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Losing heading hold on my Trex

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Losing heading hold on my Trex

Old 02-22-2006, 01:44 AM
  #1  
GreenTea
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Default Losing heading hold on my Trex

Hey all...

I've been having a problem with my Trex ever since I started flight testing it. I bought the kit with the Align 4500 motor, 35ESC, Futaba GY401 Gyro, three hitec HA-56HV servos on the swash and one S9650 for the tail.

I've put the kit together and when it works, it flies just great. No problems, tracks quite well, and a few people at the flightline have commented that it's one of the cleanest helis they've seen fly. On random occassions, however, the gyro just shuts off when the rotors spin up. I start the throttle low to allow the rotors to come up to speed, go halfway to 0 deflection, but once I start heading into the positive deflection the gyro light shuts off, or goes on and off incrementally. Needless to say, the helicopter starts to pirouette on its own until I drop the throttle down somewhat, then it holds, but then loses it again.

Some people I've spoken with think it's the batteries, but I've been using different brands that have the same effect... I thought that they're out of balance, but testing them shows that the balance difference has been minimal.

To me, it seems that once the rotor is at full speed and the deflection kicks in, it's losing power to the gyro. I'd almost suspect that there's some unseen mixing going on from the Spektrum in the 3rd throttle position (the radio's a 3 point curve), but I haven't seen anything to indicate that's what's going on. And the real pain is that the condition comes and goes seemingly at random, and very difficult to reproduce. Sometimes it'll fly like a dream, other times it's completely unhappy getting off the ground.

At this point, I'm starting to wonder if I should contact Futaba about the 401. Their products are really well made, but every once in a while something does go wrong.

Does anyone have any ideas, or has seen this sort of thing before? Thanks so much in advance!!
Old 02-22-2006, 06:00 AM
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HeliHacker
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Default RE: Losing heading hold on my Trex

I had the same symptom. For me the gear driving the tail belt came loose on the shaft. So it looks like it is working okay, then when the gear starts slipping, the tail spins. Other causes:

** Avoid sudden temperature changes. Sudden temperature changes will cause the neutral position to change. For instance, do not fly the model immediately after removing it from inside a heated
vehicle in the winter and an air conditioned vehicle in the summer. Let the model stand for about 10 minutes to allow the temperature inside the gyro to stabilize before turning on the power. Also, consider sudden temperature changes when the gyro is exposed to direct sunlight or is
installed near the engine. Take measures so that the gyro is not exposed to direct sunlight.

** LED display Gyro operation state
Rapid flash Displayed while data is being initialized at power ON.
Steady light Indicates that the gyro is operating in the AVCS mode.
Off Indicates that the power is OFF, or the gyro is operating
in the normal gyro mode.

** Slow flash Displayed when there are no rudder operation signal being input from the transmitter. At this time, the rudder servo does not operate.

**Intermittent flash Alarm display when the power was turned on in the normal gyro mode. For the rudder neutral signal to be read correctly, set the transmitter to the AVCS mode and turn on the gyro power again.

**Double flash Displayed when the rudder signal from the transmitter in the AVCS mode is different from the neutral signal memorized in the gyro. Also flashes when the rudder stick was operated.
Old 02-22-2006, 10:13 AM
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GreenTea
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Default RE: Losing heading hold on my Trex

Well, it's not the tail belt-- I checked that, and it's perfectly taut. However, the temperature change thing is quite possibly the culprit... I've been coming home and trying to fly, and it's been extremely cold. I never would have suspected that as a cause at all, but the TRex is in the Align case, which does insulate it quite nicely from the outside.

The heli will initialize, the speed controller will start its initilization sequence, and then the light will go solid. I start to give it throttle and everything is fine until the blades go positive, and then the light goes out entirely.

What is AVCS mode... ? I believe it's set up correctly, but since it's just a series of blinking lights, I'd appreciate if you'd explain in detail for a newbie!

Thanks in advance...

ORIGINAL: HeliHacker

I had the same symptom. For me the gear driving the tail belt came loose on the shaft. So it looks like it is working okay, then when the gear starts slipping, the tail spins. Other causes:

** Avoid sudden temperature changes. Sudden temperature changes will cause the neutral position to change. For instance, do not fly the model immediately after removing it from inside a heated
vehicle in the winter and an air conditioned vehicle in the summer. Let the model stand for about 10 minutes to allow the temperature inside the gyro to stabilize before turning on the power. Also, consider sudden temperature changes when the gyro is exposed to direct sunlight or is
installed near the engine. Take measures so that the gyro is not exposed to direct sunlight.

** LED display Gyro operation state
Rapid flash Displayed while data is being initialized at power ON.
Steady light Indicates that the gyro is operating in the AVCS mode.
Off Indicates that the power is OFF, or the gyro is operating
in the normal gyro mode.

** Slow flash Displayed when there are no rudder operation signal being input from the transmitter. At this time, the rudder servo does not operate.

**Intermittent flash Alarm display when the power was turned on in the normal gyro mode. For the rudder neutral signal to be read correctly, set the transmitter to the AVCS mode and turn on the gyro power again.

**Double flash Displayed when the rudder signal from the transmitter in the AVCS mode is different from the neutral signal memorized in the gyro. Also flashes when the rudder stick was operated.
Old 02-22-2006, 10:17 AM
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Wazmo
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Default RE: Losing heading hold on my Trex

Are you using a separate RX battery or a UBEC? If you're using the ESC's BEC, it's possible the digital tail servo is drawing too much current.
Old 02-22-2006, 10:43 AM
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GreenTea
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Default RE: Losing heading hold on my Trex

Yep-- using the ESC's BEC entirely. I suspected it was a current draw issue from the beginning, because only when the blades start to encounter resistance and the TRex has to spin up faster does the 401 shut off.

What's the "U" in UBEC?

Thanks very much-- I'm starting to feel that I'm honing in on the problem with everyone's help!!

ORIGINAL: Wazmo

Are you using a separate RX battery or a UBEC? If you're using the ESC's BEC, it's possible the digital tail servo is drawing too much current.
Old 02-22-2006, 10:53 AM
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Default RE: Losing heading hold on my Trex

[link=http://www.hobby-lobby.com/ubec.htm]"Ultimate" BEC[/link]
Old 02-22-2006, 04:52 PM
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GreenTea
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Default RE: Losing heading hold on my Trex

Thanks... I ordered one, so we'll see if it does in fact remedy this [:@] problem!

ORIGINAL: Wazmo

[link=http://www.hobby-lobby.com/ubec.htm]"Ultimate" BEC[/link]
Old 02-22-2006, 09:39 PM
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Default RE: Losing heading hold on my Trex

AVCS is heading hold mode.

I wasn't referring to your tail belt - it is the pulley and gear assembly that drives the belt. I know of several instances where the pulley loses its bond to the small shaft and begins to slip. Its the pulley slipping on it shaft, not the belt. So when you start the pulley is not slipping, but as you spool up the pulley will begin to slip causing your gyro to lose its neutral point and causing the heli to spin. The gyro led's should blink when you lost the neurtral point. You will have to remove the belt and be able to restrain the gear and try to twist the pulley to see if it slipping.

If it was your BEC from the ESC, the symptom is usually the motor shuts down because the ESC shuts everything down.

If the gyro led goes out and stays out, the gyro is not getting a signal from your receiver. You will need to be able to check the receiver operation.
Old 02-22-2006, 11:06 PM
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GreenTea
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Default RE: Losing heading hold on my Trex

I understand now what you mean-- thank you. I'll check into this as well, if the "easier" fixes by adding the UBEC and being aware of temperature changes do not fix this issue...

I really appreciate all the help. From you, and everyone else. It means a lot to know this collective brain trust is out there, helping.

ORIGINAL: HeliHacker

AVCS is heading hold mode.

I wasn't referring to your tail belt - it is the pulley and gear assembly that drives the belt. I know of several instances where the pulley loses its bond to the small shaft and begins to slip. Its the pulley slipping on it shaft, not the belt. So when you start the pulley is not slipping, but as you spool up the pulley will begin to slip causing your gyro to lose its neutral point and causing the heli to spin. The gyro led's should blink when you lost the neurtral point. You will have to remove the belt and be able to restrain the gear and try to twist the pulley to see if it slipping.

If it was your BEC from the ESC, the symptom is usually the motor shuts down because the ESC shuts everything down.

If the gyro led goes out and stays out, the gyro is not getting a signal from your receiver. You will need to be able to check the receiver operation.
Old 02-23-2006, 06:19 AM
  #10  
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Default RE: Losing heading hold on my Trex

I forgot to mention. It is not the temperature change. This shows itself as a very slow drift so the heli will not stay centered in heading hold. If your heli is actuallly spinning, that is not temperature change.
Old 02-23-2006, 01:19 PM
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GreenTea
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Default RE: Losing heading hold on my Trex

No, that's exactly what it's doing. It takes off and slowly starts rotating counter-clockwise as viewed from the top. It's not spinning as if the tail weren't operational... and the gyro light is turning off when it lifts off.

After I install the UBEC I'll see then, and follow up with another post...

ORIGINAL: HeliHacker

I forgot to mention. It is not the temperature change. This shows itself as a very slow drift so the heli will not stay centered in heading hold. If your heli is actuallly spinning, that is not temperature change.
Old 02-23-2006, 04:00 PM
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Default RE: Losing heading hold on my Trex

Check that you dont have some sort of mixing that is kicking the gyro out of HH mode when you give power or switch to idle up.

Best is to disconnect your motor and see whats going on when you start giving throttle or switch flipping.
Old 02-25-2006, 03:40 AM
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GreenTea
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Default RE: Losing heading hold on my Trex

So the UBEC arrived today in the mail, and going over the instructions, I have a couple confusing issues...

If the BEC is designed to cut off power to the motor to maintain the control authority of the servos, why is it wired in parallel to the battery? It seems to me that when the BEC identifies a low voltage, it will try and cut off the power to the motor through the ESC, but the battery is still plugged directly to the ESC regardless. What's preventing the motor from continuing its operation? I feel like I'm missing something obvious, but I'm really tired.

Secondly, the Hobby Lobby website states "The last thing to do is to disable the BEC function of your speed control if there is one. This is usually accomplished by pulling the red pin out of the servo lead on the speed control." Will this work with the Align 35ESC?

Thanks!!
Old 02-25-2006, 08:57 AM
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Default RE: Losing heading hold on my Trex

both the BEC and the ESC are hooked to the battery... then plug the ESC into the throttle channel, just like you always have.. and remove the red pin... this stops the power from the BEC from going to the RX, but still allows the throttle signal to get back to the ESC...
then the BEC plugs in to any available channel on your Rx... if you do not have a free channel, use a "Y"


the BEC supplies power to the servos, it has nothing to do with the motor.....
Old 02-25-2006, 12:22 PM
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GreenTea
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Default RE: Losing heading hold on my Trex

I understand. I also thought that the new BEC will decrease power to the motor in favor of the servos/receiver when it drops too low; this setup seems to me that it'll just pull its own current for the receiver from the battery, and not have any protection built in. Isn't it supposed to do the former?

ORIGINAL: exeter_acres
the BEC supplies power to the servos, it has nothing to do with the motor.....
Old 03-04-2006, 10:22 PM
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Default RE: Losing heading hold on my Trex

Would anyone know if wrapping the RX or any other part in copper foil prevent radio interference? if so I have a cheap available fix!
Murt.
Old 03-05-2006, 09:23 PM
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Default RE: Losing heading hold on my Trex

GreenTea:

Problem does sound strange. I'm not acquainted with the Spectrum, but are you sure it's not the radio erroneously programmed, removing the AVCS mode with throttle 'up'? Are the gyro & gyro gain plugs plugged into the correct receiver slots? CHECK IT!! Or is the ESC or Motor too close to the 401, which can create interference. The 401 is not 'shutting off'--it's simply going out of AVCS(HH) mode. Another critical factor--Is yout receiver Antenna(any bare wire) touching the carbon frame? That can cause the receiver to pick up wild interference and totally unpredictable operation!!! When the heli is pirouetting on lift off, do you have rudder control? The ESC is programmed to cut MOTOR power if the Voltage drops too low--Not BEC power. Doubt that the 9650 is drawing too much power. Assume you're using a good LiPo---3 cell---

Good luck

Lloyd
Old 03-06-2006, 12:51 AM
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Default RE: Losing heading hold on my Trex

GreenTea:

The more I think about it, the fact that it's an intermittant problem, really suggests electrical interference, or an intermittantly bad component (ie: radio or gyro). Check the factors I suggested.

Lloyd
Old 03-07-2006, 10:50 PM
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GreenTea
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Default RE: Losing heading hold on my Trex

Thanks for all the replies and help.

After checking the batteries, checking the charger, replacing the BEC, trying to ground the frame to prevent static buildup... it turns out it was the receiver on the heli.

I spoke with the creator of the Spektrum radio-- quite a nice and very helpful guy, who pointed me in a number of different places to try and rectify the problem. I finally hit upon the solution by chance. Since one servo was glitching where the others were fine, I tried swapping that one (the front left) with the elevator servo, and voila, the elevator started glitching. So I narrowed it down to not being the servo, but still not knowing if it was interference with the radio or some malfunction.

On a fluke, while the flybars were rotating at speed, I wiggled the "aux" BEC connector on the receiver, and suddenly the servo started glitching violently. Then, if I leaned it towards the tail, the glitching stopped. If I leaned it towards the nose, the glitching went wild.

With the help of the guys at HeliHobby (where I bought the TRex) and Horizon Hobby working together, I was able to get a replacement receiver, and the helicopter now flies without any glitching whatsoever, and is locked on heading. No gyro drift, no sudden shifts in attitude... it's like a new bird. I just spent four battery packs this afternoon finally enjoying my model, and had a huge smile at the end!

Again, thanks to everyone for their advice and thoughts!
Old 03-08-2006, 02:04 AM
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Default RE: Losing heading hold on my Trex

Glad the problem was solved. After around 30 great flights of my recently finished SE, Past 2 days have brought annoying intermittant motor cut off at totally random times, totally UNRELATED to 'set' cut off volage. Starts up again after a few seconds but I'm totally paranoid about gettng it above 3 Ft !! Obviously an intermittant problem almost certainly related to vibration. So far no damage, but got a Phoenix 35 at my LHS today, and he'll send it back to Align for a credit. I feel the Phoenix is a much better ESC anyway, and I'm sure the credit will be useful for "spare" parts.

Lloyd

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