Gtb/13.5 problems.

cola · #1 05-05-2007, 10:19 PM

I am running the novak gtb and 13.5 in my xxxcr and almost every lap it will act like one of the sensors is bad. It does it when I get on the throttle really hard. I recently purchased a hitec 5925 and it has occurred ever since then. I ran it before with a hitec servo and didn't have this problem. I don't think the rotor is bad because I just purchased the motor and speed control new about three weeks ago. Does anyone have an ideas what it might be?

Thanks,
David

GSMnow · #2 05-06-2007, 10:37 AM

What exactly is the symptom that "it will act like one of the sensors is bad"? Is it a stutter at full throttle? Make sure your motor and battery high power leads are as far away from the receiver, antenna, and servo leads as possible. It may also be a good idea to keep the motor sensor cable as non parallel as possible from the motor current leads also. Braid the 3 motor power wires tightly and twist your battery leads. And of course check all your battery and motor connections. You are using high current connectoirs, right? No melting Tamiya nylon. If your battery is not up to the current demand, that can also cause odd things to happen. Different radio gear can do different things. For example, the servo may stay where it is at, but the throttle drops to zero until the voltage comes back. Even though the 13.5 is a"mild" stock like brushless, it can still pull huge current at high throttle and low rpm.

If all of that checks out, then you may still have a sensor issue, but Hall sensors are very reliable themselves. Inspect the cable for any damage. You can get replacement cables in different lengths now. Does the motor shaft have end play? In the Novak, the sensors are on the end with the face aimed towards the magnt on the end of the rotor. If the rotor moves too far towards the output shaft end bell, it might get the magnet too far from the hall sensor for a good signal. I tried using hall sensor as wheel speed inputs on a full size car, and rim flex was enough to have the signals cut out in hard corners.

Hope this helps
Gary

nicholcgn · #3 05-06-2007, 04:08 PM

Well I am the second to have a problem like this at my track. Normally the GTB's are great. Can't really complain as I have had tons of time on mine. It starts with a studder when you nail the throttle. It is not all of the time just some of the time. We think the cap is gone when this starts. Soon it ends up with the magic white smoke. One we had returned repeated the problem.

I hope that yours is radio problems. I tried 3 different motors in mine. Gettiing ready to send it in for replacement.

so you might want to check the cap if you can confirm no radio problems. I would try the old servo again to see if it disappears.

cola · #4 05-06-2007, 06:07 PM

I practiced on Thursday and it did it but only once in a while. But on Saturday during practice, qualifiers and main it got worse. I already sent my servo in. I don't think it is the radio because everything was fine during indoor season. The only times it really stutters is when I have the servo turned all the way in any direction. It works fine at full throttle. I changed chassis's on Thursday night and when I took the GTB out of the old chassis the cap smelled kinda like a fried speedo. So I will try that out also.

ta_man · #5 05-07-2007, 03:54 PM

If it happens when you have the servo turnned all the way in one direction or the other, it may be that the servo is trying to turn the steering past its limits and is drawing a lot of current from the BEC, thus causing the radio receiver to cut off briefly.

If you have Steering ATV on your radio, turn down the endpoints so that the servo does not try to go past the steering tracle limits. If you don't have ATV, the only thing you can do is make adjustments to the servo horn.

NovakTwo · #6 05-07-2007, 03:59 PM

I suggest you e-mail cs@teamnovak.com and describe your problem.

Quote:

Originally Posted by cola

I practiced on Thursday and it did it but only once in a while. But on Saturday during practice, qualifiers and main it got worse. I already sent my servo in. I don't think it is the radio because everything was fine during indoor season. The only times it really stutters is when I have the servo turned all the way in any direction. It works fine at full throttle. I changed chassis's on Thursday night and when I took the GTB out of the old chassis the cap smelled kinda like a fried speedo. So I will try that out also.

CharlieS · #7 05-07-2007, 04:07 PM

Hi Guys,

The servo endpoint adjustment/check is certainly a very good idea. A Servo adding extra load to the BEC could cause some funny operation for sure.

Also, if the motor is the standard Rotor, it is still possible it has been weakened. If you can simply try a installing a Sintered Rotor, usually that solves any issues created by the Rotor "right away".

It's possible for the ESC to have a problem that causes a stutter, but those situations are not very frequent at all. I see rotor issues from weakened/heated rotors.

Steve Weiss · #8 05-07-2007, 04:07 PM

It's impossible diagnose whatever problem might be present without actually seeing the whole vehicle or system ...but from the sounds of it your servo might definately be part of the problem with you system.

Just as was recommended you should try adjusting your end points so that the tires only just reach full lock when the wheel on your transmitter reaches full lock.

If the servo is trying to push it further than full lock it can cause undo strain on the BEC in the ESC and I can see that possibly leading to problems.

Someone else mentioned checking the endplay in the motor and that is a valid concern as well. You want to make sure that you only have a small amount of endplay in the rotor... too much and you can run into some stuttering issues like what you have described.

Also, is your motor equiped with a sintered rotor or the stock bonded rotor? Usually the sintered rotor does not have hall/sensor related stuttering issues ever... but sometimes the bonded can have issues if the rotor shimming is not quite right.

cola · #9 05-07-2007, 05:54 PM

I am using an Airtonics M8 and I already have the epa's set so the servo won't keep pulling when the carrier is already as far as it can go. I am using the new 13.5 with the finned can and sintored rotor. I check the motor also and there is barely any play in it.

NovakTwo- You have mail.

tireshredder · #10 05-08-2007, 05:21 AM

Quote:

Originally Posted by cola

I am using an Airtonics M8 and I already have the epa's set so the servo won't keep pulling when the carrier is already as far as it can go. I am using the new 13.5 with the finned can and sintored rotor. I check the motor also and there is barely any play in it.

NovakTwo- You have mail.

I have seen the new digital servos pull huge amounts current!
What servo did you install? An internal bind in the servo can cause this, as esc bec's are only good for a few amps, and state of the art servos can demand more than the esc's bec can deliver.

Later,

tireshredder · #11 05-08-2007, 05:29 AM

Sorry,
I see you have posted that it is a Hitec HS 5925. This is a programmable Digital servo with serious position holding strength and the accuracy of digital step technology. It has a torque of 128 oz-in and Speed of 0.08 Sec/60 Degrees. Just the kind of servo to pull a huge current load if bound up at all.
Great servo! By the way.
Later,