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Spektrum / Mamba Max/ BEC glitching problem

Spektrum / Mamba Max/ BEC glitching problem

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Old 05-01-2010, 11:32 PM
  #16  
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Well, this is an odd one, but I may finallyhave an answer.

I got ahold of a tech at Spektrum on the phone. Went through a bunch of the usual questions of all the stuff I already tried, but then was asked if I changed the steering servo. The servo is working perfectly, and sterign glitches have been on the rare side, so I was not looking there. I have seen other posts where the servo was causing issues, but everything my car did was not pointint there at all. I had the Spektrum TX and 3 RX's boxed to send for repair and had picked up the Cheap Airtronics for the interim while I waited, and for a solid 2 packs, it appeared the glitching was gone, so I really figured the radio system had to be the issues. but sure enough, on my third pack, I got a few glitches. THe Airtronics system responded very different. The ESC was pulsing power, but never hitting brakes like it was on the Spektrum. Coming onto the main straigh, it would take off, but then I would hear the gear noise quiet down 4 or 5 times as it past the driver's stand. And one time in the sweeper the steering just opened up as I lost power, for just a blink, but the car went a good 4 feet high in the turn. As I ran deeper into the third pack it got worse and worse. I even lost power going over some of the jumps.

When I got home I rigged a servo extension cord with my amp meter it in. Wow, that Airtronics digital servo will stall out at 1.2 amps, but in dynamic run, it went as high as 2.2 AMPS!! I swapped the meter around to check the BEC voltage. At neutral with no load, it was dead on 6.0 volts, static loading the servo, It dropped just a tick to 5.8, but when I did some quick turning, I was it dip under 4.5 volts once in a while. This is still okay for the RX, but it was not hot after 2 pack at this point. I guess my servo may be an issue after all.

I dug through my box and found a decent older analog HiTec 1/8 steering servo, metal gear and ball bearing. I checked the current on that one, it hardly topped 0.5 amp, even in fast dynamic moves. IT is not quite as quick so I used a slightly longer bell crank on it to get a little speed, and had to dial the end points way down, to like 60%. I ran the entire club race tonight with no hickups at all. I will try sticking the Spektrum back in and se if this cures it there too. If so , I guess my servo will be taking a trip to Airtronics.
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Old 05-02-2010, 07:18 AM
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I have a dx 3.0 also and experienced the same problems
with a tekin system. Its like it would stutter the 1st few laps
stop for a second . The hardest part was the the issue
was never at the same point . I also just before experienceing
this issue switched from a jr650 to a xp ds1313. This is when
I started to glitch but never put 2 and 2 together . Every one said
I had to much timing ,I running no timing on the tekin and motor
Just to isolate it. I ended up getting rid of the unit and bought a mm pro
set up which I like a lot and had none of these issues since. Its good to
know for future use. I heard of people putting on a capacitor for the
servos.

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Old 05-02-2010, 08:53 AM
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Next chance I get open practice, I will be trying each combination of gear on the Spektrum and make sure it is just the servo. I will also try powerng the servo on a separate 4 cell pack jusr for curiosity. I really like the steering feel on that Airtronics Digital servo, and it worked perfectly for about 3 months. It just seems odd to start causing this problem now and still steer near perfect.
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Old 05-02-2010, 10:51 AM
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Originally Posted by GSMnow View Post
Next chance I get open practice, I will be trying each combination of gear on the Spektrum and make sure it is just the servo. I will also try powerng the servo on a separate 4 cell pack jusr for curiosity. I really like the steering feel on that Airtronics Digital servo, and it worked perfectly for about 3 months. It just seems odd to start causing this problem now and still steer near perfect.
The same thing happened to my friend when he went to the Tamiya nats. In his case, it was a HiTech digital. If you measured 4.5 volts with a volt meter you were probably going much lower except it was fast spikes that the volt meter didn't catch. Another test you can do for this is to do an AC measurement on the voltage and see what it reads. If there is a significant AC voltage on your BEC, it may oscillating or cutting in and out. This is why big caps are a band-aid fix for this problem. They filter out the AC and the receiver never sees it..... if you use a big enough cap for the problem at hand.
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Old 05-02-2010, 11:16 AM
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Originally Posted by kufman View Post
The same thing happened to my friend when he went to the Tamiya nats. In his case, it was a HiTech digital. If you measured 4.5 volts with a volt meter you were probably going much lower except it was fast spikes that the volt meter didn't catch. Another test you can do for this is to do an AC measurement on the voltage and see what it reads. If there is a significant AC voltage on your BEC, it may oscillating or cutting in and out. This is why big caps are a band-aid fix for this problem. They filter out the AC and the receiver never sees it..... if you use a big enough cap for the problem at hand.
What does not make sense is that this servo with the common sense BEC worked perfectly for 3 months, many hours of track time. So it seems something has failed. If something in the servo is making it pull more current, how long before it just goes up in smoke? I changed out the ESC from the old Mamba Max with the Common Sense BEC to the Mamba Max Pro with the internal switching BEC and the problem seemed about the same. That seems very odd, unless both BEC's are reacting nearly identical to over current spikes?? Changing to the Airtronics radio made it react very different. In hind sight, this could just be how the RX reacts to voltage dips. I do have a scope I can put on the RX power buss and see what it is doing. Hopefully I will have some time to get into this later this week.
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Old 05-03-2010, 02:25 PM
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A similar prob kept happening to me last Saturday at HRH. At an idle, my car would start accelerating abruptly on its own. If I turned off the my TX and back on, it would work fine again. This happened quite a few times. I'm running a Spektrum SR3500 micro rx.

To resolve the issue, all I did was disconnect all of my servos and went through the whole initial binding procedure again. After I did that, the problem went away. One thing to note about 2.4GHZ wideband or frequency hopping narrowband radio systems is that the RF channels CAN and WILL saturate if there are enough radios turned on and can throw things out of wack. Being that Spektrum is the most popular 2.4 system, it's not impossible to saturate the channels that it uses during a big race. But anyway, going through the re-binding procedure always helps.

It really sounds like an RF interference issue though since it would work fine when you turn your TX on and off. If it was a power delivery issue, I would think that the issue would continue regardless of whether your TX is on or not. When your TX is off, the RX is still sending PWM signals on all channels on your servos. The only difference is that it's sending the PWM signal encoded for your failsafe positions.
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Old 05-04-2010, 08:23 AM
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Originally Posted by GSMnow View Post
What does not make sense is that this servo with the common sense BEC worked perfectly for 3 months, many hours of track time. So it seems something has failed. If something in the servo is making it pull more current, how long before it just goes up in smoke? I changed out the ESC from the old Mamba Max with the Common Sense BEC to the Mamba Max Pro with the internal switching BEC and the problem seemed about the same. That seems very odd, unless both BEC's are reacting nearly identical to over current spikes?? Changing to the Airtronics radio made it react very different. In hind sight, this could just be how the RX reacts to voltage dips. I do have a scope I can put on the RX power buss and see what it is doing. Hopefully I will have some time to get into this later this week.
If you have a scope I would definitely take a look at the power coming out of the BEC and/or the receiver buss.
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Old 05-15-2010, 07:12 PM
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I have not resorted to putting a scope on it, but I did do a few other tests. I now have yet another old Hitec servo in the car, and it has been working great, with botht he Airtronics and the Spektrum radio systems. I cleaned up the wiring on the car and added a reciever capacitor bank (3 x 680uf caps) close to the RX to give me a little extra margin. Even with the old analog servo, the cap bank just seemed to make the control a bit more direct. So I decided it was time to try the Airtronics digital servo before I send it in. With no linkage even connected to the servo, I plugged it in and just wiggled the steering. Thanks to the cap bank, it did not make the ESC take off, BUT the yellow LED on the Mamba Max Pro was dimming in pulses, even when I turned the steering fairly slow. There is a serious problem with that servo. I plugged the other one back in, and sure enough, the LED's are solid as a rock, not even a hint of flicker.

I am calling Airtronics on Monday.
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Old 05-16-2010, 04:10 AM
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Ya, sounds like you found the real problem. That is the problem with noise... anything can generate it and anything else can react to it!
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Old 05-16-2010, 10:52 AM
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As far as servo glitching the easy fix is the spektrum spm1600 cap or the novak glitch buster.

If you want to diy the spektrum uses a 4600uf 10v cap and the Novak uses a 5600uf 10v cap. Both work fine for people having problems with digital servos.

The digital servo's just pull too much amperage when used very quick. If your running something like a GTB the cap is already built in the to esc and it can run a consistent 3A, if your running something like a MMP then you'll need a cap to plug into your RX because a MMP and many other's don't actually run @ 3A no matter how high you turn up the voltage from the esc.

http://www.rcshortcourse.com/forum/s...ead.php?t=7442

There's another discussion on it.
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