me because I'm real shy.

6. I like to fly full throttle. Its fun. Whatever.


Jul 13, 2001, 01:13 AM
Registered User
1. I am using the stock little white gunther props.

1.5 I cut the canopy holes.

2. The esc was sitting directly on top of the battery. This is really the only place it could go given that the receiver was mounted in the nose. (i am going to move it to the wing now)

3. I am aware of the esc cut-off feature, but all of these cases are ones in which I am flying at full throttle and the battery still has 100-95% power. My zagi is pretty heavy (I guess) so once the battery power output to the motor starts to fade, I just bring it in.

The more I think about it now, I can't believe that the zagi instructions tell you to put the receiver in the nose. That is stupid. In my last crash the reciver got smashed because the power wire from the esc to the receiver was passing over the front of the battery from the esc that was sitting on top of the battery. As I said above, there is no other way to place this given the lengths of the wires configured on the esc (the two I have had at least). When the plane smacked the ground nose first (from 5-10 ft in the air) the battery came forward but ran into the receiver power wire. I had installed a string holding the battery plug on the esc to the motor mount so the esc wasn't going anywhere. The receiver was pulled up a bit (it was a little loose from a couple of nose crashes previously) allowing the battery to smash it.

* Maybe I just need to get a better esc?? I like to fly full throttle the whole time. I like to fly fast. Gliding is OK, but only if you have to in my present view. HELP PLEASE!
Jul 13, 2001, 02:17 PM
Registered User
As many people have said... You are flying through your batteries! People are not getting 15min FULL THROTTLE flights out of their stock Zagis. You can achieve 15mins with throttle management, but not WOT (wide open throttle). Anybody who claims they are is not using a timer, or is not telling the truth. The only way you could fly a stock Zagi setup for 15mins at WOT is if the setup pulled about 6.5 amps... And you'd have a slow Zagi, 'cause that's a little more than half throttle normally.

If you want the theory... here it is... basically...

NiCD batteries by their nature have very flat discharge curves. That means they provide a relatively constant voltage over most of their charge life, and then voltage quickly drops off. NiCDs do not work like more conventional cells. They don't slowly die over time. You will get up to 90% power for up to 90% of the time, and then stuff will just die quickly.

What you are experiencing regarding the restart of the motor over and over is the tendency for NiCD cells to regain a bit of their voltage for a bit after resting. This fools the low voltage cut-off in your BEC temporarily until voltage drops again. Regardless, you are at the end of your charge. Flying until your plane goes out of control means you dropped the pack well below cut-off and are risking the health of the battery itself. You should never fly a pack that low. It results in cell voltages lower than is healthy, and it might lead to cell reversal. The general practice is to quit before or at first cut-off, and to not drop below 1 volt per cell. This means a measured 8 cell pack voltage of 8 volts.

However, since batteries perform differently under load than when they're just sitting. It is unlikely you will actually measure a static 8 volts. Voltage will almost always rise in a pack when it's not doing anything, but that DOES NOT mean that you have more power.

Your problem is that you have no problem... You are flying into a LOW VOLTAGE situation.


[This message has been edited by Jeff Goldman (edited 07-13-2001).]
Jul 13, 2001, 02:40 PM
Registered User
e-sailpilot86's Avatar
This case is similar to one that I had. I was drawing too many amps (20 to be exact) from a small pack (5 cell) which caused a voltage drop, leaving the ESC with no choice but to shut down the motor. This is happening to you at the end of the motor run, not throughout like mine, and I'm almost certain it's your BEC cutting the motor out. Nothing unusual, I guess an upgrade would help if you really need full throttle near the end of a run.