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MM Pro BEC not holding voltage under load
Upon running my Mamba Max Pro in my 8ight, i noticed that the LED's from both the esc and the transponder would flicker when turning the servo with noticeable performance issues. In fact, adding a slight resistance to the servo caused the transponder LED to turn off completely. My Mamba Monster does not have this problem, and neither does another's mm pro running the same servo (JR 9100s). This can't be solved with a "glich buster" capacitor, because this is a sustained current issue.
Is it just my unit that is bad or is this a common issue? If so, is this/has this been addressed by Castle? I would really like to continue being able to use my MM Pro in my 8th scale. It runs cool and is small and light. May or may not matter: Set bec at 6.0 volts Used Zippy Flightmax 4000 mAh 40C 4s pack w/ Tekin 1900 |
Probably just BEC gone bad. A guy at the track last week had exact same prob with a Tekin ESC; to the point that the steering would not even work if used too much (quick back and forth). Send it in to Castle, they will fix ya up.
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are your endpoints set correctly. might be stalling the servo pulling alot of current
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I've tested the BEC on a couple of MMPros and the voltage seems to cut out somewhere around 2-2.5A load:
5.94v unloaded 5.76v @ 0.48A 5.72v @ 0.64A 5.70v @ 0.95A 5.63v @ 1.87A 4.16v @ 2.77A |
Any suggestions on what to do about this? I am concerned about this as I'm planning on running a Ve8 on 6s with the MMP and will be using a relatively high draw 1/8 servo, spektrum rx and transponder all running off the MMP bec. I suppose I could run an external bec...
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Yeah, you can add a 1,000-2,200uF capacitor rated for 10v or more on any unused receiver port. This will help provide extra current for those bursts.
Or, use an external, beefier BEC. |
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Patrick actually mentioned a problem with some JR servos here:
http://www.rc-monster.com/forum/showthread.php?t=24293 And here is what he said: Quote:
Jeff |
Yeah, that particular servo has issues, but any high torque/speed servo can pull more than 2.5A depending on setup, tire size, etc.
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that's why I sold my MMp....
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I typically use Ace servos which are generally considered power hogs, so I would guess it probably pulls some decent amps. I'll try the cap first and go from there.
I have an MMP in my Xray T2 and so far with a Hitec 6965HB (think thats whats in there), its performing flawlessly, althought that servo and car doesnt put anywhere near the load on the bec that the ace in an 1/8 scale would. |
Well Patrick did say that the BEC in the MMP is just as capable as the one in the MMM.
Jeff |
Sure a capacitor might help with the performance issues, but when the servo is turning around a corner that takes half a second or more to complete, the transponder will remain off the entire time, and a capacitor will have run out long before. I didn't mention the fact that 1/3 of my laps were skipped during the MM Pro's maiden race in 1/8 scale. (It seems to be fine in stock touring with a less powerful servo)
I am not going to run an external bec, or a loaner transponder, which sort of defeats the purpose of running the MM Pro over th Mamba Monster, which has been trouble free. @brushlessboy, The end points were set correctly with 5% extra wiggle room. The lights flickered just by turning the wheels in the air, there was no binding, and a slight touch of the hand to add constant resistance to the servo would turn the transponder led completely off. |
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Patrick |
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Depending on the duration, amount, and frequency of the bursts, you might even want something like 3300-4700uF.
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People run caps about that size on their ESCs to help with ripple current, is it really necessary to run that much on the Rx?
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I guess I will try a novak 2700 uF 25V cap that I have lying around. Or will that draw too much current when charging? My main concern is whether I will have this problem if I buy another MM Pro. The one I have now was for my touring car, though I tried it in my 8ight to see how it would work. Also, like I said before, another person running the exact same servo doesn't have this problem.
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I ran 6600uf and was still able to get the transponder/RX to cut out... in a t4/6.5 on carpet with a bms617 servo and MRT transponder, not stressing the esc by anymeans:whip:
I wouldn't mind paying a few $$ more to have a WORKING bec:diablo: |
Do you have an Eagle Tree datalogger or can you borrow one? You can measure Servo current with it.
Jeff |
Wow, I wonder if there is something wrong with either that servo or the BEC? ~2.5A with a cap that size should have solved it.
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the MMp isn't the first esc to cut out when useing them, the stock SC10 esc will also do it. I know for a fact that the MM will not cut out.:neutral: |
That's because it's a linear regulator. They tend to be more bullet-proof, but also heat up a LOT more especially with higher currents and higher differential voltage.
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i have a servo guage tester which measures peak and ave servo draw...
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It's entirely possible that there is a bad chip, cracked solder joint, etc. etc. Feel free to send it in for a checkup.
Patrick |
You can easily make your own. Simply take a servo extension lead, cut the red and black wires somewhere in the middle, and put connectors on them that match whatever you have on the ET wires.
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http://www3.towerhobbies.com/cgi-bin...?&I=LXSDX4&P=7 |
Yes, that will work, and can probably measure smaller currents more accurately, but a simple Y harness can be used to measure voltage and current just like how it would measure ESC current.
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I just bought a new align servo for my 10th scale rt5 its model DS610 i connected it to my mmp and the reciever started to lose power when turning fast. This is with no load on the servo. I also have a JR 9100 high torque servo which i tried on the mmp and had no problems, this was just to test the BEC with a known trouble servo. So at this point i assumed I had a bad servo but when i connect it to the rx8 in my 8ight it works fine. This servo is smaller than my JR and does not have nearly the torque. What is going on? Was the fix mentioned earlier in this thread about adding a delay ever implemented in new mmps. Should I send the mmp in?
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Do you have the steering EPA set so that the servo doesn't try to go beyong the steering system's mechanical limits?
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The epa was set to 100 for left and right which i believe is the stock setting, it goes to 120. This setting was used for both servos that i tested.
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The actual % doesn't really matter. Start at something low like 50%, activate full steering throw one direction, and increase the EPA for that direction until just before the steering assembly's mechanical limit. Repeat for the other side.
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There is no mechanical limit the servo was not installed in the vehicle i powerd it up to center the servo for the spline to be attached.
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Hmm, that's odd then. IIRC, Castle mentioned something about certain servos drawing more current under normal operation than others. Maybe that brand happens to be one of those. Let's hope Castle chimes in...
BTW: Welcome to the forums! |
Yeah thanks for the help. I have read many of your post on here and the traxxas forum i just dont post much because i can usually find what im looking for.
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